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You will have much more torque with cathedral port heads than ls3 heads, especially in the low end, it has been tested plenty of times.
Depends on what you mean by low end. If you are talking about at 3500 RPM and the car has a 4000 RPM converter, who cares? Right?
Even if you have a 3500 RPM converter, once you shift at 6500-7000 RPM at the top of first gear the RPMs will only drop down to 5500 RPM or so. So once you get rolling, you aren't going to care what it does at 3500 RPM. The higher flowing head is going to go faster.
If his budget dictates that he either gets prc stage two heads or stock ls3 heads, then both are equal in terms of flow, so in this particular case, I would imagine that the prc heads would make more average power and actually be faster.
However, like I said earlier, the prc heads are as good as they are going to get. Stock ls3 heads allow for room to grow.
Depends on what you mean by low end. If you are talking about at 3500 RPM and the car has a 4000 RPM converter, who cares? Right?
Even if you have a 3500 RPM converter, once you shift at 6500-7000 RPM at the top of first gear the RPMs will only drop down to 5500 RPM or so. So once you get rolling, you aren't going to care what it does at 3500 RPM. The higher flowing head is going to go faster.
Well I mean lower end more for a daily driver car, but I forgot that he wrote that the car is no longer his daily driver, I just re-read the first post. But I know what you mean when the rpms don't drop as much when you shift.
If his budget dictates that he either gets prc stage two heads or stock ls3 heads, then both are equal in terms of flow, so in this particular case, I would imagine that the prc heads would make more average power and actually be faster.
However, like I said earlier, the prc heads are as good as they are going to get. Stock ls3 heads allow for room to grow.
They may have similar flow at high lift, but look at flow through the midrange, say about .400".
You will have much more torque with cathedral port heads than ls3 heads, especially in the low end, it has been tested plenty of times.
How much more we talking?
Not my daily anymore but I don't wont it to be a dog down low either.
Originally Posted by speedtigger
Depends on what you mean by low end. If you are talking about at 3500 RPM and the car has a 4000 RPM converter, who cares? Right?
Even if you have a 3500 RPM converter, once you shift at 6500-7000 RPM at the top of first gear the RPMs will only drop down to 5500 RPM or so. So once you get rolling, you aren't going to care what it does at 3500 RPM. The higher flowing head is going to go faster.
How about 6sp? Will it still put down enough down low to not feel lazy? If it only gives up like 20 down low but still puts down decent numbers and picks up lots more up top I would be ok with that.
Originally Posted by speedtigger
They may have similar flow at high lift, but look at flow through the midrange, say about .400".
I will look into this too. Never even thought about ls3 heads so I will have to look up to that. I am glad you and a few others brought it up because I want to look down every avenue. If it can knock money off the build or be very close but out perform it I am all ears
It was just my opinion, I rather have a 500hp with 480tq than a 520hp with 400tq, I just think that the cathedral heads give you more balance as far as hp/tq comes but if it's not your daily driver and is an M6, you can launch you car a little harder and take the advantage of the power up top. Edit: It also depends on the cam you choose.
It was just my opinion, I rather have a 500hp with 480tq than a 520hp with 400tq, I just think that the cathedral heads give you more balance as far as hp/tq comes but if it's not your daily driver and is an M6, you can launch you car a little harder and take the advantage of the power up top. Edit: It also depends on the cam you choose.
If that were the case, that would be a good argument. But, it is not the case.
Here are two actual real world examples of very similar builds. a 418" LS3 engine with the much lauded 237 TFS cathedral port heads and a 403" LS2 with the new Dart Pro1 LS3 heads. Let see who has what for torque and horsepower.
First, the TFS 237 cathedral port 418" LS3:
Originally Posted by helicoil
- 418 (LS3 block, 4.070" bore)
- 4" Compstar crank, Compstar H-beams, Wiseco -3cc pistons
- 237cc Cathedral port heads (Trick Flow porter castings worked by Chris Frank)
- BTR .660 spring kit
- small solid street roller (250/254 .650/.620 112lsa)
- 11.75 comp (pump fuel)
- Edelbrock SV 4150 top
- 1 3/4" headers stepped to 1 7/8"
- 850 Q series QFT carb
- KUP front dizzy kit
- wet sump
676 Horsepower @ 6900 RPM & 568 Foot Pounds of Torque at 5500 RPM
Now the Dart Pro1 LS3 headed 403" LS2
Originally Posted by speedtigger
403"
4.005" LS2 Block
Callies Compstar 4"crank and 6.125" Compstar rods
Bullet CP 11.5:1 compression flat top pistons
Dart Pro1 LS3 heads milled to 65 cc.
FelPro 1161-.041 MLS gaskets
247/259 110.5+3.5 .660"/.650" Cam Motion Low Lash Roller
Edelbrock Victor Jr. intake
835 CFM 4150 Holley
1 7/8" ARH headers
Melling 10295 pump and a Mast Oil Pan.
707 Horsepower @ 7100 RPM & 578 Foot Pounds of torque at 5500 RPM.
So there you have it. Two very similar builds done by highly capable builders with similar compression, cams, intakes, headers etc. The smaller 403" engine, with a smaller 4.005" bore made more torque and horsepower than the 418" engine with a 4.070" bore. The difference? Cylinder heads. The Pro1 LS3 heads made 10 more ft lbs of torque at the same RPM than the cathedral port heads and 30 more horsepower at 200 RPM higher. Also, the cathedral port engine used a vacuum pump which boost power while the square port engine did not.
Disclaimer: These tests were done on two different dynos at different times with all the variable that can imply.
Last edited by speedtigger; Oct 29, 2015 at 02:47 PM.
I, personally, like the cathedral port heads due to the balance between intake and exhaust flow. Call me old fashioned, but balance and symmetry just make sense to me.
I think it's obvious that GM is clearly favoring the intake on the square and rectangle port heads. This is evident in that the cam now has to carry the neglected exhaust.
I don't want anything to have to carry anything. I want my exhaust to be able to carry its own weight, so to speak. Getting the exhaust out is just as important as getting clean air in. I view the cathedral port heads as more efficient, more versatile, and more balanced.
Not trying to preach gospel, because ultimately, I don't know ****. But 75-80% exhaust flow ratio makes a whole lot more sense to me than 65-70%. Choking is choking, it doesn't matter if it's because you can't inhale or you can't exhale. And, I have seen plenty of cathedral port heads produce all the power I'm interested in, so there's literally no advantage to the square and rectangle port heads, in my under educated and over voiced opinion.
That is a lousy comparison. He added a 1/2 point of compression, went from a Victor Jr. to a Fast intake and most certainly had the wrong cam in the first engine for the Victor Jr. intake. He also did not make note of the weather (D/A) where he ran the new setup in November and the old setup in the summer? Just the D/A alone could make that much difference.
It was just my opinion, I rather have a 500hp with 480tq than a 520hp with 400tq, I just think that the cathedral heads give you more balance as far as hp/tq comes but if it's not your daily driver and is an M6, you can launch you car a little harder and take the advantage of the power up top. Edit: It also depends on the cam you choose.
Another 416 w/ inefficient LS3 heads, 11.6:1 CR, stock intake, no TDs through a 9 inch. Nowhere near being maxed out either! If you're only making 400wtq on a 400+ LS engine something is seriously wrong!
That's just it... There is no fair comparison between cathedral port and rectangle port heads. They are two entirely different design philosophies.
If you wanted to stay with stock head castings, you're comparing a 210cc runner to a 260cc runner, a 2.00" intake valve to a 2.165" valve (respectively).
I think it's just a matter of personal preference, and people will adamantly argue both sides, but trying to draw a comparison is fruitless.
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