3.8l race engine

scott.k · scott.k's Garage

Hello,
Im thinking of building a 3.8l race engine for my 1980 911 sc. I will run the stock engine until the build is complete. I was wondering if there are any good guides/instructional books/ manuals on how to build a racing engine. It will be my first one and I would like to learn how to do it. It will be a project so I do not need it to be built really quickly or anything. I have a few things that I think that I would like to run on it like pmo 50mms, and a few other "external" things but I dont know much about what things to run internally. I was thinking of doing it mainly stock internally except for racing cams, and maybe a few other things. I would like to have a durable engine that does not need frequent rebuilds like many race engines do. Any feedback/ suggestions would be helpful. Which race parts on a race engine will need to be replaced frequently?
THanks
Scott

Bill Verburg · Bill Verburg's Garage

Quote:

Originally Posted by scott.k

Hello,
Im thinking of building a 3.8l race engine for my 1980 911 sc. I will run the stock engine until the build is complete. I was wondering if there are any good guides/instructional books/ manuals on how to build a racing engine. It will be my first one and I would like to learn how to do it. It will be a project so I do not need it to be built really quickly or anything. I have a few things that I think that I would like to run on it like pmo 50mms, and a few other "external" things but I dont know much about what things to run internally. I was thinking of doing it mainly stock internally except for racing cams, and maybe a few other things. I would like to have a durable engine that does not need frequent rebuilds like many race engines do. Any feedback/ suggestions would be helpful. Which race parts on a race engine will need to be replaced frequently?
THanks
Scott

I'd rethink the whole proposition, a healthy 3.8 and 915 isn't the happiest combination i've ever heard of, what organization and class will this be for?

at minimum you will want pauter rods to raise the rev limit, along w/ a more rev-able valve train. The best engines will start w/ a GT3 crank & oil pump, Ti rods and custom pistons.

GrantG · GrantG's Garage

This one looks to be done right:
New Porsche 3.8 Race Motor 410 HP

Mahler9th · 10-31-2010, 07:58 AM

I run a 3.8 in my 1975 911. I started with about 330 bhp and now I have about 360+. I run a 915... no problem. We have lost of guys running this level of performance with 915s in the Porsche Racing Club. For a street car/hot rod, I'd probably want a G50... there are trade -offs that are helpful to understand.

Looks like you live in Norcal. There are a lot of resources here. If I were going to build a 911 engine for the first time, I'd fight really hard to get into the upcoming class at Jerry Woods Enterprises.

If I decided instead to have the 3.8 built by someone else, I'd choose from among the experts like Mat Lowrance up in Reno (he built mine), or Jerry Woods down here.

Mahler9th · 10-31-2010, 08:13 AM

The guys at Engine Builder's up in Reno are a great resource as well. I have a GT3 crank... and Porsche Motorsports rod bearings... others in our area run JWE's coated rod bearings. Neither are a panacea... if you run the engines hard and high in the revs (7.5-8k rpms), the rod bearings will need replacement at 20-25 hour cycles most likely. There are lots of considerations... what makes the most sense depends on how the thing is going to be used and the specific performance and service requirements.

GaryR · GaryR's Garage

I would think that will be at least a $30K+ proposition to do it right and not something for a 1st timer to do just to have missed something and be out $30K when it grenades. Why do you want a "race engine" in a 1980 SC? How is the car prepped? Have you ever driven on a race track?

scott.k · scott.k's Garage

ok, thanks for the help,
Right now I have the car gutted with the engine out and the roll cage just went in. I was thinking of running in the 911 spec class when I put my engine back in and then down the road running in a modified class. I have indeed heard of Jerry woods and I know he does great work, I just would like to do it a little cheaper and on my own so that class does sound very good. I think I will run a 915 with it.

I am planning on it being a project that will take a long time. There is no rush because I plan on running the stock engine until I am done with the build. I have done a lot of other car work on my car and another, I just havent yet gotten into the engine building area and would like to now.
Thanks for the help

Mahler9th · 10-31-2010, 08:50 AM

That JWE class might be perfect for you. And if you intend to start racing with the PRC in Spec911, check out some of the recent postings and links on the racing/AX board. Several of our Spec911 guys do their own engine work and a few of them are active on these BB's. All are happy to help newcomers.

I may try to organize another "off-season" PRC open house in Jan or Feb-- could create an opportunity for in-person networking... stay tuned.

Bill Verburg · Bill Verburg's Garage

What's wrong w/ these statements

Quote:

I run a 3.8 in my 1975 911. I started with about 330 bhp and now I have about 360+. I run a 915... no problem

Quote:

the rod bearings will need replacement at 20-25 hour cycles most likely.

So a stock 915 will run forever but you need to worry about rod bearings after 20-25 hrs?

I suspect that are glossing over steps that have been taken to enhance durability of the 915. It's still not going to be a good idea

Gary's est. is going to be at the low end for the engine, budget another $10k+/- to try to make the trans live.

What am I missing here?

According to POC spec 911 rules there are 2.7, 30 and 3.2 classes, nothing else

winders · 10-31-2010, 10:33 AM

Quote:

Originally Posted by Bill Verburg

So a stock 915 will run forever but you need to worry about rod bearings after 20-25 hrs?

Bill,

I am not sure I follow you here. What does the durability of the 915 have to do with the service life of the rod bearings in 3.8L race engine? They are completely unrelated.

Scott

Bill Verburg · Bill Verburg's Garage

Quote:

Originally Posted by winders

Bill,

I am not sure I follow you here. What does the durability of the 915 have to do with the service life of the rod bearings in 3.8L race engine? They are completely unrelated.

Scott

They are not unrelated, the 915 is drastically overstressed, the bearings, assuming rev limits only somewhat elevated from stock are not. Late Cups running to ~8500rpm advise rebuilds of both engine and trans every 30hrs, w/ lower rev limits longer btbr is greatly reduced, the weak link in the Cups is the 8:32 cwp, if a 9:31 was used btbr would also go up

the most extreme factory use of a 915 was in the '742.14L turbo race cars, 400 lb/ft of torque but rebuilt after each race and even then subject to reliability issues

winders · 10-31-2010, 11:30 AM

Quote:

Originally Posted by Bill Verburg

They are not unrelated, the 915 is drastically overstressed, the bearings, assuming rev limits only somewhat elevated from stock are not.

Bill,

But the mechanical limits of the 915 and rod bearing life of a 3.8L engine have no relationship. None. Zero. It's the torque of the 3.8L that causes the 915 problems. The Porsche factory had plenty of low torque, high horsepower, high RPM, short bearing life engines that would not stress a 915 like a 3.8L race engine.

S-

911st · 10-31-2010, 11:52 AM

Quote:

Originally Posted by scott.k

ok, thanks for the help,
Right now I have the car gutted with the engine out and the roll cage just went in. I was thinking of running in the 911 spec class...

Just a suggestion. Make the spec911 class your goal and put the 3.8 idea on the shelf. You might find you like it so much you may stay there for longer than you might originally plan. You can also poke around the GT class for ideas before you start to build your monster motor.

You probably know they run basically a stock SC block with carbs or a chipped 3.2.

Basically a 2350 lb with driver 220whp race car. I think that might be a better power to weight ratio than a euro 930 turbo.

Just a thought.

Mahler9th · 12:48 PM

Well... I am not sure I understand Bill either. Let's take three of my friends/competitors in GT2 here locally with 3.8 liter engines. Let us call them M1, M2 and (Peter Smith, who is the PCA head tech person). Let us say their engines are 3.8 liter racing engines with aggressive cams, all running 350-400 bhp and revving above 7500 rpms. Now the M1 and M2 engines were built by the driver, M1, with IMSA pro experience dating back I do not know how far. And Peter'seEngine was built by Peter, likely with with help and advice from Jerry Woods. All of these engines are run such that the owners/builders service rod bearings at somewhere between 20 and 30 hours. They likely use different bearings, cranks, oil pumps, pistons, et cetera, but all benefit from unquestionable expertise and experience.

All three of these cars run 915 transmissions. Like mine. And there are several others in our area that do so with similar performance. Most or all of these folks have access and resources that could result in G50's being used... but they choose 915's. Why.....? There are trade-offs. That is why I caution against absolutes. None of these 915's have external cooling either.

There are trade-offs. There are plenty of local, regional and national resources that never visit the internet that can and do help folks understand the trade-offs. As these cars have been raced in anger since they were introduced in the 60's, in many situations where money was no object, I like to tap into resources with broad and deep experience, especially when it comes to performance/racing applications.

Bill Verburg · Bill Verburg's Garage

Quote:

Originally Posted by winders

Bill,

But the mechanical limits of the 915 and rod bearing life of a 3.8L engine have no relationship. None. Zero. It's the torque of the 3.8L that causes the 915 problems. The Porsche factory had plenty of low torque, high horsepower, high RPM, short bearing life engines that would not stress a 915 like a 3.8L race engine.

S-

they are related because the author is misdirecting by omission anyone that may read this, he is not divulging the full story wrt to either statement

I have used a 3.8RS w/ a late 915, I have seen first hand the distortion of the output shaft seals due to 3.8RS torque, there needs to be a commensurate internal distortion of the cwp. I also have a stock 3.8RS that is tracked heavily hooked up to a race g50/30, w/ stock 6800rpm rev limits bearing life is considerably greater than ~20hrs.

Sure you can modify the 915 to be better but you had better factor in the cost of all the Wevo upgrades and more frequent rebuilds to boot. Additionally I strongly suspect that a 3.8 that needs main bearings replaced @~20hrs is not seeing sub 7k rev limits, if it is not then there are other issues.
people do strange things all the time, doesn't mean it's a good idea to emulate them.

The factory felt that the limiting factor for 3.2 was the 915 hence the g50 intro

I stand by my statement, 3.8 and 915 is not a good idea, but what anyone does w/ their $ is their business

Joe Bob · Joe Bob's Garage

My 915 didn't last long with the 3.6. I take care of it after the rebuild.....and the $$$ that flew outta my pocket.

winders · 10-31-2010, 12:49 PM

Quote:

Originally Posted by Bill Verburg

they are related because the author is misdirecting by omission anyone that may read this, he is not divulging the full story wrt to either statement

In other words, as I said, they are not related at all.

Scott

Mahler9th · 10-31-2010, 12:56 PM

Tomato, tomato. Most of the 915 transmissions to which I refer do not have any WEVO parts. I used my car for 2-3 seasons with a stock 915 without any issues.

Most of these local 915s do not see service every season.

My suggestions is only to be wary of absolutes like you have to have a G50 with a 3.8, and you cannot run Redline synthetic in a 915, and you must have external cooling with a 915. Learn about and understand the trade-offs.

I always suggest taking max advantage of local resources with pedigree as a primary focus, as opposed to using internet resources as primary. Since the original poster is apparently in NorCal, he has great local resources.... with plenty of experience regarding trade-offs.

Bill Verburg · Bill Verburg's Garage

Quote:

Originally Posted by winders

In other words, as I said, they are not related at all.

Scott

You are certainly entitled to your opinion

Bill Verburg · Bill Verburg's Garage

Here's a 915 that was used in a tracked 3.6 t/p
Notice any issues?

this is far from the only one I've seen like it