compression ratio

korina.........remember you still have a 4.22 ratio in the tail of that thing which has a huge effect on 1/4mile times.

Bob

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Originally posted by kaamacat:
korina.........remember you still have a 4.22 ratio in the tail of that thing which has a huge effect on 1/4mile times.

Bob

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I understand. I just always read in the old Pantera stuff that the later cars would only do about at 14:50 at best. Factor in the fact that the car is old and I'm doing the work on it. If I had to drive the car to work, I'd be unemployed.

To my knowlege, there is NO way to tell externally whether you have open or closded chamber heads. The various bumps, letters etc simly are undepenadable. However, if the markings indicate a '72-up manufacturing date, it DEFINITELY is not closed chamber since 4V closed chambers were only built 1970-71. These marks are under the valve cover.

Jack.......whats the cfm difference in the standard Autolite carb vs lets say the Holley 600 (seems that most put on)?


Bob

quote:

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Originally posted by kaamacat:
Jack.......whats the cfm difference in the standard Autolite carb vs lets say the Holley 600 (seems that most put on)?


Bob

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So If I'm understanding this right, all differences in compression are due to the open or closed chambering of the heads and the pistons are the same. That being true, what is the CC difference between the two to get the couple of points difference of static compression?
Danke Shein Darlings, Danke Shein

Vince. Jack as always is spot on. U can't tell from outside if they are closed or open chamber. However, as u already know, u can tell if they are 4v or 2v, since thats stamped on the outside edge of the head. To check if they are closed or open u have open to look. It will be very apparent. To give u a baseline to start from,- my heads (closed chamber 'quench' hds.)are 62.4 cc. measured with a burette, or was it a pipette? -
Looks totaly different to the open ones which run 76 to 80cc's & are shaped totally diferentely.( See photos in book)- Big difference. IMHO the only hds.to use are these closed-chambered ones. The thing to remember in trying to suss-out your potential comp.ratio is to decide what pistons u will use in combination with these hds.My combo is; 4V, closed-chamber with flattop pistons. This gives -+ 11.00 to 11.50. depending on cc's in your chamber, which of course u will only determine on cc'ing the hd.chambers.( pop-ups will naturally give u more.)-which u should not go to, if u want run pump-gas. Before u say 11.0 is to high, let me say that I believe this to be incorect, in my experience. Only the Chevy-Boys will tell u this. I have run this combo for many years on 94 octane pump-gas here in South Africa and u guys, i recall have much better, higher octane gas.
OK, so now we have 4V, open & closed chamb.hds & 2V's with only open chambers. The 4v (fourbarrel) hds are the so-called 'trick' Ford production 351C hds.- with monster 2.19inch inlets, & 1.71 exh. valves & ports to match. (worth buying the one-piece, one-grove, up-graded valves since they are big & heavy, due to their size.) The 2V hds run 'small' 2.05 & 1.65's valves, still bigger than the biggest Chevy std. hds...( To make Chevy hds flow like 351C, 4V hds u have to spend alot of $ at machine shop or buy aftermarket fancy hds. The Ford Performance "bible" says that u should not touch the ports of the 4V's at all, just un-shroud the inlets to assit the incoming mixure flow coming thru the inlet port. (see photo in book.)-Thats ALL that needs doing for it to flow like gang busters. The 4V closed-chmb. 'quench' hds are good for almost 1.50 points compresion increase over the open ones. - These hds. are so-named cause they put out the combustion chamber flame-front coming from the iginited plug as the flame-front it moves across the chamber, & since the smaller chamber cools it all down more,- thus allowing it to tolerate higher compresion ratios. Plus,- and here's the thing: this design configeration creates turbulence in the chambers, which way improves the feul & air mixture. The Ford book says this occurs especially @ low revs giving more complete combustion & greater LOW & mid range torque. Magic.- Show me an un-modified prod. Chevy head that can make this claim.
So when the pundits say; dont use the 4V hds with big valves & ports on the street, as they are too big and slow down the air/feul mixture causing low-speed bogging-down or lack of torque @ low revs. B.S. -If the 4V hds are closed-chambered this no longer applies. Now as Jack has mentioned often, & one has the budget, u can further increase the incoming mixture velocity-flow (more torque) by using taller inlet-trackt manifolds & perhaps also running IR,(Induvidual Runner) inlets & F.I. or downdraft Weber IDA's with tall velocity stacks.
The 4V hds are basically the race-proven Boss 302 hds.
Anyhow, sorry to go on, but these hds are IMHO what makes it all this 'madness' worth while,- going the 351C 4V route. And thats why the Clevor-Combo Clevland hds. & Windsor block,)- but thats another story.
The Ford book to get is: "Ford Performance" by Pat Canahl - S-A Design Publishing Company, 515 W. Lambert. Bldg. E CA 92621-3991.-
Enjoy,- tai.

Here is what I have read: 1. '74's ARE 8.0 to 1 compression ratio because they DO have open chambered heads AND dished pistons. 2. The australian heads are disirable because they have the smaller '2v' ports AND the 'closed' chambers. So you get the high velocity for chamber filling AND the 10.5 to 1 compression ratio, when using flat-top pistons!. 3. The years(72-73??)that had open chamber heads WITH flat-top pistons were at 9.5 CR. 4. The 71's and I 'think' the Boss 351 had closed chamber heads with pop-up (domed)Pistons, OR were they flat-top? Their C. Ratios were 10.9-11.2 to 1. 5. Lastly; from the book "How to rebuild Ford V-8 Engines, the chamber CC's were: 75.8, 91.4, 73.5, 96.2, and 89.0 that is all. Regards, Marlin.

[This message has been edited by MARLIN JACK (edited 06-29-2004).]

First, please remember you're dealing with a 32-yr-old engine thats survived god-knows-how-many rebuilds, each of which will change the combustion chamber volume and c.r. Clean-up bores with new pistons do the same. So as-new info on possible engine combos are likely not to be of any value except to mislead you. There is NO reliable way to find out what you want without gritting your teeth and reaching for the wrenches. Once the heads are off, you can cc them and possibly the pistons also. 351-C pistons were once commonly available with dish, flat-top or domes, all of which influence compression ratio. I have a set of hardly-used 351-C domed pistons that delivered 9-1/2: 1 in open chamber heads & 12:1 in closed-chamber heads.

Bob, the Holley 600 vacuum-secondary carb is SO different from the Autolite carb that even the intake gaskets won't reliably interchange. For openers, the Autolite has a monolithic carb top similar to a Rochester Q-jet; which, once removed, exposes both floats & bowls from above. The Holley has dual cup-shaped float bowls hung on both ends of the carb body. IMHO, only die-hard purists and period-correct restorers will spend time searching out parts to rebuild these obscure carbs. Sorry.

Jack....thanks.

Hate to say it but I'm actually used to a q-jet rebuild....reminds me of a mousetrap when putting it back together. The darn holley (for a while) have the *^$& powervalve that blows on a backfire. I gotta say I love my BarryGrant 650......which brought me back to my comment originally......

It always sounded like you could do some "simple" things to the 351C to add some power.......open the exhaust a little, carb, manifold....upgrade to year2K rubber, and get some decent 1/4mile times out of it.


Bob

You should not be losing power valves on a BG-Holley to backfires. Unless I'm terribly mistaken, all Holleys including tuner-carbs built since about 1980 have an anti-backfire checkvalve built into the throttle base. The ball-check is retained by the body-to-throttle base gasket. This mod can be added to older units with little cost but some effort, as well. Many years ago, I used an old bicycle ball bearing and a small drill to create the required passage in a 1969 Holley. I'd carefully check to see if your base gasket between body & throttles is blocking the check-valve hole.