Thread: open vs. closed chamber; oval vs. rectangular ports?

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It doesn't look like I'm going to be selling my 468 now, so I'm gonna try to keep going on the project (if the wife lets me!).

So I've been asked if my motor is an open or closed chambered head motor. All I have is the short block right now, and as I understand it, you can run whatever you want, open or closed, it'll just change your CR. Is that accurate?

And if I'm building strictly for the strip, how much do I gain from rectangular ports as opposed to oval, keeping in mind that I'm only hoping to turn about 6000 - 6500 rpms and the budget is strictly impaired.

NO the closed chamber piston will work in a open head and the closed chamber hi hp domes 0.250 will hit on the side of the O port closed chamber heads the full open chamber pistons 12 to 1 have to be ran with a open head and when doing any head change you should clay it to check for if the piston hits . and the O port will get the job done for you

Firstly you need a Closed Chambered WIFE!!! Just Kidding... There was a great article in CHP about these combo's, I will check my stash and see if I can find it.

Originally posted by new-velle
Firstly you need a Closed Chambered WIFE!!! Just Kidding... There was a great article in CHP about these combo's, I will check my stash and see if I can find it.

You may have been kidding, but you're pretty much on the money as far as I'm concerned. I absolutely do not understand how a guy can let his wife dictate what goes on in the garage.

trashburner, no need to get bent out of shape over this, it's just that I'm passionate about keeping my wife and her opinions out of my garage. She understands that she does pretty much what she wants to with the house, but the garage is off limits.

no wife one dog and two cars

Originally posted by pat mccarthy
no wife one dog and two cars

You are a blessed man
It's not that I don't love my wife, I do, very much, but I don't let her control me when it comes to the garage.

Originally posted by techinspector1
You may have been kidding, but you're pretty much on the money as far as I'm concerned. I absolutely do not understand how a guy can let his wife dictate what goes on in the garage.

trashburner, no need to get bent out of shape over this, it's just that I'm passionate about keeping my wife and her opinions out of my garage. She understands that she does pretty much what she wants to with the house, but the garage is off limits.

My wife doesnt control what goes on in the garage at all, I do what I want...however, I do know of plenty of people who dont understand the concept of paying bills & making sure the family comes first, & there wife has to remind them when they go buy a new project car, or motorcycle, etc. but the family cars tires cords are showin, or the refrigerator is about shot. John

Well it wasn't my intention to move this forum to our wives but here is my formula. I buy a new carb 850.00, this is the calculation. If I buy, see buys!! It works like a charm.. But here is the most important part, the equation. Must be done in green backs for the formula to work.

$ 850/2= 425 so since the heads are twice as important as a new Area Rug, hence divided by two. So i spend 850.00 she spends 425.00
850.00+425.00= 1275.00
So the heads cost me 1275.00.. See its easy...
P.S. Lose the Summit Catalog..!!! So there is no verification..

A set of oval port heads will run fine to 6500 but that is pretty much it . The rectangular are for high R.P.M. 6500+ they move huge amount's of air and fuel. It's your choice . Your not going for gas mileage anyway if your in the big -block forum .I have a wife also that would be mental if I bought a 8-71 out of Jegs . You are not alone my friend . Anyone that say's there wife isn't involved in there garage is full of B.S. or they are about ready for divorce.

My computer crashed and I just got it back. I never imagined I would get such a response, especially about a little comment. I love to talk about bbc's, but insight about our wifes vs. our passion in the garage is also interesting. Believe me, the ol' motor projects have been a sore spot with her since we've been together. They just don't get it, do they?
Anyway, thanks for the response, I appreciate it. As a man on a strict budget and engine knowledge in progress, I love talking to people about chevy motors.
So as the 100th person to ask on this forum, any suggestions as far as heads and valvetrain?
What we've got so far:

1990-91 Chevrolet 468 short block. 4 bolt main, Mark IV.
Cam is a Crane Cams Mechanical Commander (older cam, but never used) 272/280 @.050" Duration, .659"/.679" lift.
Valve springs will be Crane Cams 1.460" diameter, 120# seat pressure, 394# @1.175" open load pressure.
TRW pistons .580" domed forged aluminum, dome volume 50cc.
Rods are cast.
Crank is cast, unfortunately, but oil holes are radiied(?) and chamfered, prepped and lightened, as I was told.
Rotating assembly has been balanced.
Carb is a Holley 750 3310-3 with vacuum secondaries, but should be good for now.

I see a mismatch here. In your opening statement, you say you want to turn the motor 6,000-6,500 rpm's. The cam you plan to use will make power from about 4,700-8,000 rpm's with minimum 12.25:1 static compression ratio.

Your 0.060" over block with 50 cc pistons, 119 cc heads and 9 cc gaskets with zero deck will make 12.65:1 static c.r.

Originally posted by techinspector1
I see a mismatch here. In your opening statement, you say you want to turn the motor 6,000-6,500 rpm's. The cam you plan to use will make power from about 4,700-8,000 rpm's with minimum 12.25:1 static compression ratio.

Your 0.060" over block with 50 cc pistons, 119 cc heads and 9 cc gaskets with zero deck will make 12.65:1 static c.r.

yes the cam is big it will need very hi stall on the converters. is this what you want? all this will work .have done it. but this is not a daily driver .the O ports will work but they will need some work and the cast crank will work i have used them .

Yes, the cam card says 4800-7800 rpms. I said my goal was 6000-6500 because I don't think my rotating assembly could handle any more. What do you think?

Yes, definitely not a daily driver! It will be for strip only. I haven't seen a comment on turning >6500 rpms yet, but if it's possible with what I have, then I'd probably go for the rect. port heads, which I've read reach their potential at speeds >6500 rpms. I'm hesitant to make that one of my goals, because I've always read and heard that its expensive and hard to make a BBC run >6500 rpms.

have built big blocks with stock rods with arp blocks in them and stock steel and cast cranks in them and have been to 6800 many times. i see one thing. i would like to see more seats pressure about 140 the rectangular ports will work but i have built them about ways and but do not understimate the O ports they will work good on the 468 big block the rec ports will make HP but very hi up in the rpm