Aftermaket Dilema - Rectangle or Cathedral?
Launching!
Joined: Feb 2015
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I have similar goals and purchased a low mileage L92 pullout. I'm keeping VVT and put a Texas Speed cam in it which according to dyno data will get me there with headers and a tune. Having VVT should definitely help the low end. My car currently has an Olds 403 which is all torque and will blow sticky tires off in second gear at a 25mph roll. I would rather safely hook and pull hard at the top end. For this reason I expect and welcome less low RPM torque from the L92. My car is a street car so I don't want to mini tub it or put stupid tractor tires on it. Considering your LS3 was designed for rectangular port heads and you would have the added expense of switching over your top end to cathedral port I would stick with rectangular.
I'm on a SBE LS1 and Mamo 220's with a 225/227 cam. Yes I'm leaving a lot on the top end on the table but it drives darn near stock down the road. Pulls great up top to about 6800 and the low end torque is pretty awesome. It will never be a 400+ stroker for sure but the head port you use has got to be THE most important part of a build. Almost everything else revolves around it.
Good SCR and DCR help a LOT too. I had PRC 5.3L heads with a 228r cam and hated it down low. It definitely had that "soggy" feeling. My new setup has none of that and I don't even have a FAST 102 on it like the old setup did. Old setup was around 10.8:1 SCR and
Good SCR and DCR help a LOT too. I had PRC 5.3L heads with a 228r cam and hated it down low. It definitely had that "soggy" feeling. My new setup has none of that and I don't even have a FAST 102 on it like the old setup did. Old setup was around 10.8:1 SCR and
Thread Starter
On The Tree
Joined: Jan 2012
Posts: 101
Likes: 10
I have similar goals and purchased a low mileage L92 pullout. I'm keeping VVT and put a Texas Speed cam in it which according to dyno data will get me there with headers and a tune. Having VVT should definitely help the low end. My car currently has an Olds 403 which is all torque and will blow sticky tires off in second gear at a 25mph roll. I would rather safely hook and pull hard at the top end. For this reason I expect and welcome less low RPM torque from the L92. My car is a street car so I don't want to mini tub it or put stupid tractor tires on it. Considering your LS3 was designed for rectangular port heads and you would have the added expense of switching over your top end to cathedral port I would stick with rectangular.
I will be likely limited to a 305 width tire and I am expecting traction to be an issue. I helped a good friend of mine swap a stock LS6/T56 with long tubes in his 91 RS (mine is a 90RS) and he can't hook at all. He has new sticky 275's out back and still can break loose in 2nd and 3rd gears.
Likewise, as mentioned above, port design is critical, which lead me ask the question in this thread. How much better (drive-ability, tip-in, throttle response, etc) are the aftermarket rectangular heads in the mid to low range compared to explosiveness of a properly dialed in cathedral head from Tony. I realize I could leave power on the table, However, I would be leaving money in my wallet.
In the end, time and money will dictate this. A living, breathing 470rwhp car is a lot more fun than a theoretical 500+rwhp car still in planning/budget mode.
If you have the coin, go cathedral, either Tony's 235cc heads or AI's 230cc offering using Trickflow castings. With a ported FAST 102 and matched cam you won't give up anything down low and easily eclipse 500rwhp with supporting more.
You can get there at 500+ with ported stock rectangles if you're careful with the cam specs and conservately ported stock rectangles. AI has a good 267cc design for one that does make good tq. Throttle tip in wont be quite as explosive, but above 3500 the differences start to blur. You can save $ by going with a ~$350 Rick Crawford LS3 intake and ported TB vs aftermarket, not to mention cheaper oem castings.
I'm still a cathedral head guy, but I'm also not one to deny what can be done on stock rectangles on a stock stroke setup either. The rectangles just have a narrower window to hit for best results.
Jason
You can get there at 500+ with ported stock rectangles if you're careful with the cam specs and conservately ported stock rectangles. AI has a good 267cc design for one that does make good tq. Throttle tip in wont be quite as explosive, but above 3500 the differences start to blur. You can save $ by going with a ~$350 Rick Crawford LS3 intake and ported TB vs aftermarket, not to mention cheaper oem castings.
I'm still a cathedral head guy, but I'm also not one to deny what can be done on stock rectangles on a stock stroke setup either. The rectangles just have a narrower window to hit for best results.
Jason
Thread Starter
On The Tree
Joined: Jan 2012
Posts: 101
Likes: 10
Rick goes by 'G8-4-speed' here, or search Facebook for Rick Crawford Racing. I think there is an alternate company by the name of GPI who Rick taught to modify the manifold in the same manner.
Thread Starter
On The Tree
Joined: Jan 2012
Posts: 101
Likes: 10
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Granted those heads aren't being discussed here but.....
The "rectangle is the best" is blindly based on flowbench numbers. They have their place but blanket blind belief in their superiority is ignorant at best.
People make all kinds of excuses about "the cam" that doesn't quite pan out, so next is cam lift well how many of us can afford or want to maintain a .700lift valvetrain on our street car, then there is "the FAST intakes are crap and homogenize the results". Always an excuse for why the rectangles massive flowbench advanatage doesn't pan out in the real world.
The intake design and cam lift may well be legitimate reasons for why the rectangles don't shine in the real world BUT we have legitimate reasons for using sub .700lift and front feed plastic intakes. Not many of us are up for cowl hoods and $500 springs 1-2 times a year
Granted those heads aren't being discussed here but.....
The "rectangle is the best" is blindly based on flowbench numbers. They have their place but blanket blind belief in their superiority is ignorant at best.
People make all kinds of excuses about "the cam" that doesn't quite pan out, so next is cam lift well how many of us can afford or want to maintain a .700lift valvetrain on our street car, then there is "the FAST intakes are crap and homogenize the results". Always an excuse for why the rectangles massive flowbench advanatage doesn't pan out in the real world.
The intake design and cam lift may well be legitimate reasons for why the rectangles don't shine in the real world BUT we have legitimate reasons for using sub .700lift and front feed plastic intakes. Not many of us are up for cowl hoods and $500 springs 1-2 times a year
With stock displacement I'd say it boils down to whether you want 1) a little more throttle responsiveness and torque in the lower RPM's and pay more for the cathedral FAST intake, or 2) save the money and use the OEM intake and lose the throttle responsiveness. I only went with #2 because I received a great deal on the LS3 conversion and it was the quickest way to get my daily driver back on the road.
I can get new assembled LS3 heads with hollow intake valves for $1000 shipped, I do not know if the greatest porting & valve job in the world will offset the larger intake port volume compared to a well ported LS1/LS6/5.3L head. You only need about 300CFM to feed the motor for a 7000RPM redline, so really anything above that won't be realized immediately but offers room for future growth. It seems as if the best porters charge about $1500 to port the stock castings, so you're already at the price of an aftermarket head like AFR/PRC/TFS, etc. Of course you can save money on OEM heads if you choose to buy them used, but I'm personally hesitant to buy used on major parts.
If it were my choice and money wasn't a concern, I'd pick the AFR or PRC cathedral heads and mate it with an LS6 intake to begin with. If tuning shows a significant kPa loss at WOT, upgrade to the FAST setup and sell the stock parts to help offset the loss.
I can get new assembled LS3 heads with hollow intake valves for $1000 shipped, I do not know if the greatest porting & valve job in the world will offset the larger intake port volume compared to a well ported LS1/LS6/5.3L head. You only need about 300CFM to feed the motor for a 7000RPM redline, so really anything above that won't be realized immediately but offers room for future growth. It seems as if the best porters charge about $1500 to port the stock castings, so you're already at the price of an aftermarket head like AFR/PRC/TFS, etc. Of course you can save money on OEM heads if you choose to buy them used, but I'm personally hesitant to buy used on major parts.
If it were my choice and money wasn't a concern, I'd pick the AFR or PRC cathedral heads and mate it with an LS6 intake to begin with. If tuning shows a significant kPa loss at WOT, upgrade to the FAST setup and sell the stock parts to help offset the loss.
I've had both TFS 225's (By TEA) and Stock GM 821's on my 416. Both heads were milled to make 11.2 - 11.3 cr.
The cathedral setup with a slightly worked fast 92 and 239/246 cam
The LS3 heads setup with a stock LS3 intake and 232/240 cam.
End result was 15lbs more torque at 3k rpm with the stock GM heads. Both combos peaked at 475 rwhp around 6000rpm. The cam used in the LS3 combo had 12.5 degrees less overlap and drives a hell of a lot nicer on the street.
The cost of a stock LS3 top end is about 1/3rd the cost of the aftermarket cathedral.
I ran 2 mph faster in the 1/8 mile with the stock GM LS3 top end.
My opinion is probably pretty obvious
Others have had better results with the high-dollar heads...just didn't play out for me I guess.
The cathedral setup with a slightly worked fast 92 and 239/246 cam
The LS3 heads setup with a stock LS3 intake and 232/240 cam.
End result was 15lbs more torque at 3k rpm with the stock GM heads. Both combos peaked at 475 rwhp around 6000rpm. The cam used in the LS3 combo had 12.5 degrees less overlap and drives a hell of a lot nicer on the street.
The cost of a stock LS3 top end is about 1/3rd the cost of the aftermarket cathedral.
I ran 2 mph faster in the 1/8 mile with the stock GM LS3 top end.
My opinion is probably pretty obvious
Others have had better results with the high-dollar heads...just didn't play out for me I guess. On a chassis dyno 3000rpm is lower than usually tested so we have few results there. The magazine engine dyno results all agree given the same or similar cams specs rectangles are down below 4000 even on a stroker. Of course the setup with the smaller cam with less overlap drove better.
You changed cam specs enough that your's is a valid comparison of setups but not heads, the 1/8th mile favored a smaller cam.
You also didn't post lift?
Same tuner? Overlap requires fairly significant tuning effort to make drive right, few bother
http://www.hotrod.com/how-to/engine/...re-port-heads/
Same stroker shortblock, same rectangle spec cam, lower compression for the 317s and it won out by 15ft.lbs at 3000rpm, if it were 243s and the same compression I think everyone would agree the difference would be greater. More lowend opens up the possibility of using less stall which improves drivability.
Magazine tests are imperfect, but they give us far more data than those who change heads and cam and then attribute the differences to the one part they want to argue in favor of.
You changed cam specs enough that your's is a valid comparison of setups but not heads, the 1/8th mile favored a smaller cam.
You also didn't post lift?
Same tuner? Overlap requires fairly significant tuning effort to make drive right, few bother
http://www.hotrod.com/how-to/engine/...re-port-heads/
Same stroker shortblock, same rectangle spec cam, lower compression for the 317s and it won out by 15ft.lbs at 3000rpm, if it were 243s and the same compression I think everyone would agree the difference would be greater. More lowend opens up the possibility of using less stall which improves drivability.
Magazine tests are imperfect, but they give us far more data than those who change heads and cam and then attribute the differences to the one part they want to argue in favor of.
Thread Starter
On The Tree
Joined: Jan 2012
Posts: 101
Likes: 10
I've had both TFS 225's (By TEA) and Stock GM 821's on my 416. Both heads were milled to make 11.2 - 11.3 cr.
The cathedral setup with a slightly worked fast 92 and 239/246 cam
The LS3 heads setup with a stock LS3 intake and 232/240 cam.
End result was 15lbs more torque at 3k rpm with the stock GM heads. Both combos peaked at 475 rwhp around 6000rpm. The cam used in the LS3 combo had 12.5 degrees less overlap and drives a hell of a lot nicer on the street.
The cost of a stock LS3 top end is about 1/3rd the cost of the aftermarket cathedral.
I ran 2 mph faster in the 1/8 mile with the stock GM LS3 top end.
My opinion is probably pretty obvious Others have had better results with the high-dollar heads...just didn't play out for me I guess.
The cathedral setup with a slightly worked fast 92 and 239/246 cam
The LS3 heads setup with a stock LS3 intake and 232/240 cam.
End result was 15lbs more torque at 3k rpm with the stock GM heads. Both combos peaked at 475 rwhp around 6000rpm. The cam used in the LS3 combo had 12.5 degrees less overlap and drives a hell of a lot nicer on the street.
The cost of a stock LS3 top end is about 1/3rd the cost of the aftermarket cathedral.
I ran 2 mph faster in the 1/8 mile with the stock GM LS3 top end.
My opinion is probably pretty obvious
Others have had better results with the high-dollar heads...just didn't play out for me I guess.You mentioned the overlap difference in cams but how did the two drive in normal street driving? Why did you prefer the LS3 set-up?
A lot of these results (all the mag tests) are on larger cubed motors which can make better use of the LS3 large ports. I am pretty sure I am over thinking this and I should just go the route which is friendlier on the wallet, albeit at the expense of some of the desirable features of a cathedral setup. If there was in intake/TB/injector combo for the cathedral heads that could financially compete with the LS3 intake I would go cathedral and call it a day.
If you have room the "TBSS" intake is cheap and better than an LS6 and while it falls well short of the FAST for peak numbers does GREAT in average numbers.
http://www.hotrod.com/features/1507-...ifolds-tested/
Granted that test was with an aftermarket TB but stock on those is 87mm I believe.
If you don't have room, you don't have room, I really don't know how much space the third gen has vertically.
People act like there is the LS1/ LS6 and FAST and that is it, and that almost is in for a 4th gen, so little room, but for retrofits with more space the cheap truck intakes can be great, the early truck intake matches the LS6 and the and the TBSS intake pretty well matches the FAST in everything but peak HP, it matches peak torque, exceeds average torque, matches average HP.
http://www.hotrod.com/features/1507-...ifolds-tested/
Granted that test was with an aftermarket TB but stock on those is 87mm I believe.
If you don't have room, you don't have room, I really don't know how much space the third gen has vertically.
People act like there is the LS1/ LS6 and FAST and that is it, and that almost is in for a 4th gen, so little room, but for retrofits with more space the cheap truck intakes can be great, the early truck intake matches the LS6 and the and the TBSS intake pretty well matches the FAST in everything but peak HP, it matches peak torque, exceeds average torque, matches average HP.
11 Second Club
Joined: Sep 2011
Posts: 390
Likes: 2
From: The Burnie, MD
If your goals are really 450-480hp/tq, just run the stock LS3 top end. I'm making 465/450 with a stock LS2 bottom and untouched LS3 heads/intake with a fairly mild cam (222/230 .59x/.60x 114+2)
I didn't realize the 821 heads jumped in price that much...they were $315/ea a couple years ago.
Anyway, here's the dyno sheet. Makes plenty of torque down low.
I didn't realize the 821 heads jumped in price that much...they were $315/ea a couple years ago.
Anyway, here's the dyno sheet. Makes plenty of torque down low.
On a chassis dyno 3000rpm is lower than usually tested so we have few results there. The magazine engine dyno results all agree given the same or similar cams specs rectangles are down below 4000 even on a stroker. Of course the setup with the smaller cam with less overlap drove better.
You changed cam specs enough that your's is a valid comparison of setups but not heads, the 1/8th mile favored a smaller cam.
You also didn't post lift?
Same tuner? Overlap requires fairly significant tuning effort to make drive right, few bother
http://www.hotrod.com/how-to/engine/...re-port-heads/
Same stroker shortblock, same rectangle spec cam, lower compression for the 317s and it won out by 15ft.lbs at 3000rpm, if it were 243s and the same compression I think everyone would agree the difference would be greater. More lowend opens up the possibility of using less stall which improves drivability.
Magazine tests are imperfect, but they give us far more data than those who change heads and cam and then attribute the differences to the one part they want to argue in favor of.
You changed cam specs enough that your's is a valid comparison of setups but not heads, the 1/8th mile favored a smaller cam.
You also didn't post lift?
Same tuner? Overlap requires fairly significant tuning effort to make drive right, few bother
http://www.hotrod.com/how-to/engine/...re-port-heads/
Same stroker shortblock, same rectangle spec cam, lower compression for the 317s and it won out by 15ft.lbs at 3000rpm, if it were 243s and the same compression I think everyone would agree the difference would be greater. More lowend opens up the possibility of using less stall which improves drivability.
Magazine tests are imperfect, but they give us far more data than those who change heads and cam and then attribute the differences to the one part they want to argue in favor of.
Cathedral combo cam specs were 239/246 624/595 113+2
Rec port combo cam specs are 232/240 631/621 116+4
I think it's fair to say the stock rectangle heads held their own with smaller cam. Also fair to say if I put that same smaller (more street friendly) cam in a cathedral combo it wouldn't have made as much power as the REC ports.
Can't really just compare heads...you kind of have to compare combos since the intakes & cams aren't really compatible.
