LS7 RPM Limit
07-20-2007, 09:18 PM
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LS7 RPM Limit Why do all of the LSx engines usually only turn up to 7000 rpm?
Can they not handle 8000+ like the "old" small block chevy engines? Both of my circle track engines turned 8200 rpm, with stainless valves, good springs and mechanical roller cam.
Is the hydraulic cam the only thing holding them back??
Can they not handle 8000+ like the "old" small block chevy engines? Both of my circle track engines turned 8200 rpm, with stainless valves, good springs and mechanical roller cam.
Is the hydraulic cam the only thing holding them back??
07-20-2007, 09:29 PM
#2
Originally Posted by jkittleson
Why do all of the LSx engines usually only turn up to 7000 rpm?
Can they not handle 8000+ like the "old" small block chevy engines? Both of my circle track engines turned 8200 rpm, with stainless valves, good springs and mechanical roller cam.
Is the hydraulic cam the only thing holding them back??
Can they not handle 8000+ like the "old" small block chevy engines? Both of my circle track engines turned 8200 rpm, with stainless valves, good springs and mechanical roller cam.
Is the hydraulic cam the only thing holding them back??
07-20-2007, 09:36 PM
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So if you upgraded to solid roller, good valve springs and Jesel you could turn these things up to 8000? I wonder if the LS7 heads and intake would still make power up there?
Any downsides to running solid roller on the street besides frequent valve adjustments?
Any downsides to running solid roller on the street besides frequent valve adjustments?
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07-20-2007, 11:34 PM
#8
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Originally Posted by jkittleson
So if you upgraded to solid roller, good valve springs and Jesel you could turn these things up to 8000? I wonder if the LS7 heads and intake would still make power up there?
Any downsides to running solid roller on the street besides frequent valve adjustments?
Any downsides to running solid roller on the street besides frequent valve adjustments?
With the large intake valves, mass (weight) is a problem as is strength to withstand the acceleration loads the valve sees in the 8000 rpm range. You certainly would have to use the best (stiffest, lightest, lowest inertia) valvetrain parts. That might actually be the limiting factor if you are planning to use the lobes you need to move the wind. I'm not sure if the currently available stuff can hack the job. Yes, solid roller, and springs are available but not necessarily at Jegs or Summit. None of this stuff is cheap; it's outright friggin' expensive.
If you want to play in the big sandbox you not only need deep pockets, you need to find the right parts. Some of them may still in someone's imagination or on the back of an envelope. If we find that LS7-style heads can support over ~2.2 hp per cube in 7-8L NA engines in the next few years, the valvetrain pieces will become available. They may rival the cost of the full-blown ported and dressed heads, but as Stroker McGurk once said: "Speed costs money; how fast do you want to go?"
I liked a lot of the things Stroker McGurk said.
Last edited by Old SStroker; 07-21-2007 at 12:47 AM.
07-21-2007, 01:37 AM
#9
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Originally Posted by jkittleson
Why do all of the LSx engines usually only turn up to 7000 rpm?
Can they not handle 8000+ like the "old" small block chevy engines? Both of my circle track engines turned 8200 rpm, with stainless valves, good springs and mechanical roller cam.
Is the hydraulic cam the only thing holding them back??
Can they not handle 8000+ like the "old" small block chevy engines? Both of my circle track engines turned 8200 rpm, with stainless valves, good springs and mechanical roller cam.
Is the hydraulic cam the only thing holding them back??
I believe it to be near 100% valvetrain related. The cam, lifter's and rocker assemblies are my guess. Ti valves, shaft assemblies, mechanical lifters and a more aggressive camshaft could easily polevault an LSx into 8k plus RPM use.
Without braking a sweat I should add...
07-21-2007, 07:27 AM
#11
I beg to differ. The limit is piston speed. At 7000rpm with a 4.000" stroke, mean piston speed is over 4600fpm. Very high for an endurance race engine let alone a production engine. Sure there are drag race engines with rediculouly higher piston speeds, but coming from an endurance racing engine builder, its high enough for us.
The short stroke Sneak Attack LS7 uses production LS7 valvetrain with Cadillac Racing's high speed lifters and revs to 8000rpm.
The short stroke Sneak Attack LS7 uses production LS7 valvetrain with Cadillac Racing's high speed lifters and revs to 8000rpm.
07-21-2007, 08:59 AM
#13
Originally Posted by See5
With the stock and most intakes the power is dropping pretty fast past 6,200 so you might be better of playing with the lower rpm torque.
7000 to 7100 rpm, 26" tyre, 3.42 rear end - you have a healthy 200 mph 5th gear and carry 60mph in 1st.
All specifications the C6 Z06 meets readily in stock form - so with 600+ crank HP a tweaked LS7 is a great high hp/high speed super sports car power plant
Hell - with the right power + 150 wet shot, 7000rpm and 3.15 gears, an LS7 powered C5 has a good shot at 200mph in the standing mile I should imagine.
For a number of excercises it would seem rpm is important to get the right work out of the torque a setup produces.
Last edited by RC45; 07-21-2007 at 09:07 AM.
07-21-2007, 09:32 PM
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Originally Posted by Katech
I beg to differ. The limit is piston speed. At 7000rpm with a 4.000" stroke, mean piston speed is over 4600fpm. Very high for an endurance race engine let alone a production engine. Sure there are drag race engines with rediculouly higher piston speeds, but coming from an endurance racing engine builder, its high enough for us.
The short stroke Sneak Attack LS7 uses production LS7 valvetrain with Cadillac Racing's high speed lifters and revs to 8000rpm.
The short stroke Sneak Attack LS7 uses production LS7 valvetrain with Cadillac Racing's high speed lifters and revs to 8000rpm.
Thanks Jason, that makes sense. The motors I turned over 8K were 3.48 stroke, one with 4" bore and the other 4.125". I guess it makes sense with the 4" stroke is to turn less rpm "7K" and use all of the torque.
07-22-2007, 12:00 AM
#15
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Originally Posted by Katech
The limit is piston speed. At 7000rpm with a 4.000" stroke, mean piston speed is over 4600fpm.
07-22-2007, 01:29 AM
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I just took a ride in a certain Colorado based LS7/Z06 that had the redline owner adjusted to 8K..1st gear burn out was bouncing off the 8K redline with nothing more than a glorified ls1 cam ( from a well know endurance motor vender..available at 1/2 the price FWIW) and a spring/retainer change. all else in valvetrain land was stock.
This could quite possibly be the fastest steer car I've ever ridden in since driving a modified 97 TT 911. I'd have more concern for losing the big end of the sodium filled exhaust valves at high RPM/Lift than anything else.
This could quite possibly be the fastest steer car I've ever ridden in since driving a modified 97 TT 911. I'd have more concern for losing the big end of the sodium filled exhaust valves at high RPM/Lift than anything else.
