LS3 LS7 head interchange

[JANNETTYRACING]

Originally Posted by S-eatin-grin

Sorry Ted...but now I'm totally confused...I thought high boost in FI led to blow ups in unforged LS3's/L99's?? I've read about lots of folks on here talking about blower cams being beneficial because they lower boost. Then I've also read that superchargers make their power by making boost. So adding a blower cam to a SC can cause loss of power if you don't pulley down? I need a nap and a year or two in performance auto mechanics...

You asked about a 416 which would be fully forged and lower compression.

Ted.

[CC Performance]

If your forcing air through the heads then its not as critical on the intake as touching up the exhaust side of things and the cam wants to be biased for FI as well again for the exhaust side of things.... Then you have HP goals as well and better heads do make better power but again with FI and forcing the air through them its not a critical an area but aftermarket heads usually have thicker decks and 6 bolt options as well so its really how much boost and hp are you looking to make.
If your building a 416 then you can run what ever you want for boost as long as you deal with the compression smartly. Its not a contest to see who can run the most compression and boost at the same time...

[S-eatin-grin]

Yeah...my bad, for some reason I reverted back to the unforged boost limits. I still didn't realize after forging that boost is recommended to be run that high.

[S-eatin-grin]

My goal is about 600 rwhp with 416 ci and stock heads (modified as recommended) and a ZR-1 cam. I have the e-force and 1 7/8" LT headers already and am making alittle over 500 rwhp now. Most of the build threads I've read for FI 416 ci are using a 9.5:1 cr so that's along the lines of where I thought I'd want to be...I don't know if my goals are too modest or too much for that setup. I'd also be doing the ADM dual fuel pumps, JRE e-force fuel rails and upgraded injectors to at least 65lbs.

Originally Posted by CC Performance

If your forcing air through the heads then its not as critical on the intake as touching up the exhaust side of things and the cam wants to be biased for FI as well again for the exhaust side of things.... Then you have HP goals as well and better heads do make better power but again with FI and forcing the air through them its not a critical an area but aftermarket heads usually have thicker decks and 6 bolt options as well so its really how much boost and hp are you looking to make.
If your building a 416 then you can run what ever you want for boost as long as you deal with the compression smartly. Its not a contest to see who can run the most compression and boost at the same time...

[danhr]

600 should be cake work for any shop, if you already have a lower compression/forged bottom end to work off of.

def. should NOT have to step up to aftermarket heads or a 6 bolt block/head.

[axis]

Originally Posted by S-eatin-grin

Sorry Ted...but now I'm totally confused...I thought high boost in FI led to blow ups in unforged LS3's/L99's?? I've read about lots of folks on here talking about blower cams being beneficial because they lower boost. Then I've also read that superchargers make their power by making boost. So adding a blower cam to a SC can cause loss of power if you don't pulley down? I need a nap and a year or two in performance auto mechanics...

You are making the wrong assumption about FI. SC's and turbo's don't make boost, they push air. The restrictions in your motor, and exhaust are what cause the backpressure known as boost. A SC with "X" pulley will push "X" amount of air through your engine. If you add LT's to this car you relieve some back pressure so your boost should drop a little. The SC will still push approximately the same amount of air through your engine since you didn't change the pulley size. Same goes for a cam and proper porting. They make your heads more efficient so your relieving more of that pressure, while not changing the SC besides making it more efficient. Many will change pulley size to increase the amount of air the SC puts out since it won't affect the boost pressure as much. Pressure is much harder on the engine than HP increases. This is why turbo's react so well to exhaust upgrades, porting, and cams. Turbo's have BOV's that blow off at "X" psi. If you relieve backpressure, the turbo will keep pushing more and more air till it reaches the blowoff PSI. This is one of the advantages that turbo's have over SC's. No need to buy and swap pulleys to get the added airflow. It happens automatically.

[S-eatin-grin]

Makes sense...I'm just trying to find the right balance of power and engine strength....thanks!

[GTRacer87]

Just so everyone here knows, You absolutely cannot use ls7 heads on an ls3 unless the bore exceeds 4.100. The intake valve will hit!!! There is only 22-32 thousanths clearance between the intake valve and piston. hopefully no one has made this mistake.

[CGT]

Originally Posted by GTRacer87

Just so everyone here knows, You absolutely cannot use ls7 heads on an ls3 unless the bore exceeds 4.100. The intake valve will hit!!! There is only 22-32 thousanths clearance between the intake valve and piston. hopefully no one has made this mistake.

I have been told by a few good sources that LS7 heads will clear a 4.065 bore, not ideal but will clear. I assume you are talking about .022-.032 valve to piston clearance? You talk about it needing a 4.100 bore, but yet say the intake valve will hit the piston? Can you clear that up? Interested to hear from someone whos been there.

[Jason 98 TA]

We offer a cnc ported 390cfm LS7 head that clears the stock bores because we relocated the valves. You cannot put a stock LS7 head on a LS3 engine properly. The good news is our aftermarket casting LS7 small bore heads fit properly & gives you lots of features over a stock gm head.

[Cpanthers85]

Does the LS7 head require a different header than the LS3?! (a la the LSX454?!)

not to hijack but I asked this in another thread and never got a response. I have Kooks Stepped headers (which prob would be too small for the 454 anyway) but I am just wondering if regular 2" headers will bolt right up or if you need custom made headers..

Thanks

[CGT]

Jason, any dyno testing on the LS7 top end on an LS3?

[Motion427]

As far as I know,LSX454 will work with your LS3 headers.You'll need to change the intake to a LS7 or a aftermarket intake because the intake ports are not the same as the LS3.

[jhormilla]

The LS7 is a great head but with the right porting LS3 heads can perform very well on the LS3 or L99. Check out the link below.

http://www.camaro5.com/forums/showthread.php?t=187554