Generation IV External Engine - L92's or 243's????
03-26-2012, 09:28 AM
I'm building a 402 ci ls2 in the near future and Ive heard that l92's don't like big cams and I would be better off with 243's ... I just want to know if this is true or not... Idk what cam I'm going with or anything but I plan on running as close to 11:1 compression
03-26-2012, 03:34 PM
someone must know the answer to this :/
03-26-2012, 04:10 PM
I have a 402 with 317 heads on it ( same port as a 243 ) and it popped 482 rwhp with a 231/237 cam though 1 3/4 headers with a fast 90/90 though a 6 speed and 3.42 gear.
I talked with Richard @ WCCH as I was thinking of going to L92's.
To try and obtain optimal HP, I'd have to change the cam as l92's and ls3 heads like a 10 to 12 degree split. RIchard said as long as the 402 remains a 402 the 317's would be ok. If I was to go larger displacement, the l92's - ls3's would be better.
Check around on the cams as I've seen like 225/237 and others with a wide split in duration.
03-26-2012, 04:16 PM
Do the 317's on your 402 have any work done to them?
Thanks for the info
03-26-2012, 05:09 PM
Yes, they are ported and I think they have a lil larger intake valve.
03-26-2012, 06:04 PM
Rectangle port heads are newer and much better design than the old cathedral port heads.
It's a no brainer which heads to use!
03-26-2012, 07:13 PM
I agree with Dyno. GM is using retangular port heads on 376's and larger, and cathedrals on anything smaller, they clearly have access to both designs, and they chose the bigger port for the bigger engines. They are probably using some computer modeling, and finite element analysis to determine this that is way to go, well beyond anything any hotrod shop could ever dream up. Your 402 is bigger than a 376, why reinvent the wheel, GM engineering has done the work for you. I think the rectangular ports work fine with big cams, you just have to consider the size of the intake compared to the exhaust. The intake valve and runner is capable of significantly more flow than previous designs, and the exhaust is basically carryover from the catherdral port heads. A rectangular port cam needs that bigger split. I think you can get by with less overlap and still make good power with the bigger intake valve. You can close that intake valve sooner, because it fills faster through the big valve and keep it more streetable. I think this is probably the thoughts in the engineering department at GM. They can't meet emissions with a radical cam, and were searching for more VE, for improved performance.
I can see it now, "hold my beer, while I sketch out this monster BBC rectangular port and put it in an LS head". It probably happened about 6:30 in the afternoon in a major BS session. They all kick around till about 7 just to look like they are working hard, but everything after 5 is mainly a social deal and little work gets done. I'm and engineer so I have a feel how some of this stuff happens.
03-27-2012, 03:30 PM
Who told you don't like big cams ? What is the logic behind that statement ?
03-27-2012, 04:02 PM
Out of those 2 head choices I would go for the L92 heads. If you go with a cathedral port head it would need to be a set of AFR, or TFS heads to get the most out of it. Also an L92 works just fine with a large cam.
03-27-2012, 07:15 PM
I vote a quality aftermarket (AFR, TFS, etc) cathedral port for port velocity. I haven't really seen square port heads shine until 427 and up. My .02
Check out this very recent thread. http://ls1tech.com/forums/dynamometer-results-comparisons/1530621-402-ls2-535rwhp-490rwtq.html#post16129668
03-27-2012, 07:25 PM
Lets keep in mind the valve size difference that these 243 heads have versus the L92/LS3 heads. The intake valve is huge on the L92 head. This plays a critical role in the aspect of cylinder head/intake valve shrouding, which would hinder the erformance of any engine combination.
The 243 heads are a great choice if you are using a 4 inch bore or smaller or if you don't want to spend a little extra time with the came selection process that running a set of L92 heads sometimes requires. They both are great heads, and will result in huge horsepower...it just depends on budget, and your will to research the correct parts, for your project.
I would run the L92 head with a bigger bore engine (nothing less than a 4.060 inch bore). That's NOT to say that you couldn't run them with a smaller bore with good results, because you can, but let's consider what GM put the heads on, originally...greater than a 4.0 inch bore engine.