924Board.org

[safe]

[MikeJinCO]

The following is just my opinion,

Before I lost my race car to a fire (Apr 2022)I had 2 sets of JE pistons on order including rings and pins for about $800 per set. The pins were smaller and took a different bushing I believe from a Saab (about $10 ea)and they were available from JB Racing?(the folks in Reno who also had under size rod bearings and main bearings). The Pistons I had on order were for a 931 head and 10.5CR for use with 45DCOE Webers.

The pistons would be much lighter so balancing would be necessary. They would also have modern and much better thinner rings I believe .040+- rather than the stock much thicker ones. I worked for 14 years in the piston ring industry way back when.

I my opinion doing it this way is not much more expensive and the result is better than spending at least $250 decking a block that much(I paid about $100 for about .005" on a head last winter) Then some different pistons for at least $250 and then coming up with a different cam belt system.

The one thing I have learned from racing the past 6 years is that it is much cheaper in the the long run to do it the right way the first time.
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Mike


'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

[Cedric]

Regarding the gearbox, Endurance racing banging shifts is completely different, then you get heat dissipation challenges which can be hard to get around, and if you shift them fast you will have to do regular rebuilds, they arent built for fast shifting. But if you already have a G31, run with it, they have been proven to take alot of power. Maybe not suitable for drag strip launches, but other than that I think it will be just fine for what you will do with it.

Corvette boxes are absolutely massive and would need alot of cutting in the body, at least here in europe there are a bunch of more modern audi boxes that could be used with an adapter plate to an audi based torque tube, and maybe boxster/cayman ones.
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1980 924 Turbo
www.instagram.com/garagecedric/

[safe]

[Mclaren924]

Absolutely right about the comparisons, what's good for the goose might not be good for the gander. There's, A LOT of hypothetical stuff here that I've described so absolutely you are right Cedric, really just need to try and find out what it does. I see no reason these rotating assemblies can't take the abuse so lets put this theory to practice.

Beartooth I remember that exact piston rod setup you are talking about, I think you posted about it on ideolas stroker build? Welding and grinding the crank or maybe just offset grinding is a big intertest of mine but ultimately very expensive for not a huge performance gain. IF this idea of mine works, there will be a built stroker motor in the future following similar principles. For now the idea is can I build a 10-1 motor for around 1000$ including machine and new bearings/gaskets/studs. The G31 is a good strong transmission but ultimately they do not like aggressive driving from a stand still and there will be a lot of this how I drive. I foresee a boulevard of broken dreams just like Britain if I stick with g31 as long as he did. Lot's of the LS swap guys in 944 do the 01E swap but for the price and added effort you can swap the corvette 6 speed for the same or less, I got the entire pedal box and tranny for 2000$, 01e are basically that price starting if not more out here, not to mention hard as shit to find . I plan to follow Britain's approach for install so it will result in better cv axle angel but will need a custom tunnel.

Custom pistons would be roughly 1000$ plus machine work of probably 500$ or more, it would still need to be decked for flatness so another 250$. 350$ for bearings and a cometic HG, 150$ for head studs and you haven't even lapped a valve in the head yet, let alone new valves and VJ is another 1000 easy $. Very easily could spend 5000$ plus getting a block completely built and redone, and if I'm putting all the work in for custom pistons, it's almost required I do the rest new or rebuilt/upgraded. Skimming the block is cheap and easy, if something goes wrong, I blew up a 1000$ max engine and I drive 1 hour to buy another 924 engine for 100$ and do the same thing, or maybe a little different lol. I'm not saying forged pistons are bad or a waste or anything like that, Its just very east to quickly sink a ton of money into it with pistons. I do understand what you're saying though Mike, it is cheaper and or easier to build it to the tits once and be done than to build 5 like mine. Like Cedric said, let's go find out
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1980 931 "Salt" Bucket wannabe racer (not started)
1979 924 Sebring "Pepper" -Sold
1980 924 "Donnie" (Parts car)-DEAD
1977 924 Slicktop "Pennie" Bucket turned Silver Spoon

[Beartooth]

I remember posting in that thread, so I probably said about the same thing there. I'll probably go the custom piston route if it's less than $1000 out the door; I was thinking it could be as much as $500 per piston. Assuming Wiseco will sell you a set of four pistons, that Chrysler piston would probably have you out the door for close to $500 for the set with rings - just the compression would be an issue. You could probably chance it with stock boost (9:1); might be good for a NA race or hot street motor (you'd probably need a thick head gasket - 12.7:1 compression with stock deck height and gasket...). That said, I do think there's enough advantage to having some quench on an all-out boosted motor that the custom piston route is borderline to a no-brainer. I would love some day to build the kind of custom setup I talked about: you could pick up some displacement and lose a lot of rotating mass - quicker revving and less vibration.

On the transmission, I'm not trying to nit-pick; hope I'm not coming across that way! I figured getting the transaxle and torque tube would be quite a bit more than $2000. I suppose that's partly a matter of luck, but at least it's in the same ballpark as as getting a decent G31 and associated parts. The other issue in the back of my mind is what Cedric mentioned, and really, even putting aside having to build space for it, fitting it all together is another challenge. One of those "it's there [G31], it might do the job, why not give it a shot?" things to my mind. But on the other hand, you do have Britain's pattern to follow, so that gives you something to copy as opposed to figuring it all out yourself. Looking at what Britain can do with cars - fitting whole sections of another car to fix crash damage or other issues - I'm a little in awe. Some day I hope to have the skill and resources he does... One of those areas where I could probably copy him with some success, but what he could do in a month would probably take me a year - give or take, depending on how many re-attacks it takes before I get it right.
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1980 931 diamond in the rough

[Mclaren924]

Nothing to worry about Beartooth I always appreciate the knowledge and insight. There is a large realm of possibilities from pistons, completely custom and picking a bore size to match, or going with pre existing ones that are within our bore capabilities. The rabbit hole is endless. The price gets insane quickly with custom pistons, the coatings you can put on, then the machine work required to fit said setup correctly. The forged piston route with a custom designed quench zone and height and surface with valve recesses would be the best, but ultimately stupid money to do. Would be interesting to see forged pistons in a similar config to stock and how they hold up at similar boost levels. I feel like these motors with stock rotating assembly can be pushed to a point where no stock 924 trans is going to hold on. I wont speak for him but I assume from what Safe said earlier, he is nearing this point with his build.

Currently have the later 5 speed H patter turbo trans in the 77 car that will be receiving this decked turbo motor, downside is it is supposedly weaker than the g31 but you can throw on the short shifter kit and bushings onto it, which you can't with the g31. I have a small shaft g31 sitting around that could be used and I also have a bigger diameter one in my 931 currently that can be sacrificed as well. Drag strip racing and similar racing on the street is a majority of the driving I do, say 75% of all racing activity. The corvette 6 speed will wait for a while, it is not a simple bolt in swap. It was out of a friends wrecked vehicle so I did all the work pulling it out which made the price better. I see them on ebay for around 4-5k when I look. Still pretty similar in price to the 01e swap kits I see going on the 944 group pages.
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1980 931 "Salt" Bucket wannabe racer (not started)
1979 924 Sebring "Pepper" -Sold
1980 924 "Donnie" (Parts car)-DEAD
1977 924 Slicktop "Pennie" Bucket turned Silver Spoon

[safe]

if its street/drag racing you haven't thought about some kind of automatic gearbox?
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/Magnus, Stockholm Sweden
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Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe

[Mclaren924]

[safe]