Cam for L92 Heads: Lessons Learned
06-19-2011, 11:38 AM
#401
TECH Apprentice
iTrader: (2)
Join Date: Jul 2005
Location: Texas
Posts: 305
Likes: 0
Received 0 Likes
on
0 Posts
Dynoed my 6.0 Thursday. It's bored .030 w/ untouched L92 heads. Milled .020,thin head gaskets,flycut pistons for the cam. Cam is 238/250 113+3 .604 int .598 exh. Dyno numbers were 485/425 at the wheels. It was 115 degrees in the shop so I was suprised at the numbers.
06-23-2011, 01:06 PM
#405
On The Tree
iTrader: (1)
Join Date: May 2010
Location: Fort Walton Beach, FL
Posts: 131
Likes: 0
Received 0 Likes
on
0 Posts
Unopened engine, so stock 10.7:1 compression.
Contemplating on something with slightly less lift but a bit more duration, but the same minimal overlap. I might stick with it as it's my DD, but with a manual tranny it can be a bit frustrating to drive when I'm not in the mood to deal with all the tourists hogging the left lanes around here
Contemplating on something with slightly less lift but a bit more duration, but the same minimal overlap. I might stick with it as it's my DD, but with a manual tranny it can be a bit frustrating to drive when I'm not in the mood to deal with all the tourists hogging the left lanes around here
06-23-2011, 01:51 PM
#406
TECH Fanatic
Join Date: Jun 2006
Location: Hayward CA
Posts: 1,326
Likes: 0
Received 0 Likes
on
0 Posts
im running a 230/244/598/612/114lsa in my lq9/ls3 stroker silverado... but the set up my change.. gonna drop it in a 99 fbody with a th400 .. so i might step up the cam a bit.. around a 237/251 or a 239/252.. not much of a difference but ill see
07-11-2011, 08:34 AM
#409
This is some good information I found on another thread from Patrick G
Here's what the collective resources are showing so far:
The bigger L92 numbers for 400+ CID motors seem to favor an intake valve closing point of 50-52 degrees ABDC at .050" (just like a cathedral-port motor).
The L92 motors like around 4 degrees more ignition timing than cathedral port motors. If you're running less than 30 degrees of timing, you're probably leaving power on the table.
The L92 motors respond well to higher DCR as long as it does not limit total ignition timing (see above). Better to have full timing and lower DCR than high DCR and low ignition timing.
The 400+ CID L92s seem to be more exhaust sensitive. 1 7/8" headers seem to help more than on cathedral port motors.
The L92 402s don't seem to not like much more than 15 degrees of overlap at .050" (which baffles the hell out of me). Start making more overlap than 15 and they really start to get lazy down low.
I think with the large intake port, the airspeed must be pretty slow. This might explain why they're so overlap sensitive. This does not mean you have to run a wide LSA cam or a narrow one, you just have to hit the valve events that fit the critical criteria (IVC and overlap).
The bigger L92 numbers for 400+ CID motors seem to favor an intake valve closing point of 50-52 degrees ABDC at .050" (just like a cathedral-port motor).
The L92 motors like around 4 degrees more ignition timing than cathedral port motors. If you're running less than 30 degrees of timing, you're probably leaving power on the table.
The L92 motors respond well to higher DCR as long as it does not limit total ignition timing (see above). Better to have full timing and lower DCR than high DCR and low ignition timing.
The 400+ CID L92s seem to be more exhaust sensitive. 1 7/8" headers seem to help more than on cathedral port motors.
The L92 402s don't seem to not like much more than 15 degrees of overlap at .050" (which baffles the hell out of me). Start making more overlap than 15 and they really start to get lazy down low.
I think with the large intake port, the airspeed must be pretty slow. This might explain why they're so overlap sensitive. This does not mean you have to run a wide LSA cam or a narrow one, you just have to hit the valve events that fit the critical criteria (IVC and overlap).
Last edited by Samer; 07-11-2011 at 10:32 AM.
07-22-2011, 10:10 PM
#410
I've been playing with cams for my 404 L76 in Performance Trends Engine Analyzer Pro. My calculations all used the stock LS3 head flow numbers obtained by Richard at WCCH, with a stock intake manifold. Many many hours. Intake durations varying from 232 to 245 hardley changed the horsepower. I've settled on an intake duration of 238. What I did find interesting was the exhaust duration. All of comp cams LS3 cams have about 15 degrees more exhaust duration than intake. I will have an exhaust that flows as well as open headers and always thought that 15 degree split was a bit much. Originally I was sure that a 6 degree split would be ideal. But Analyzer Pro showed a loss of only 1-2 hp over 6000 rpm, and a strong gain of 13 ft lbs almost everywhere below 5000 rpm by reducing the split exhaust/crutch to only 2 degrees more than the intake at 0.050"!
I really didn't expect to see that since EVERYONE runs silly large splits on rectangle port motors.
The only other thing that I found interesting by messing with as many variables as I could was the change from swapping the stock intake manifold for tunnel ram style (new holley anyone?!). Over 6500 a tunnel ram picks up a huge 50 hp. But it doesn't come free, with a loss of upto 60 ft bls below 4000 rpm.
I really didn't expect to see that since EVERYONE runs silly large splits on rectangle port motors.
The only other thing that I found interesting by messing with as many variables as I could was the change from swapping the stock intake manifold for tunnel ram style (new holley anyone?!). Over 6500 a tunnel ram picks up a huge 50 hp. But it doesn't come free, with a loss of upto 60 ft bls below 4000 rpm.
09-20-2011, 09:27 PM
#411
TECH Enthusiast
iTrader: (6)
Join Date: Aug 2002
Location: Readsboro, VT
Posts: 529
Likes: 0
Received 0 Likes
on
0 Posts
Not everyone. Spinmonster has been singing the praises of single pattern cams (or close to it) for ls3s for quite a while. For whatever reason, he seems to be largely ignored here, but there are a lot of c6s putting down big numbers with his cam.
09-21-2011, 04:00 AM
#412
09-21-2011, 07:43 AM
#413
TECH Enthusiast
iTrader: (6)
Join Date: Aug 2002
Location: Readsboro, VT
Posts: 529
Likes: 0
Received 0 Likes
on
0 Posts
09-26-2011, 08:12 PM
#415
Thanks for the link. I've been getting alot of calls about the Spinmonster Cams and was like "whats a Spinmonster".. LOL
Either way,my shop has been running minimul split,less overlap Cams in LS3's for a few years already. Learned a long time ago the L92/LS3's like smaller cams,tight splits and less overlap. My personal 11 Camaro gained 115rwhp with an intake,headers and 224 Cam.
09-30-2011, 11:48 AM
#417
TECH Enthusiast
iTrader: (6)
Join Date: Aug 2002
Location: Readsboro, VT
Posts: 529
Likes: 0
Received 0 Likes
on
0 Posts
I wound up having a good discussion with Don at Slowhawk about cams for my car, and ordered a custom grind from him. It has a bit less intake duration than I had planned, but I trust his experience over my internet homework! I can't wait for it to get here so I can finish the long block. 
09-30-2011, 01:31 PM
#418
Teching In
Join Date: Feb 2009
Posts: 48
Likes: 0
Received 0 Likes
on
0 Posts
I'm doing a 403 build also. Just got my block and rotating assembly. Went with k1 crank and rods with wiseco flat tops 3cc. Next purchase will be some bare ls3 heads. I was thinking of something like 230/243 with low .600 lift and maybe 113 lsa. I like the hotrod lope but it's a DD. Whatcha think?
09-30-2011, 08:22 PM
#419
TECH Enthusiast
iTrader: (6)
Join Date: Aug 2002
Location: Readsboro, VT
Posts: 529
Likes: 0
Received 0 Likes
on
0 Posts
I'm certainly no expert, but I'd go with a whole lot less exhaust duration in order to get your overlap at 4 degrees or less. The cam I was leaning toward was a 231/236 originally, but I wound up Following Don's advice and getting one that was just a little bit smaller. He felt that the 231/236 I was looking at could still have some minor surging at low speeds. LS3 heads have such big intake ports and valves that they are sensitive to overlap, and from what I've seen on the forums, anything above the low 230s on the intake and mid-high 230s on the exhaust seems to be about the point where going any higher seems to start giving rapidly diminished returns in the power department, but really start to make idle quality suffer.