V2Rocket

Oh great supercharger gods...
I seek your assistance.

I'm putting an Eaton M90 roots-type on my 944. I have most of the stuff figured out but I'm curious what you guys think about boost levels..

The 944s specs are this:
Stock (rebuilt 3 years ago) engine, 2479cc
9.5:1 compression
100mm bore/78.9mm stroke
6500RPM redline
Stock intake/exhaust (really well made pieces just FYI)

Overall the engine is a pretty efficient design making the most of 1980's computer technology.

The stock size pulley on the M90 on a 944 is good for around 12psi. I only have access to 91 octane gasoline here in CA. Is 12 psi too much for a 9.5 CR motor on 91 octane?

It will be intercooled with a water/air unit with a dedicated cooling system/heat exchanger. I will also be running some kind of alcohol (probably methanol) injection system switched to activate at maybe 4psi.

AO

Well it sounds like you've already decided to go above 4psi.

Seriously though, a lot of it has to depend on your ability to control detonation. I know nothing about 944's so bear with me on this.

Do you have knock sensors?
Do you have the ability to modify the ignition maps? (I believe you do, but do you plan to do so?)

Many of the TS 928 guys are running 10-12+psi (not sure if any in CA are doing this) , but they can only do this if they tune the fuel and ignition maps to prevent lean and knock conditions. If you do this, I don't see why you can run the same amount of boost (or maybe even higher) without the methanol injection. THe 91 octane is going to limit your boost somewhat, but I don't know how much.

Bill Ball

As to DR's change to 3/16ths" spacers....

I hope he will clarify this. I measured the stock S4 gasket and came up with 3/16ths". So, a 1/8th" spacer seemed right on the money, providing a 1/3rd compression.

DR

Sorry, I forgot to do that last week.

Disclaimer: Keep in mind I can only reference this regarding my lower intake as it is very stiff and precisely milled to an even flatter tolerance than the factory head surfaces. I for sure would NOT recommend this using the Supermodel Cast lower intake as it is thin and not as perfectly flat. Some of the hand made welded Supermodel lower intakes would probably be OK since they were made with thicker and fairly flat stock.

Here is part of the message I sent Brian a few weeks ago discussing this subject, too busy to retype...

I am convinced the 3/16 spacers are the way to go. What we found on some short term (couple months) tests with the 1/8" spacers was pretty scary. The intake gaskets were literally torn to shreds in some places from the rubber "carrying the load" instead of the spacers. If you put one of the 3/16 spacers in a new factory gasket it is just barely thinner than the gasket AT the mounting holes... That was my mistake! The factory gaskets have additional "ribs" around the port sealing surfaces that are what is designed to seal the ports. When you add their additional height it becomes obvious the 1/8 are way too thin. I also did a bench test with an S4 Intake and all the factory mounting hardware (rubber bushings, metal sleeves, cup washers etc) and when I torqued all the bolts to factory spec on one of my intake "test plates" (1/4" plate that is a mimic of the head mounting surfaces ).. guess what spacing I got in between the test plate to the intake surface... yep, these 3/16" bushings fit in there like they were made for it. I went further and torqued to 25 ft/lbs and no change. The tapered metal sleeves used on the factory intake keep that same spacing amount on the gasket when installed. I repeated the bench test with the original used factory fasteners (rubber bushings etc,) and got the same results.

I haven't done any long term test to be 100% sure, but I am pretty darn sure 3/16 is THE way to go. I will be doing another install ina few weeks with these bushings and will do some extensive pressure testing and let you know if I have any negative issues.

McMaster Part # for the plated steel ones I used is 92415A861.(they have to be drilled out slightly to fit perfectly over the studs)

Hope that helps,

Louie928

You are going quite a bit beyond a bolt on SC install. You may be able to go to about 5 psi without doing much else, but surely not 10 or 12 psi. As a ballpark number figure of needing to retard the spark 1 degree for each lb of boost. It may be time to think about going to a different ECU altogether that will allow tuning both fuel and spark timing.

V2Rocket

Using the stock DME I can retard the timing about 3 degrees and I can increase fuel by 6% IIRC. I will be using 944 turbo injectors (~36lb/hr @ 2.5bar) to keep up with the fueling.

I am actively searching out other pulley options in case I need to go bigger. The stock pulley is 3.125" across. Keep in mind that Speedforce Racing sells a bolt-on centgrifugal supercharger kit for the 944 that uses 951 injectors and a 951 (air/air) intercooler that runs at 8PSI and puts down around 220WHP. However the centrifugal is much different from a roots in thermal efficiency so I don't know how applicable those are to the roots.

Another user on here ran 12PSI non-intercooled with E85 as his primary fuel and put down around 230WHP. But that is a whole other monster.

Is knock dependent on temperature in the chamber or sheer pressure? Doing some math I've figured that after the intercooler (without accounting for methanol) my temperature gain at 12psi would be only around 20 degrees F. However I do not know how high it will get in the chamber once compression starts.

AO

I know you posted on this thread, but the MAX HP Lit looks very promising for your application. Don't know anything about it, but sure looks like you need this or something just like it to tune your system.

Knock is ... ahhh here. Read this. Enigne knock.

Louie928

The 3 degrees retard will help a little, but not enough to make up going to boost above about 5 psi. The normal spark map will have some safety built in so you can press closer to the limit by using your safety margin. Because someone else has done X doesn't necessarily mean that it is advisable. They may be one tank of bad gas from disaster. Usually 9.5CR and boost above about 6 psi has to be taken very cautiously and incrementally with complete control over fuel and timing. Knock sensors especially.

Bill Ball

DR: THANKS for the details on the 3/16ths spacers. My manifold is not cast but is top and bottom plate against walls.

hans14914

DR,

What is the thinking about using the mcmaster spacer and stock gasket trick with your first generation setup? Is the lower casting strong enough for stock gasket use, or should we stick with the green gasket material?

bd0nalds0n

Hi Charles,

Did you cut your own gaskets? What did you use as a template? Where did you source the gasket material? And did you use a gasket punch for the holes, or an exacto?

Thanks!

If my foray into trying to use OEM gaskets doesn't work, I may be back to using a different, sturdier gasket to try to overcome warping via clamping.

DR

Bill,

(Hans, this will answer your question also)

Here are some more details for you, just to clarify again all of my recent info, tests etc, are only regarding my current style intake. But I feel the more info I pass along, combined with the info from the rest of the gang, will hopefully help you and others make an informed decision for their setup. I also think it would help you guys a lot if you disclosed what type of intake manifold contruction you have when sharing info with each other since there seems to be so many different configurations.

Below is a pic with snippets of some of the gasket damage we discovered after using the 1/8" spacers with the stock gasket (factory torque) for a few months. On that system we removed the bushings and went back to our earlier custom reinforced 1/32" silicone gaskets (no RTV sealant, just factory style spray on "shellac") until more testing was done. It has been perfectly fine since then.

There is now a system with the 3/16" spacers, will report back later on how it is doing. If I see any signs of negative issues with it I may try some 5/32" spacers, if that doesn't work good enough for me I am sticking with my earlier tried and true method and moving on.

Of course I could go ahead and stay with the tried and true now and move on, but I am striving so hard with my system to use as many factory parts as possible. In my mind it will it easier down the road for owners to get replacement maintenance parts, just in case there was a worse case scenario decades from now with me or my company (just being realistic). I have already successfully fought thru many "battles" with other such items as the stock MAF, TPS, etc. It would always be easier to not do it this way, but I am a firm believer in non-proprietary parts whenever possible, especially wear and maintenance parts.

BTW, reading Brian's new thread yesterday about using the 3/16" spacers and reporting a lower idle than before was originally encouraging. When he PM'd me about the spacers I did not know he had the cast lower intake and therefore didn't originally give him the "Disclaimer" about doing this on the cast version in my PM. Brian, sorry I forgot to ask you about that.

However, reading later on in his thread he thinks it may be leaking after spraying starter fluid on the sides of the intake(BTW, personally that scares me). This doesn't necessarily mean it is the gaskets as he has also had issues sealing the cast intake halves together due to warpage on the thin lower casting (I still remember those days). As you know the sealing surface and intake gaskets on the 2 piece cast intakes are within a few mms of each other, IMHO it would be hard to know which is for sure leaking by just spraying starter fluid, without somehow totally isolating one from the other. Pressurizing the intake and spraying soaping water on those areas will show the real deal. My guess is that is is both.

On those older cast thin lower intakes I still feel using the 3/32" gasket material with sealant is the best way to go for the best seal (obviously not the best for removal later on).

OTOH, Ralph said he is having good luck so far using 1/8" spacers with stock gaskets, but his doesn't appear to have the cast lower intake since his is Non-IC'd and he has mentioned milling the lower mounting surface of his "pizza box" completely flat. I assume he has the "flat plate stock" aluminum lower (probably 1/8" thick) similar to yours. IMHO, more time will be needed before that will be completely proven for his type setup. But, after seeing the stock gaskets with the 1/8" spacers after a few months I know for sure they aren't right for my style intake system.

In reality the best solution may end up being somewhere between 1/8" and 3/16". As I said I will probably try 5/32" spacers, just not gonna have some made until some more testing with the 3/16" because they seem to fit so good.

Hope that helps,

Bill Ball

DR: Scary pictures there! Since my manifold is not cast, maybe there is hope. I've had mine on since September. No change in the way it runs in that time. Warm idle is SOMETIMES lumpy-bumpy, maybe an irregular miss, othertimes smooth as butter. But it doesn't surge or idle high and anything off-idle is VROOM! I'm still not Sharktuned other than some casual street tuning. Maybe in the next month or so, I'll pull the manfold and have a look.

Pizza

Brian,

Yes. I cut my own gaskets. I used a legal file folder to make my template by placing it on my heads and shading it with a pencil to get the outline of the heads surface. I got the gasket material at a local oilfield hose and gasket warehouse. It's light green, 3/32" thick and has this info ( www.teadit.com NA1001 ) printed on it. If you can't find any I'll be glad to send you some. Exacto knife? NO WAY. This stuff is stout!! I sandwiched a piece in between 2 pieces of 1/4" plywood with wood screws around the edges. Then I traced the template on the 1/4" plywood and cut it with a jigsaw and drilled the holes with a regular drill bit. I used a Dremel sanding wheel to clean up the edges. It sands well. I haven't tested mine for leaks yet but with the spacers and this green gasket material I can't imagine it leaking from around the heads. Everything torqued up nice and tight.

Good luck!

bd0nalds0n

Thanks for the info! How tight did you crank things down?