SloMo228

One of the major points in my long-term plan for my S is to rebuild the engine, both for better performance, and peace of mind that it will continue working long into the future. It runs fine now, but it has put a lot of miles behind it and I know it won't last forever, plus a little extra kick is always appreciated.

I like the character of the engine and want to accentuate its rev-happy nature. So I am thinking a lightweight NA build will be good and I'm hoping of achieving an output of at least 200 whp. I think this is doable without getting too crazy with the build.

Anyway, this is all at least a year or two off, since I want to get Megasquirt up and running well on this car first, and the transaxle is the next thing that needs attention anyway. But I thought it might be a good idea to get some input from the 944 experts here to see what you think of my rough outline so far.

I am planning to have the head rebuilt at a machine shop familiar with 944 engines. I don't feel that this is something I want to attempt with my skill level. New valve guides and seals, hotter cams from Jon Milledge (the 4V "Mild" cams on his site, most likely), and do some lightening of the valve train with lightweight lifters and springs. I'm assuming my stock valves will be OK for reuse.

The block will be checked out by a shop familiar with 944 engines as well. I don't really have any oil consumption even after 200,000+ miles, so I'm hoping that there won't be any major issues with the cylinders. All seals and bearings will be replaced. I'm considering bumping the compression up a touch but don't know if it will make much of a difference since the S is already fairly high-compression to begin with.

I plan to have the crankshaft lightened, and will also be using the lightweight N/A Pauter rods. Hopefully I can also find lighter pistons, although I have considered the possibility of changing the bore to allow the use of non-Porsche pistons, I'm not sure that that would be worthwhile. I will also be using a lightened flywheel and pressure plate, and plan to have the entire rotating assembly balanced.

I will be adding a crank scraper and oil pan baffles to help with that issue as well, and reinforcing the oil pickup tube. I am hoping to be able to reliably spin this engine up to a 7000-7200 RPM redline. I think the lightening efforts will help with that but I'm no expert.

I am on the fence about deleting balance shafts as well. I know it's a relatively small performance boost, and a fairly small weight reduction, but I don't know how effective they are once the weight of the rotating assembly is changed anyway. Plus I think that removing the shafts and welding up the oil supply passages to the balance shaft bearings can only help with oiling the crank and rods.

Feel free to tell me I'm way off on this build, I have only been doing some daydreaming and window shopping so far. Every now and then I get that mad itch to toss the Porsche motor and fit a V8 in its place, as well, so that's an option that gets more tempting as the potential costs of building the 2.5 16V go up...

V2Rocket

- Rebuild the motor to fully stock spec, maybe fit 0.50 or 1mm oversize Wossner pistons to freshened bores, if your block is out of spec as-is.
- Make sure your exhaust is not clogged, keep the cat (unless your state allows its removal)
- Fit your MegaSquirt system.
- Getting rid of the AFM and having control of the tuning will get you past 200bhp on a 944S engine, no problem...I am confident of this.
- It may take the hotter camshafts to get to 200whp...
- Keep the balance shafts. No good reason to delete them.
- You are in Michigan, check out Molnar connecting rods, they make an H-beam for the 944 for about $600/set. Racer's edge is a dealer for them, where you can also buy the aforementioned Wossner pistons.

924srr27l

Are the figures quoted by Porsche Flywheel or Rear Wheel ?

R

V2Rocket

flywheel

SloMo228

Yep, I'm starting with 188hp at the flywheel. Although it's certainly somewhat less than that after all the miles.

Yeah, MS will be going in this summer most likely. Looking forward to the better driveability, reliability, and performance.

Thanks for the tip about Molnar rods, I will look them up. $600 a set is a pretty good price.

924srr27l

ok, and how much loss 20%?

V2Rocket

around here people throw out 15-20% as estimate...

i did dyno testing with fully stock engine and found that to be about right.
US early NA rated 143hp crank, put out 121hp at wheels...121/143 is about 85%.

924srr27l

Ok thanks,


So getting back to this thread, that would be 170 bhp at the wheels for a stock 2.5 S 16V? which is about the same as the 3.0S2 ?


R

H.F.B.

hm,

as stated by V2Rocket: 143 x 0,85 = 121,55

then

188 x 0,85 = 159,8

211 x 0,85 = 179,35

924srr27l

SloMo228
I'm hoping of achieving an output of at least 200 whp. I think this is doable without getting too crazy with the build.


This would equate to 236BHP then for a 2.5 16V ?


+48 HP ? I wonder if this is achievable without getting too crazy?


R

H.F.B.

nearly correct: 200 / 0,85 = 235,2941176470588

Achievable, why not, but streetable is the other question.
For sure not with a stock AFM.

Noahs944

SloMo, I like the sounds of this possible build.
---

The biggest hurdle from what I have read is proper oiling.

SloMo228

Yeah, I know that will probably be the main obstacle to overcome in terms of being able to spin the engine up higher. There are lightweight valvetrain components available (I could even go for titanium valves if I felt like spending some real money) but only so much you can do for oiling short of a dry sump.

And I'm not sure a dry sump is a great idea on a street-driven car. I could be wrong, though. I'm thinking that a crank scraper and windage tray will be a good improvement, though. 7200 RPM is only 400 RPM higher than the stock redline for the S, although I know that energy increases with the square of velocity...

Arominus

Getting past 7100 is where things get harder IIRC, the oil pump starts to cavitate at that point. You want those hot cams, cams are how you are going to make more power in this motor along with the MS and a good tune. 7100 is a decent target though, my 968 motor is chipped to rev to that point and has no problem doing it, though i don't tend to get it wound up much past 6900ish.

V2Rocket

Set the redline a few hundred rpm past max power for whatever cams you've got.
No point going to 7200 if your cams peak at 6000 or wherever.
Lightweight lifters are available from 928 motorsports...
Run a good (thick) oil. 50 or 60 weight, to keep oil pressure up at high RPM...

...or...add displacement
If you will keep the engine NA forever, I bet you could find some clean 944S2/968 pistons and bore your block to fit.
Doesn't cost any more to bore to 104 than it does to 101mm. The cylinder walls will still be thick enough. You would need longer rods if using the 2.5 crank though.

Adding displacement has the effect of moving down the power range of cams...more cubes = less revs required to flow a certain amount of air, to make target horsepower...