I needa rough HP estimate.

[COBRAIIW]

I am getting a short block built at the machinist.

It's a late 70's 351w roller block bored 40 over, with stock crank and rods.
pistons will be 10.5-1, block will be professionally balanced.

I have heads from an 86 302HO with larger valves, and ported.(flow rate unknown) with 1.6 ford SVO rollers. 58cc. chambers.

I am using a retrofit roller cam thats not race, more like "3/4 race" (no exact specs).
I have an Offenhauser dual plane intake, with a Holley 650cfm carb,
Blackjack long tubes.

MSD-6A ignition, with original Duraspark Distributor.

This motor will be the base for future mods, but what HP can I realistically expect when it's assembled?

 

[Power Surge]

No such thing as a "late 70s roller block", the only 351 roller block was used from 94-96.

Your compression should give you a nice kick. Have you verified that compression ratio used with the 58cc heads, or are you just going off piston specs?

Typlically, 86 heads are the one year bastards of the 5.0 world. Not the greatest heads. Make sure you have them machined to work on the 351 (might need to enlarge bolt hole size).

The 650 should work well with the mild heads. If you put some better heads on, I'd step to a 750, depending on what rpm you plan to turn.

Be VERY careful with the "retrofit" roller cam. I guy on the Cobra forums got screwed by Comp Cams when they told him the wrong dist gear to use and it wiped out his cam. They make the retro fit cams in both steel and iron, make sure you use the right gear on the dist!!

As for power, I would estimate that you should make about 350 to the wheels with that setup.

 

[COBRAIIW]

Thanks , what I meant was the block was a 70's that had holes drilled and tapped for the "spider" retainer. so I could use roller lifters.
Did this on my old block.
The cam worked very well on my old block as well, and the heads were machined for 1/2" 351w bolts.
Basically the only real difference will be the higher compression, overbore, and balancing.
One of these days I gotta take the BPT/LI ferry to visit your shop.

 

[Power Surge]

One of these days I gotta take the BPT/LI ferry to visit your shop.

Gonna be a long boat ride, I'm in FL now .

 

[Steel Steeds]

Hmmm. Similar setup to the one I've built, except that I'm using AFR 185 heads with the 2.02 valves, same CR with forged flat tops and 62cc (IIRC) chambers. My big problem initially is the stock II exhaust manifolds I'll be using until I can figure out custom headers to fit in there with the 351. Even with the manifolds, I'm having to grind off the ribs on the passenger side. I was only expecting about that much power, but I think my heads are capable of putting out more than those 86 heads.

 

[barrylee66]

dont use the pinto swap headers I am in the middle of putting them on my 76 coupe. pita. mine has a69 block with eagle long rods 68 302 heads ported by champion head service in jax fl. balanced forged sealed power forged pistons fly cut for giant cam and valves.570lift hyd cam victor jr intake. if your intake is the port o sonic with the split runners it will make massive low end,but probably not turn past 5500/5800 I think it says 360 on it. really good for mild motors

 

[Blue Thunder]

10.5 is too high for iron heads, unless you add a few gallons of race fuel every fill up. If they were aluminum heads you'd be approaching the limit of pump gas. I run 10.95 with aluminum heads and enough valve overlap to yield only 7" of vac idling at 1300 rpm, and 93 octane is barely enough for it. With the iron factory heads, you shouldnt go higher than 9.5:1. Also, those ported 302 heads will be suffocating the 351W on the top end, so a relatively mild cam will give you the best overall performance.
I'd say 325-340 hp if the fuel and ignition curves are tuned to perfection, and 350-360 ft/lbs at a fairly low rpm if you select the proper cam.

 

[parthos]

I'm getting away with about 11.5:1 with aluminum afr heads and 91 ocatain. Runs mid 6s in the 1/8th on pump.

 

[Dano78]

Well.... I'll tell you guys what. Your C/R isn't something to dink around with. I bought '78 Supercab with a 9.98:1 '71 460 that only has a little over 25k on the engine. And now I'm spending another $1100 rebuilding the bottom end because the damn pistons are comming apart from detonation. Of course I didn't know any of this until I tore the head off investigating a broken valvespring.

There are alot of factors involving how much of a compression ratio you can get away with.
First off, you have your available fuels. But who wants to run $4.00 a gallon super unleaded all the time?
Then there is cyl head design and composition. Alum heads usually allow for a little more, ususally .5 give or take. And the design of the chamber or 'swirl effect' is a big player too.
Your local area -- or altitude. The higher up you are the less dense the air is effectively reducing your compression ratio. I believe that for every 5000 ft of elevation, you loose one point of compression. Albuquerque was 5500 ft and it wasn't uncommon to see 10:1 street cars running on 87 octane.

I would keep your C/R between 9:1 and 9.5:1. Believe it or not, but compression ratios don't play as big a role as say a proper cam selection do or a nice set of cyl. heads when it comes to horsepower gains-to-dollar ratios. My 8.87:1 289 in my II now is pushing 366 to the crank. Pretty good numbers for a lower compression eng.

You'll definately be tied to 112 trick fuel at 10.5:1 in and around sea level. And the last 5 gal can I bought was $45 (counting our lame taxes too)and that was last summer when gas wasn't nearly as $$$ as it is now!

Post some more specs on your engine. Just saying you've got a 3/4 race cam doesn't really say much... And be sure to port the hell out of the exhaust side of the heads as well as adding at least 351W valves or better yet 1.94/1.60s. Just clean up the intake side a bit, gasket matching and such. You will need to drill the headbolt holes for the larger 351W head bolts. Not a big deal, I've had it done before.

 

[COBRAIIW]

Well, i got the heads off now, and sent the 351w block to the machine shop as a core trade.
i was wrong, he's going with 10-1 pistons.
my heads are already using the largest possible valves, and have been machined at the bolt holes to be used on a 351w block.
i just need to clean up the ports a little more.
the cam is okay for street use, nothing radical, but i did add a vacuum canister so it wouldn't die out when i used my brakes.

 

[barrylee66]

the intake runner size is what the big difference between 351 and 302 heads. so I would hog the intake runners as well as the exhaust. also with 58 cc chambers you will have to have a pretty deep dish piston or it will be more like 10.5 11.0 with the shallow dish. and please dont tell anyone you have a 3/4 cam, get the specs and memorize them because every gearhead you run into wants to know at least how much lift it has. I am gonna guess around 350 hp

 

[COBRAIIW]

Thanks, I am sure that my machinist has the lift specs on hand, he sold me the cam last year.
The heads have been ported somewhat, but I think I can do more with them.