FlyLS6

Greetings.

The '73 has been in the family since '76 and in '77 the original big block was tossed and an over the counter LS6 crate motor was installed ( '77 casting date ), equipped with 188 open chamber heads.

5,000 miles ago the motor was torn down and rebuilt by an old school engine builder in Denton, TX, into a "detuned" state. Headers/cam/scatter shield/ DP were all tossed.

Yea, it's not near as fast as it used to be but it sure is more pleasurable to drive.

Compression with the heads is supposed to be 10.2, according to the "book" with this combination.

Carb is now a 770 SA; intake is a 198 high rise.

Cam is a Crane; http://www.cranecams.com/product/car...detail&p=23804

Factory exhaust manifolds, 2.5" back all the way to Flowmasters.

Pic and dyno results are below. I'd be curious to hear from those with more dyno experience what kind of "crank" numbers the HP and torque might translate to.

Also, I realize more cam and headers would make a big difference, but I really don't want to go there. I'm curious however, if it looks like it might take a little more cfm in the carb.

The motor will take more rpm than is on the charts, they just backed off just past peak HP.

Alan 71

Hi Fly,
I showed my 350/270 the picture in your post and she would like a date with your 'big boy'!
Well Done!
Regards,
Alan

7T1vette

Very nice! But, I'm wondering why the torque starts dropping off as early as 4000 rpm? I would have thought it would be pretty flat up to near 5000 rpm. Just curious. {Carb secondary rod type/size issue? Secondary throttle plates not fully opening? Exhaust restriction, possibly?}

63mako

You are probably over 400 ft lbs of torque at the flywheel from 2000 to 4500 RPM. You are running factory heads, exhaust and intake manifolds and a mild hydraulic flat tappet cam. The carb sizing is fine though you might have a secondery issue as 7T1vette suggests, you are running a little rich all the way through as well. That is probably all your getting out of your combo, the stock components flow capabilities limit what you can do. You have a nice street engine as is. Some "stealth" type modifications you can do are Extrude hone your intake, exhaust manifolds and heads and a roller cam. Not cheap but very effective if you want more power and a factory look. I have heard up to 30% increase in flow on factory components.
http://gethoned.com/process.html

zwede

That's not bad at all! You're looking at about 400 hp at the crank and 450 ft-lbs.

ajrothm

Heads too big, cam too small, exhaust too restricive(especially the manifolds)...Intake is not doing you any favors...

Is the car auto or stick? Old Vettes have a lot of parasitic loss, especially if its auto... If its a stick and assuming 20% loss, that gets you 403 crank hp. If its auto and assuming atleast a 25% loss, that is 430 crank hp.... The stock clutch fan is a HP killer as well...

Realistically I bet you are losing 30% from the exhaust system as well as the other parasitics.... That would theoretically put you at 461 crank hp...


Ofcourse all of this is in theory... I would at a minimum put headers and a good exhaust system on it...

Budman68

I think he achived his goal. Some minor tuning to the carb and she should be make max hp for that combo. As the OP said the car is driveable.

FlyLS6

I'm really appreciating the commentary.

As I mentioned, when motor was originally installed in the car, the factory LS6 cam/intake was tossed. Back then, it had a 7000rpm cam, scatter shield (just in case), DP, and full length tube headers.

When it was recently rebuild, I just really didn't want to go there. One of my big concerns was tractability with the heads and L88 intake, after switching to a moderate cam, smaller carb, and factory manifolds. I was worried that it'd be virtually undriveable around town as I recognize the mis-match of parts in the "classic" sense.

However, toss a perfectly good intake and a set of 188 heads (also date coded '77, along with the engine block)?

Yea, round port stuff might actually give me better numbers, but I really want to build up a tractable motor with the existing base parts, and tweak it to a good driver.

I want all the HP I can get, but within limits. And, I've been very satisfied with the results so far. If someone didn't know what intake and heads the motor was equipped, 99% probably wouldn't have a clue about it just from driving the car. One thing I'll definitely do is work on the jetting and check out the secondary system, and maybe this fall re-dyno it in something less than 90 degree weather.

Anyway, I'm 66 now, and when I have my 3rd childhood I'll have the basics there when I go wild and crazy again.

Thanks again for the responses and thoughts.

drwet

Sweet motor. I bet its a blast to drive, but you know, headers would really wake it up and wouldn't make it any less driveable.

63mako

Headers would be the single best upgrade you could make.