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Topic Review (Newest First)
01-24-2013 04:33 PM
LATECH Using a cam to bleed off excess compression will result in a car that is a real pig on the street off the line, especially if it has a tall gear .
01-24-2013 01:51 PM
cobalt327
Quote:
Originally Posted by jeffs66 View Post
Hiya, I have a 66 Catalina.It has the 389 2v engine.well recently I put on #62 heads w/ I beleive the 72 cc combustion chamber.Heres my ?.I know Pontiac used a basic flat top piston and would change compression with head swaps.Well does any body have a guess on what compression I have now,or how I may find out without tearing the motor back down?I know its up there cuz its got a bad case of the rattles if I dont burn premium,even when I back the timing down.plus the little extra power.
The difference in head chamber volume between the heads you removed and the replacements is not that great either way, unless they've been milled excessively. So it should exhibit the same tendancies it did before the head swap.

The exact CR is hard to say as has been said already. Using a quench distance of 0.055" (0.040" head gasket and the piston about 0.015" in the hole at TDC), a piston valve relief volume of 6cc and stock 389 bore and stoke, you're near 9.7:1- which is stretching the limits of pump gas detonation resistance w/an iron head Pontiac if you're using best power total timing- as you've found out.
01-24-2013 01:36 PM
cobalt327 Pontiac intakes ALL have air under them. If you want the intake to run cooler you need to block off the heat crossover.
01-24-2013 12:20 PM
jeffs66 Ok,Im not really having any problems.I have an edelbrock intake w/ a holley 650 vac 2nd.I just wanted to know my my cr for piece of mind and if I decide to go with a bigger cam,Ill have that knowledge for when i look.The motor's plenty strong,but theres ALWAYS room for improvement,ys kno?
01-23-2013 06:28 PM
hcompton Headmen makes headers that fit the grand prix and other big pontiacs with the engine set low in the frame.

Dcr is the best way to solve things without using a thick head gasket or changing heads back. A much larger cam will solve some of the knocking issues. Poncho wont make power if you cant get any timing into the motor.

I am looking into a product to coat the piston tops and valve heads to help keep knocking down in my engine. Also i recently read a good article from david vizzard about controling detonation.

An aluminum intake that lets some air under it may help alot if your still running cast. But sounds like your problems are much bigger than a little air temp is going to fix.

Also change ypur thermostat to 170 if at all possible. Keep it running cool will help the most with knocking.
01-23-2013 01:04 AM
jeffs66 Thanx all but Im still trying to find out if any other full size GMs have a similar front end cuz ball joints for this thing are way crazy expensive..Thanx again
01-21-2013 08:56 AM
MouseFink The finest headers made are "Headers by Ed" Welcome to the Home Page of HEADERS BY "ED", INC. *May you learn a lot as you go through our website! in Minneapolis MN. He makes headers for any stock vehicle and can "custom" design and produce headers for any chassis / engine combination. Headers By Ed has been making headers since 1962. In 1964 I installed a set of Tri-Y Headers By Ed on my 1959 Impala 2-dr. HT. The only problem for those on a budget... "they ain't cheap"
01-21-2013 08:32 AM
Mr. P-Body Mad Dog offers headers for the B-body, both d-port and round port. Good stuff, Mad Dog. And it's true, with minor "alterations", first gen Firebird headers can "fit".

Most 62s I've CCd as"known virgin" come out to about 74 CCs. The statement about NOT using factory specs is RIGHT ON THE MONEY. Not just with Pontiac, but most American cars of the era, the published data is "nominal" and not necessarily accurate. The chambers MUST be CC'd to really KNOW what they are. Sometimes, you just gotta do the "leg work".

A standard bore 389 should be about "right" for 93 octane with 78-80 CCs in the chamber. The valve reliefs are about 6. Cutting a "dish" in the piston to enlarge the chamber is commonly done.

On that, the pre-67 performance heads were 19 degree valves, and the valve reliefs are close to the center of the piston. For '67, with a couple rare exceptions, the valve angle was changed to 12 degrees, moving the reliefs "out" closer to the bore. With cams under .470 " valve lift, this is no biggie. For more than that, there COULD be valve-to-piston interference. For rebuilders, this is the purpose of that horrid looking 8-relief piston.

FWIW

Jim
01-21-2013 04:22 AM
MouseFink The factory rated the compression ratio at 10.5:1 in 1966 with 72 CC heads. When you determine what the static compression ratio is, you will not be able to use the current cool aid quality pump gas. All Pontiac 389 / 400 / 421 / 428 CI engines and and head combinations produced before 1970 cannot use pump gas without retarding the initial timing advance to 10 degrees. You can experiment with the initial timing advance but you will find that the engine will likely have less power and run at a higher temperature with retarded timing. Try it and see. You must use dished pistons or 1971-1979 heads to use 93 octane pump gas. Otherwise use a 50 - 50 mix of 108 octane racing gasoline and 93 octane pump gas. You can successfully use E85 pump gas with up to 10.5:1 compression ratio but station that sell that stuff are difficult to find. At least they are in the Dallas area. I live in a suburb of Dallas and only one station here sells E85. My highly modified 1991 Chevy S10 Blazer 4.3L V6 has 10.20:1 SCR and 8.50:1 DCR. It has a ICM and a ESC knock sensor. I can use Mobil 93 octane pump gas with Techron to keep the electronic fuel injection clean.

Headers for a 1967-1969 Firebird will fit a large Pontiac chassis with only minor modifications.
01-21-2013 12:25 AM
cadillacdave1 Sorry, I mistyped but it is a 389. These were high compression motors. If it is a flat to[p piston check how deep it sits in the hole, cc the chamber and that should give you an idea of the compression. Otherwise the listed factory compression is a starting point. You can work backward and determine if you raised or lowered the compression if you look up what size chambers the factory heads were.
01-20-2013 11:58 PM
WDCreech
Quote:
Originally Posted by cadillacdave1 View Post
The original factory motor 289 2v had 10.75:1 compression. Check what the stock cc of the heads were vs the cc of the heads you just put on. Then use a compression calculator, you can find online. I hope this helps.
Pontiac never produced a 289, and you can't go by the factory advertised compression ratios.
01-20-2013 10:15 PM
cadillacdave1 The original factory motor 289 2v had 10.75:1 compression. Check what the stock cc of the heads were vs the cc of the heads you just put on. Then use a compression calculator, you can find online. I hope this helps.
01-20-2013 08:55 PM
LATECH wallace shows the heads at 70 CC
Kens shows them at 62 CC
At 70 CCs the static will be ...9.85
At 62 CCs the static will be 10.72
You need to tear it down and CC the heads to know for sure.
How does it run? does it ping?
01-20-2013 08:41 PM
jeffs66
Pontiac engine question

Hiya, I have a 66 Catalina.It has the 389 2v engine.well recently I put on #62 heads w/ I beleive the 72 cc combustion chamber.Heres my ?.I know Pontiac used a basic flat top piston and would change compression with head swaps.Well does any body have a guess on what compression I have now,or how I may find out without tearing the motor back down?I know its up there cuz its got a bad case of the rattles if I dont burn premium,even when I back the timing down.plus the little extra power.
Also,What other header would fit this car?theyre a lil hard to come buy .Will like the Bonniville or the Tempest work?Im pretty sure the firebird wont fit.The steering box is behind the crossmember so theres a little snaking around to do.
One last thing.What other ball joints would fit this.The oem parts are outta hand expensive so there has to be like a chevy full size that would fit,right? I know its sorta a crazy car but Ive already muscled it.lol..Thank s folks!

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