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Old 01-26-2001, 12:49 PM   #1
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How to Match Heads to Cam and Intake aka Building an Engine

Greetings. This is the first engine I have ever built. Right now it is a 350, but I am going to get a kit from Powerhouse to make it a 383. According to the kit, it is already going to be balanced. The engine has Corvette heads on it (or so the seller said - will get #'s later today), timing gears, a Performer intake, and everything else is up in the air as far as I know. Is there any way to find out the cam specs? It is a 1970 block from a 3500 truck. I haven't taken it apart yet, but I am assuming it is a 4 bolt with one piece oil seal. What I am really after is how do I match a cam to the intake and the heads? I have heard people say that this is a crucial part to engine building. I want this motor to produce over 400 HP. Any tips for a first-timer? Anything will help me (especially figuring out what the cam specs mean!).
Thanks in advance!!!!!!

Vman

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Old 01-26-2001, 01:15 PM   #2
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If it's a 1970 block, it's a 2-piece seal. I wouldn't worry about what cam is in it; a cam is $100, which is a drop in the bucket compared to what the project as a whole will cost, and there's very little chance that it's the right thing anyway.

Basically, what you need to do re. the cam & heads, is first figure out what your goal is. 400 HP is a reasonable place to start as far as that goes, maybe even a little consevative for a 383. Then determine approximately what RPM that will occur at. That is influenced heavily by the induction system you are putting on it.

So start there... is this carb? TPI? if it's TPI, will you use the stock runners or one of the other top ends? I would urge you not to consider trying to adapt a TBI to this, havein gbeen there with a friend already, I can tell you that you will never ever get it to run right no matter what TBI you put on it.

Next you need to consider what this engine will be pushing around. What car? auto or stick? what gears?

Some sort of idea what the car's use will be would be helpful. daily driver? street moonster? occasional strip use? race only?

The more info you can supply about the application, the better a choice you can make about parts that will get you there.

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Old 01-26-2001, 01:25 PM   #3
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It is going into a 69 Camaro. 4 barrel carb (have yet to decide on type of carb). Sorry it isn't a third gen, but I will use this info to build an engine for a third gen! It will see mostly street use, with a few performances on high school drag night @ the local track. I don't really care about gas mileage, I just want a nice car running in low 12's high 11's. I have a 700R4 that is going behind it, and the rear, right now, is a 2.73 open. As far as I know, the only air system I can put on is an open filter on top. Any ideas? Thanks for all the help!

Vman

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Old 01-26-2001, 02:02 PM   #4
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OK that's good so far. Now for the hardest question of all: realistically, what's your budget? Keep in mind that there will be all sorts of things that you won't foresee that you'll have to deal with. You will probably spend at least twice what you can identify on the front end, because of all the nickel-and-dime stuff that just continually pops up.

If this is a stock-bodied car, it weighs about 3400 lbs. It's going to take alot more than any 400 crank HP to get a 3400 lb car into the 11s. My estimate would be that if you get perfect traction, that much power in that car will put you at about 12.8; realistically, probably 13.1 or 13.2. However, with that gear, you'll be lucky to crack into the 13s at all. 3.73 is closer to what you'll need.

The cam, gear and torque converter have to work together to allow the engine to spend as much of its time as possible in the range where it produces the most power. A typical carbed 383 that will make 400 HP should produce peak torque at about 3800 or 3900, and peak HP at about 5300. So, you want a gear that will allow it to go through the traps in 3rd gear at just above 5300, say 5500; you want to shift it at about 5100 or 5200, which will drop the RPM to about 3500 after the shift; and you want a converter that lets it rev to near 3000 at the line. Look for a cam that is specified to produce its max power in those RPM ranges. About 225 to 230 intake duration would be the right range. A set of good-flowing stock heads (not late-model truck heads, or 327 2-barrel heads, or any of that) with a mild port job should work OK. Make sure you get enough valve spring for the cam.

I'd suggest one of Comp's Xtreme series, specifically the 268 or the 274. Those are 224 and 230 intake duration respectively. They have the exhaust lobe larger than the intake, which is desirable with stock heads to help make up for the lesser flow of their exhaust ports.

As far as heads, about half of the motors ever sold in the world somehow have Corvette heads on them. I don't believe a word of that crap until I see them. And even then, some Corvettes came with the same s*** that every other mid-70s 180 HP 350 had... garbage. Don't assume that just because the seller invokes the magic "C" word, that some kind of magic will leap out and endow the heads with superior characteristics. The heads don't care what sheet metal (or fiberglass) they've been wrapped in over the course of their life.

Good luck! Post a casting number from the heads when you get them, that is the real deal that tells the unbiased truth about what they really are.

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Old 01-26-2001, 03:09 PM   #5
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Okay, I got the #'s off the heads:
378246
B126

Are they any good? They have some aftermarket valvetrain components on them, so I am guessing some kind of work has been done to them. Thanks!

Vman
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Old 01-26-2001, 03:40 PM   #6
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3782461?? Casting date should be B426???

Those are good flowing heads, however they don't have the accessory bolt holes in the ends of them. IIRC the 69 Camaro needs those, although it's not insurmountable. They have small chambers; the CR will be close to 11:1 with flat tops. You'll need dished pistons. Also, since they're the original "fuelie" heads, they're the ones that are very prone to detonation; you'll probably do best to pick pistons to go in the kit that put the CR no higher than 9:1.

The rest of the stuff I put in should work well with those. A Holley 750 vacuum secondary carb would go good on this.

What sort of aftermarket valve train parts? What diameter springs? That will tell you how far you can go with the cam.

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Old 01-26-2001, 04:05 PM   #7
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Yeah, you were right on the first #. It is 3782461, but the second is B126 for sure.
As for the accessory holes, what can I do about this problem? Is the only solution buying a different set of heads? The car does not have AC.
The pushrod guides are aftermarket. I don't really know how to tell about the rest of it. The spring diameter is 1 3/16". How large are the chambers in the heads? I think a CR of 11:1 might be a bit high. Any thoughts on what I should do?

Vman
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Old 01-26-2001, 04:52 PM   #8
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On the accessory brackets, with some headers you can use brackets to mount an alternator. If this is a manual steering chassis then that's probably the easiest way to handle it. The header brackets suck as they come but it is easy to add a brace to the bottom of the alternator to a water pump bolt, which will keep the bracket from stripping the bolt holes in the head as they always seem to do.

That's weird about the head date... B126 would be Feb 26 in a year ending in 1, and those heads are mid-60s, like 63-66 or 67... oh well, no biggie

Those heads are 64cc at most, maybe as small as 62cc; if they've been milled they're smaller than that. Just for reference, a flat-top 350 under 64cc heads is 10.3:1; a 400 with 12.5cc dish and 64cc heads is 10.4:1. A 383 with 12.5cc dish should give about 9.8:1. That is absolutely all the piston you could run and expect it to tolerate modern pump gas, and even then getting a good timing curve will be a problem. Pistons like that are typical for blower use so they shouldn't be hard to select for your kit.

Starting in 69, they modified the combustion chamber design of the "double-hump" heads to make up for the decresing quality of fuel that was available. Pre-69 heads on almost all V8s from all the mfrs were the reason those old cars had to have 98 octane gas. The later ones, as well as any of the modern aftermarket ones designed for street use, are much more tolerant of low-octane fuel.

Stock valve springs are 1.25", or 1", outer diameter. So at least we know that the spring pockets haven't been cut out to fit springs for use with cams giving over .500" lift. At least get new ones according to the recommendation of the mfr of the cam you decide to go with. With that CR situation you should use a slightly bigger cam than otherwise (kind of bleeds off a little cylinder pressure); the XE274H from Comp would be my pick. If you either get other heads or get those worked, you would benefit significantly from 1.6 rockers, which will give you enough lift with that cam that you will need the 1.45" springs such as Comp 986.

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Old 01-26-2001, 05:29 PM   #9
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Quote:
That's weird about the head date... B126 would be Feb 26 in a year ending in 1, and those heads are mid-60s, like 63-66 or 67... oh well, no biggie
I'm pretty sure B126 is Feb 12, 1966. Not 100% sure, but I can look it up it need be. That makes sense, since, as far as I know, they were crankin' out 461 castings in 1966. Click the image to open in full size.

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Old 01-26-2001, 05:42 PM   #10
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You could be right... I dont' decode them much, I could easily have the digits misplaced, and 66 makes more sense.

"The simplest explanation that fits all the facts is usually the right one."

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Old 01-26-2001, 09:00 PM   #11
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Sorry, this might seem a little funny, but are they really off of a Vette?

Vman
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Old 01-26-2001, 09:19 PM   #12
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You won't like the 700R4 at the drag strip. The gear ratio between first and second is too wide. It's a great street tranny but you need to over rev first gear so that the engine will come down to the bottom of the power band when you shift to second, not way below it. I ripped mine out after a year of racing and put in a TH350.

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Old 01-26-2001, 09:47 PM   #13
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I figured I would go with the 700R4 because it is going to be a daily driver with limited track use. I need the 4th gear. I have a Turbo 350 though just in case I get unhappy.....
So, how do I match the heads to cam and intake? And as to the heads situation, would you keep the heads I have and bolt accessories to the headers, or save up and buy new heads with the holes? I need to stay on a budget of $1000. Thanks for all the help, I really appreciate the info!!!!

Vman
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Old 01-26-2001, 09:53 PM   #14
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Look into the 200-4R, it doesnt have such a large gap from 1-2 and has overdrive. And dont let anyone tell you it cant handle abuse, it can.
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Old 01-26-2001, 09:53 PM
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