Which stock casting head is best on a LQ9?
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Teching In
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Which stock casting head is best on a LQ9? I'm sure this question has been asked a thousand times, but I can't find the thread. I have an iron block 6.0 LQ9 with 317 heads on it. I also have a good set of 243's. Would L92 top end be better for a N/A motor in a truck? Looking for big power in a heavy truck, no power adders other than maybe a small shot of nitrous down the road someday.
If you're looking for "big power" as you stated, then the L92s would be the better choice over stock 243s.
For a better driving vehicle I do agree with the others in the 243s. But as far as making power up top, out of those 2 options, the L92s will blow away the 243s.
For a better driving vehicle I do agree with the others in the 243s. But as far as making power up top, out of those 2 options, the L92s will blow away the 243s.
The "advantage" of L92s for a peak number is overstated and the penalties at normal driving rpm understated.
For a truck no reason whatsoever to consider them. The trucks that got them stock have VVT and the 6speed's 4.03:1 first gear both of which are used to compensate for poor lowend.
You have a light car and 4000rpm stall decent amount of gear and they become reasonable to consider if the peak number is your goal.
For a truck no reason whatsoever to consider them. The trucks that got them stock have VVT and the 6speed's 4.03:1 first gear both of which are used to compensate for poor lowend.
You have a light car and 4000rpm stall decent amount of gear and they become reasonable to consider if the peak number is your goal.
L92s don't suck. Avg power is still higher with L92s. You just have to cam them correctly. But you'll never have small block torque off idle with the LS architecture.
Will smaller ports create more port velocity? Sure, but the shape of the rectangle ports means you can't simply compare a cathedral port's volume to that of a rectangle port. The CSA is actually much closer. The bigger issue is the larger valve in the L92 head. That hurts efficiency more than the port.
Will smaller ports create more port velocity? Sure, but the shape of the rectangle ports means you can't simply compare a cathedral port's volume to that of a rectangle port. The CSA is actually much closer. The bigger issue is the larger valve in the L92 head. That hurts efficiency more than the port.
Average power is often quoted starting at 3500rpm, honestly how much time does a truck spend over that?
http://www.hotrod.com/how-to/engine/...re-port-heads/
243s are recognized as making more power than 317s because they have a smaller and better chamber making more power even when compression is equalized with milling the 317s.
In that test the peak difference is 38hp but the compression and cam favored the rectangles and 243s would have reduced that difference up top and increased it down low, and this was a 408 which should benefit more from the big heads than a 6.0l....... and without even the .030 overbore that motor had the valves would be more shrouded.
I looked at other threads to see what truck you have, looks like a 2009 half ton? You have the 6l80 so you do have the first gear to try and use the L92s, that is good, but it also means you already have the best factory cathederal port intake and the 243 or 799 heads, use what you have.
The 243s will get the job done with less stall and gear, they may not make the same peak number but in normal rpm range will be a significantly better. I have an LS3 car(stock) and find the lowend disappointing.
Dyno testing alone doesn't tell us everything, for one it often doesn't start till 3000-3500rpm and most engines spend a vast majority of time, even accelerating below that. They also only tell us WOT.
http://www.hotrod.com/how-to/engine/...re-port-heads/
243s are recognized as making more power than 317s because they have a smaller and better chamber making more power even when compression is equalized with milling the 317s.
In that test the peak difference is 38hp but the compression and cam favored the rectangles and 243s would have reduced that difference up top and increased it down low, and this was a 408 which should benefit more from the big heads than a 6.0l....... and without even the .030 overbore that motor had the valves would be more shrouded.
I looked at other threads to see what truck you have, looks like a 2009 half ton? You have the 6l80 so you do have the first gear to try and use the L92s, that is good, but it also means you already have the best factory cathederal port intake and the 243 or 799 heads, use what you have.
The 243s will get the job done with less stall and gear, they may not make the same peak number but in normal rpm range will be a significantly better. I have an LS3 car(stock) and find the lowend disappointing.
Dyno testing alone doesn't tell us everything, for one it often doesn't start till 3000-3500rpm and most engines spend a vast majority of time, even accelerating below that. They also only tell us WOT.
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for one it often doesn't start till 3000-3500rpm
They also only tell us WOT.
most engines spend a vast majority of time, even accelerating below that.
Look I'm a 243 fan, and yes I agree it will provide an overall better accelerating car throughout the range. But as far as "big power", which is exactly what the OP said, you can't begin to compare those to L92s.
If he asked for the best overall driving head, yes 243s are the answer out of those two choices. But he didn't, he said and I quote again "big power". Why do you keep mentioning things about down low torque and all that jazz when he cares only for big power?
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Interesting discussion. Perhaps if he was towing the 243's would be a better option. Other than that why would anyone dispute the higher flow and power numbers offered by L92 heads for "big power"? It's been documented countless times.
Been documented that the flow of rectangle ports does NOT equal HP, cathederals down a fair amount on flow can make the same peak numbers and more average.
Not OEM heads but when they rested Mast catherderal vs. rectangle, the rectangle flow doesn't work out to numbers.
http://www.superchevy.com/how-to/ght...-head-to-head/
and that is on a stroker.
The rectangle port is not that efficient, not even when the aftermarket does it. Now for something like the LS7 huge lowend would be unmanageable in a 3000lbs car.
I believe the rectangle ports are deliberately compromising lowend while still making a peak number for the sales brochure.
Far as "racing" my "cam only" Caprice ran about what my SS does,
similar weight with the advantage to the SS,
The Caprice ran 13.2 at 103 with 290rwhp
SS ran 13.1 at 107 and stock is usually 355ishrwhp
Wish I still had the old slip for the Caprice, bet it beat the SS to the 1/8th Caprice had a 2800 stall but a LOT LESS effective first gear given the tranny difference the SS would need 2.60 rearend gears(has 3.27) with the 6l80 to compare 3.42s/4l60. So the SS has a BIG gear advantage.
Peak HP numbers don't tell he whole story the LT1 made a lot more lowend and a LOT less HP but ET was basically the same, the LS3 just takes some rpm to get moving. If you are willing to give a truck enough gear and stall to get it to 4500rpm+ instantly and keep it there it can work, but given truck tire height and other truck uses I am guessing you don't want 4000stall.
I know my SS will wake up with tuning and I think it would LOVE some stall and that can be fine in a 4000lbs car. In a truck I would be less tolerant of stall and would worry about having to change axle gears as well to avoid lugging in OD.
Throwing an L92 topped 6.0l in a 3500lbs car with 4000stall and 4.10s is different than a 5000lbs truck.
For the same peak HP number you are going to need more stall to make it work with rectangle port heads because they are down on lowend. If you give it enough stall
Not OEM heads but when they rested Mast catherderal vs. rectangle, the rectangle flow doesn't work out to numbers.
http://www.superchevy.com/how-to/ght...-head-to-head/
and that is on a stroker.
The rectangle port is not that efficient, not even when the aftermarket does it. Now for something like the LS7 huge lowend would be unmanageable in a 3000lbs car.
I believe the rectangle ports are deliberately compromising lowend while still making a peak number for the sales brochure.
Far as "racing" my "cam only" Caprice ran about what my SS does,
similar weight with the advantage to the SS,
The Caprice ran 13.2 at 103 with 290rwhp
SS ran 13.1 at 107 and stock is usually 355ishrwhp
Wish I still had the old slip for the Caprice, bet it beat the SS to the 1/8th Caprice had a 2800 stall but a LOT LESS effective first gear given the tranny difference the SS would need 2.60 rearend gears(has 3.27) with the 6l80 to compare 3.42s/4l60. So the SS has a BIG gear advantage.
Peak HP numbers don't tell he whole story the LT1 made a lot more lowend and a LOT less HP but ET was basically the same, the LS3 just takes some rpm to get moving. If you are willing to give a truck enough gear and stall to get it to 4500rpm+ instantly and keep it there it can work, but given truck tire height and other truck uses I am guessing you don't want 4000stall.
I know my SS will wake up with tuning and I think it would LOVE some stall and that can be fine in a 4000lbs car. In a truck I would be less tolerant of stall and would worry about having to change axle gears as well to avoid lugging in OD.
Throwing an L92 topped 6.0l in a 3500lbs car with 4000stall and 4.10s is different than a 5000lbs truck.
For the same peak HP number you are going to need more stall to make it work with rectangle port heads because they are down on lowend. If you give it enough stall
Thread Starter
Teching In
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Average power is often quoted starting at 3500rpm, honestly how much time does a truck spend over that?
http://www.hotrod.com/how-to/engine/...re-port-heads/
243s are recognized as making more power than 317s because they have a smaller and better chamber making more power even when compression is equalized with milling the 317s.
In that test the peak difference is 38hp but the compression and cam favored the rectangles and 243s would have reduced that difference up top and increased it down low, and this was a 408 which should benefit more from the big heads than a 6.0l....... and without even the .030 overbore that motor had the valves would be more shrouded.
I looked at other threads to see what truck you have, looks like a 2009 half ton? You have the 6l80 so you do have the first gear to try and use the L92s, that is good, but it also means you already have the best factory cathederal port intake and the 243 or 799 heads, use what you have.
The 243s will get the job done with less stall and gear, they may not make the same peak number but in normal rpm range will be a significantly better. I have an LS3 car(stock) and find the lowend disappointing.
Dyno testing alone doesn't tell us everything, for one it often doesn't start till 3000-3500rpm and most engines spend a vast majority of time, even accelerating below that. They also only tell us WOT.
http://www.hotrod.com/how-to/engine/...re-port-heads/
243s are recognized as making more power than 317s because they have a smaller and better chamber making more power even when compression is equalized with milling the 317s.
In that test the peak difference is 38hp but the compression and cam favored the rectangles and 243s would have reduced that difference up top and increased it down low, and this was a 408 which should benefit more from the big heads than a 6.0l....... and without even the .030 overbore that motor had the valves would be more shrouded.
I looked at other threads to see what truck you have, looks like a 2009 half ton? You have the 6l80 so you do have the first gear to try and use the L92s, that is good, but it also means you already have the best factory cathederal port intake and the 243 or 799 heads, use what you have.
The 243s will get the job done with less stall and gear, they may not make the same peak number but in normal rpm range will be a significantly better. I have an LS3 car(stock) and find the lowend disappointing.
Dyno testing alone doesn't tell us everything, for one it often doesn't start till 3000-3500rpm and most engines spend a vast majority of time, even accelerating below that. They also only tell us WOT.
I do drive an 09 half ton, but that is my daily with nothing more than a Dod delete and mild camshaft. This set up I'm discussing is going into another truck that will definitely be a weekend toy. Honestly, I'm not looking for a lot of torque down low, if anything, this old turd is meant to be a sleeper.
If you plan to roll around on a 30X12 drag radial and a 4000 converter then probably the L92s are right for you.
I would do some math about the rpms seen at the MPH you plan to play around at, truck tires are generally tall and unless you give it a crap load of gear you might not spend much time at high rpm if doing under 1/4 mile from a stop.
Wouldn't think you would be using a truck for roll racing topping 100mph a lot because aerodynamically that is scary.
Maybe you are a street racer and don't want to show your hand, but it is hard to get good answers with only half the background.
Wouldn't think you would be using a truck for roll racing topping 100mph a lot because aerodynamically that is scary.
Maybe you are a street racer and don't want to show your hand, but it is hard to get good answers with only half the background.
Do you have an E.T. goal or a HP goal Jmmartin1275?
I always like to start at square one when considering how to build a particular engine, which IMO is HP to weight ratio. How much power will it take to run the E.T. the customer wants?
As far as square port heads don't make good average power, torque and/or can't tow well. I always come back to this. "The General" felt that the square port heads was good enough for towing 10,000+ pounds in its flagship truck, The Silverado. That should give anyone doubting the torque production of the square port head a second opinion as to just how good these heads are at making power AND torque.
With a square port head, you're always moving more airflow at piston positions where the highest cfm demand is placed on the port, and at lower lifts as well. If you can capitalize on this additional airflow by utilizing the proper valve timing, then the result should always be positive.
The main problem I see and that I find with square port camshafts is the intake valve closing event. The charge inertia that a square port head possesses versus a cathedral port is very different. Because of this the IVC event is crucial in maximizing trapped intake charge and maximizing low speed torque production.
I always like to start at square one when considering how to build a particular engine, which IMO is HP to weight ratio. How much power will it take to run the E.T. the customer wants?
As far as square port heads don't make good average power, torque and/or can't tow well. I always come back to this. "The General" felt that the square port heads was good enough for towing 10,000+ pounds in its flagship truck, The Silverado. That should give anyone doubting the torque production of the square port head a second opinion as to just how good these heads are at making power AND torque.
With a square port head, you're always moving more airflow at piston positions where the highest cfm demand is placed on the port, and at lower lifts as well. If you can capitalize on this additional airflow by utilizing the proper valve timing, then the result should always be positive.
The main problem I see and that I find with square port camshafts is the intake valve closing event. The charge inertia that a square port head possesses versus a cathedral port is very different. Because of this the IVC event is crucial in maximizing trapped intake charge and maximizing low speed torque production.
The main problem I see and that I find with square port camshafts is the intake valve closing event. The charge inertia that a square port head possesses versus a cathedral port is very different. Because of this the IVC event is crucial in maximizing trapped intake charge and maximizing low speed torque production.