702 heads on a low RPM 496?

[rustbucket79]

Can you not find a flat top for your application?

[1980RS]

I have a 1966 396 with 702 heads in a 1972 K10 longbed that I drive for fun and plow my driveway with. Looking at sensible options for giving it a little more power.

I’ve read that the closed chamber 396 heads can do ok on a 454. I ran the numbers on a compression calculator and it seems like you could even use them on a 496, but does anyone actually have any experience with this? Sometimes things like piston and combustion chamber shapes can make what seems reasonable on a calculator turn out to be a bad idea in practice.

Just toying around here. Thinking of a baby flat tappet hydraulic or maybe hyd roller, dual plane intake with functional heat riser, exhaust manifolds with straight 2 inch duals, maybe even modifying a thermac air cleaner to fit my 3310 holley.

Sort of like if GM had built a stock 496 for these trucks. Shift at 5000 rpm. Hyper or 4032 pistons, cheaper I beams, cast crank, nothing crazy.

Her is my opinion take it for what it's worth. I would put a set of 360 casting peanut poet heads on that 496 and here's why. I truly believe that open chamber heads even with lower compression will make more HP than the closed chamber heads. I used to think the same about the closed stuff until last year when I did try the closed stuff and the combo failed miserably with no extra power over my old 236 pp heads. Another reason is the peanut ports will make way more low end torque for that truck and with the right cam can easily pull 6K. I would not hesitate to put my peanut ported 461 with a smaller hyd cam in a truck and smoke the tires off the thing. Like Vortecpro says "oval ports are worth about 20hp over a good peanut port head", just ask Mark for his opinion on head, he might tell you the same.

[i82much]

Can you not find a flat top for your application?

they do. my understanding is that i’d need to run about .060 quench to get a reasonable pump gas compression ratio for iron heads. not sure whether that’s the right way to go or not? i see 781 and 049 cores for reasonable prices on craigslist in other cities, but i don’t see much locally. not a huge fan of buying remotely, not just the shipping cost but you never know what you’ll get in terms of defects on the parts.

[i82much]

I have a 1966 396 with 702 heads in a 1972 K10 longbed that I drive for fun and plow my driveway with. Looking at sensible options for giving it a little more power.

I’ve read that the closed chamber 396 heads can do ok on a 454. I ran the numbers on a compression calculator and it seems like you could even use them on a 496, but does anyone actually have any experience with this? Sometimes things like piston and combustion chamber shapes can make what seems reasonable on a calculator turn out to be a bad idea in practice.

Just toying around here. Thinking of a baby flat tappet hydraulic or maybe hyd roller, dual plane intake with functional heat riser, exhaust manifolds with straight 2 inch duals, maybe even modifying a thermac air cleaner to fit my 3310 holley.

Sort of like if GM had built a stock 496 for these trucks. Shift at 5000 rpm. Hyper or 4032 pistons, cheaper I beams, cast crank, nothing crazy.

Her is my opinion take it for what it's worth. I would put a set of 360 casting peanut poet heads on that 496 and here's why. I truly believe that open chamber heads even with lower compression will make more HP than the closed chamber heads. I used to think the same about the closed stuff until last year when I did try the closed stuff and the combo failed miserably with no extra power over my old 236 pp heads. Another reason is the peanut ports will make way more low end torque for that truck and with the right cam can easily pull 6K. I would not hesitate to put my peanut ported 461 with a smaller hyd cam in a truck and smoke the tires off the thing. Like Vortecpro says "oval ports are worth about 20hp over a good peanut port head", just ask Mark for his opinion on head, he might tell you the same.

opinions are what i am here for, so thanks!

i see chevy sells an HT502 crate engine that has peanut ports type heads on it. it’s basically what i am looking for - very mild cam, low compression, big inches, lots of torque. but there are a few things i don’t like about it. first, the cam doesn’t come with a fuel pump lobe. i have functional saddle tanks so a mechanical fuel pump is a must. second, for the money, those 502 blocks don’t really impress me - from what i understand, you’ve only got one overbore left in the block and it’s junk. i can’t see spending 6500 bucks for a long block only to have to replace the cam and then knowing it’s really only got one rebuild in it.

i am kind of toying with just stroking the 396 with a 4 inch crank. they make pistons for the closed chamber heads, i already have the block and heads, and i’m not looking to make big power anyway. just something that runs well, can get up and go a little bit, and won’t hurt a stock TH350. the real problem with making big power isn’t the cost of the engine itself, it’s all the upgraded stuff you need in the driveline to handle the power!

right now my 396 is hurting a little bit, vacuum gauge is vibrating very quickly at idle but only 1 inch or so of fluctuation. i should probably do a leakdown test, might be able to get away with a valve job or just lost a cam lobe or something. but if i have to pull it, i may as well go back with something more exciting.

[ou812]

We used Isky's 221-232@ .050 cam, .543-.560 lift on a 114lca. Stock semi closed chamber heads, just typical 3 angle style valve job, back cut both intake and exhaust valves due to wide lobe center cam.
Flat top pistons, zero decked, 6.385 rod, rpm intake and Edelbrocks new AVS 2 800 cfm carb. Accell distributor, truck pan. We used good 1.7 Scorpion rockers, and 3/8 pushrods.
We dyno'd with 1 7/8 headers, 3" mufflers, but it's getting OEM manifolds. Customer loves it! Very docile, but mean at the touch of the pedal.

Brian

[i82much]

question - i can get peanut ports for dirt cheap, and my performer manifold is perfect for those small intake ports.

what if i stroked the 396 and used peanut port heads? does the bigger bore of a 454 block make much difference when you are talking about little intake ports like that? maybe even find a cheap factory 454 crank?

[tenxal]

This was a pretty popular deal back in the day when 454's were the engine of choice for race car haulers. And it still works today.

The 702 heads on a 454 (or bigger), a decent set of flat top pistons, a nice little hydraulic cam with the Performer intake and a decent carb will give tons of torque and throttle response up the wazoo. Just keep the cam specs reasonable (.480-.500 ish and .220's @ .050 on a 110-112). Resist the urge to put too much intake manifold on it...the Performer is just about right, as are the early pre-1970 'tall' cast iron QJjet intakes. Take the time to get the total deck height correct as having a bunch of extra volume there isn't what you want.

This combo works on everything from the 396's to 496's. The bigger ones just get you more juice for the same squeeze. Honestly, dollar for dollar, I'd not mess with the 496" deal...just do a basic 454" and enjoy.

[HDBD]

Agree with that. A semi-open chamber will work well with a very small dome piston or the truck 427 heads with larger valves and rotators gone with flat tops all are high torque combos. Even peanut port heads at 9:1.

[bobmc]

make sure to use MarkIV heads not GenV peanut port heads, just mill them to the chamber size you want

[i82much]

so um ... i’m still not sure i really believe this, but i put some seafoam in the gas tank and then shot a can down the carburetor per the instructions and, as of right now, the vacuum gauge appears to have stabilized. will have to see if this is still the case a few days from now.

i swear this is like the third time this old truck has “healed itself” after not being driven for awhile. it’s almost like, if you let them sit for awhile, you have to kind of run them for a bit and after being put into use for long enough they “get better.”

if this holds up i can probably sell the running 396 to someone while it is still in the truck. gives me time to get some cores together. or maybe just keep the 396 around as a spare engine. i’ve never built an engine before, might be kind of fun to put together a peanut port 454 in my shop. if i screw it up i can always put the 396 back in. would also give me a chance to clean up the 396, replace the oil pan, etc.