Advanced Engineering Tech - LS7 Compression ratios

Guys,
I am building an Iron blocked drag race engine with a set of modified LS7 heads, chambers are stock. It is going to be a 8000+ RPM combination with a very big solid roller cam (280's @.050 and 850 lift) and one or two carbs. My question is how much compression have folks been able to use with the Factory LS7 head (4 bolts per cylinder) without trouble. The bore is going to stay at 4.125 but I have not decided on the stroke yet. I have an LSx Block and a sleeved 6.0 with the Katech caps and bushed lifter bores. Any suggestions?

We've run 13.5-14.0 to 1 with stock GM heads and gaskets. With a good tune on the motor, I don't see a problem running in that range. There may be others here who have gone higher but you'll have to leave it to them to say.

Shane

Thanks Shane!

Your going to need alot more than a Titanium intake valve to spin that high... And can the LS7 heads be machined enough for .850 lift?!?! Hope you plan on a sheet metal intake...
I am going to do a 12.5:1CR on PRC LS7 heads and stock LS7 GM MLS gasket and i am not worried...

IMO you need to look at WCCH LS7 heads...

What are you looking to do exactly? Goals? Plans?

Gordon,


Goals:
Limit to 427 cu in
Make 950 HP Naturally Aspirated


Plans:
Sleeved 6 liter iron block bored to 4.125
Katech Caps
Lifter bores bushed
Crower Crankshaft
Howards 4130 Rods 6.125
Solid Roller Cam
Modified LS7 Heads
Del West Valves and room for .850 lift and proper springs
T&D Rockers
Jesel Belt Drive
ATI Balancer
Daily Single Stage External Oil Pump
Daily Vacuum Pump
Hogan Intake
2 1050's

Rational:

NHRA Super Stock 427 Chevy's are making almost this much power with similar flow numbers on the heads, one 850 carb and 12.5 Comp Ratio.Throw in all the NHRA rules just for fun and this is pretty impressive. These engines run to 8800 RPM with 3/8 stemmed steel 2.19'" valves.

The LS engine has a lighter rotating mass, lighter pistons, smaller domes, better valve train geometry, shorter pushrods, symetrical port head, better valve angle and lighter valves

I can use any compression ratio, intake manifold, carb or carbs

seems like it should be achievable

What do you think?

Two things that stick out:

Sleeved 6 liter iron block bored to 4.125

950hp does not seem to be a problem with the LS7 block, or a Darton sleeved LS2 block. Both are aluminum, so that would cut weight almost 100 pounds!

Modified LS7 Heads

I seriously dought that the LS7 heads would take you to 950hp even fully CNC'ed P&P.
The WCCH LSW heads by ALL PRO would definitely take you there! They flow and pull through the high RPMS with the right cam. (i am not someone who knows anything about cams)


Sounds like a nasty build!!! Those are the only two things that would be my consern.
There is someone on here or the Corvette boards that had a 427 with the WCCH heads and made something like 825hp on pump gas N/A. I'll try to look for the build and send it to you.

Keep Us All Posted!

Gordon,



NHRA Super Stock 427 Chevy's are making almost this much power with similar flow numbers on the heads, one 850 carb and 12.5 Comp Ratio.Throw in all the NHRA rules just for fun and this is pretty impressive. These engines run to 8800 RPM with 3/8 stemmed steel 2.19'" valves.




What do you think?

I think those old boat anchors sure are impressive considering their limitations!:D

Gordon,


Goals:
Limit to 427 cu in
Make 950 HP Naturally Aspirated


Plans:
Sleeved 6 liter iron block bored to 4.125
Katech Caps
Lifter bores bushed
Crower Crankshaft
Howards 4130 Rods 6.125
Solid Roller Cam
Modified LS7 Heads
Del West Valves and room for .850 lift and proper springs
T&D Rockers
Jesel Belt Drive
ATI Balancer
Daily Single Stage External Oil Pump
Daily Vacuum Pump
Hogan Intake
2 1050's

Rational:

NHRA Super Stock 427 Chevy's are making almost this much power with similar flow numbers on the heads, one 850 carb and 12.5 Comp Ratio.Throw in all the NHRA rules just for fun and this is pretty impressive. These engines run to 8800 RPM with 3/8 stemmed steel 2.19'" valves.

The LS engine has a lighter rotating mass, lighter pistons, smaller domes, better valve train geometry, shorter pushrods, symetrical port head, better valve angle and lighter valves

I can use any compression ratio, intake manifold, carb or carbs

seems like it should be achievable

What do you think?

I'm not so sure you are going to achieve your goals with some of the parts listed. The fastest NA LSx engine are not using steel rods, for one, and they use a 5 stage dry sump, rather than a wet sump. The camshafts are closer to 1.00" of lift as well. I don't think a factory LS7 head could support the flow or the spring requirements to achieve this either.

How do you know that they turn 8800 with 3/8" steel valves? That really seems a little unrealistic.

that power with those parts n/a i dont think so.check out gmpp,s uncle robins ta built lsx it is wicked and made some thing like 830hp n/a with better parts.the same guy who built that motor built mine.

We have several Super Stock Big Block Chevy's (454's and 427's) we run. We use big springs and have to check them and change them quite a bit but 8800 is pretty typical for us. They are 3/8 stems for sure or we get thrown out during tear down. You can go here for a few photos:
https://www.autoimagery.com/store/cgi-bin/imageFolio.cgi?search=Bryan%20Broaddus&img=108&cat=all&bool=and&numtolist=12&sortfiles=2

Bryan,
I don't mean to sound smart but if you are building Super Stock engines/cars, maybe we should be asking you the questions??? :huh:

melsie68, Thanks! I will take that as a compliment.

I have seen other engines with the 4 head bolt configuration have trouble sealing higher compression ratios so I thought maybe someone here had more experience with this engine. The new LSx head is a 6 bolt configuration so it made me think. I know there are a bunch of guys running a ton of boost on the engine so my assumption is I can run as much as I can stuff in it naturally aspirated.