2.5 shor stroke engine, my plans Options

[michel richard]

So here's what I'm doing for the engine as part of my "GT style" conversion. First and foremost, I figure that an engine in a GT style car has to be rev-happy.

So, here's what I'm putting together, with the help of my trusty wrench, Ron Green of Campbell Gararge in Montreal:

Short stoke 2.5 Porsche engine:

1) Used 7R engine case, align bored, Timeserted, shuffle pinned
2) 90 mm JE pistons, 10.5 compression ratio
3) 90 mm replated Nickasil cylinders, sourced from EBS
4) Standard piston ring set
5) 66 mm counterweighted crankshaft
6) GE 80 camshafts
7) EBS racing valve springs
8) EBS valve spring retainer set for above
9) 2.0 connecting rods
10) ARP rod bolts and nuts for above
11) twin plugged heads
12) Electromotive HPV twin ignition
13) Turbo lower valve covers
14) front mounted ol cooler with "GT Style" installation
15) new bearings and gaskets all around
16) miscelaneous engine parts, stock.

I still need to figure out what to do with the port sizes in the head. The target is to have a 8,000 rpm redline, and 250 hp, although the redline is more important than the hp to me.

So that's the plan. I pulled the trigger on the hard parts above today. ( I already have the crank and the miscelaneous parts).

Induction is going to be 40 mm PMO carbs, jetting to be determined.

I'll post to this thread as progress is mad on the engine.

Michel Richard

[d914]

most of the race 2.5 go with 46's one locally went to pmo 50's. 2.5 at 8k is a large air pump.

[michel richard]

Greg,

I hear you. To me, this is mostly a street engine, with a little track time, so I don't want to lose tractability. I'm told that the GE 80 cams on that engine should still provide smooth idle.

The 8,000 rpm thing is mostly because I find high reving engines to be thrilling. If I miss a few hp because of the small (relatively) carbs, so be it. Still, if you tell me that 40 mm is much too small, I'll certainly investigate. I would think that Richard Parr at PMO should have good data on these things.

Michel

[d914]

I would check them out, little to prove my point but as you open those 40's I think that you lose some of the venturi's effect. Air speed with 38's in a 40 or 38's in a 46..?? I'm a not a techie by any means and my 40's despite spending nice money getting them rebuilt never seemed to "fit" the motor. The 46's went from a 2.9 to my 2.5 and I never touched them again.

Check with some one who really knows, unlike myself!! (IMG:http://www.914world.com/bbs2/html/emoticons/ohmy.gif)

[kevgentile]

8,000 is to high for a mag case. you will walk the crank right out of the case if you take it that high too many times. i have a 2.5 with much higher compression and could take it to 8,500 very easily. found no difference in power at over 8,000 then that at ~7,200, and the motor will last longer. which is a good thing when the motor cost 25,000.

[d914]

agreed, but mine was in an old AL case, had red line set at 7k and rev limiter at 7500.....based on my cam not much more up there power wise, but damn it sounded good.

[campbellcj]

Sounds fun. If I ever build a new motor for my current 914, it would probably be an "old school" 2.5 alum case w/ Webers...an MFI 2.8RSR spec would not be bad either...for now I'm saving my pennies and hoping this one doesn't go BOOM too soon.

[Brett W]

I agree with Greg, I would look at a bigger carb and then get some custom venturies to keep the velocity up. You could go with a little higher compression. This will help get some of the bottom end back. Do not worry about smooth idle. You can make any cam idle smooth with individual runner intake systems. I would throw a little more lift in there, but don't go up on the duration.
What is the duration on the GE80s? What are your plans for an exhaust system?

I would really look at a programable fuel injection system, it will allow you to get some more HP and drivability out of it.

[Trekkor]

I love the sound of the high revs, too.

I keep my limiter set at 7k and just smile when the motor tickles it. (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)


KT

[fiid]

QUOTE (Brett W @ Dec 20 2005, 09:08 PM)

I agree with Greg, I would look at a bigger carb and then get some custom venturies to keep the velocity up. You could go with a little higher compression. This will help get some of the bottom end back. Do not worry about smooth idle. You can make any cam idle smooth with individual runner intake systems. I would throw a little more lift in there, but don't go up on the duration. What is the duration on the GE80s? What are your plans for an exhaust system? I would really look at a programable fuel injection system, it will allow you to get some more HP and drivability out of it.

(IMG:http://www.914world.com/bbs2/html/emoticons/agree.gif) I think an FI system is a better option. More control is gud.

[messix]

i'm not that experienced with porsche engines, let alone the six's. but it seems that the 40's would be to small for 8k rpm. try jogging and breathing though a straw! it would most likely struggle to rev that high and flatten out. larger carbs will let'r breath. big carbs can be made to work.

[Brett W]

(IMG:http://www.914world.com/bbs2/html/emoticons/agree.gif)

You can make big carbs work better on the bottom end than you can make little carbs work better on the top end. You could always pick up the Vario Ram intake froma later model engine and control it with an aftermarket EFI. THis would give you both, torque and HP.

[TimT]

Id shy away from using the 2.0 rods. They are the least desirable rods to use on a performance engine. A few months ago someone on Rennlist was selling set of Carrillos, they have probably been snagged by someone already.

Pauter makes nice rods, but there prices go up everytime we buy a set (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif)

everything else about the build looks good

What heads do you have? I ported the heads on my personal engine 38/38, which is S configuration. the carbs I used before I went to EFI were 40 mm webers with 34 mm chokes.. btw my engine is 2.2

I had web-cam grind me a cam that is a cross between a S and 906 cam. which I timed so peak power occured at 7000 rpm. I got the cam timing zeroed to where I like it on the dyno

I havent built an engine with GE 80 cams yet but I have heard great things about them.

[Brett W]

How long are the stock 2.0 rods? What kind of rod stroke ratio do they generate. You can use the rod ratio to tune some better low end drivability into the engine if you want.

[Mark Henry]

For the price of those PMO's I'll get you a deal on an SDS FI system. (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif)

The PMO's are nice, but I wouldn't go back to carbs if you paid me.

/6 SDS is under $2k for crankfire...some MFI intakes, $400 in injectors...WB meter.
And you'll still have money left over.

[michel richard]

OK,

Thanks for the collective wisdom. I'll comment and react to the various input:

First, generally, I'm a big believer in the fact that good enough is often just that: good enough. And in keeping a firm eye on the target.

Once again, I'm building a "sport" engine, one that I hope will be fun and exciting on the street, and be track-able once in a while.

So:
1) on the mag case and 8,000 rpm. I've taken my 2.2E built on a 5R case to 7,500 several times, without any problems. I'm pretty sure that the 7R case and upgraded valvetrain will safely take me to 8,000. Not for extended periods, and admitedly at a certain cost in engine longevity, but I doubt 8,000 will blow the engine. Sure, an aluminum case would be better, but they're hard to come by. They're non-existent, that I know of, in Montreal.

2) On the induction. In view of the number of comments above, I will certainly investigate. I think it's probably a good idea to at least start the engine with some carbs, because it's easy to do so. I would probably go to some sort of injection if I need to move away from the PMO 40s. The problem with fuel injection systems is that they sound good on paper and in theory, but they're a lot harder to get support for and lot harder set up. I agree that once dialed-in they'd be much easier to run.
I'll certainly talk to PMO to see what they think. And once again, I'm not looking for an engine that is at its most efficient at 8K, only an engine that is able to run and sound exciting when up in the upper reaches of the rev range.

3)on the 2.0 rods: Carillo and Pauter rods are approximately 5 times the price. And the 2.0 rods will work.

4) The heads are from my stock 2.2 E. We'll keep the valves (they've got less than 5,000 miles. Spoke to my mechanic last night, and his suggestion is 37/35 (IIRC) for a streetable engine. He says he would recommend another couple of millimeters if i was going for a screamer of an engine. That is one area where my mind really is not made up.

5) Mark, are you saying that a /6 SDS system that would do both injection and ignition would be under C$ 2K ? I have'nt bought the Electromotive system yet, so it's not too late.

Thank you all for your input.

Michel

[Mark Henry]

I'd have to check it out...but I know a guy who bought a twin plug system 3 years ago and it was about $1700 US...so a single plug system must still be under 2k canadian.

PM me if your interested and I'll find out.

QUOTE

The problem with fuel injection systems is that they sound good on paper and in theory, but they're a lot harder to get support for and lot harder set up. I agree that once dialed-in they'd be much easier to run.

Both SDS and I will support you 100%.

The SDS will come loaded with the base program to your spec and injectors. I have 911 maps on file.

I could lend you my WB.

No Carbs needed for break in.

If your builder doesn't know squat about PEFI I'll talk him through it.

Hell... give me a bit of gas money and a place for the family to stay for the weekend and I'll come up and help you break it in. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

As long as the car is "on the road" I can have it "dialed in" in one day.

SDS is simple.

[Brett W]

I know Mark and some others like the SDS system, but in my opinion it is just that Simple. It works OK as a replacement for a carb system but it does not have the flexibilty to be tuned as well as a true standalone system such as the Autronic or Motec. There is plenty of support for each system. Many companies have systems for the 911 based engine.

In the beginning setup on the FI will be a little more laborious than carbs, but in the long run the mileage and drivability will always beat carbs.

[Mark Henry]

Brett...Have you used an SDS?

What do you mean "true stand alone"?

QUOTE

In the beginning setup on the FI will be a little more laborious than carbs

That tells me you haven't used an SDS.

[michel richard]

Mark,

Because I have the carbs, I would like start with those.

Does the SDS take care of the ignition too (i.e. is it an engine management system) or just the injection ?

Inviting you to come over and set it up in the spring is not impossible. Or me drving it down to your shop on the carbs. That is all several months away, though. (note to California guys: we got a foot and half of snow last week)

Can you point me to a good web page with details on the system ?

I already a pair of WB sensors, with the Innovate hardware. Oh, and please remember I'm doing a twin plug system, you were talking about single plug prices in your next-to-last post.

Michel