422"/PRC LS7's/big cam, Going to try upgrade to 3/8" pushrods to see difference
03-28-2009, 11:46 AM
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422"/PRC LS7's/big cam, Going to try upgrade to 3/8" pushrods to see difference I just finish dynoing a 02 Z06 we just finished.
Made 577 rwhp but peaked at 6200 rpm. 515 rwtq.
Funny thing is it passed 500 rwhp at 5300 rpm climbing hard,but leveled out and started falling off after 6200. By 7000rpm it was down to 540.
Motor combo:
LS3 4.100" Bore, 4.0" Stroke - 422"
PRC LS7 Heads, hand finished, titanium valves, 400cfm
Custom AFR extreme springs (dont have the open/closed pressures in front of me), but much more than your standard PRC Double type spring to handle the camshaft.
Ported LS7 intake
1-7/8" ARH Stainless longtubes
Custom CSP 252/260, .65x/.66x camshaft /w 1.8 Yella Terra ultra light shaft rockers.
The one part of the combo that I feel could be a shortcoming is the chromemoly 5/16" - 7.6" long (or 7.7" cant remember) pushrods.
I am really thinking with the amount of camshaft and spring pressure that the 5/16" pushrods are probably like guitar strings / spagetti at high rpm.
So we are going to get the new pushrods and swap them back to back with some 3/8" tapered LS7 style pushrods on the dyno (since the ls7 heads already are clearanced for the bigger ones) and see what type of results we come up with.
Made 577 rwhp but peaked at 6200 rpm. 515 rwtq.
Funny thing is it passed 500 rwhp at 5300 rpm climbing hard,but leveled out and started falling off after 6200. By 7000rpm it was down to 540.
Motor combo:
LS3 4.100" Bore, 4.0" Stroke - 422"
PRC LS7 Heads, hand finished, titanium valves, 400cfm
Custom AFR extreme springs (dont have the open/closed pressures in front of me), but much more than your standard PRC Double type spring to handle the camshaft.
Ported LS7 intake
1-7/8" ARH Stainless longtubes
Custom CSP 252/260, .65x/.66x camshaft /w 1.8 Yella Terra ultra light shaft rockers.
The one part of the combo that I feel could be a shortcoming is the chromemoly 5/16" - 7.6" long (or 7.7" cant remember) pushrods.
I am really thinking with the amount of camshaft and spring pressure that the 5/16" pushrods are probably like guitar strings / spagetti at high rpm.
So we are going to get the new pushrods and swap them back to back with some 3/8" tapered LS7 style pushrods on the dyno (since the ls7 heads already are clearanced for the bigger ones) and see what type of results we come up with.
Last edited by SoCalSpd; 03-29-2009 at 12:21 AM.
03-28-2009, 04:34 PM
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That's about all you are going to get with the LS7 intake manifold. It becomes a restriction at about 650 crank HP. The new LSXr manifold should be out soon and will help some. Or, you can have the stock intake ported and cleaned up, that was worth 11 rwhp peak on my LS7.
03-29-2009, 12:12 AM
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LSxGuy widda 9sec Mustang
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With the stout valvesprings, 1.8 rockers and a longer pushrod like the LS7 heads require, I would not run 5/16" pushrods at all. I've been using 3/8" tapered 7.750" with no issues.
03-29-2009, 12:27 AM
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That's about all you are going to get with the LS7 intake manifold. It becomes a restriction at about 650 crank HP. The new LSXr manifold should be out soon and will help some. Or, you can have the stock intake ported and cleaned up, that was worth 11 rwhp peak on my LS7.
The heads arent even as they came from PRC, they were professionally hand finished and showed some additional gains (mainly exhaust side). Heads are even milled for more compression.
Somethings missing here unless the 600 rwhp ls7 results ive seen from other shops are getting are inflated.
Ive done a few factory ls7 cars and they all made peak power pretty high...last one was cnc heads, 23x/23x smaller cam, stock ls7 intakelongtubes and rest stock in 06 C6z06 and it made 555 rwhp peaking near 7000rpm, but it had 3/8" pushrods.
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03-29-2009, 08:06 AM
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I agree with intake being a restriction, but not this much. With it peaking at a low rpm with that much camshaft doesnt seem normal. This intake/throttle body was fully professionally ported as well. Also weve got every bolt on down to Yella terra rockers, electric water pump, underdrive, lightweight wheels, careful valvetrain setup/preload etc with attention to detail. I've even got a methanol kit on the car that im spraying on top of the 91 octane and getting 29 degrees of timing in it with no knock retard. I did a tune with and without methanol (with the mild weather right now, no real gains, but when its hot out I expect it maintain power.
The heads arent even as they came from PRC, they were professionally hand finished and showed some additional gains (mainly exhaust side). Heads are even milled for more compression.
Somethings missing here unless the 600 rwhp ls7 results ive seen from other shops are getting are inflated.
Ive done a few factory ls7 cars and they all made peak power pretty high...last one was cnc heads, 23x/23x smaller cam, stock ls7 intakelongtubes and rest stock in 06 C6z06 and it made 555 rwhp peaking near 7000rpm, but it had 3/8" pushrods.
The heads arent even as they came from PRC, they were professionally hand finished and showed some additional gains (mainly exhaust side). Heads are even milled for more compression.
Somethings missing here unless the 600 rwhp ls7 results ive seen from other shops are getting are inflated.
Ive done a few factory ls7 cars and they all made peak power pretty high...last one was cnc heads, 23x/23x smaller cam, stock ls7 intakelongtubes and rest stock in 06 C6z06 and it made 555 rwhp peaking near 7000rpm, but it had 3/8" pushrods.
03-29-2009, 11:20 AM
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LSxGuy widda 9sec Mustang
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TSP keeps the 7.750" 3/8" pushrods if that's what it needs, those fit most PRC LS7 heads.
I looked over your post and somehow missed the YT rockers. Here's what I would try if you have the time and access to the stock rocker arms instead:
Test 1: 3/8" tapered pushrods with stock rockers compared to current dyno
Test 2: YT rocker swap compared to Test 1, if a clean pull leave them on, if not go to stock.
I have not used the YT or HS aluminum rockers on an LS7 head. I've had some HS for several months in the box for our shop car but can't bring myself to test them. I have had what I called valvefloat (at the time) with LS7 heads on an engine dyno, but was using 5/16" .080" pushrods, I think 5/16" .120" walled would have fixed that one (which I have used on LS1 heads), but never had another opportunity to duplicate that issue on the LS7. I just automatically run the largest pushrod diameter that fits usually... to minimize issues.
I looked over your post and somehow missed the YT rockers. Here's what I would try if you have the time and access to the stock rocker arms instead:
Test 1: 3/8" tapered pushrods with stock rockers compared to current dyno
Test 2: YT rocker swap compared to Test 1, if a clean pull leave them on, if not go to stock.
I have not used the YT or HS aluminum rockers on an LS7 head. I've had some HS for several months in the box for our shop car but can't bring myself to test them. I have had what I called valvefloat (at the time) with LS7 heads on an engine dyno, but was using 5/16" .080" pushrods, I think 5/16" .120" walled would have fixed that one (which I have used on LS1 heads), but never had another opportunity to duplicate that issue on the LS7. I just automatically run the largest pushrod diameter that fits usually... to minimize issues.
