Engine update

[Matt Holcomb]

John Gregory decided that the time was right to put the car on the dyno, so we did -- on Friday.

It wasn't long before it became apparent that the engine was getting too hot too quickly. Friction, and lots of it. It's still warm down here, and while the engine has hit 100C (during spirited runs) on a few occasions since it was put back together with the 10.5:1 JE pistons (the actual CR is closer to 11.1:1 than 10.5:1) and the GE-60 cams, I was pretty sure that the high engine temps had more to do with ambient temperature and a still-fresh engine than a compression ratio that's too high.

In a fortnight we'll be taking the heads off so that we can reduce the compression ratio. Thankfully, John is considering this "part of the job", as it's the first time he's rebuilt an engine with non-German, high-domed pistons. He wanted to see if he could get away with that compression ratio, and to his credit, he came close -- very close. We could leave the engine as it is, and it would be fine for spirited street use. However, since the engine is going to be raced, we have to reduce the compression ratio (by modifying the pistons) down to 9.8:1 to make sure it can be raced for a few seasons.

In case some of you are wondering what sort of power the engine is currently developing (I know there's a few of you!) we were able to get one reading (at only 6,000rpm) before the engine reached 100C:

220bhp, at the flywheel.

Not brilliant, I know. We're a long way from our lofty claims of 260-270bhp, but the engine was only going to develop that sort of power with modified stacks, a special exhaust system, and after 8-10,000kms of use. With a compression ratio of 9.8:1, 260-270bhp is now impossible without modifying the heads. But I'll be happy with 240-250bhp, and John won't be satisfied until the engine is developing that sort of power after the necessary modifications are made.


Matt Holcomb
1974 911 Carrera 2.7 RoW
1975 Mercedes-Benz 280SE
Dedicated Homepage
Engine Rebuild Homepage
Porsche Owners Gallery Profile
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[jluetjen]

I must of missed something here... What is the John's engine spec? Engine size? Fuel System? What kind of fuel were you using?

This sounds intreguing. I always love to see real data. BTW; what did the HP curve and torque curve look like using the GE60 cams and the race compression pistons? I'm thinking of using a similar configuration when I convert my car to track only use in the "near" future. Since it will be a competition car, I'm torn between going all out with a GE80 or using the less wild GE60.

Thanks for sharing!

[Matt Holcomb]

John,

We rebuilt my 911/83 (2.7) engine. The fuel system is MFI. As for the type of fuel used, we have a couple of 98-octane fuels in Oz. I like Shell Optimax.

The HP and torque curves were as you would expect from the GE-60 cams, but the high engine temps meant that we had to predict the curves above 6,000rpm.


Matt Holcomb
1974 911 Carrera 2.7 RoW
1975 Mercedes-Benz 280SE
Dedicated Homepage
Engine Rebuild Homepage
Porsche Owners Gallery Profile
Pelican Gallery Profile

[Early_S_Man]

Um Matt ... about that power level ... nothing to apologize about there! You were, by my estimate ... AT LEAST 300 - 400 rpm BELOW the power peak! So, it may very well already be making 240 - 250 hp ...

Had you planned, or have you already changed to a synthetic oil? That might help the high temps a bit! Of course, a bigger cooler, fan, etc. in the right fender might help, too!

[Adam]

Matt,

I have to say that 220bhp surprises me. I expected it to read much higher, given my tried and trusted "Seat-of-the-pants" dyno!

Seriously, I am surprised that it's heating up so much, given it's temprement on our Pelican Drive Day.

[Bill Douglas]

Matt, I know you would have checked all the obvious things.... But could it be something like oil not circulating properly due to a valve in bac-to-front or something similar. It just seems a shame to pull the engine to bits again. Bill.

[CamB]

So is it getting too hot from detonation Matt? I'm guessing John Gregory has seen enough to know if there is a correctable cooling issue.

Could you find some race gas and try running it on that, just to check

Otherwise, I hope the work to get it down to a nice reliable c/r is successful.

Oh, another thought - if it is detonation, could you twin plug it (I like using other peoples cheque-books).

Cam

[Matt Holcomb]

Warren,

Detonation at full throttle meant that we had to severely retard the timing, but in doing so it caused the engine to run hot. On the dyno, the engine raced to 100C before we could get a maximum power reading. With the engine temp at 100C and climbing, a reading at 6,400-6,800rpm would have probably shown an increase of only 5-10bhp; we couldn't get ahead of the dyno, if you know what I mean.

I'm going to be upgrading to a radiator-style cooler, but if we leave the engine alone, it would have a negligible cooling effect given how much we have to retard the timing to stop the pre-ignition.


Adam,

I'm surprised, too! But, a standard RS Touring is still a pretty quick car.

Now we know why I had trouble keeping up with the front-runners during our convoy! I didn't think shot front shockers would make the car that much slower!


Bill,

It's the pre-ignition that makes another tear-down unavoidable.


Cam,

Reducing the CR to 9.5:1 should do the trick, and will be cheaper than twin plugging it. Man, if only I had more cash to take advantage of this free tear-down!


Matt Holcomb
1974 911 Carrera 2.7 RoW
1975 Mercedes-Benz 280SE
Dedicated Homepage
Engine Rebuild Homepage
Porsche Owners Gallery Profile
Pelican Gallery Profile

[Rufblackbird]

Matt,
Having heard what you've done to the engine so far from Adam earlier today, I'm surprised, too, at "only" 220hp, as I believe a stock MFI Carrera was rated at 210hp.

What will be done to the pistons so that they will reduce the compression ratio? And wouldn't that mean less power?

[Wayne 962]

What octane were you running? If you've come this far, I would go with twin plugs and an electromotive distributor-less system. At least you don't have to buy a 12-plug distributor...

Probably cost you about $1500 (the head work is really not that expensive) - the electromotive stuff is only $1100...

-Wayne

[Matt Holcomb]

Jeff,

John is going to machine the pistons and add an extra spacer to each cylinder to lower the compression ratio.

Heat is power's enemy, and if we don't twin plug the car, or do what Wayne has suggested, then a lower compression ratio will make the engine more powerful as there won't be any excessive friction and pre-ignition.


Wayne,

I only use 98-octane fuel. Can you tell me more about the electromotive distributor-less system?


Matt Holcomb
1974 911 Carrera 2.7 RoW
1975 Mercedes-Benz 280SE
Dedicated Homepage
Engine Rebuild Homepage
Porsche Owners Gallery Profile
Pelican Gallery Profile

[CamB]

Matt

Electromotive have a website:

http://www.electromotive-inc.com

Also, Steve Weiner @ Rennsport Systems has put together some really useful info on twin-plugging options at:

http://www.rennsportsystems.com/~porsche/2a.html
http://www.rennsportsystems.com/~porsche/2f.html

Steve is the man on ignition...

Your usual problem will be the Australian Peso. Just be glad you aren't a Kiwi. Electromotive looks like it needs a crank sensor arrangement (and the alternatives for sale are absurdly expensive), two ignition packs and headwork to accept the extra plugs. It will be pretty expensive...

Lots of research if you have the time!! Good luck.

Cam

[Wayne 962]

http://www.emi.cc/

Richard Clewitt is our supplier for the Electromotive products. Feel free to give him a call, or visit his website. He will (hopefully) send you back to us for the sale if you decide to go with that option:

http://www.clewett.com/

It seems expensive at first, but if you add up all the other costs (like a twin-plug distributor), this system is much, much better...

-Wayne

[CamB]

Another option that probably won't work for you uses a 964 distributor.

I know the 964 twin dizzy can be made to work with an SC case (but I don't know how! I will have one in a month or so though). I don't know if the same applies to a magnesium case, but I suspect not or it would be more common. Wait, I reread Steve Weiner's stuff - it will work. This seems much cheaper to me. Seems to me you need twin plugged heads, modified distributor (only a few hundred??) and 2 CDI boxes (or 2 MSD boxes or equivalent). This looks like US$500+ cheaper.

Maybe someone can give more details on how this conversion works.

Cam

[john walker's workshop]

so what's wrong with 100°C? that's 212°F. lots of cars run 210-220° normally. 250° and above is trouble, but if you had a cooler with airflow you might be allright. you should run it some more and see if it hits 250°.

[Matt Holcomb]

Cam,

I'd love to twin plug it! Somehow, I don't think I'll be able to afford it! Same with the Electromotive distributor-less system. Oh well. With a lower compression ratio, we'll at least be able to play with the timing to find more power; 240-250bhp is plenty for a car that only weighs 1080kg.

Thanks for those URLs, though. It was fascinating reading!


Wayne,

I like the Electromotive stuff. Thanks very much for the info. The Australian/U.S. exchange rate just makes it prohibitively expensive.


John,

I agree: 100°C isn't that high, but it's reaching that temperature (on warm days) after only 20-30 minutes of "normal" driving! At the track, and on a warm day, 250°F would be very achievable after three hot laps, even with a radiator-style cooler and a fan.

It's that darn pre-ignition.


Matt Holcomb
1974 911 Carrera 2.7 RoW
1975 Mercedes-Benz 280SE
Dedicated Homepage
Engine Rebuild Homepage
Porsche Owners Gallery Profile
Pelican Gallery Profile

[CamB]

Matt

I just had another think about the "cheap" 964 distributor option and I suspect it will have no provision for mechanical advance, so would require something extra for that anyway (ie an ignition computer or full EFI computer).

In other words, it wouldn't be cheaper... unless you were changing induction anyway to EFI, as computer-controlled ignition only would be an expensive add-on.

Or I could be talking out my ass... apologies if anyone reads this and thinks I am full of crap. But there may be a cheaper way...

Is there any way you can get hold of some 100+ octane race gas to test if it still has pre-ignition problems - no long term solution but it would be great to know how it goes.

Cam

[Matt Holcomb]

Originally posted by CamB
Is there any way you can get hold of some 100+ octane race gas to test if it still has pre-ignition problems - no long term solution but it would be great to know how it goes.

Cam

Cam,

Sure, I could try a tank of Avgas, but the Porsche Club of Victoria has banned it!


Matt Holcomb
1974 911 Carrera 2.7 RoW
1975 Mercedes-Benz 280SE
Dedicated Homepage
Engine Rebuild Homepage
Porsche Owners Gallery Profile
Pelican Gallery Profile

Me think's your building too much cylinder pressure.
Wrong cam for that compression ratio probabely could use a few more degrees of duration just a thought.

964 distributors are $460.00 plus shipping for a brand new one complete with caps and rotors.
A MSD timing computer or one of the new wizz bang ignition sytems they sell should work, some are laptop programable ie the digital 7.
Chris

[beepbeep]

Vanilla MAP-equipped EFI, twin plug and knock sensor will fix all this...those heads ain't the best when it comes to pre-detonation.

SDS is there, it's cheap and it works. Autronic is your local (and pretty expensive) alternative...very advanced. Haltech is old food. Low on cash? Try Megasquirt...



MFI?? Throw it in the river or sell it to some "purist"....