A 1980's 'what if' motor for Group C/IMSA GTP

[Rossriders]

I've played the demo for a few weeks prior to finally deciding to get the supercharged edition. I'm still trying to learn what I can given everything else I'm dealing with. But at the least I figured it would not hurt to show something I have been working on, that's been on my mind prior to even hearing of this game.

The engine below is a 'what if' motor if someone insisted on building a racing motor for Group C endurance/GTP era of the time, though what if said engineer insisted on a pushrod design over an overhead camshaft setup and here's one such result, with the help of twin turbos.

4 liter prototype 2.png (867.29 KiB) Viewed 8051 times

Year: 1981
V8 Crossplane
Cast Iron block and Cylinder head
85.2mm bore
87.7mm stroke
Capacity: 4000cc

Forged Steel Crank
I beam Steel Conrods
Hyperutectic Cast Pistons

Pushrod 2 Valves Per cylinder (16 valves)
Cast iron head matereal
7:1:1 Compression
61 Cam profile
No VVT or VVL

Twin Turbo Ball Bearing turbo
Water-Air Large Intercoller
Compressor: 63.5mm
Turbine: 68.0mm
Ar Ratio: 0.74
Max Boost: 1.96bar

Mechanical fuel injection
Throttle per cylinder
Racing Intake
Regular unleaded 91.0 octane
Fuel Mixture: 10:1:1
Ignition timing: 100
RPM Limit: 6500rpm

Short Cast headers
Dual Exhaust
Bypass Valves
2.75 Exhaust Diameter

three way catalytic converter
Strait through muffler
Strait through muffler


While I've spent time tweaking things, given I've only had the game for a few days, I'm still learning, even in spite of having been messing around with the demo (and getting either a silver or gold in nearly every scenario in said demo sans the military gen set)so....yeah.

Hope you all find interesting if nothing else.

Until I post again.

[CNSpots1]

Believe it or not, this engine is likely being held back by the fact that it's as large as it is.

A key concern when designing a racing engine, especially a turbocharged one, is getting it to rev higher. Naturally, revs are hard to get with pushrod engines, but a heavy 4.0 liter isn't going to help your performance much.

I'll go to drawing board and see what I can whip up with a OHV engine, I'm fairly sure downsizing it would actually increase output.

[Rossriders]

The input is appreciated and I'm curious to see what you're going to make. That being said, a reason for why I went for an OHV was for it to be in theory a more compact and lighter package compared to an engine that uses an OHC setup of the same cubic capacity.

That being said, even prior to your post, I had been and still am doing further changes with the engine.

A thing I failed to mention earlier was that getting outright power hasn't been too much an issue.

It's getting that power by some very specific means. Namely the fuel used is unleaded 91 octane. The highest octane level on the sandbox as of now for 1981 is 98 leaded octane.

Granted on one end it may no matter much if any concern is given to reduce emissions with a racing engine among many, but this was also an attempt to see what I could actually have done with 91 octane gas over the leaded 98. I had also went with cast iron initially for just strength, but when I saw just how heavy it was, I went for Aluminum over cast iron. That and going for leaded 98 fuel for now.

One other issue is engine response or there lack of, not to mention overall power curves. Since your post and as of this post I've now got the engine to around 811bhp.

But responsiveness is at 35.8, granted the responsiveness before was nothing remarkable earlier. But I'm still trying to find a more even power curve, or as much as you can with twin turbos in the 80s as of this game build.

All I can do is keep at it and tweak things further. One thing that's kept me going even when messing around with the demo with just 4 cylinders and being N/A only was seeing just what I could actually do, and in spite of what I do know, I've still got a distance to say the least.

Here's one take on that revised motor...I'm still working on it when I can spare the time so...we'll see.

[Junny]

"race fans do not come to races to watch an economy run!"

From my readings this type of racing was in the same league as the insane Can-am racing of the 70's... absolutely all out over the top Aero and insanely powerful engines. Revs, Raw power and Torque are the answer it seems which is just up my alley ill see what i can come up with

only problem i see is that IMSA GTP used alot of really highly modified v6 and rotary engines and those are not available yet

[Rossriders]

Not gonna lie, I am waiting for V6s and rotaries if/when they arrive, though this engine design is something that has been on my mind for a while. That and it's one other reason why I included both Group C and IMSA GTP besides how both had broadly identical rules. A key difference being that Group C had a fuel limit as to how much fuel you could use per race.

So while there was an open rule to what kind of engine you could build, just how much it consumed fuel was a different story. As stated, it's a 'what if' since the overall goal (that I've yet to achieve) is to make an engine of it's size so it can hopefully fit in a prototype chasis, have the power but also be durable, and economical (within reason). Granted an engine is only one part of an equation to a winning car, but it can help or hurt things.

I'm still tweaking and messing around with things, plus alongside this motor, I'm also pursuing another angle with an attempt to build an N/A that has it's own advantages and distavantages against the rest of the field.

But one other key factor of course is what kind of car/chassis for either engine or any engine, the team, driver tallent and so on.

I'll show more when I can show more, till then, and thanks for the reply.

[Junny]

I hope you dont mind i made myself one .

Inspiration
1984/1985 Nissan GTP ZX-Turbo


now I know this was powered by a VG30ET a highly modified V6 twin turbo I felt like could replicate a decent tribute using the in game 6 cylinder. Bore and stroke remain true at 87.1 x 82.8 and compression also remains at 8.6:1 what follows is some serious hand crafted master work backed by a 70mm Ball bearing Turbo pushing 38 psi.


MTBF sits at around 24900kms so not bad... Dat fuel consumption I am very impressed how broad the torque curve is with almost 4000 rpm of usable power band, its almost a shame the game does not have bigger turbo options.

[nialloftara]

It's the 80's who care about economy,
More POWER!

[USDMFTW]

It's the 80's who care about economy,

With that terrible turbo lag and power band no team will use the engine because they dont want thier drivers to die. Instant wheelspin is bad for life insurance policy holders.

[Rossriders]

It's something that's too glaringly obvious, granted some RL racers had powerband issues comparable to these, but it still stands.

It's why one other thing I've considered is a higher displacement N/A motor, so far I'm trying to see what I can get out of 4.5, 5 and 6 liter OHC configurations, and while I'm clearly going to have trouble even trying to match the power I've got out of the twin turbo setup, (which is assuming I even can reach it to begin with) part of me also sees an NA/varaint, even if less powerful than a comparable turbo as something more useable.

It's nice and a small achievement for me to get so much power so far and trying to find ways to push even further, but at the same time it's no use if you can't actually use it, I've played too many games to know that. If you can't get the power down for a given reason if not several, it's not much use. I could only really see this engine being useful on a circuit for very high speeds, while Le-mans would be one candiate...part of me is doubtful.

That being said, I am trying to make an engine that's using the twin turbo setup but has more controllable power, though how...it'll take some time.

Apart from that, it's interesting to see what other engines have been built, including a flatplane motor. I've yet to download the file for the sledgehammer engine, but this is just an assumption that the block and head matereal must be cast iron right? I say so given comparable weight I had when my initial motor was that, I had also picked the matereal because I wanted to get more power out of the engine. But like stated, decided to just stay with a lighter allow and work with that.

That's enough rambling out of me for now, until later.

[Junny]

What lag? My engine i posted above is a 3 litres single turbo and has 4000-8000rpm usable power band and 800+ hp.... it also happens to be cheaper and lighter than any N/A engine and still put up with 25000km of abuse...

[nialloftara]

It had a aluminum block iron head, the block didn't really add any power as iron but the heads did so i just saved weight on the block. Well according to this rule book http://www.imsaracing.net/Archive/Rules ... 0Rules.pdf they had only a few engine qualifying for group C, as it turns out I already had a Datsun 280zx engine built, so here is a all aluminum 702hp 2.8 liter sohc 12 valve L28ET

[nialloftara]

And because More Power! and "what if". Heres the 800hp SOHC 24 Valve and 870hp DOHC 30 Valve models they should have made.

[RobtheFiend]

OS Geiken made a DOHC 24v engine in the early '70s, a modern remake came out a year or so ago.

http://www.speedhunters.com/2013/02/eng ... -tc24-b1z/

I'm in love with that exhaust manifold.

[Rossriders]

@Junny, I was actually meaning more with my motor. Though yeah, your engine is actually very very nice. Granted the only real issue I can think of is what chassis to fit it in be it an car chassis that existed at the time or a new one that's within rules.

For now I think until I can actually sit down and spend more time on it, the farthest I've pushed this motor for this year is 837bhp, again on leaded fuel.

But again I've still got an issue with extreme turbo lag, which is why I'm working on another approach.

That approach being that while this other configuration pales in comparison in power even to other competetors including the 956 at that time far as engine power goes, one major advantage this engine should have is far more torque at far earlier an RPM. While the curve is still sharp, it's a bit more controllable.

I keep saying this but I'm still figuring things out, and for now I can work with 91 octane fuel (unleaded) given what RON ratings I've been getting. Plus with it's current MTBF, while it may not have absolute power, it does have durability...in theory.

I'll be honest, given my history at other forums, was unsure if anyone was even going to respond but it's been quite interesting seeing other people's engine designs and their take on things.

One thing I'll also mention is for anyone else reading this...don't be afraid to go further down the timeline or even earlier, I say this becuase in one sense with how engine testing may take, one can only do so much with given time and budget, and what one struggles with one year may become easier down the line.

I say this also since I'm working on a more updated version of my 4.0L OHV bi turbo design, and trying again an angle on a N/A motor with comparable power, or at the least have more useable power in general racing situations.

@RobtheFiend that's quite the history, and I feel like trying to maybe duplicate that.

Although I'm also wishing and waiting patiently for being able to make V6 and I5 motors...we'll see.

And now those two engines.

the high output motor.

4 liter prototype hi output.png (1.02 MiB) Viewed 7586 times

And one more for torque at lower RPMs

4 liter prototype hi torque.png (1.03 MiB) Viewed 7586 times

[Junny]

I tried to make a 1973 917/30 inspired engine but i could only get around 1330hp from a 5.4 litre engine wherase the real car made 1500+