What is the Downside of doing a 4.0 Air cooled Engine?
03-10-2012, 08:26 PM
#1
Race Car
Thread Starter
What is the Downside of doing a 4.0 Air cooled Engine?
May be inline for an engine rebuild..... Will post photo's of what I have found.
What are the downsides of going to a 4.0 liter engine.
Can it affect the case? Bore size etc.....
Your thoughts are appreciated....
What are the downsides of going to a 4.0 liter engine.
Can it affect the case? Bore size etc.....
Your thoughts are appreciated....
03-11-2012, 08:30 AM
#2
Addict
Rennlist
Site Sponsor
Rennlist
Site Sponsor
How long have you got....?
In a nutshell, biggest problem with stock-stroke 4.0 litre conversions will be bore distortion and piston ring seal issues which both affect reliability. We calculated the stress of the aircooled cylinder under race loads and came to the conclusion that 103mm was about the limit to which we were willing to push reliability. Three years later Porsche did the maths for the GT3R program and selected 102.7mm....
In a nutshell, biggest problem with stock-stroke 4.0 litre conversions will be bore distortion and piston ring seal issues which both affect reliability. We calculated the stress of the aircooled cylinder under race loads and came to the conclusion that 103mm was about the limit to which we were willing to push reliability. Three years later Porsche did the maths for the GT3R program and selected 102.7mm....
The following 4 users liked this post by NineMeister:
03-11-2012, 01:01 PM
#3
Race Car
Thread Starter
I have no time at all 
I found the following bits on the sump plug magnet.....
So does that make the 3.9 the highest practical limit of a stock stroke aircooled engine?
I found the following bits on the sump plug magnet.....
So does that make the 3.9 the highest practical limit of a stock stroke aircooled engine?
03-11-2012, 06:15 PM
#5
Pro
Join Date: Apr 2008
Posts: 661
Likes: 0
Received 0 Likes
on
0 Posts
Steven - I wanted to post early, but I wanted the others to give their opinion first. I think you should talk to Charles Navarro at L&N Engineering. I emailed him about issues involving the 4l kit and he said the old kits were horrible.
He said he had a 100hr p&c 105mm L&N p&c in his office and it looked like new. I know that may sound biased, but I took his word for it since they have a good reputation.
I only logged around 2,500 kms so I cant tell you anything about longevity.
With regards to the cases, yes, you have to machine the cases to accept the 109mm sleeves. So the reputation of L&N is what I relied on before making the purchase. People will say, you cannot go back to 3.6 or 3.8, but why would I?
I love my engine. We recently had a trackday, and it performed beautifully. With your ecu, and put in a decent cam from John Daugherty, your car will be really nice
Paul
He said he had a 100hr p&c 105mm L&N p&c in his office and it looked like new. I know that may sound biased, but I took his word for it since they have a good reputation.
I only logged around 2,500 kms so I cant tell you anything about longevity.
With regards to the cases, yes, you have to machine the cases to accept the 109mm sleeves. So the reputation of L&N is what I relied on before making the purchase. People will say, you cannot go back to 3.6 or 3.8, but why would I?
I love my engine. We recently had a trackday, and it performed beautifully. With your ecu, and put in a decent cam from John Daugherty, your car will be really nice
Paul
Trending Topics
03-11-2012, 08:10 PM
#8
Rennlist Member
Let's see, we've got one world renowned expert posting here...........
My recommendation would be to figure out what you're trying to accomplish, and if that means pushing the envelope, work with such a world renowned expert on something that's bulletproof for your application. (In practical terms, I find that ~70hp my faux RS is short v. 996 GT3 equates to about 1.5 second difference from throttle on apex T14-to-turn in T1 at Thunderhill. Which is a 55-130ish-95 exercise.)
Now, if you just want to rebuild stock, most any of us can bolt something like that together.
My recommendation would be to figure out what you're trying to accomplish, and if that means pushing the envelope, work with such a world renowned expert on something that's bulletproof for your application. (In practical terms, I find that ~70hp my faux RS is short v. 996 GT3 equates to about 1.5 second difference from throttle on apex T14-to-turn in T1 at Thunderhill. Which is a 55-130ish-95 exercise.)
Now, if you just want to rebuild stock, most any of us can bolt something like that together.
03-11-2012, 08:28 PM
#9
Instructor
Join Date: May 2006
Location: Ottawa, Ont.
Posts: 246
Likes: 0
Received 0 Likes
on
0 Posts
Sorry to see this. I guess the only upside is maybe you can get a great motor built, but how to pick type of motor to be built and who to build it.
NineMeister seems to be the man, but he's a fair piece away. Let say a well set up 993 is 250hp at the wheels, how hard would it be to get 350hp
at the wheels and the big question, what would it cost?
Would a normal 3.8 rebuild be $2OK, and 350hp at wheels be $40K. I'd love 350hp at the wheels in a motor that would last say 25000 miles
I will be watching this post and wish you well with this situation.
NineMeister seems to be the man, but he's a fair piece away. Let say a well set up 993 is 250hp at the wheels, how hard would it be to get 350hp
at the wheels and the big question, what would it cost?
Would a normal 3.8 rebuild be $2OK, and 350hp at wheels be $40K. I'd love 350hp at the wheels in a motor that would last say 25000 miles
I will be watching this post and wish you well with this situation.
03-14-2012, 04:07 PM
#10
RL Community Team
Rennlist Member
Rennlist Member
In automotive manufacturing everything runs through test cells to take every conceivable cost out of a design while retaining service life benchmarks... Seems to me a change as you are contemplating throws that all out the window and you can be sure to see some expensive issues down the road.
Andy
Andy
03-15-2012, 01:34 AM
#11
Rennlist Member
03-15-2012, 05:05 AM
#12
Rennlist Member
03-15-2012, 10:42 AM
#13
Race Car
Thread Starter
03-15-2012, 11:31 AM
#15
Seared
Rennlist Member
Rennlist Member
Andreas