ROUTE 66

I just heard about GM PERFORMANCE HEADS for the Z06 motor.
Do any of you know if the same valves are used in this type of head as in OEM heads. I am concerned about rotating mass. Thanks..

AzDave47

I believe you are talking about the complete stock heads fully assembled that are listed in the GM Performance catalog.

One of our forum buddies (Hib) got these as his replacement heads when his first set had guides out of speck. He had a local shop check them before they were installed and the valve seats were not all concentric and needed to be machined. Without that work they would have failed again. So much for 100% GM inspection since Feb. 2011

Mark2009

Yes they are. Says so in the description.

ROUTE 66

Thank you. This looks good.
Will my intake manifold and other components bolt to these heads with out any mods?

JoesC5

Some flow numbers for you at .600" lift.

Stock LS7 head---351cfm intake/209cfm exhaust
GM performance--348cfm intake/219cfm exhaust
PRC265 heads----383cfm intake/235cfm exhaust.

rsalco

Everybody quotes peak flow numbers as THE metric for performance. However, 85% of cylinder-fill occurs at 50% of valve lift therefore intake velocity is much more relevant to making power, especially torque.

Velocity is affected by port shape and intake runner length/shape. Bigger is not better even if it produces higher peak flow. Smokey Yunick figured that out in the '60's.

erick_e

If you are talking about the GMPP LSX-LS7 heads, then yes. Same valves, but have upgrades PAC nitrated springs.

I have some detailed picture in my FS thread.

https://www.corvetteforum.com/forums...9201806-a.html

JoesC5

Care to share the velocity numbers of the stock GM LS7 head, the GM performance LS7 head and the PRC265 head, so we can see the difference.

It's clear that you have superior knowledge of engine head design that I don't have, so you should have no problem letting us lay people know which head of the three I mentioned(and also the WCCH ported heads) has the highest "velocity".

Oh, and I ported my first set of small block Chevy heads in 1961. I wanted horsepower from 6500 to 8500 RPM so I went with the largest ports and valves I could get without going into the water jacket.

rsalco

The velocity numbers are not published so far as I know, and I haven't done the testing myself on LS heads. Individual engine-builders do their own testing/shaping/fabricating and are not likely to share that information with 3rd parties. The parameters influencing port velocity go well beyond port size or shape, to include bore/stroke, cam profile/timing, manifold design, etc. Charge-air velocity has to be observed in full-scale mock-ups or modeled with very sophisticated simulation programs. A flow bench, which is what most head shops and aftermarket vendors have is useless to measure velocity.

BTW, it's clear that you consider yourself an expert, while I'm just a simple staple salesman so I'm sure your choice of head and head prep will be the best possible. But, a teensy-weensy suggestion: do some more reading on the subject...you seem to be a smidge behind the curve. Or, if unwilling to undertake that journey, give Roush-Fenway's engine shop a call. Perhaps they'll share some tech info with you.

"Oh, and I ported my first small-block heads in 1961."

I'm happy for you, but Smokey would not have been impressed. Does the phrase "...it's the area under the curve that matters." ring any bells?

JoesC5

Just as I thought. You can't back up your statements about "velocity" being the end all in head design. So, tell, me how would you go about choosing which head is best? The stock GM head? The GM Performance head? The PRC265 head? The WCCH stage 2 ported head?

I go with what information is available that is published for the world to compare, and that is flow numbers.

You keep going with the invisible "Velocity" numbers which you have no idea what they are when selecting how you are going to spend several thousand dollars for a new set of heads. I spent my money on a set of PRC265 heads. Which heads did you purchase for your Z06? A set from Smokey? Or a set from Roush-fenway?

I'm not an expert on heads, but I do know how they function. Even as a 19 year old kid in college in 1961, I was porting my heads on my 1932 3 window coupe that I ran in A/G, long before you read a book about it. I don't have the expertise or equipment today to properly port a set of LS7 heads, so I rely on the companies that do, thus I look at the info they publish, (ie; flow numbers) and assume they are knowledgeable enough not to screw up the port design when designing replacement heads or porting GM heads.

But, you keep on reading, while I'm out driving my Z06 with PRC265 heads with their higher "flow".

Undy

It's a blend between port velocity (FPS) and flow (CFM). You want to maintain good velocity (makes good torque) while moving as much CFM as possible (makes horse power). This is a generalization but the concept remains true.

That's why TSP recommends their PRC265s to the lion's share of us instead of their PRC285s. Short of 440"+ or EXTREME FI the 265s just don't have the needed velocity to work well. They'll be down on torque, which puts very large smiles on most of our faces when it's up.

JoesC5

And that is why I went with the PRC265's instead of the PRC285's. I retained the stock cam, the stock intake and the stock exhaust. I believe the WCCH stage 2 heads are very popular. Increased flow over the stock GM heads at the expense of "velocity".

If I was going with a big cam, a FAST intake, and a set of 2" long tubes, I would have considered the PRC285's, as I know those additions would give me horsepower at the expense of low end torque and the PRC285's would flow better in the upper RPM range(the same place the Big cam, the FAST intake and the 2" long tubes would excel). If I went with the big cam, the FAST intake and the 2" long tunes but stayed with the lower flowing stock GM heads to retain their "velocity" I would have chocked the engine to death and it would have run like crap.

Michael_D

Jeezus.....

Posted flow numbers are nothing more than marketing BS. To be fair to all heads when comparing, tests need to be completed on the same bench, same pull, same pipe size and the min CSA and FPS needs to be measured. This argument is ridiculous. Common guys, chill and be open minded.

Mark2009

Keep in mind that there are at least two GM Perf Parts heads for the LS7....

-- the 'stock' head 12578449

-- and the LSX-LS7 head 19201806 with the thicker deck and the extra head bolts (which you don't have to use) and the aftermarket beehive springs, which are advertised as having "as-cast" ports (no CNC work). These have the Ti and Sodium valves also. They also make some LSX heads for circle track and drag strip use, but I have no idea if those are plug-and-play nor what components they use.

For a stock engine I can't see any need for the LSX head.

.

American Heritage

100% agree!

Flow benches vary GREATLY. In order to have an even playing field all data needs to come from the same bench.

Flow bench computers such as "port flow analyzer" can accurately measure port velocity, swirl, stability, ect...

ROUTE 66

Thanks To all of you. You have been a great help.

gonefishn

My understanding was the LSX-LS7 uses an 8mm valve stem versus the LS7's 7mm valve stem. Although they may be the same size they shouldn't' be the same valves.

Mark2009

Stock LS7 valve stem is essentially 8mm (.3135" = 7.963mm)

Cobra R

I have the LSX-LS7 (6 bolt) CNC Gm performance heads. The exhaust valves are the same ones used in the stock heads.

The "as cast" (6 Bolt) version has the same port size as the stock head, but are not CNC like a stock head and also have a thicker deck. The overall height of the cylinder head is still the same.

CNC version is the same as above, but have some CNC work done to them. The ports are substantially larger than stock LS7 heads. I didn't measure how much though.


With the CNC version, Ragin Racin lethal cam, ported stock throttle body, ported fast, LG 1 7/8 headers, no cats and corsa mufflers made 566 rwhp and 522 rwtq. With poor track prep it's ran a 10.66@135.5 so far.