FLYNAVY30

iTrader: (1)

Im building a '69 Corvette as a toy for spirited back road blasts and occasional auto cross work. I really like the idea of doing something different that rev's extremely fast and has a power band that continues to climb all the way to 7500 or 8000 RPM. Ive done some research, and found a few people running destroked LS7s at 388 cu in with great results (Danny Popp). That however seems like a very expensive route. Another formula Ive found is using the aluminum 6.0L block and the 4.8L crank. TPiS recently built a similar motor (http://www.superchevy.com/how-to/eng...-heavy-hitter/) but designed for boost at 9.5:1 compression. N/A, the motor still made 505 HP and 438 TQ before the turbo. I was thinking of copying the build, but bumping the compression to somewhere between 10.5-11:1. Ideally, with minimal accessories, and a TKO600, that would net close to 400 and 400 at the wheels with sharp throttle response. At this point, Im just kicking around ideas, but would love to hear anyones thoughts on the topic.

Thanks

uxojerry

I just completed a destroked BBC of 3.75 x 4.5. When it was getting built I asked the builder what he thought it would make. He said 600-800 because he had never built one. It ended up 810/660 and a max rpm of 7000.

Now I wish I had done a 3.5 x 4.6 to knock the tq down from 660. 660 is still a bit much for a C3 irs, but it did come in under the limits of my T56.

Hot Rod magazine built an SBC DZ 302 and it dyno'd at 420hp. They then put a set of afr 210 heads on it with no cam swap. They got 520hp out of it.

Destroking is way of extracting hp and limiting tq. If your upgrading an entire drivetrain, it is not necessary. When your trying to live with the limits of your current parts, it makes sense.

If you take your current plan, I would buy a good top end and pinch pennies on the bottom end. That way if you decide to restroke the block, the top end can handle it.

11.5 to 1 and 7000rpm would be decent compression and the rpm would not require a solid roller or shaft rockers. An SBC would probably be cheaper to build IMO.

FLYNAVY30

iTrader: (1)

Agreed. One of the many reasons Im looking to go this route is the C3 IRS, and the fact that Im not going to flare or tub the rear end, so I cant go wider than a 9 inch tire so torque much in excess of 400 at the tires is useless. Additionally, I already have an aluminum 6.0L block and a 4.8L crank from previous projects so even with doing forged rods and pistons, and a stout top end with LS3 heads, I could still bring this together without getting excessively pricey.

JS01

iTrader: (10)

I would not put the 4.8 crank in it, just use a standard crank. if it is traction limited just knock the bottom out of it in the tune. Fast revs are a side effect of light rotating assy and alot of power. I dont think this engine would rev any different than every other LS with the parts you described. Making it carry power to 7500-8000 will depend mainly on the intake manifold choice. I would use a single plane or tunnel ram with shorter runners, that will also help knock out some of the low end.

uxojerry

My guess is with an LS3 top end, your numbers for hp will be equal to a longer stroke motor, and your tq numbers will be lower. Peak hp will probably be in the 6500-7000 range, not 7500+.

I came up with my guesses by comparing my 3.75 stroke motor to a 4.00 stroke with a similar top end and cam. Hp for both motors came in the same range with the 4.00 stroke making 70tq more across the board.

It might be interesting to talk to a machine shop about lightening your crankshaft to determine if it is a cost effective option. I also doubt you will need forged parts for the kind of power you want to make. Stock parts will save you $$$.

I just looked at an ls3/525 dyno sheet. It made 560/480 at 6400 rpm. With less stroke and the same heads/cam/intake, you should be able to make the same hp at higher rpm and maybe -400tq. Just a guess.

Sales3@Texas-Speed

iTrader: (2)

I see your theory but understand you will be spending a lot of money to get the same power as a stock cube, cam only ls1. You can get a cam and valve train that will make great midrange and top end that will climb rpms quickly. You can also get steeper gears if you want it to rev even faster. Granted it won't climb to 8,000 rpms unless you get a solid roller set up and like someone else pointed out, a short runner sheet metal intake. I've known people who built set ups like you're describing and their expectations were always higher than the end results. It really seems like a lot of work and money to only get 400 rwhp. The easiest set up would be ported heads with a small combustion chamber to get you around 11:1 and a good all around cam like our 224R cam. Very snappy response, strong midrange and good top end.

Lonnie

FLYNAVY30

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Lonnie, PM sent, thanks!

TT427

iTrader: (1)

C3 IRS is fine for what you want, its drag racing and clutch dumps that break things. Surely you are on Corvette Forums, ask around there about the diff and what you are intending. Has any of it been upgraded? Do you know the condition of the diff?

FLYNAVY30

iTrader: (1)

The diff is in good shape....car only has 42K miles on it. I just opened it up to look at everything and change the fluid...looks damn near new.

I am over on the Corvette Forum, but since ditching my C5 for a C3, I don't post a whole lot....chalk marks, hose clamps, and NCRS awards aren't really my thing.

It sounds like the stock cube 347 with a forged rotating assembly and a stout top end is probably the way to go for what Im looking to do with the car.