big split for LS7 headed motors
big split for LS7 headed motors I've been messing around with software trying to help get a head start on a good cam for LS7's...at least mine. Since the ex/in ratio is nowhere near as good as it was on ls1/6 type of heads, wouldn't the motor respond much better to a BIG split?
What about something like 25* of split or more?
This split seems way larger than most people 'in the know' run...but after talking to a couple of vendors, I cant see how a 243/250 for example, which is what a lot of people run in ls1/6 headed motors, would be good in an LS7 headed motor.
The Hotcams (and stocker) also have a large split. However, they may have been designed with stock manifolds in mind...
LS7 Heads
Lift.....Int.....Exh ex/in ratio
0.100 71 60 0.85
0.200 145 120 0.83
0.300 223 160 0.72
0.400 270 191 0.71
0.500 316 208 0.66
0.600 349 218 0.62
0.625 351 220 0.63
0.700 360 223 0.62
'Ported' LS6 Heads
0.200 156 136 0.87
0.300 212 172 0.81
0.350 236 186 0.79
0.400 259 193 0.75
0.450 280 202 0.72
0.500 294 213 0.72
0.550 302 219 0.73
0.600 312 228 0.73
What about something like 25* of split or more?
This split seems way larger than most people 'in the know' run...but after talking to a couple of vendors, I cant see how a 243/250 for example, which is what a lot of people run in ls1/6 headed motors, would be good in an LS7 headed motor.
The Hotcams (and stocker) also have a large split. However, they may have been designed with stock manifolds in mind...
LS7 Heads
Lift.....Int.....Exh ex/in ratio
0.100 71 60 0.85
0.200 145 120 0.83
0.300 223 160 0.72
0.400 270 191 0.71
0.500 316 208 0.66
0.600 349 218 0.62
0.625 351 220 0.63
0.700 360 223 0.62
'Ported' LS6 Heads
0.200 156 136 0.87
0.300 212 172 0.81
0.350 236 186 0.79
0.400 259 193 0.75
0.450 280 202 0.72
0.500 294 213 0.72
0.550 302 219 0.73
0.600 312 228 0.73
Last edited by Greg Fell; Jan 13, 2006 at 08:01 PM.
I noticed that too Greg. The intake flows a lot more than the ls6 but the exhaust is closer to the ls6 hence the big split. It would seem that we might be doing exhaust porting and running two inch headers in the future...what do you think? I talked with gunnar from patriot today to try and get a feal for when they would be doing the 92 truck heads. I was going to get some ls7s but I think I would save some money and maybe hassle with the worked over 92s. Are the weights of the intake going to be a problem on the ls7 heads...extra strong springs?
I'm not sure putting a 2" header on a port that doesn't flow that well will help matters, it may make things worse.
I'm going to use TI intakes. No way am I going to use a heavy 2.2" stainless, thats longer than the ls1/6 valves too.
I'm going to use TI intakes. No way am I going to use a heavy 2.2" stainless, thats longer than the ls1/6 valves too.
I agree Greg. I meant after solutions to the flow of the exhaust port are found the larger primaries will help the flow. If you look at big blocks...the ls engines are getting in the same hp range and 2'' primaries are not large on a mild bigblock. I know the engines are different but flow and hp are pretty much directly related.
The stock cam has 20* of duration difference from intake to exhaust. All of the GM Hot cams that were tested by Katech have large splits like you mentioned, but the manifolds certianly do not necessitate the need for the big split, its the fact that the engine was born in the C5R/C6R using a restrictor.
6600 rpm clutch dump of death Administrator
Joined: Dec 2001
Posts: 4,983
Likes: 13
From: Texas
Look at LG's results with 1 3/4" headers. The stock Ls7 exhaust port is basically not much more thana stock Ls6 port. It can use a lot of help.
The math seesm to indicate a 1 7/8 primary is the best tube. but, in looking a the current results of 1 7/8 vs 1 3/4, it appears tha the 1 3/4 are doing better.
This may be due to the fac that the 1 3/4 is keeping velocity up, and doing a better job of scavenging the port. I think going up too big is going to kill velocity, and show a power loss.
The math seesm to indicate a 1 7/8 primary is the best tube. but, in looking a the current results of 1 7/8 vs 1 3/4, it appears tha the 1 3/4 are doing better.
This may be due to the fac that the 1 3/4 is keeping velocity up, and doing a better job of scavenging the port. I think going up too big is going to kill velocity, and show a power loss.
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Verdad Gallardo 6600 rpm clutch dump of death Administrator
Joined: Dec 2001
Posts: 4,983
Likes: 13
From: Texas
Originally Posted by Greg Fell
J-Rod, what results for 1 7/8 do you speak of?
I'm not doubting Lou, but I'd like to see them quantified at an independant shop. But, so far Lou is ahead of the headers with 1 7/8" primaries which is not what I expected to see on the ls7. In speaking with other folks its theorized that the smaller tube is keeping up velocity, and is thus doing a better job of scavenging the cylinder. Thus, Lou's smaller tubes with better velocity, etc... seems to work better with the rather poor exhaust side on the stock LS7.
This is strictly based on posted data, and not on any testing I've done.
I think a good indicator would be flow of the intake with the intake manifold in place and flow of the exhaust with the header or atleast a pipe in place. This should go along way to increasing the E/I precentage. I think this head will benefit from some kind of split but not 25 or so, that's a ton of split and you'd likely be blowing alot of the power stroke right out of the exhaust valve, unless you are spinning to the moon, in which the ls7 intake may not be the best design for that anyway. Only time and further testing will tell
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