hp estrimate again.
 

saw a similar thread and was womndering the same thing on my setup. about what horsepower can i expect? the machine shop didnt give me a real soild answer all they said was "it is easy to make one horsepower per cid" so i didnt know how to take this

i have a fresh rebuilt 350
forged 10:1 pistons
bored .040
crane cams z-274 ( i can get specs later)
the heads were rebuilt, valves, guides, new seats, the whole nine yards (not sure what heads they are, i know their not double humps or anything like that just some basic 350 heads)
edelbrock performer intake
holley 650 with vacuum secondaries
hei distibutor
full length headers
thats about it for power adders

if someone could give me a rough estimate thatd be great!
this engine is mated to a 700r4 with 2000 stall converter and 4:11 gears

Re: hp estrimate again.
 

How do you know the engine has 10:1 if you don't know anything about the heads? The two most important parts are the heads and cam. Since you have no info on them it would be nothing but a guess at best. The heads, Head gasket and deck height determine your static compression ratio.

Re: hp estrimate again.
 

Fat fingers on a small phone! Also the piston shape and number of valve reliefs are part of your compression calculation!

Re: hp estrimate again.
 

machine shop said i had 10:1 compression

Re: hp estrimate again.
 

they said the heads were 1978 model year with the hardened seats if that helps any

Re: hp estrimate again.
 

We'll I looked up the cam specs. Your TC stall might be a bit tight and if you have power brakes you might have a firm pedal if you can keep it idling in gear. Did you put matched valve spring in your heads? Because your heads are going to limit peak power. I think you may have a 375 hp motor. We're you thinking more?

Re: hp estrimate again.
 

That cam is fairly stiff for a DD truck. NOT radical by any means just on the upper end of a DD working truck (2200-6400). Those heads are killing the power potential of this engine. Maybe 325hp on a nice cold day. A set of DoubleHumps that are port matched would really wake this thing up.

With 76cc heads your actual CR is likely closer to 9:1.

Re: hp estrimate again.
 

1978 wasn't known for high compression heads. And it is possible to build a 9:1 compression motor with advertised 12.5:1 pistons. I Need to know combustion chamber size, thickness of head gasket, camshaft profile, cylinder size and piston dome size/shape to guesstimate compression ratios. A flat top piston with 2 valve reliefs are commonly called 10:1 pistons, but they dont make that compression with every head.

It has happened that some people put 305 heads on a 350 to get better compression, but the valves are shrouded by the small combustion chamber which reduces flow around the valves.

Re: hp estrimate again.
 

the machine shop built the heads the same time they built the motor, they used springs that were matched to the cam. and yeah i have power brakes, that was one consideration we had when choosing a cam. they said this will be a good performign cam that has a nice lope to it but can still be used with my power brakes. the end goal is to have a truck i can stomp on the gas and be put back into my seat, something i can lay some rubber with, i can jump in and drive it around town if i want, something i can take down the track if i want. basically a fun driving truck that i can do anything with. to hear 375hp is great! i was expecting somewhere around 350hp. eventually the motor will get pulled again (long term goal) to throw a nice set of heads (maybe vortecs, or some good aftermarkets) and an air gap intake on, which i am hoping will get me closer to 400hp. long term goals here haha :metal:

Re: hp estrimate again.
 

You put about the biggest cam it you could get away with! Premium gas at 12 mpg can get expensive for a day driver! Anyway have fun with it.

Re: hp estrimate again.
 

Haha yeah thats about right. Theres a reason i put the 700r4 in it lol. But hey cams arent to expensive, if i dont like it ill stick a smaller one in. Thanks for your help man! Greatly appreciated

Re: hp estrimate again.
 

I agree! That cam doesn't match that intake or the heads. Also, the headers might help a little in the mid range, but the peak power of that cam is way beyond what those heads are capable of. Actually, nothing matches or compliments each other on this whole build! 325 at best. You'd be much happier with a much smaller cam if your going to run that intake and heads. Two different ways to correct this. Better heads and rpm performer intake. Or smaller cam. Something around 1500-5000 would work much better with your current setup.

Re: hp estrimate again.
 

I was planning on in the next year or so to buy a performer rpm or some kind of air gap intake. Is there a way with the motor already assembled to figure out compression ratio?

Re: hp estrimate again.
 

Stay away from the airgap for a DD rig.

A plain old performer RPM would be the best bet.

Gary

Re: hp estrimate again.
 

The regular Performer will be fine, but it will need to be Port-Matched to the heads.
Being in WI. you will need the warmth of a regular style intake verses the "Air-Gap" type.

Re: hp estrimate again.
 

With '78 model unported heads (probably 882's or 624's), there's no way that engine is anywhere near 375. With flattop pistons, and 76cc heads (that's what '78 model heads would have been) the engine is probably around 9 : 1 or a little under. Your pistons would be 10 : 1 with 64cc heads. To acheive 10:1 with 76cc heads, you need a .125" domes.

I'd estimate the engine in the 300-ish range, maybe a touch more.

What you have is basically a stock engine with a cam. You have to consider that pre-1972 (pre net HP ratings) 9 : 1 CR 350 4bbl made between 260 - 270 HP. Depending on which heads you actually, they will either be comparable or flow less than earlier heads. A performer intake is equivalent to a non smog 4bbl intake in terms of airflow, and your 650 Holley with vac secondaries gives up a little power compared to a new tuned 750 Q jet.

Taking that into consideration, your cam and headers are really the only power adders. A camshaft and headers alone can not gain 100HP over what is basically a stock engine.

Re: hp estrimate again.
 

BTW, I don't mean to sound harsh, I'm just giving you the reasoning behind the estimate. ;)

Re: hp estrimate again.
 

I'd ask that machine shop why the 1970 L46 350/350 HP Corvette engine needed 11 : 1, 2.02"/1.60" 186# double hump heads, 765 cfm carb, and a .450/.460 lift cam with 224/224 duration cam.

Here's a great article dyno testing the 350 HP L79 327 and L46 350 engines.

http://www.superchevy.com/technical/..._dyno_testing/




The "Its easy to get 1 HP per cid" thing gets thrown around a lot these days, but it takes more than most people thinks it does with 30+ year old stock small valve heads. Its much easier with ported or modern heads. Its even easier with LSX engines, again, mainly because of the airflow of the heads.

Re: hp estrimate again.
 

I agree with 67_C-30. Probably around 300. The cam doesn't match the rest of the engine. Late 70s cylinder heads were usually light duty and not suitable for high performance engines.
By the way, a Performer RPM almost matches the cam, but I'd keep the Performer and switch cams instead. It will take more work to build a high rpm engine, and won't be that great in such a heavy vehicle. You want torque, and lots of it!

Re: hp estrimate again.
 

I agree. This is what I was thinking too is that it's easy to get 1 hp per cid with LS engines. I'd say 325 hp at best. That cam isn't going to work the best with those heads.

Re: hp estrimate again.
 

The only way I know how to get accurate compression ratio is to cc the chambers and calculate the piston to deck height as well as add in your bore. Other factors can come into play here though. No need to do a long write up on that since your doing a pretty basic rebuild. Summit racing has a compression calculator that is pretty handy. You need to know what the specs are first though.

Re: hp estrimate again.
 

thanks for your help guys, i will look further into what heads i have. is there a way to decode the heads (serial number or something?) or any identifying marks to know what i have. the motor is assembled (heads on, intake on, carb on, painted) so id rather not take the heads off if i absoleutely dont need to

Re: hp estrimate again.
 

The head numbers are under the valve covers beside the valve springs. The 6 digit number will tell you what they are. The other number should be a letter and 2 numbers, that is the date code. Post those 2 numbers and someone will tell you the year and what they are.

Re: hp estrimate again.
 

As min said, the casting numbers are the best way to ID them, but most have markings on the front of the head that can give you idea of what you have.

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That engine should be fine for your aplication , if you want more power vortec heads will really boost your numbers without makeing your engine "radical" they do it with efficiency , or complete burn , gaurentied 30 hp gain