Pelican Parts Forums - Need help and advice in 3.3L short stroke engine build

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Need help and advice in 3.3L short stroke engine build

Hey Guys, My car is a 1981 911SC with the stock 3.0L. I have seen tons of info on the 3.2SS build but not much on the 3.3L. I have no HP goals set in mind and hope to not over build the car buy making it unpleasent for daily driving. I will list my build plans below and hopefully you guys can chime in on any wrong doings.

I have aquired a set of 100MM P&C's
Pistons are JE 10:1 compression
ITB's with CoilPacks, EFI, and MegaSquirt will run it all.
Camshatfs are undecided thinking DC-40 or somethings like it. Advice?
As of now, I plan to keep my stock heads and port match them to the gaskets. Advice?
No plans for Twin Plug but I do have a set of 3.2 heads if bigger ports are nessary. Advice?

My car already has a Bitz-EZ-EFI kit, turbo valve covers, APR Head Studs, 3.2 timing chain tensioner, Dual Oil Coolers, headers, and 2 in, 1 out, exhaust system already on the car. Car runs excellent but I'd like more power. Thanks in advance!

everything Ive found in the research for my SC indicates anything over 9.5:1 without great gas (read: 100 octane) requires twin plug or you're having to pull so much timing you lose power...

curious what coil packs are you going to go with and how you will trigger the MS - Im doing a similar setup but dont have the blitz and dont know if it comes with crank and/or cam triggers?

Quote:

Originally Posted by 911ducktail (Post 9121902)

everything Ive found in the research for my SC indicates anything over 9.5:1 without great gas requires twin plug or you're having to pull so much timing you lose power...

curious what coil packs are you going to go with and how you will trigger the MS - Im doing a similar setup but dont have the blitz and dont know if it comes with crank and/or cam triggers?

My main reason for 10:1 compression is that I've seen tons of Euro Cars running on 92 pump gas here locally with no problems. 3.0L at 9.8:1 and 3.2L at 10.3:1. Plus I've read Steve form rennsport write that a 10:1 3.2SS is ok with single plug in another thread. Steve also mentioned about the timing curve but I was under the impression it was for much higher compression. Maybe he will chime in on his. I'm also hoping that my dual oil coolers are more then enough to keep the engine at a safe temp. It also dosen't get that hot here on Oahu.

I've bought my coil packs from dyiautotune.com along with the signal trigger. They are extreemly helpful and quick to reply via email. They have everything you'll need to get the job done and your engine running right.

Quote:

Originally Posted by Steve W (Post 7377309)

As mentioned, the taller the piston dome, the greater the need for twin plugging. Taller piston domes are typically used when trying to achieve high compression while providing a deep enough pocket for for high lift/duration cams. The result of the high dome is it divides the combustion chamber into two pockets, where the one with the spark plug gets fired first, and the other later or not completely, thus the need for the second plug. If you look for example at the piston of a 3.0 or 3.2, it has a dome profile specifically shaped for single plug setup, where the dome peak is offset to one side to squish the whole mixture into one smaller pocket towards the side of the spark plug, thus you don't run twin plug with that. It's actually an efficient design for single plug and needs less ignition advance to achieve optimum power vs other dome shapes which alter the combustion pocket. Similar to the concept of a four valve head, allowing the spark plug to be ideally right in the center for efficient combustion. Having spent much time on the dyno over the years, one will find different brands of pistons require different ignition advance curves for optimum power because of the different resultant combustion chamber shapes.

Since twin plugging fires the mixture from both sides of the chamber, the time to propagate the flame and complete combustion is faster so less ignition timing advance is needed vs single plug, typically 7 to 9 degrees. The later firing of a twin plug setup reduces the time the piston is traveling upwards while the mixture is still expanding, thus reducing the upward pumping losses, increasing hp a bit.

High compression pistons exceeding 10:1 compression begins exceeding the predetonation limits of pump gas with single plug, so one either has to reduce ignition advance sufficiently to prevent predetonation, (but if you have to do that, it's better to reduce compression and increase ignition advance to improve the torque response of the motor). Twin plugging allows you to run the reduced advance while achieving the power as if you ran the full advance for optimum power.

If fuel octane is not an issue (race fuel) , and the cylinder bores are not excessively large (i.e. 100mm or larger), then one can build a high compression single plug motor outputting high hp. There are stock Motronic/stock cam'd 3.2 race cars out there outputting in excess of 250 hp at the rear wheels on a Dynojet, or almost 300 hp at the flywheel on single plug reliably.

http://forums.pelicanparts.com/porsche-911-technical-forum/743735-twin-plug.html

Its a different Steve but still a smart Steve ;)

Quote:

I've bought my coil packs from dyiautotune.com along with the signal trigger. They are extreemly helpful and quick to reply via email. They have everything you'll need to get the job done and your engine running right.

yes, their customer service is excellent. But Im going a different way - Clewett crank and Clewett cam sensor for full sequential ignition control (Im keeping my webers for the time being while building an EFI setup) and it'll drive twin plug logic-level red top VAG/Audi coil-on-plugs

Quote:

Originally Posted by 911ducktail (Post 9121975)

yup, Ive read those as well. Have you seen this? this is a good thread with pretty much all the big brains in it :)

fwiw the way I read it is that a 100mm cylinder is borderline "excessively large" and 10:1 is high

http://forums.pelicanparts.com/porsche-911-technical-forum/743735-twin-plug.html

Its a different Steve but still a smart Steve ;)

yes, their customer service is excellent. But Im going a different way - Clewett crank and Clewett cam sensor for full sequential ignition control (Im keeping my webers for the time being while building an EFI setup) and it'll drive twin plug logic-level red top VAG/Audi coil-on-plugs

Very Good Write up, but the very first sentence in bold says clear as day that high compression "exceeding" 10:1 require twin plug or large advice curve. Not the case with my engine as 10:1 will be its highest, but most likely be slightly under with factory cosmetic head gasket. Anywho, I'm more then confident my engine management and tuning will keep the engine running safe at this compression ratio. My biggest concern is head choices and cam sizes. Any one care to share flow numbers or ball park figures on how the top end should flow with this bottom end setup? Thank you guys!