Destroking 964 3.6 to a 3.4
 

Hi all:

I'm looking to build a motor for PCA and NASA club racing. I want to stay within the middle class (GT3 if I remember correctly) which allows 2.8 to 3.4 liter engine. I was initially looking to build a 3.2 into a 3.4 with bigger pistons and cylinders, but my mechanic suggested using a 964, grinding down the crank, and using different custom rods to destroke the engine to 3.4 (while using stock 11:1 964 pistons). I would indeed prefer to use the 964 case because it's stronger and already has dual plugs. Has anyone done someting like this? Is it possible to use an earlier crank (3.2 carrera) in a late 964 block in order to destroke the engine? Thanks!

I've made custom small bore 3.6 cylinders anywhere from 95 to 98mm for that same purpose, then you just need cylinders and pistons and would retain the stock rods and crank. I'm pretty sure that JB Racing has made something like this before too with their sleeved cylinders. Just another option for you to consider.

Both the 3.2 (74.4 stroke) and 3.0 (70.4 stroke) crank will fit in the 964 case with no modifications.
74.4 x 100 = 3.5
In fact, a 3.0 crank with 100 mm (stock cylinders) and custom pistons will make a very nice short stroke 3.3.
Because of the improved rod length to stroke ratio (3.0 rods are longer than 3.6 rods) and the great flow characteristics of the 964 heads these engines are capable af some very high RPM. I recently heard of one of these engines turning a sustained 9000+ RPM in race trim.

I'm in the process of designing a 66X100 engine using the 964 case and heads with titanium rods with hopes of reaching a usable 9200 RPM.
Only time will tell.

Yeee-ha!

66*100!

Nice Henry, very nice indeed..

Tell us more please..

Kind regards
David

You can see an example of a de-stroked competition motor here:

http://forums.pelicanparts.com/porsche-911-technical-forum/275995-my-race-car-project-finally-finished.html

3.4 from a 993, 3.0L crank and then over-bored pistons/ cylinders.

Couple thoughts-
If you use the stock pistons, you'll get a lower than stock compression due to less swept volume. You'll also be limited on the cams you can put in it due to piston to valve clearance issues.

If budget isn't your driving factor I'd go for the shorter stoke/ larger bore option- the larger valve and piston area plus higher revs should mean more hp, all else being equal.

Done right I've seen dynos of a couple short stroke 3.4s making north of 360 hp. Not cheap, though.

If you're making a full race motor I'd look into high compression pistons with more valve clearance for a big cam- probably good bang for the buck in terms of $ per hp.

Came across this old thread while searching for something - now wondering how this turned out

ditto

Question your basic concept here. (oops, I see now that this is an old thread...)

PCA CR (in the GT classes) is based on theoretical hp/weight and NASA is based on actual dyno hp/weight.

Air cooled cars in PCA are assigned a theoretical 110hp/liter; in the GT4 class, a 3.6 would then run at 2677#, a 3.4 at around 2520 (regardless of actual hp). Currently, both a 3.4 and a 3.6 are running at National levels while several 3.8s (running closer to 2900#) are also winning. These are all HIGHLY developed cars with very expensive 60hr engines. Light 3.0L cars with highly developed engine also are very competitive in GT4, but the larger engines seem to have the current edge.

In the NASA GTS series, things are a bit more simple. A 3.6, for instance, with 306 RWHP will run at the very top of GTS4 at 2627#. Displacement here means nothing as the weight and class are determined solely by dyno results. A stronger engine would have to carry more weight, or move up to GTS5.

9200! I'd really like to hear how that turned out (literally!). :)

The engine turned out pretty sweet. It is now running around Europe in a 77 911 Chassis.
The engine consistently runs to 8800RPM on street gas.

The build :
Supertec 3.1 liter (66 X 100 mm) Short Stroke 2 valve 9000 RPM (red line)
3.2 Carrera case with shuffle pins
50 mm PMO
Extreme cylinder heads
Custom DC 90 cams
Supertec Head studs
JE forged side relief pistons 11.5:1
LN Nickie cylinders
Supertec RSR cylinder tin
Supertec SuperCrank
Carrilo rods
GT3 Rod bearing set
GT3 Main bearing set
Burnham Performance twin plug
Amber fan shroud
Supertec Power pulley
996 TT oil pump
Burnham Performance sump cover
Supertec tensioner arms
Reconditioned forged rockers
964 steel countershaft
Wrightwood Racing gaskets & seals


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Neat engine.

Sweet!

Thanks Henry. She's a beaut!

I'm dying to hear that thing at 8800rpm- GT3 territory! Got any dyno vidoes?

We sent the engine to the owner (in Italy) without running it. That's why I am making no HP claims.
He stuck the engine in the car and used the Sicilian roads "big dyno" to tune the engine. Carbs makes tuning a relative cake walk.
He's driven it (over a year now) without relaying any dyno results. If he relays any information I'll make it available.

I see what appears to be a M&K muffler. What headers are on the motor?

European Racing Headers (George) with ceramic coating inside and out. 1 3/4 inch.

http://forums.pelicanparts.com/uploa...1434120368.jpg

Obviously the old adage about if you have to ask, but I'm curious what something like that costs?

Right around $ 45K

This is why many end up opting for Spec Boxsters. Kind of out of reach for many. Nice to have customers like that, though.