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Yes, custom Carrillo rods / CP pistons. Saved a fair bit of weight. I guess we'll have a look to see how feasible it might be to retro fit b/shafts. If too hard we will have to deal with it. Car is built for very short duration bursts rather than enduros so that should help too. But, yes, spanner checks are a constant.
Assuming you've got something like a Lindsey 3 piece crossmember fitted, it shouldn't take all day to pull the bottom cover off the engine after every hour or so, to re torque every nut and bolt you can see.
Quick update and comment on my experience. As the registry list says, I ran an S2 based 3L for over 10 years with very minimal problems. It was under-stressed, making 340 WHP 380 TQ. I eventually scored the cylinders by overheating (100% operator, me, error). When I took it down, we discovered that I had a cracked saddle just like 333PG333. I had never run balance shafts because at one point the upper one had become very difficult to turn, so being cheap and lazy, I wired them in place and then removed entirely at the next opportunity. Oh, I shifted at 6K, but would run higher, <7K if it saved an up/down at the end of a straight, and it ran an S2 balancer.
Anyhow, I had the block welded up and put a head stud in place of that girdle stud to get some extra "bite". See cheap and lazy comment above. It has now been rebuilt as a 3.4 stroker with dry sleeves. It only has about 20 hours on it and I'm still sorting, but the plan is to run it like I did the 3L - about 1 bar boost and 6K soft redline. Before you all rush to your keyboards to tell me I'm an idiot, consider this - I'm the guy testing stuff that might not work so you don't have to. :-)
I'll post an update when I get some real hours on it.
That really is a nice torque curve and the exact reason I bought a 968 engine to build up.
I mentioned the rpm because 2nd order vibrations increase exponentially with rpm and you stated 8800 which is considerably higher than stock. The rpm’s on that dyno graph look a lot more reassuring.
The 2nd order vibrations are very minor at lower rpm’s and I predict balance shafts were only necessary for the last thousand rpm or less in the stock motor and rpm limit. By lightening the pistons and rods it could be possible to shave close to 30% in piston weight as the stock items are so heavy. But because of the exponential factor this is only going to increase the vibration threshold rpm limit by a fraction of 30%. So a balance shaft delete engine is very feasible but how high you set the rev limiter is the factor of wether or not it will survive.
You also have the factory nanny level of safety margin that a race engine can do without. So there’s likely a few hundred rpm to be had there. It’s just important to know a race engine built to the limit needs more care and attention and will ultimately have less reliability. Checking the main stud torque after a couple of sessions would be high on my list. If they are all good you won’t need to check them again all season. Also keeping the rev limit down and only using those additional rpm’s when absolutely needed will be key. At a 6000rpm rev limit I would consider your engine and level of build as an endurance engine. Raise that past 8000rpm and it’s now a qualifying engine.
I doubt we'll be going up any higher than dyno rpms. There is an element of mechanical sympathy for the motor now. We may just stick to 1bar. There will be a new aero package on the car that should make up for any power losses through low boost. The ultimate goal is to get it going, compete in WTAC '23 and sell it while it's hot. Start saving now Luke!
Originally Posted by blade7
Assuming you've got something like a Lindsey 3 piece crossmember fitted, it shouldn't take all day to pull the bottom cover off the engine after every hour or so, to re torque every nut and bolt you can see.
We don't run that 3 piece item. Going to be a bit of a pita to do this.
Originally Posted by Weston Dillard
Hi all,
Quick update and comment on my experience. As the registry list says, I ran an S2 based 3L for over 10 years with very minimal problems. It was under-stressed, making 340 WHP 380 TQ. I eventually scored the cylinders by overheating (100% operator, me, error). When I took it down, we discovered that I had a cracked saddle just like 333PG333. I had never run balance shafts because at one point the upper one had become very difficult to turn, so being cheap and lazy, I wired them in place and then removed entirely at the next opportunity. Oh, I shifted at 6K, but would run higher, <7K if it saved an up/down at the end of a straight, and it ran an S2 balancer.
Anyhow, I had the block welded up and put a head stud in place of that girdle stud to get some extra "bite". See cheap and lazy comment above. It has now been rebuilt as a 3.4 stroker with dry sleeves. It only has about 20 hours on it and I'm still sorting, but the plan is to run it like I did the 3L - about 1 bar boost and 6K soft redline. Before you all rush to your keyboards to tell me I'm an idiot, consider this - I'm the guy testing stuff that might not work so you don't have to. :-)
I'll post an update when I get some real hours on it.
West
Thanks for your post West. Be interested in your 3.4L build specs. Was going to do something similar many years ago. Have you any dyno sheets from it?
Originally Posted by Chris White
Nice torque curve on that one!
btw, something to keep in mind with balance shafts - they spin at 2x crank speed, so a 8800 rpm engine would be spinning the balance shafts at 17,600 rpm!!
As you might have guessed, this project started years ago when Sid (Blown 944) was around. Jeff (Dizzy J) and I split a box of forged, coated Chevy pistons, had cranks offset ground and used Eagle rods out of a Mitsubishi. I'm running Microsquirt off a base tune I got from Doug (Dougs 951s). Doesn't all that take you back 6-8 years? Life has kinda gotten in the way for both Jeff and me, but we aren't giving up. We recently made a pact to get them both out again. No dyno numbers yet, but will be happy to share we have some.
Ha, yes that does take us back a generation or two. I was actually looking at an old post that goes back to 2007 with a lot of old heads and interesting cars. https://rennlist.com/forums/944-turb...ick-951-s.html
What's the bore and stroke of your new motor out of interest?
Some news now… the 3L 16V block is mounted, waiting now to finish the head with special springs that are in production now, NOT as most think harder, but softer than NA springs… investigated a lot on this topic and finally understood what Porsche did at the time and why!
and today the turbo itself arrived, a beauty… a bit larger than original, with ball bearings by ETG in Germany
Some news now… the 3L 16V block is mounted, waiting now to finish the head with special springs that are in production now, NOT as most think harder, but softer than NA springs… investigated a lot on this topic and finally understood what Porsche did at the time and why!
and today the turbo itself arrived, a beauty… a bit larger than original, with ball bearings by ETG in Germany
1. as for every turbo engine the boost and exhaust backpressure will put more force on the valves - so while they are closed the force has to be higher as on NA engines
2. the 16V valvetrain is beyond reliability in serial status - having broken teeth on the camshafts and lenghtend chains is usual - so you would not want to increase the load, if it isn't needed. Having the valves completely opened it's not needed to have a higher force on them (unless you want to run higher rpm's) as the gas flows and the pressure is irrelevant. It just needs to be ensured the cam doesn't fly off the lifters on the changing point of movement - and this is proven to work on thousands of NA engines
conclusion: longer, but softer springs are needed to fulfil both requirements. And by the way: this is exactly what Porsche did on the 944 turbo compared to the NA engines. Reverse engineering
1. as for every turbo engine the boost and exhaust backpressure will put more force on the valves - so while they are closed the force has to be higher as on NA engines
2. the 16V valvetrain is beyond reliability in serial status - having broken teeth on the camshafts and lenghtend chains is usual - so you would not want to increase the load, if it isn't needed. Having the valves completely opened it's not needed to have a higher force on them (unless you want to run higher rpm's) as the gas flows and the pressure is irrelevant. It just needs to be ensured the cam doesn't fly off the lifters on the changing point of movement - and this is proven to work on thousands of NA engines
conclusion: longer, but softer springs are needed to fulfil both requirements. And by the way: this is exactly what Porsche did on the 944 turbo compared to the NA engines. Reverse engineering
My experience is that softer springs and high boost equals valve float and **** hits the fan.
If the valve springs are longer the preload will be higher so they will be stiffer anyway?
It seems unnecessary to try to reinvent the wheel There is no evidence that stiffer springs cause issues with variocam, chain or sprockets.
At one point I thought stock S2 springs on a ~400 hp 3.0l 16v turbo would work for low boost but in reality the engine couldn't handle more than 0,5 bar before the valves didn't fully open and the power curve just died. Slightly stiffer springs solved that.
Regardless of diagrams or calculations the amount of real life experiences confirming issues with too soft springs is just overwhelming. If you want to go another route please do. Just surprised you're not interested in real life experiences from 944/968 engines between 300-1000 hp.
There is no evidence that stiffer springs cause issues with variocam, chain or sprockets.
just went to my stock and picked 4 random camshafts of the box - 100% stock NA engines with soft springs... so I'm sure I don't want to put more load to them
Originally Posted by Duke
Regardless of diagrams or calculations the amount of real life experiences confirming issues with too soft springs is just overwhelming. If you want to go another route please do. Just surprised you're not interested in real life experiences from 944/968 engines between 300-1000 hp.
I am and appreciate your input - but don't you think thousands of 951 engines are also real life experiences? thats exactly what they did - original turbo springs are softer as NA springs... and at no point the force on turbos valves is lower as on NA springs
I took all these measurements and trials because I knew the standard springs are not working (from the first 16V engine I build 3 years ago) but the car owner wanted it that way...
02-09-2023, 08:52 AM
There is no evidence that stiffer springs cause issues with variocam, chain or sprockets.
