IF I were to build a motor to LS6 specs, what kind of power could I expect on a chassis dyno? I have seen one member post 340 rwhp. The low riser intake is a concern, any idea what you lose compared to a Performer RPM?

I would probably go with GMPP alum heads and around 10.5 to 1 compression. This is a pipe-dream at present, but curious if anyone out there has much experience with these motors. Thanks in advance.

 

Doug:
I can't offer you much assistance but I wouldn't be too worried about that LS6 intake. I remember Norval saying that he used to run it on his 460 big block and loved it. He switched to a Victor Jr. in hopes of better performance but was disappointed and thought his LS6 intake performed better. If I recall correctly his LS6 was gasket matched though. Hopefully he'll chime in and give you some of his insite.

 

I would imagine 340 RWHP will be no problem.

My brother put together a 461 CI, 9.1 to 1, oval port heads, with Comp Cam 294 solid and it put out 325 RWHP. This was with the Performer RPM and 750 3310 Holley. It ran out of steam at 5500 rpm or so. Pushed the 4400 lb car to 13.40's:) I love it.

He wanted more compression and with the much better heads you are looking at...I think no sweat.

:)

 

Hi Shane. I used the stock LS6 high rise intake not the low rise. I also milled part of the divider out like the L88 and also totally ported the intake. In search of more performance I went to a victor junior and lost performance. To make the high rise fit under the stock hood I went with a 2 inch airfilter and cleaned up the underside of the hood. I could close the hood but the air cleaner left marks on the underside of the hood. I really liked that intake.

 

A good streetable 454 based engine can easily put out over 400 RWHP. It all depends on cam, compression and heads. Since you are looking at aluminum heads already, you are way ahead of what was originally installed on LS-6's. If you sneak in a little healthier cam ( the LS-6 cam is no slouch though!) and keep 10.5 or so honest compression you will be there. The old L72 type high rise aluminum intake is a good runner. I've been involved several times over the years where a new style single plane was installed that may have made more Hp but didn't get the car down the track any better. The RPM air gap is even better. I'd use it for a good street motor.

Just for reference my old 427 made 423 RWHP at only 5850 rpm with oval port Merlin heads and a 288* street roller on pump gas through 2.5" pipes. The difference will be what you do for exhaust and make sure you feed it with a big enough carb. Use 2" headers preferably an 850 cfm carb. A 750 will work, but the 850-950 will be better. Use a DP, NOT a vacuum secondary one.

Don't strangle it with too small a cam. People often times use small block #'s and forget how many cubes they are feeding. You need to be in the high .500's to low .600's on lift and in the 250-260* range on duration with a solid flat tappet. you can drop down to the 245* range with a roller if you want to.

Jim

 

Thanks for the feedback. I guess what I am thinking is if engine "A" is put together like 427Hotrod suggests and generates 425 rwhp, how much do I lose by going the nostalgic route by using 30 + year old designs for cam and intake, and maybe heads. 75 hp?

The only other advantage to this would be I could use my old BB hood (which I prefer). I have the original LS5 motor sitting in my garage, which would be a good candidate for the build.

I would like more overall power and bottom end grunt than my current motor has (333 rwhp, 388 rwtq). Maybe my impression of an LS6 is greater than the reality. Anyone have any opinions on the performance of this motor in a street car?

 

I have a Chevy aluminum low rise rectangular port intake manifold if anyone is interested. With a Holley, it will fit under a stock '74 style hood.
Gary Hoffman
603-682-8073