2.7L Race Motor -> 2.5L Race Motor- need help with some info

[Plavan]

I have done a search on 2.5L race motors and found some interesting information. Here is my problem- I have a very nice 2.7L race motor with all the upgrades (racing valve springs, cams, J&E's 9.5:1). My racing group VARA will only allow 2.5L race motors for vintage racing. I also have a 2.2l T motor in my garage I was going to rebuild into my new 2.5 race motor with a 2.7 crank and 10.5:1 J&E's 85mm pistons.
I need some advise on what to do?

I now understand I can find a 66mm crank (counterwieghted) and install that with 2.0L rods into my current 2.7L race motor to make it a 2.5L (race legal). Anyone know what the compression would be?
OR:
Continue with my current plan of rebuilding the 2.2L T motor to a nice race 2.5 with a 2.7 crank/rods and 85mm J&E pistons. What valve sizes would you recommend with this motor?

If I convert my current 2.7 race motor to a 2.5, the cost will be very reasonable because all the machining/upgrades have been done to the case etc. I then could use the 2.7 crank/rods on my 2.2 and have a spare 2.5l motor.

HMMMM.... this board has me thinking about two different 2.5L motors now... What would be the performance difference between the two motors? Anyone have experience with what I am trying to do? Any help would be great because I am truly stuck on what to do.
Thanks in advance-
Chad

[Scott Clarke]

Chad-
The option of de-stroking your 2.7 has one major shortcoming: it won't get you under 2.5. You need 89mm cylinders to accomplish that. So, It might be better to build a long-stroke 2.5. However, your 2.2 case might not be a great place to start. If it is a '70 it won't have piston squirters. In addition, it will be a little weak for a race motor.

Come to think of it, perhaps it would be best to buy a set of 89mm pistons and cylinders of the proper compression ratio for your 2.7, and use a 66mm crank. This would be expensive (you would have to use Mahle pistons/cylinders), but might produce the best results.
-Scott

[Plavan]

Hmmm. Thanks for the info. I will have to get the number off of the 2.2L. I'm not sure if it is a 70 or 71 and have yet to rip it apart. I will get the engine number off the case and post it. The 2.2l already has tons of upgrades also..oil fed tensioners, turbo valve covers etc.
They allow for a .60 overbore on the race motors... am I safe now with the 90mm? I'm a noob when it comes to displacement figures.... what would the displacement be with the 66mm crank and 90mm pistons?

[Vintage911Racer]

You are on the right track Chad and I applaud you for making the change. You did great in Vegas and it would be unfare to you if you kept the 2.7 because you would have to run in the modified class for no points. Considering how well you did, you could really give the CP3 guys a good run for there money if you made the change. So again, I applaud you.

As far as your motor goes, If you take your 2.7 now and destroke it here is what you come up with.

9.0 X 9.0 X 6.6 X 0.7854 X 6 = 2.519 (2.520) So you see, you would still be over the 2.5L maximum. Not by much, but enough to make people say NO. And if you are going to do it, do it right.

The 2.2 and the 2.4 both use 84mm Pistons. the only difference is the stroke. 2.2 (2.194) is short stroke, 2.4 (2.327) is long stroke.

So change the stroke in your 2.2 at home and make 2.4 out of it. You will not need all the fancy stuff inside. Look at Terry's O's Motor. It would be the same motor as his pretty much.

And my 2.0L which has 3 years on it now (no joke 12/00) was when i last rebuilt it. Runs just fine. YOu were behind me in Vegas. Did it not pull very strong. That has NO internal mods done to it. Just 81mm JE Pistons. 10.3:1. So build a mild 2.4 for now using your 2.2. take your 2.7 and tear it aprt slowly and make a nice 2.5 race motor out of it after you do some research.

Lets get you legal and running for the championship next year.

Later Bro.
Mark

[304065]

Displacement.

Recent thread on displacement.

Factory 2.5 used 86.7mm pistons!

[andrew15]

Oddly enough, the factory quoted the same hp and torque figures for the short and long stroke 2.5 L engine.

[Plavan]

Mark-
Thanks bud. It's nice to have a car that is finally running right. The Fuel Safe defect should be on Fuel Safe's website so people do not run into the problems I did all last year.
Doesn't the .60 overbore rule apply to all race motors in CP class?

[Vintage911Racer]

Yes it does. But VARA is only allowing a 2.4 with a .60 overbore. That woudl be just under a 2.5. So you could not have a 2.5 with a .60 over. Does that make sense? I know it is confusing, but the best bet is to build a 2.4 or a 2.4 with .60 over if you want to go maximum displacement.

I guess you could also destroke your 2.7, sleeve the cylinders and have some custom 89mm Pistons made, or sleeve it enough to put 84mm pistons in it. that way you could use your same case.

Maybe someone else could chime in if that might work or not. I am not sure. But it sounds possible.

[Plavan]

Yeah that makes since.
My 2.2 liter motor in the garage is #6106939. My records indicate it is a 1970 2.2L. I guess I will need to add squirters to it. It is a late build motor so maybe...(keep fingers crossed) it might have the 1971 stuff in there but I doubt it.
Hey Mark when are you and my dad going to make your motors legal???? I just got done looking at the rulebook online... hehe ... I wont say anything... our little secret. See below

"11. Engine - Same type/size as year of manufacture (0.060" overbore limit).
Period correct roller rocker arms are ok. No stud girdles. Compression Ratio is limited to 10 to 1 maximum unless it can be documented as higher from the factory as delivered for street use. Block and heads must be OEM and period correct. No aluminum flywheels. No dry sump oiling systems unless originally sold as such."

[Vintage911Racer]

Chad,

What you were looking at is for group 1 cars. if you scroll down further, you will see the Non goup one rules.

"Engine:
Original type and manufacture. Must declare accurate displacement in cc's or cubic inches. Block and head material and stroke must be as original. Stroke should be original. Stroker cranks are prohibited. Internal engine components are free. No late production heads allowed (i.e. SVO or slant plug Chevy small blocks). After market aluminum or cast iron heads ( World, Dart or OEM) which closely match original specifications may be allowed. Ignition may be upgraded to electronic type. Rocker arms are free. Lubrication is free. Engines may be over bored a maximum of .060”.

So no talk of max compression for Non group 1 or 3 cars.

So there. We are legal. So stop going fisihing.

[RPMClassic]

It seems that you are looking at the classic debate( as did the factory...) of having a low compression 2.5 with 66mm crank or a 74.5 mm long stroke with higher compression. The factory kept breaking flywheel bolts using the bigger crank and in some cases snapped cranks altogether,

The difference in HP is real. 220-230 at 7500 RPM for the 66mm crank and north of 280 HP and 8000 RPM using the 74.5.

According to the factory manual the GT4 spec 2.5 liters were allowed to "lower the valves" in the heads to get more compression running near 10:9 on pump gas with 12 plug distributors.

Cool stuff no matter which version you end up building.

[Plavan]

I was not fishing... Just having some fun with ya... Just seeing if I could keep our CP class rep on his toes
Like I would rat on you and my Dad ...hehe... Just having some fun. It looks as if the 2.2L motor in my garage will be coming apart soon. I just ordered the engine yoke.

[Vintage911Racer]

Very Cool Chad.

Talk to John Dayton. I talked to him yesterday. You know it has been 3 years since I rebuilt my motor last.

December 2000, was when I rebuilt it. I cant beleive that shiznit.

I will have a new BECKS Motor next year.

I cant wait.

[awis321]

Guys,

For those of us that haven't witnessed, let alone ridden in, an early series car with a +2.4 or a 2.5... what's it like in terms of street performance, are we talkin SC territory as far as torque? Would it be a night/day difference from my 71 2.2t?

[901/05]

Plavin and all that have participated. awis321 has asked the same question that I have.

There is a great earlier photo thread with a bunch of the ST cars. Curt cegerer has linked a great site featuring his car with specs and a (pre sport exhaust) sound sample.

I wanna build one of these and drive it. Is it really worth the expense? There are a few here that are building or already have the 2.5L engines...please provide input. It seems to me that awis321 would have the perfect engine (with case squirters) to upgrade to a 2.5 liter short stroke version?? Given the $$ of course. Any thoughts.

2.5 liter wanna be, Shawn.

[Plavan]

Mark-
I plan on building it myself with the help of Wayne's book. I have already read it cover to cover 4 times. I love building stuff. I just hope it works :P. My mechanic said he would come over to help out if I run into trouble. Not only did I order the engine stand today from pelican... I ordered all the tools needed. I do not want to pay $4k in labor again when I will enjoy doing it myself. I will just make sure to triple check everything.

[jluetjen]

RPM;
The factory quoted the same CR, HP and torque figures for both versions of the 2.5 liter ST engine. I think that the lower HP number that you are quoting is for the 2.3 ST engine.

[RPMClassic]

Well there are 2 911 ST's with long stroke that I have seen, and I drive a 2.5 short stroke everyday. I don't see how its possible that the compression and HP are the same...additionally the factory racing manuals clearly layout different set up and specs for each version. If you know of a way to make a 2.5 with 66mm crank to rev to 8000 RPM and have over 280 HP - let as all know! Regardless, they are all fun motors and worth the effort.

Jim

[Vintage911Racer]

I may be wrong here but arent short stroke motors the ones that can Rev beyond belief. I mean there ar eguys racing with us that rev theres to 8500 and sometimes 9000 with there short stroke motors. The 2 guys with the long stroke motors are shifting them at about 7200.

[RPMClassic]

Well sure. I can change the rev limit and try to get the needle to 10,000 on the tach, but my motor won't last very long either. These motors are expensive to rebuild properly, I can't imagine having to rebuild every 40 hours or even every year. What do you think that lifespan is on the guys motors who are reving to the moon? It can't be that long.