Your guess on HP #s?

[rdane]

Here are the specs of my new engine as it goes back together. This is a knowledgable bunch, where do you think I'll end up for HP?

'79 3.0 case which has been boat tailed
74.4 crank ('88 3.2 crank)
Mahle, Max Moritz, 98 mm P&Cs @ 9.8:1 compression
Pistons have a ceramic coating on the crown and dry film lube on the skirts.
Cylinders are half mooned
Pauter light weight billet rods and bolts (6 of them weigh the same as 5 Porsche rods)
20/21 Web cam
(makes a 3.356L other wise known as the 3.4 and a jump of 12% on displacement)

Valve job as follows:
Valve and seat machining performed on SERDI machining center, five angle intake seats and narrower seat faces for improved flow and better seat seal at high RPM. Full port smoothing, (NOT PORTING, no cross sectional increase of ports).

Ti retainers and EBs HD valve springs
ARP case studs

New ejectors
Big bore throttle body
Light flywheel
single plug
magcor wires
Back dated heat
CIS injection
SSIs and a Dansk 2/2

I started this project with the same exhaust, 20/21 cams and 182hp at the rear wheels.



I would appreciate any opinion. Feel free to break down where you think the HP was added and what was a waste of time.

Major case of cabin fever going on here

[beepbeep]

CIS and single plugs are keeping you down on that one. Otherwise very sound concept.

As stated above: maybe 240hp at crank.
With dual-plugs and EFI: approaching 280...

Engine will like to rev with those lightweight rods and valve-hardware. Lightweight components won't give you much additional HP themselves but will increase rev-margin and allow you to use hotter cams.

[ChrisBennet]

rdane,
Sounds like a fun project. On my '86 case the cylinders only protruded into the case about 2mm so I didn't bother to moon them. Is it different for the earlier (sump plate) cases or did you remove case material?
thanks,
Chris

[rdane]

Chris, here is a quick look at the internals. We didn't cut as much off the cylinders when half moonig as expected because the pistons have such small skirts in comparison to the stock CIS parts. Well advised? I suspect not in retrospect. Hopefully the boat tailing on the case, the smaller profie of the new Mahle MM pistons and the half mooning will open the case up a good bit. I had posted a similar question on the general foum but has few serious replies on engine design.

Quick question though for Goran or others, how does CIS limit a car when it is easily good for 400 hp as an induction system? I am only looking to get into the mid 200s. The machine work is being done for twin plugs as I have the car put back together. Just undecided when to add them at the moment.

My intention was to keep the user freindly CIS and at least duplicate the original SCRS's #s @ lower rpms..

250 hp @ 6,500 rpm
184 lb-ft @ 6,500 rpm
0/60 5.0 secs
top end 155

I am adding 12% in displacement and upping the compression by 1.3 points from a measured original 215 @ the crank.

[snowman]

I would vote for BeepBeeps numbers being very close. The port "smoothing" if done wrong could hurt as much as it helps. Removing flashing bumps is generally beneficial, but to much polish can actually hurt air flow. The exhaust valves outside edge, the edge inside the combustion chamber, around the margin should be rounded. The intake could be swirl polished. THe air flow actually measured on a flow bench and the heads modified accordinly, and your wish is very reasonable.

[ChrisBennet]

Originally posted by rdane
Chris, here is a quick look at the internals. We didn't cut as much off the cylinders when half moonig as expected because the pistons have such small skirts in comparison to the stock CIS parts.

Would the piston's skirt be a factor with half mooning? The material removed from the cylinder lines up with the "skirtless" part of the piston right? Perhaps I'm not understanding correctly.

I originally asked because I'm curious what changed between the 3.2 style case and earlier ones. Did the old cases have deeper spigots or did the old cylinders protrude further into the case?
-Chris

[rdane]

Chris, I believe the alignment you are thinking is correct. No idea on the comparison of cases. I didn't do the work but had it done. I was surprised that more material wasn't removed on the cylinders until I compared the two pistons. Original 95mm, 3.0 CIS on the left and the new 98mm CIS Max Moritz on the right. The skirts are so different that if I had noticed it before the half mooning was done I suspect I might have passed. Looks to me like the Max Moritz pistons were intended to be a big performance improvement over the stock pistons.

Polish and head work is being done by a well respected Porsche race shop, owned by a ex-Porsche Works mechanic. I believe they understand what I am attempting to do with the CIS and limited mods to squeeze the most out of what we have.

[ChrisBennet]

rdane,
I see what you're talking about now. I hadn'd remembered SC pistons skirts were like that (sticking out on the sides).
-Chris

[Wayne 962]

Your cam (needed to run with CIS) and CIS is your big hold back there. I would ditch them both and run a hot cam with Webers.

-Wayne

[snowman]

I agree even more with Waynes approach, why settle for 240 and IF everythings done JUST right 250 when you can get a whole lot more without much risk, or supernautral performance enhancements. Dump the cis.

[rdane]

Thanks Wayne. Trust me, the cam/induction decision has been long fought on this project. Your engine book encouraged me to build the engine as I have. You mentioned the 3.7 CIS (280-300hp) Andial did in your favorite engines list. I got the impression CIS hadn't been pushed for several reasons, cost and the availability of good used Motronic 3.2s being the best initially and then later the 3.6 transplants. I realise it has limitations but where they are is the question and why I am building this one.

Wayne mentioned Andial's 3.7 CIS which is 19% larger than a 3.0 (and I suspect that number is actually inflated). Similar cams and and exhaust in what I am building. Twin plugs and a compression bump of 1.5 gave that engine a jump from 180 hp stock to 280/300hp. Call it 100 hp more than a stock '79 on their 3.7! Well over the expected 19% which would be only 256hp. (based on my '79) Compression jump is similar @ 9.8 (1.3) and twin plugs are an easy addition. What did I miss in my design to drop the 25/45 hp that the Andial 3.7 gained over a simple displacement increase?

Will CIS support 400hp in a NA engine as it does in the turbos. What do you think twin plugs would add to my engine design? I am not looking for a high reving engine, just some more torgue and a bit more power.

I have left open the option of twin plugs and different induction system being added (now or later) if I don't reach a power level and drivability I think is acceptable. But for me, useing carbs are out.

I stopped at 98s with a CIS design to avoid any more case work and the possibility of using a single plug at 9.8:1 compression.

Have I maximized what can be done with CIS @ 98mm and single plug? Or did I blow it and should have twin plugged and gone to 10.3 CIS from the get go?

[beepbeep]

Originally posted by rdane

Quick question though for Goran or others, how does CIS limit a car when it is easily good for 400 hp as an induction system? I am only looking to get into the mid 200s. The machine work is being done for twin plugs as I have the car put back together. Just undecided when to add them at the moment.

As far as i remember , CIS used on 930 is bigger than one used on SC's. Also, CIS used on ROW 930's is bigger than one used on federalized 930's.

The biggest ROW CIS can flow enough fuel for around 400 hp, but it's already "blowing in the wind" at that stage and choking the turbo. It can be tweaked beyond that number by modifying fuel head but then you are really into area of diminishing returns.

That being said, I suppose you have stock SC CIS that has smaller diameter of it's air-plunger plate and I see it as a major obstacle in your hunt for horsepower. Also, add the fact that CIS is notoriously intolerable of wild cams and you'll see that it has to go.

If you don't have the means for EFI then I suggest you to go Wayne's route and fit carbs. They are also hard to tune and generally messy but I bet they will give you more power (but not necessary driveability) and engine sound to match.

Good luck with your project and please post more!

Regards,
Goran

[rdane]

I have tracked down a couple of posts here by respected members that says CIS is good for an easy 250 hp and another that says 300.

Andial did somewhere between 280 and 300 on the 3.7 again with CIS.
I get more curious and more curious by the moment.

Easy enough to add carbs or EFI but I don't want to do either at the moment for various reasons. The most important one is I want to personally see how far CIS can easily be pushed for a street car.

[Wayne 962]

You are missing somethings. While I did not build this "experimental" motor (you might want to call them and ask them - the name of the customer who has this engine is Steve Lee), I am aware of the things they did to get this right.

First of all, they did not simply smack the stock CIS system onto the car. When increasing the displacement of the engine, you must make sure that the fuel distributor is adequately matched to the car so that it can supply the proper fuel ratios and not run too lean. Have you checked your mixture, while driving? (We sell a new tool that is very useful for that, that I am evaluating right now).

Secondly, they went to twin-plugs, which means that the engine timing could be adjusted for maximum burn and power. They also ran at a slighly higher compression ratio too.

Your dyno tests (I'm assuming) is of rear-wheel HP. This means there could be a number of lossy mechanisms in the measurements. If you have 182 at the wheels, then you have 220-240 at the engine, most likely, which is probably just about what I'd expect. Nix the CIS and those soft cams and you will get some more power.

-Wayne

[rdane]

Wayne thanks for your time and your answer. I have spoken with Andial on several occasiosns. I'll get more specific about their 3.7 next time. According to Peter @ Andial, their street 3.4s are pretty basic. Normal CIS fuel distributor, stock runners and no twin plugs on the 9.8s. Pretty much a plug and play.

The dyno sheet shown in my previous post was from my car as a 3.0L and the original CIS P&Cs @ 8.5:1 with 20/21 cams and SSIs 6 months ago. My new engine with 98 P&Cs and a 74.4 crank is not back together yet but coming along very well.

I will be tuning the new engine on a dyno when it is done.

[snowman]

I remember seeing several posts on this forum stating the big problem with CIS is reversion. Long duration cams have a LOT of reversion therefore only short duration ones work well with CIS injection. Something about messing up the air flow measurement in the AFM.