I've purchased a set of extensively worked 781's. They've been flowed but I don't have the numbers in front of me. What matters to me is they were on a 468 in a '69 Camaro that runs 6.20's at our local 1/8th mile track. Here's my two choices I'm contemplating:

1. bolt on the heads using a steel shim gasket and run these on my virtually new 461 shortblock. Problem is my static compression ratio is around 10 to 1 with my current 100cc closed chambered heads. These 781's have been angle milled and cc'd at 112. So am I going to speed up because of the better flowing heads, or slow down with the loss in compression?

2. Option number 2 is sell the 461 and use the freshly machined 4 bolt block (thanks Joe graemlins/thumbsup.gif )and stuff a stroker kit in it and have a 496 with some super flowing heads. :D

My goal is to be able to run constent 7.50's at our local 1/8th mile track. Any faster than that and I have to put a bar in it....

somebody help...

this one that tough? :confused:

Happy Turkey Day everybody!

I like the 496 idea,but I bet you'll need a rollbar as I will next year :D

Compression wont be too terribly low. I did come checking and with an even 10:1 now, you should end up with a tick over 9:1 compression after the swap. Not all that high, but not incredibly low either. Depending on your car and chassis, you could pull it off with the right camshaft and drivetrain, but it may be a stretch. If your shortblock is up to it, you could use a solid roller camshaft capable of roughly 6500 rpm under those heads with a 4.30 gear and 3800 converter and probably run the number or close to it, but that might not be your best bet if this is a street car cause itll run sloppy at lower rpm and not cruise as nice as it could. If this is the case, the stroker would probably be a little easier all together to make that kinda power, and have some degree of street manners all at the same time. but then again, is your chassis capable of putting almost 500 cubes of motor to the ground to run consistent? You could aslo use the relatively low compression to your advantage and strap on a blower or supercharger on the current motor. Or juice it. That would be nice too, cause you could build a more mild mannered motor thats still plenty fast(mid 12's easy for street driving), but then put a healthy dose of juice to it and easily run your goal. Once again though, the big torque gains with juice may make it a little tough to be consistent unless your chassis is up to it. If it were me, Id like the all motor, larger cube setup cause its nice to use all the displacement to your advantage and be fast along with some street manners to boot.

I'd sell the 781's and get your closed chambered heads "worked"

I personally don't think most guys that have 496 motors really ever see the benefit from the motor. When you throw all that extra torque at the car, you have to be able to get it to the ground. Most guys never upgrade the chassis to take advantage and the car never gets any faster.

My suspension currently consists of SSM lift bars, air bag, Moog coil springs, Monroe sensa-trac shocks. Right now I have great weight transfer and no wheel hop at all. Of course that could be because I'm running 325/50's.

the reason I like the 496 idea is not having to ever turn it over 6000 to achieve the desired ET. Theoretically easier on parts right?

several more foot pounds of torque too,lower rpms,thats why I let the machinist talk me into a 505,,,just gotta hook it now.

Thats true, but not completely. If you had a 454 and a 496 and spin both of them at 6000rpm, its harder on the 496. The reason is because the 496 has a longer stroke, so even though the cranksafts in both motors are spinning at the same RPM count, the piston in the bigger inch motor has to travel a further distance with each stroke cause of the longer stroke length. This means at the same rpm the piston is traveling faster in the bigger motor, even though the overall engine rpm isnt higher. As far as piston speed alone goes, spinning a 496 at 6000rpm equates basically the same piston speed of 4250 ft/min as spinning a 454 at roughly 6400 rpm. Not a huge difference, but its something to think about. Still though, with the right combo built around the stroker cranskshaft, you can make huge enough power at or under 6000rpm that the swap is worth it. But, even though the piston speed itself is similar(or can be similar depending on what kinda rpm the 454 would need to see), there are still other reciprocating parts along with moving parts in the valvetrain that will be moving slower at lower engine speed, so it should still work to your benefit in the longrun to keep the overall engine speeds lower.

Simple answer,,,
An engine is an air pump & the power is in the breathing ability (read heads) ;)

If you replace a set of crap heads with a set of good flowing heads that do not have ports that are too big you are going to see a substantial gain.

Lowering the compression from 10.0 to 9.0 will in theory cost you at most about 3% in power across the torque curve. It will probably be less.
Assuming 500HP you are talking 15HP.

A good set of heads over a bad set could easily be worth 50HP possibly more depending on the combination.

I will leave the math to you :D

Put the good heads on a bigger engine & it is a win, win deal as you are now requesting more air through your new heads graemlins/thumbsup.gif

Don't eat too much Turkey ;)

Imho, go with a 496, your good reworked -781 heads and a good old CC 282S solid cam and go have more fun then the Law will allow!!

That's what I have made but I went Merlin ovals b/c of being afraid I woulda got hosed bringing my good -781's up to snuff. (550hp at 5500rpm and 580t at 4500rpm per D2K sim. program sorta deal)...

BUT I'm only going to run mine like 5500 to maybe 6000 b/c it is really just a great big, "tow-truck", grunt motor to me with truck rods and good nuts and bolts and doesn't need ta go higher!!

pdq67

sweet.... thanks guys. the tryptophan, is that how you spell it, (pronounced trip-to-fan) is starting to go to work on me.....

Or just sell off your pistons and buy the right ones for 10-1 with the 781 heads, the cost will be minimal if you get a fair price selling the originals.