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GT750 Powered Race Car (D-Sports Racer)

Started by sav0r, July 22, 2019, 06:22:45 PM

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sav0r

#90
I think we will probably move to a tripod type arrangement, moving away from CV's. A little more axial movement is good for us, it just allows us so much more flexibility with setup of the rear suspension geometry since tripods provide more plunge. Also, tripods are soooo much easier to deal with compared to packing VW CVs. They just aren't that much fun even when you are good at it. We will probably buy the tripods but machine the half shafts and couplers in house. Since we aren't too concerned about driveshafts hanging out in the air stream on account of the full bodywork, we can use a fairly large OD tube for the shaft, this should afford for a very light setup, while also providing a much larger surface area for welding the splined sections to the tube. The two welds where the splined section was sleeved to the half shaft tube is what failed (twice) on our left side half shaft this weekend. Large OD drive shafts I guess are typical for just about every drive shaft known to man these days assuming aero isn't a concern.

We definitely have not decided on a differential, but we have long discussed a Quaife limited slip setup. They aren't uncommon in chain drive cars, and can be found used for reasonable prices. Building a new spool for the rear of the car is a big project, and also expensive. We may not even approach it. It would probably make us faster, but it introduces a number of other challenges to face.

Anyways, we have lots to soak up. Honestly, we have spent so much time on this project we will probably just forget about it for a month or two. Hopefully we will gain a little bit of perspective and clarity along the way. Then we will get back into the design/engineering phases. We are tossing around the idea of hitting the Put In Bay vtinage races, but we aren't sure yet. That said, my father plans to pull the head off today and have a look. There is no doubt we blew the head gasket, it's just a matter of how bad it is.

www.chrislivengood.net - for my projects and musings.

sav0r

#91
My wife just got home with my video. So I will start working on it.
www.chrislivengood.net - for my projects and musings.

sav0r

I think this was my fastest lap. I watch entirely too much in car video since I driver coach, but I was totally phoning it in. So much pace left. This video is low quality, I will get a 1080 video uploaded as well.

https://www.youtube.com/watch?v=bC5vVgyr4rg
www.chrislivengood.net - for my projects and musings.

hayduke

This is fantastic, thanks for sharing. It's great that you and the family are having so much quality time, and that this machine is back where it belongs! It looks like you weren't even really trying on that lap, so smooth and drama free. Good luck with the next steps!

sav0r

I was definitely taking it easy under braking and in the long sweepers where maintenance throttle was needed. The loose heim joints on the rear toe links offered up a challenging bit of rear steer and fast inputs caused instability. There isn't much room for error on that circuit and since we only have one of these cars and zero spares it seemed best to just be calm and let the car do the work.

That said, there's nothing wrong with being smooth. I tell drivers all the time that they need to do less work, as over driving generally just slows you down.
www.chrislivengood.net - for my projects and musings.

sav0r

www.chrislivengood.net - for my projects and musings.

teazer

Nice video.  Thanks for sharing.  Racing old cars and bikes  is a fun pastime and as they get faster and older, things start to break.  Make that part stronger and something else starts to give up under the strain. 

I like the fact that the car still looks like it did and hasn't morphed into a carbon fiber, modern interpretation.

Engine sounds good.  What's the chirping under brakes?  Is that brakes or tires or something else?

hayduke

Random direction changes are never fun, especially with the "runoff areas" full of trees, rock walls and drop-offs.

The only think that could make the videos better is to put the mic closer to the exhaust  :olaf:

sav0r

Quote from: teazer on July 28, 2021, 10:27:28 AM
Nice video.  Thanks for sharing.  Racing old cars and bikes  is a fun pastime and as they get faster and older, things start to break.  Make that part stronger and something else starts to give up under the strain. 

I like the fact that the car still looks like it did and hasn't morphed into a carbon fiber, modern interpretation.

Engine sounds good.  What's the chirping under brakes?  Is that brakes or tires or something else?

I think that chirping is the chain drive, likely the chain is a bit too loose and rubbing on the inside of the chain guard. Either that or it's the transmission. Who knows?

We have been very careful to keep the car true to its origins. Outside of safety measures and modifications required to make the car function, we have modified very little. You are absolutely correct that many convert to carbon bodywork and sorts of other items that never would have been possible in period.

That said, most of these cars end up faster than they ever were simply on account of tire technology being so much better. That of course means some things have to be modified to just to stand up to the extra stress, as you mentioned. Keep in mind we went many seconds faster around Nelson's than my father ever managed and he was on slicks while we are on grooved tires.

www.chrislivengood.net - for my projects and musings.

pidjones

Tires - SO much better for cars and bikes alike. Also brakes and shocks. You should get the braking problem sorted this winter, and the chassis looseness may require heavier components or different materials (or both). I'm sure the half-shaft problems will improve with better materials and welding technique. 
"Love 'em all.... Let GOD sort 'em out!"

sav0r

The machinist that did the half shafts has been dead for 10 years, and he did the work 47 years ago, so we can't even ask questions. Obviously it wasn't well thought out. We will certainly do new half shafts. Luckily we can just do them in house now, which wasn't the case 47 years ago. lol

Brakes, yes. Heavier heims on the rear toe links, yes. We should also jig up front and rear links and record numbers so that if we have to refit a link we can dial it in without hitting the setup pad.

p.s. teazer I owe you a water pump gear, I haven't forgotten, I am assembling 8 more gears next week and one has your name on it.
www.chrislivengood.net - for my projects and musings.

irk_miller

Really glad to join this site to be able to see this.  Great car, even with the engineering complications.  Always thought to build something off a GL1000 base, but more because of the boxer arrangement and it being a shafty seems so much easier to build retrofits, even if it's not. 

teazer

Quote from: sav0r on July 29, 2021, 02:09:14 PM
....
p.s. teazer I owe you a water pump gear, I haven't forgotten, I am assembling 8 more gears next week and one has your name on it.

No worries Chris.  I know where you live.... :whistle: :eek: :cool:

sav0r

We were gearing up for either Put in Bay or another test but I think we are going to hold off now.

The half shaft design is incoming, but more importantly, my father is prepping to move the Express chassis under the Grumman step van body. This will leave us without a tow vehicle for the time being.

We are also studying another head and cylinder, maybe a reed valve cylinder. Maybe a totally bespoke head. Lot's of work to do, as usual.
www.chrislivengood.net - for my projects and musings.

teazer

Big advantage of reeds is the added transfer port area which that motor needs. 

Disadvantage is the studs tend to get in the way and they are challenging to fit.  Check out the barrels that Brett DeStoop cast for a 1000cc motor or his 750 reed motor that made something like 176HP IIRC.

I wanted to graft a set of snowmobile top ends onto a GT750 set of cases but that requires moving the left cylinder out a bit and changing the crank and at that stage, might as well saw the transmission off and weld on a GSXR trans with stepped gears for a shorter motor....

A Zeeltronic or ignitech programmable ignition would probably help to spread the powerband too.

There was a guy in Germany that built a 1000cc motor and added powervalves to the exhaust as well as reeds.  That was a huge amount of welding and machining.  You could probably machine a cylinder from billet with modern machine tools and an unlimited budget.