I dont really know how to answer your question. Either a 347/348 with a supercharger, turbo or a 427ci+ LS motor will both produce 650rwhp, with reliable power, some street manners, and will be blast to drive.
As far as which one who be more efficient depends on many variables. Same with the TQ curve, etc, etc.

If you want 650rwhp through a a4 your really going to be spending some money, espeically if you go 427+ LS.
I would look into a 455 or larger, I think they stop at 481's but not for sure.
Pick up a set of Ls7 heads and intake work a good amount of work done to them. Get the best heads you can afford/find, because they will dictate the untimate power of the motor. Than find someone to grind you a custom and pick the bottom end.

FI- again get the best heads you can afford/find. Get a fast 90/90 intake, pick your compressor, find a cam guy, and than pick your bottom end.

Either should be able to hit 650rwhp with some reliability, driveabiltity and a little mpgs.

As i said in the begining of my post, you cant really compare the two unless you have some basic parts for a 'Combo" picked out. Than you at least have something to base arguments on.

What ever you do good luck.

 

An ~750hp NA (~650rwhp) motor is going to be a very highly developed situation. I wouldn't even think of that as a goal unless I had BIG money and lots of time. It is not nearly as easy as the above post suggests. It will be far easier and less expensive (but not cheap) to reach that number with a blower. If I was contemplating a 650 rwhp LS based street vehicle I wouldn't give NA any further thought. IOW - fuggedaboutit.

Just MO.

Rich

 

I didnt try to make it sound easy. Nor cheap, a well worked set of ls7 heads, and intake, the rest of the valvetrain could easily be 4-6k.
Depending on mild to wild. Than you have to get a good bottom end. another 4-6k(427+ cubes).
Fuel system 1k, trans 2.5k, rear end, 2k, suspension/ chasis 2k, misc. BS 1k. 15-20k total.
If your are paying someone to do everything add another 4-5k. And i probably forgot some stuff too.

 

SixSpeedsInc (formerly T56Rebuilds) will take a T56 and build it for 700rwhp/700rwtq for a lot less than that. CPT will do likewise (although they won't actually stick a horsepower number on it) with a 4L60E.

 

Like I said, the only practical way (and I use the term loosely) to have street car at those power levels is with forced induction. But everyone is going to have a different opinion. How many of them actually have a car with that kind of power? Then ask how many of them are NA?

Rich

 

I don't know of any LSx based N/A motors that are putting down over 650rwhp. Even a LSx 454 doesn't put that down, probably closer to 550rwhp. Most forced induction LSx street motors are putting down right around 650 - 700rwhp. Of course there are a few exceptions, but that is what I see mainstream around here in Texas.

 

What are your performance goals? HP goals don't mean much to me, some people really get into racing dyno's and bragging hp number but the car doesn't run anywhere near it potential. There are plenty of over rated cars out there under-performing and making themselves look bad and the mark look bad.

Built what best suits your interest and your pocket book.

 

Rapid motorsports has a SR 427 laying down 675rwhp+. Katech(sp) and a few others have 427's+ making 600rwhp+. If you spend a little time reading on LS1tech.com you will see.

PRC broke 400cfm's with ls7 heads. Several other aftermarket head companies are aound 380cfm's @.650.

I am too up to date on trans's, so thats why i was a little high. But i feel that my other numbers are close.

 

Quote:
Originally Posted by tcr98taws6
624 RWHP with this build as shown in the August 2008 Car Craft Magazine. Oh, it also got 21 MPG at 80MPH average, windows up and A/C running coming home from the 2008 Power Tour last weekend.


From LS1TECH. Dammit it didnt post the article. Think its a 454 by LME, m6.

 

Starting back in the early 60's with the (in)famous Pontiac GTO v. Ferrari GTO test I learned to read things in car mags with a BIG grain of salt. The Internet is even worse.

Rich

 

Ya think!!?

 

I understand all that. I know everyone on here has a 9 second car that no one evers gets to see hear or ride in.

But there is a thread over there titled 600rwhp n/a.
Theres about 5 pages of potential combo's. I know most of them wouldnt touch it on their best day but if you have a 370-390cfm head you should be able to get there. Especially some of the 454,481 solid roller combo's.

 

I have a 468ci BBC in my race car. The heads flow ~375 CFM. The CR is 13.5:1 and running methanol through a 2000 CFM TB with 2.25" open headers with a SR cam at about .700" lift. It doesn't make 650rwhp, though I suppose it might through a manny tranny. A pump gas 650rwhp NA OHV V-8 of <500ci is a tall order. Probably not impossible, but a lot of R&D is going to go into it. The GMPP 572R is 750hp, so it isn't 650rw and it runs on race gas. The pump gas version makes 620hp - good for a bit >500 at the wheels.

Rich

 

^^^^^^Thats why I like performance goals versus RWHP goals, a good operator can make the dyno read some pretty bodacious numbers. I agree with Rich, real 600 plus hp NA on pump swill are few and far between.

Back to the original topic, go blown.

 

Ok, you proved me wrong. I stand corrected, I am starting to understand.

But there are many LS motors that are knocking on the door of 600rwhp, NA, pump gas.

They are all 416,427+ cubes. I starting to see that 600 rw is about the limit for fully worked ls7 heads, a fancy bottom end, and a monster cam. Very few break it, but the majoirty dont. The ones that do are SR cammed, sheetmetal intake, blah blah blah.

Agreeing with others on this thread. Go blown. Cheaper to make the power, driveability will be better, much more reliable, etc.