2strokeworld

The 2-Stroke Garage => Haus of Projects => Topic started by: sav0r on July 22, 2019, 06:22:45 PM

Title: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on July 22, 2019, 06:22:45 PM
A little history on the project, my father built this car from '72 to '74. It was successfully given a log book and SCCA homologation to compete in the D-Sports Racer category. This chassis predated the modern steel roll cage rules, meaning an all aluminum (crash structure) construction was allowed, including the crash structures. Additionally, there was no minimum weight prescribed for cars under 850cc. The car is basically an aluminum monocoque, or maybe better described as a semi-monocoque as it uses effectively an aluminum tube frame with riveted and bonded panels. At the time of build the Suzuki GT750 was a popular engine, and given a proper tune could make over 100hp easily. The first engine build was performed by Eric Buell, this was back when he still lived in Pittsburgh. Later builds were performed by my father, and the engine evolved somewhat over time. The chassis was engineered by my father's friend, who at the time was a full time engineer at GM. My father constructed the car with the help of another friend and his wife. The car was raced from '74 to '79 with mediocre success and then mothballed. They participated at Nelson Ledges, Summit Point, and Mid Ohio, but with a limited budget and limited man power they never quite got it going like they had hoped. The car remained in the garage unused for 40 years. It had become such a burden on space that my father eventually mounted the car on the wall, it stayed there for something like 16 years.

Here's a bit of photo history of the car.
(https://i.imgur.com/Fw5tmis.png)
(https://i.imgur.com/lYElTNI.png)
(https://i.imgur.com/8yh88Yk.png)
(https://i.imgur.com/sUGU42e.png)
(https://i.imgur.com/zLsC2xU.png)
(https://i.imgur.com/7LYW02V.png)
(https://i.imgur.com/sOrLeMi.png)
(https://i.imgur.com/Be03qJo.png)
(https://i.imgur.com/0WNPskw.png)
(https://i.imgur.com/EO96b3h.jpg)

Here's the car as we were pulling it off the wall, I want to say this was in 2015, maybe 2016. It's hard to recall.

(https://i.imgur.com/MxZJ4io.jpg)
(https://i.imgur.com/rZK6XaM.jpg)
(https://i.imgur.com/3VzIgUQ.jpg)

Once off the wall we put the car back on the fabrication table that it had sat on for something like 20 years before. The process began. The all aluminum crash structure simple wasn't adequate. After 40 years of competition in other areas of racing my father had learned a lot from the days when he built the car. So he took the chance to update and change a number of items, but tried to be sensitive to keep the original spirit of the car. The focus was mostly on engineering issues, especially those that could be a safety concern.

(https://i.imgur.com/JuxsfR4.jpg)
(https://i.imgur.com/g8639nU.jpg)
(https://i.imgur.com/g8639nU.jpg)
Progress
(https://i.imgur.com/oi50Lsk.jpg)
(https://i.imgur.com/pALBQWx.jpg)
(https://i.imgur.com/9JODcIB.jpg)
(https://i.imgur.com/SNHgrjn.jpg)

And, this last weekend we got to the track and managed to race the car. We fought with the master cylinders right up until the race, but managed decent brakes come race time. Then of course the car overheated. But I managed the best laps of the weekend in the race, so for having basically used the race weekend for testing it was a positive result. We simultaneously got the car on track for it's 40th anniversary of retirement, and my 25th anniversary of race driving competition. A true success!

(https://i.imgur.com/bgfPSiH.jpg)
https://youtu.be/pH5OCOBPmZg

I have other pictures as well. I can also publish more detailed specs if anybody is interested. We plan to continue development of the car. It actually fits the rules for the modern P2 class which is sort of the modern equivalent of D-Sports Racing. So we could compete in national competition if we wanted, of course the car wouldn't be competitive, but it would be fun.

Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: Cobraace2 on July 22, 2019, 09:14:18 PM
Fantastic some specs on the engine . love how the chambers look like they made von a brake .
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: ~JM~ on July 23, 2019, 12:36:45 AM
SUPER COOL !!!
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: kar1zma on July 23, 2019, 02:45:28 AM
that's a real blast from the past
its great that you have so many pics from way back.

nostalgic!!!
good luck with racing this beauty again
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: RD7 on July 23, 2019, 05:36:56 AM
Great read , thanks for posting.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: mnein on July 23, 2019, 08:00:50 AM
Man that is just cool.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on July 23, 2019, 08:25:35 AM
Fantastic some specs on the engine . love how the chambers look like they made von a brake .


The engine has the cylinder raised .04" as I recall. The cylinder was then decked, as was the head. The head was welded up, the spark plugs were moved into the center of each chamber, and then the domes were reshaped. In the current form, the heads are just a circular shape without a proper squish band. This is the head as it was built 40 years ago. The ports are drastically changed, and the engine runs three VM38's using an adapter plate on the intake side of the head. The engine would willingly rev well past red line, which was an issue, because I've never driven a motor that was so willing to do so. It easily would pull to 10k plus. As a result, it got over revved several times last weekend, we haven't had a chance to tear it down, but we hope it wasn't hurt.

We have plans to redo the head though, as we have several, all it will take is welding it up and machining it. We already did all the setup work to do the machining, we just didn't have the time to weld a head up. Here's the model I made, I matched the head volume to the current volume, but we have added a squish band and slight toroidal chamber.


(https://i.imgur.com/sIEtapy.jpg)


Thanks, all for your enthusiasm. It's been a labor of love for my father especially. There are a lot of details to go through, as a result I'm confident we will be a lot more competitive in our next outing. The unofficial goal is to reset the all time lap record around the Schenely park circuit, it might take a year or two but I think we will get it.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: cygnus on July 23, 2019, 04:33:56 PM
Great history. Kudo's to your pop for keeping it and good luck with the record attempt !
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: gwcrim on September 25, 2019, 07:54:54 PM
Very cool story.  Very cool car.  I bet it's a GAS to drive!
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: Evans Ward on September 28, 2019, 08:21:27 PM
I’ve heard about the Ocelot- what exactly was it? Love the car BTW!  :righteous:
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: RDFL on September 28, 2019, 11:07:40 PM
Great car and story.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on September 30, 2019, 01:17:39 PM
Very cool story.  Very cool car.  I bet it's a GAS to drive!


It works rather well, once we iron out the bugs and I can drive it in anger, it should be a bit faster than a Formula Ford (if you're familiar).

I’ve heard about the Ocelot- what exactly was it? Love the car BTW!  :righteous:

This actually competed against the Ocelots. Basically in the D-Sport Racer" category at the time there were two displacement levels. One, I beleive 800cc set a minumum weight, it was something like 1000lbs. If you were under 800cc, then you could be as light as you wanted. My father chose that option. So he started with the 750 water buffalo and built a chassis around it. The Ocelots did the same, though they were much more successful than my father's operation.


Great car and story.

Thanks! It's great fun being able to campaign the car with my father some 40 years after he built it and after 25 years of driving myself. I visted my father last night and are scheming for 2020. Lot's of solid stuff in the works.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on September 30, 2019, 11:56:59 PM
Also, that wood block that's holding up the rear sub frame in the second picture is still in my father's shop. He still uses it in the same manner. It's just a lot smaller and more burnt, worn, and abused than it was 40 years ago.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: Evans Ward on January 20, 2020, 01:25:16 PM
Anything updates during the off season for this Water Buffalo powered race car?
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on January 20, 2020, 03:28:25 PM
Yes actually. I was just looking at the car with my dad last week.

We got the new AP floating pull masters in, both new for front and rear brakes. My dad also got a nice new balance bar TIG’ed up. Looking good! I’ll grab some photos the next time I’m up there. We also got a larger master for the clutch, and my father has gone through the clutch and is adding a high performance clutch pack and springs from Barnett. Hopefully the slipping issues go away.

I finally got my dad talked into welding up one of our spare heads and milling it completely, spark plug holes and all. And we are going to do a new base gasket, the current one obstructs the ports a tad and is in rough shape. The engine is apart right now. We are working on the sheared water pump drive, we haven’t decided on a direction for that. Maybe electric, maybe aftermarket gears.

From there it’s going to be minor stuff. Some stays for various body panels, double check all the suspension bits, scales, alignment. We hope to do four or five weekend this year and really hand it to the geezers on vintage circuits.

Also my boy is four, so I’m looking at some karting for him this year. So it should be a busy season.

Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on February 05, 2020, 10:20:18 AM
We fought a bit with the water pump gear. Basically, they don't like the RPM we turn and they were junk in the first place. There's a nice press on steel gear in the UK, but after shipping, parts, return shipping, the price is a little silly. Something near $200 all said and done. We are married to the mechanical water pump and adapted a high flow impeller and housing. We've decided against an electric pump as we don't want to carry the extra amp hours. We run total loss, and the battery is way too heavy as is. So i'm going to cut one of these guys out aluminum, but since it will be milled instead of hobbed, we expect it to self clearance a bit. It should work fine, we'll just flush the transmission once after some stand time. I may also cut a sleeve to press over the plastic gears shoulder which should make the plastic gear more reliable, but it will likely stay in the parts bin. After all, spare parts are never used.
 
(https://i.imgur.com/jEDDTa3.jpg)
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on February 09, 2020, 11:18:02 PM
We decided against the above hubbed design and instead are going for this hub-less setup. The existing G750 steel hub that's in all the plastic water pump gears will be shrink fit to the new aluminum gear. The benefit of this system is that the the gear will be removable without splitting the cases. All the other gear replacements that I've seen require the cases are split to change/remove the gear. It will be easier to machine too.

(https://i.imgur.com/WVIOujW.png)

We've also picked over our data from the single race weekend and have realized we were geared too short. Top speed was calculated to 107mph. We managed 109mph, it really likes to rev. So we are going a bit longer, it shouldn't hurt us in the slowest corners as we were too short there too. I machined the new sprockets today, looking good! It's basically free speed, we will just plain go faster. I also found in the data that I lost major time in the brake zones, I already knew this as the driver, but the decel curves were frankly pathetic. On a 20 turn course with stone walls the brake zones are pretty important. The new masters are going to be a huge gain.

https://www.pvgp.org/schenley-circuit-map/
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on February 12, 2020, 11:30:31 AM
I let the mill run through the night last night. .0625" end mill with a .0625" step down, .001" step over, at just 1.5 inches per minute. Run time was about 5 hours, more than 4 hours to just cut the teeth... I'll face the back side off tonight and then shrink fit the hub. If it works, I'll probably make as second one, there are a couple of small things that could be improved, but not bad for a first try. It's a good thing machine time is basically free.

(https://i.imgur.com/fnHVSJd.jpg)

(https://i.imgur.com/UjAXs2M.jpg)
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on February 12, 2020, 08:00:17 PM
Finished this one up as planned. Looking good!

(https://i.imgur.com/zVlpzk0.jpg)

(https://i.imgur.com/51vhgUo.jpg)
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: Evans Ward on February 12, 2020, 08:41:12 PM
Excellent craftsmanship there! On the original nylon one in your pic, you can see the cracks as it is common and I’ve never seen a used one that didn’t have one or more cracks. When that gear breaks, you lose your tach but more importantly your water pump circulation. This one broke on me 2 yrs ago 60 miles from home. I rode it back gingerly taking it down and pulling the head to see if warpage occurred. It was straight and not warped as Suzuki really over engineered those triples.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: Evans Ward on February 12, 2020, 08:44:27 PM
Here’s a new Suz nylon one for comparison:
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on February 12, 2020, 09:33:26 PM
We actually bought a new one, only to have it be cracked upon arrival. And our gear broke mid race, leaving me to retire.

We have seen 10k on the tach, which is the danger zone big time. The plastic gears just never stood a chance.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on March 05, 2020, 09:01:40 AM
My father has the engine mostly back together. Says the gear will be perfect. Obviously we need to run it, but there are no obvious issues upfront.

He bought a new impeller and housing from the UK, the impeller is missing the key slots. We aren't sure how to make it work yet. I might end up scraping a keyway for it on the mill, that will be a new one...
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: teazer on March 07, 2020, 08:26:20 PM
early style used a woodfruf key and later ones just used a roll pin.  A lot of impellers have a deep slot plus keyway so they will fit wither design of shaft.

I may have a water pump shaft I could swap for yours.  If you need one, please let me know and I'll check my spares box.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on March 07, 2020, 10:56:40 PM
My father ended up fixing the impeller with a scroll saw and some files, he just added the keyway. It has a bit of lash but it will be just fine. He spoke with BDK and they mentioned the old/new situation.

I machined up a bracket for the chain tensioner today. I'd post pictures but without context it's not really worth seeing. Suffice it to say, since the drive train is fixed and the engine is fixed there's a third sprocket that's mounted on eccentrics, the eccentrics are used to adjust the third sprockets location to control chain tension. The bracket was too flimsy before, there is an amazing amount of load on it. We should be good now.

The best news is that my father delivered the head to me today. It's all welded up and ready for machining. I've got the model all worked out. I have the game plan for setting up the head on the mill. Unfortunately my power drawbar is acting up. I might go ahead and do it with manual tool changes, but it's such a bummer running the machine like that. I've got to get some customer work straightened out then I'll make the decision on either fixing the PDB or going ahead with machining. The drawbar repair is like a two to three day affair and I need access to a lathe which is a bit of an issue currently.

(https://i.imgur.com/4gON1it.jpg)
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on March 20, 2020, 10:42:05 AM
The company that provided me with a day job shut down yesterday as a part of non-essential closures of businesses in PA. As a result I have a lot of free time. For my creative self, this is a win. We'll see how the financial self survives, but for the time being I am going to keep busy and enjoy the vacation.

So, last night I got the stock on the mill that will fixture the GT750 head for machining. For those who aren't familiar with machine tools, my mill is quite small. In fact, in the scheme of things it's basically a toy. Though I've spent a lot of time and effort to make it as capable as it is, and I manage great results on a number of projects. Keeping the size of the mill in mind, to place the 7" wide (tall in Z height) on the mill I had to remove my automatic tool changer. But, I got the stock squared up and looking good, luckily I just needed one tool to get the work done. Today I will be boring all the holes in the fixture plate, tapping said holes, and then surfacing the plate so that it's nice and parallel with my table. I've purchased Mic6 plate for the fixture, which should be fairly flat, but I want to get this right and have a nice repeatable fixture for future head reworking. Since the head will get worked over on both sides the fixture end up using the head bolt pattern and a flipped version of it. Of course the head itself will get surfaced on the fin side before further machining can be done, it's the only way to assure the head stays flat when the combustion chambers get machined. As of now, the combustion chamber cutting will take around 4 hours, luckily the machine runs itself and I don't have to pay any attention to it as it grinds away.

Short video of the stock getting cleaned up - https://i.imgur.com/btu3W2S.mp4

(https://i.imgur.com/Bgj0ESr.png)


Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: teazer on March 20, 2020, 02:37:25 PM
Sorry to hear about the work but good to see you are staying busy.

Is your mill CNC, and can you do more complex combustion chamber shapes such as different squish band angles and diameters and even torroidal heads?
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on March 20, 2020, 08:14:13 PM
Yes, it is CNC. The head design is slightly torodial, though not particularly radical in that shape. I put a piston on the mill and measured the arc of the piston top and then matched the squish to be a mirror image of it. My father gave me figures on the design beyond that, mostly squish band width, and I then adjusted the shape of the combustion chamber to give us the volume we need.

But the sky is the limit, really just about any imaginable shape can be made. The nice thing is that no special tooling is required. The entire finishing operation will be done with a 1/4" ball end mill running really slow with really small stepover.

Here's a few photos from the process. The negative of the combustion chamber provides head volume.

(https://i.imgur.com/2nE7Uz2.png)

(https://i.imgur.com/TvgLhf5.png)

(https://i.imgur.com/hAQXha7.png)
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on March 23, 2020, 05:24:14 PM
Well I came down with Tonsillitis and that slowed me down a couple of days. On the mend now, tonsils are feeling so much better.

I got the fixture plate machined. Turns out somewhere along the line my model got out of scale and that resulted in the first set of holes not lining up with the head. So, I went back and redid all the CMM because I couldn't find my original data, then redrew all the models. The CAM was good, so the machining went smooth. Literally minutes of machining and everything came out awesome, of course I spent like two hours doing the CMM and at least two more hours redoing and verifying models. All seems great though.

(https://i.imgur.com/1Rvl8WS.jpg)

(https://i.imgur.com/aER3Gsf.jpg)

(https://i.imgur.com/Bw33o5t.jpg)

(https://i.imgur.com/Yz653d6.jpg)

What a ride that was. Now onto the head. Seeing as it's the first one to hit my mill I will be taking my time.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: teazer on March 24, 2020, 12:10:56 PM
It's really important to get it right before you do my cylinder head.... :whistle:
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on March 24, 2020, 12:21:45 PM
It's really important to get it right before you do my cylinder head.... :whistle:

Fingers crossed! Working on these GT750 heads is tricky because they all seem different. There's nothing to reference, especially so after they've been welded. But I think I have it worked out.

I grooved all the large (tube) bolt holes for snap rings. This means I can bolt the head to the fixture plate with zero protruding bolts or hardware. That makes facing the head (both sides) so much easier.

(https://i.imgur.com/Z3PxgNf.jpg)

(https://i.imgur.com/JcOM5DM.jpg)

(https://i.imgur.com/N4ufGxw.jpg)

I am now ready to face the top side. Once the top side is faced, the head will be flipped over and bolted back down. I will reference it, square it up as best as possible, then actually machine the combustion chambers and spark plug holes. The plan is to thread mill the spark plug holes, but I will be taking them a size large and using a steel insert in the head. To finish, the head will have to be flipped back over, and the spark plug holes will be faced for the crush washer surface, at the same time I will set the depth of the spark plugs. With the plug holes being welded up I figured it would just be easiest to do it at the end.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on March 24, 2020, 04:02:12 PM
It needs a little deburring but it looks good!

(https://i.imgur.com/YfQK8YR.jpg)
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on March 24, 2020, 08:30:39 PM
Oh, and my father sent me this.

(https://i.imgur.com/cZ5rxgV.jpg)
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on March 25, 2020, 01:21:48 PM
Faced off the gasket surface, then roughed out the combustion chambers, and bored the spark plug holes. That weld is some sticky stuff. There's some minor porosity in the welds. My father struggled with a broken TIG torch before I convinced him to switch over the MIG machine. He suspected we'd get some porosity, but we also figure it won't matter much. If the head design seems successful we can always fill the porosity and machine them again.

(https://i.imgur.com/19vjY7d.jpg)

A video of surfacing. I just hand programmed this. I did it in two passes, the first at .02" depth, the second at .005" depth. I tossed the head on the surface plate after this and it's really good, better than I would have expected... I'll probably still lap it in a bit on the plate.

https://i.imgur.com/KDLpqqZ.mp4

Here's boring one of the spark plug holes. Pretty boring really...

https://i.imgur.com/5SOE7kg.mp4

There are only two operations on each combustion chamber left, but the run time will be around 3.5 hours to do those six operations. The first with small stepover using a ball end mill, this will still effectively be a roughing operation. This operation is needed to minimize tool load spikes for the final operation. The final operation will have an even smaller stepover, but will use a smaller ball end mill, and hopefully will produce a really clean and well finished surface. Fingers crossed, it's been a long road to get here. Let's not mess it up now!
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on March 26, 2020, 12:47:49 AM
Well, i'm not super happy. I messed up the programming on the second to last operation, I should have left more stock for the final op. That means the final operation didn't get it cleaned up as well as it should have been. Nothing a little emry cloth and some elbow grease won't fix, but not exactly the results I was hoping for. Not a major F up, it should work fine, just not the finish I wanted. Tomorrow I set the heights on the top side of the spark plug holes, thread the holes, then ream them, and install the steel inserts. The hard work is all but over now, it's down to the details. I'm pretty tired currently, luckily grandma took my son for the night. Gave my wife and I a much needed rest after the crazy 12 days or so.

I talked to my dad today, he's pretty bummed out about all the Covid fallout. He doesn't think we will see any races this year if this keeps up. Not much we can do but keep our heads down, prep the car, and hope for the best. That said, now that my current projects are slimming down, my wife's RD125 is next. The engine is coming out in the next week or so.

The images make the finish appear pretty bad, but in reality the cusps are hardly detectable with a finger nail. However, they should have come out mirror like had I gotten it all right. The next time I'll have it worked out...

(https://i.imgur.com/F8nYfOj.jpg)

(https://i.imgur.com/8KlSG2v.jpg)
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on March 30, 2020, 12:04:20 AM
This project is done for now. Spark plug sealing surfaces have been cleaned up, depth set. I milled the threads, but they will get steel inserts. I'm pretty happy overall with how this turned out. It's a great first try, on the second round it's only going to get better. Overall, this is the best head our GT750 engine has ever seen.

(https://i.imgur.com/qLMlY35.jpg)

(https://i.imgur.com/RUiSG7B.jpg)
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on April 09, 2020, 10:24:44 PM
My dad went through the motions of checking head volume, squish, etc.. Everything is looking good. The squish averages about .025" on all three cylinders. The motor will come back apart again and various items on the chassis will be checked over, but assembly for driving trim will begin soon. The new master cylinders are fully mounted with a new balance bar, the clutch cylinder has been revised, new clutch with Barnett discs and springs are in place. We should be able to run up through fifth gear without slipping the clutch from three on. And hopefully the car will be drivable in the pits too. I'm hoping to make a visits to my father's place this weekend, I'll try to grab some photos of the car.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on April 13, 2020, 08:52:08 PM
The car is looking really good. The compression ratio came in right to 7:1, stock being 6.7:1. Perhaps a spot higher than we really wanted, but it may help the systemic over-rev we weren't pleased with. My father has picked over a number of the small details on the car, nothing major to report, but this is how racing machines work. If this lock down process continues (fingers crossed), I may start machining some of the more elaborate parts for the car. Currently it uses cast iron front upraights from a Triumph, that was common for the period. We can however update those. I'd also like to get some of the rear drive train on the lathe and lighten it up, maybe replace the cast steel seal carriers with billet aluminum bits, just generally shed some weight from the car. Almost all of the major weight that is easy to get rid of is unsprung weight, for a sub 1000lbs car that's a very important area of improvement. Especially so for rough tracks like the street circuits we generally compete on. Here are some photos. Keep in mind I'm posting 12mp photos, the ports look rough but in reality they are smooth as can be. I spent the rest of the time working on RD125 parts, I'll get photos of up for that project tomorrow.

(https://i.imgur.com/bbM6yX6.jpg)
(https://i.imgur.com/X9lhRQa.jpg)
(https://i.imgur.com/bsw1hI9.jpg)
(https://i.imgur.com/TLDW1DH.jpg)
(https://i.imgur.com/6yVMBb0.jpg)
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on April 26, 2020, 08:42:01 PM
The head is officially ready to go on. My father has been picking through a few other issues around the shop (valve job on his Mini Cooper S and stand alone ECU on his hot rod Mini), so the DSR has taken a bit of a back seat. He says he ironed out some timing irregularities he think existed, definitely small but perhaps troublesome. The new chain tensioner bracket that i mentioned machining on a few posts back is in, and it seems to be really nice and stout. Other than that, not much has changed.

(https://i.imgur.com/L5kgRYz.jpg)
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on May 13, 2020, 08:48:13 AM
It's all back together. My father modified the exhaust a bit, going to a larger ID perforated tube to the silencers. He also has the PI System (now owned by Cosworth) hooked up and is trying to calibrate the three EGT's. Keep in mind this data logger is something like 25 years old, we are running the software on a HP Windows 95 laptop from a 3.5" floppy disc haha. So while the data logger is certainly modern technology in relation to the car, we've done our best to run vintage data logging too.

It runs - https://i.imgur.com/YwRdZw2.mp4

(https://i.imgur.com/iXCwFLA.jpg)
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: tony27 on May 21, 2020, 06:55:24 AM
Nice work on the waterpump gear & new combustion chambers, doing that sort of stuff is very satisfying
It's funny just how sticky weld material can become compared to the original base material, there must be a slightly different make up between the 2 materials. I have a head for my CZ400 that was welded & machined which has the same porosity issues as your head, never seemed to affect how it ran although when it turned up I was pretty unhappy after having seen the work done by the company on other heads
Did you end up correcting the slight misalignment between the cylinder bores & combustion chambers I've seen mentioned before? I assume because the whole combustion chamber was fully welded & you measured the top of the block to make your sub-plate that you would have been able to get the positioning exactly right
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on May 21, 2020, 08:10:55 AM
I think if my father had started with his MIG machine the porosity issues wouldn't exist. There was some issue with his TIG torch and he kept getting bad welds. The torch ultimately was replaced, but that was after he MIG'd the head basically problem free. Virtually all of the areas with porosity were touched by that broken TIG torch. Old dirty aluminum has proven tough to weld in general though. What also surprised me is how quickly the head naturally anodized. It was like 20 minutes at most after machining that it lost its shine. Whatever alloy these things are made of it doesn't react like any modern variants.

I got the head misalignment mostly corrected but it's not as good as i was hoping. Next time around I'll fix the head to the table, then bolt the cylinders to the head, then I'll use the touch probe to find the center of each cylinder. I'll set each cylinders center as its own work offset. The cylinder will get removed, then the program to machine the combustion chambers is run individually for each cylinder based on the real life spacing of the cylinders. This will assure that the combustion chamber is perfectly placed for each cylinder based of the cylinders themselves, also meaing the cylinder head is custom matched to each cylinder set and might not fit to other cylinders as precisely. What I tried to do was model the cylinders and reflect that onto the head model. Even after creating a dxf by touch probing the cylinder I never was able to get an accurate reflection back onto the head because there's simply nothing worth referencing on the head itself. I hope that description makes sense. Hind sight as they say is 20:20, and in the case of this head work I learned a ton. The carburetion has changed right off the bat, so something seems to have worked haha.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on May 21, 2020, 03:49:52 PM
Today they announced the cancellation of the Pittsburgh Vintage Grand Prix. It always takes place in mid to late July. I suppose it's for the best but it certainly takes the edge off the last 9 months worth of preperation.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on June 07, 2020, 11:04:32 PM
I was approached by a gentleman in Australia about my water pump gear. So I made him one and it came out pretty much perfect. The finish is exceptional.

(https://i.imgur.com/BCkaDMD.jpg)
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on July 31, 2020, 05:00:29 PM
That carb thread got me thinking about Lectrons so I got a hold of my buddy that offered us a set. It took him a day or two, but here's what he sent me.

(https://i.imgur.com/4WOBYTl.jpg)

(https://i.imgur.com/t7yXnL5.jpg)

(https://i.imgur.com/BKC5iX7.jpg)

They are 2mm larger than our VM's that we ran last year on our Water Buffalo, and they came off a GT750 from one of the cars my father raced against. Period for the vintage of car, and likely a sweet upgrade. He's going to send them to us. We will have to work out throttle cables, but I think we are going to give them a try.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: rodneya on July 31, 2020, 11:38:24 PM
Check Packard Racing for throttle cables.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on August 01, 2020, 12:44:01 AM
Our cables are pretty specialized considering they run from a throttle pedal at the front a car back to a mid engine motor in a chassis that was built by my father 50 years ago. I appreciate the response though.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: rodneya on August 01, 2020, 11:58:07 PM
Lectrons need cables with lectron threaded ends to go into the carb tops, so you need at least the piece from the carb to the splitter.
Probably worth a call.
Title: Re: GT750 Powered Race Car (D-Sports Racer)
Post by: sav0r on August 02, 2020, 03:41:02 PM
Inside the plastic organizer that had the book on top are a bunch of parts for connecting them up. The slides appear to use a standard barrel type termination, but I could be very wrong.