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Old guy44

compression ratio?

37 posts in this topic

OK just rolled under there again and can find no numbers stamped on the housing. I do not think that it has been changed as it still has the lock tabs on the u joint u bolt nuts and no one ever put those things back on. While it is still up in the air I might soak it with cleaner and pressure wash it in case the stamping is faint and I missed it.

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Posted (edited)

Old Guy,

Hope you can see the details in these photos. Took them with my phone sometimes it doesn't do so well. This manual is the one actually put out by Pontiac Motor Division..So I'm 100% sure it is accurate. Got it from my dads immense automotive library 40 some years ago.

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Edited by TWO LANE BLACK TOP

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Did not see anything in that location but will take a closer look tomorrow, right now I am putting my beat up body to bed.

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OK crawled back under and took one of those tooth brush size wire brushes and cleaned the area. The stamping is pretty faint but looks like it could be a 2

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Posted (edited)

#2= 2.69 gear ratio...Not having good day..Season opener at local race track tonight..( We are running in NASCAR Modified Division ) Had car out on track for final tuning..Early This morning was clicking off some really fast laps..Got mixed up with another car.. Went ass end into wall hard..Driver OK.... Car not so good...

Edited by TWO LANE BLACK TOP

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2.69 is about what a 3.5 would be with a 700 R4 in overdrive. Sounds like it might all work out for cruising mileage. It should be ok in town also, the trans is geared low enough in 1st gear that even as sour as the engine was running it had good throttle response at stoplights. Frankly better than I ever expected for a two barrel single exhaust engine.

Sorry to hear about the car but rear is better than front. A whole lot less moving parts back there. Are you going to try an all nighter to get it back on the track for the race or have you just resigned yourself to see the race from the stands?

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Two lane,

IT'S ALIVE! The car is running, I have been driving it for a couple of days and the camshaft seems to be exactly what I was looking for. The low end throttle response is so good that I had to jack up the trans throttle pressure linkage because the trans was shifting way too soon. This should result in improved fuel economy and it appears that it might have but the carb still seems to have problems. What slight amount of driving I did before I took it apart it was sucking fuel faster than I drank beer in my teen years. It is still sucking fuel but not nearly as bad. It has that nasty rich odor when running but not bad enough to be blowing black. I pulled the plugs for a read but I have not had to read a plug since the switch over to unleaded fuel and am not sure what to look for. With about 70 miles on the plugs they look like they just came out of the box. In all my years I have never tweaked any Rochester carb, my carb of choice was AFB for street and end bowl Holley for performance. I know that the end bowl Holleys were notorius for feeding too much fuel when they were in the transition stage coming off of idle before the throttle was open enough to be feeding off of the venturi cluster. Is it possible that the 2GC Rochester suffers the same problem because on the surface streets the throttle is never open enough to reach the venturi cluster. Back in the dark ages we used to plug and meter the transition passage on the Holleys to lean them out while in the transition stage and I would guess that it should be possible on the Rochester if I need to figure that out, or possibly there is another answer. I went through the carb and found no cracks or warpage anywhere everything looked good with a straight edge and the gaskets that came out all had good sealing marks. I plan to take it off and take it apart again this morning to see if I might have missed anything but I don't think so. 

I am not too familiar with anything east of the Rockies but do not think of Indiana as having extreme elevations so I would not think that the original jetting is incompatible with the 1100 ft elevation of Oak Park. 

Have you ever heard of anyone converting one of the late 80's early 90's GM throttle body injectors as they were two barrel and would fit on my two barrel manifold. The two problems that immediately come to mind would be a distributor that would fit in the Pontiac that has the internals to trigger the injector and a crank position sensor. Those post date my years of crawling around under hoods professionally so do not know if they ever used that system on a Pontiac. 

How is the race car. Did you get it on the track for the race or chuck it and go home. Bad omen for opening day, hope the rest of the season improves.

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Posted (edited)

Hello Old Guy,

Hope you can see these photos..and that they actually help you. The special tool that measures the float level is unneccessary..there is a measurement that it is supposed to be..Will have to find out what that is. Will get back to you on that..Sorry I Haven't gotten back to you earlier. Rained out races Sat. night. Race car is going to have to have rear clip put on it. Probably going to be a few weeks before track ready again..We are just doing for fun this year anyway wasn't going to run full schedule anyway..Still sucks though...One major thing between present day gas and what was used in the good old days. When you could buy real gas besides the lead is the ethanol. Gas here in NC uses 10% ethonal..Don't know about Cal Fuel blends..Do know that they're different out there. Anyway ethonal laced gas doesn't get as good mileage because ethanol doesn't have as much energy in it..A gallon of ethanol will not have as much energy as a gallon of gas therefore you can travel farther a gallon of gas than you can with gallon of ethanol..with gas blended with it.  Will hurt gas mileage in the long run..Have a place here where can still buy nonethanol gas. Although more expensive..Can go almost 10 miles farther on a tank of it. Than Can with blended gas on my carburated motorcycle. They  did use throttle body fuel injection on Pontiac but it was the corporate (chevy) engine. In the 1980s..

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Edited by TWO LANE BLACK TOP

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Just signed in with my laptop instead of my phone. Was hoping the photos would be clearer. Don't know what if anything.I can do to remedy that..Any suggestions would be greatly appreciated. Think Mrs. Two Lane might have a way to scan them onto her work computer and then post them directly with out having to take pictures with my phone. Will ask her. As far as throttle body conversion I have never done one so I honestly don't know that much about it. I have always gone the other way from throttle body to 4 bbl carb especially in a performance build. Although I do have a HOT street combination that works really really well with tuned port injection..Hoping these photos will answer some of your carb questions. If you can not see these photos well enough for them to be of any use please let me know will do something different....Mrs. Two Lane just got home she says that she can scan them but will be a couple of days..before she can do it..

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Two Lane,

I did take the carb apart and took another look at it. I had forgotten that the idle circuit on that design carburetor two and four barrel was fed through metered tubes in the main jet wells. Short story is that they are much better metered than the earlier end bowl holleys. It is my understanding that Holey has fixed all of its gremlins in the past few years but I digress. When I pulled the top off of the carburetor the fuel level looked high and with a float in it it would be even higher. I lowered the float about a quarter inch from the level shown in the instructions that came with the carb kit and went out to run a few errands. When I started it up I let it warm up and found that I needed to lean out the idle screws, a good sign, and driving it with the top down you get a lot more of the exhaust smell than you get top up and the nasty rich exhaust smell seemed to be gone. Something as simple as the float level? Anything is possible.

Re: cal gas. We have the winter and summer blend. More ethanol in the summer blend. We are still on winter blend. 

At any rate I will drive it for a while and see what happens. I might drop one jet size and see what happens, It has 64's in it right now.

On another subject I just picked up a 4 row aluminum radiator, with A/C on a 110 degree summer day in our lovely L.A. stop and go traffic I do not think that there is such a thing as radiator overkill. Question is which coolant to run. When I had the Ford diesel I switched it from the green to the red coolant on the advice of a friend that used to be a heavy equipment mechanic with Caltrans. Something to do with the egr cooler. When I did the 100,000 mile service on my wife's Lexus I put it in that and what the h... did the Mercedes SL at the same time. The A/C I put in the car is out of a late 90's Crown Victoria which has an aluminum heater core that did have the predisposition for premature failure in the police cruisers. Ford came up with a variable restrictor in the inlet hose that helped until motor transport found a source of copper heater cores. I checked and the copper cores are no longer available, haven't checked with ford on the variable restrictor yet. So with all the aluminum which coolant is the least corrosive.

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Use the green.. I use it in all my cars..Changed the red out years ago. Have rebuilt several late model engines with aluminum blocks and heads and the ones that had red antifreeze in them almost always have corrosion issues with head gaskets the engine block decks..Cooling passages and the cylinder heads, heater cores etc..Have seen blocks and heads corroded to the point where they couldn't be reused. Especially if is not flushed and replaced every couple years. Basically turns the aluminum into a white powder..the red creates an electrolysis similar to a galvanic reaction like when aluminum is bolted or rivited to galvanized steel without some sort of barrier between them.  Over a period of time it just eats the aluminum...Just curious were you able to make out the photos or do I need to try something different??

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I can sort of make them out but lowering the float level about 1/4 inch lower than the instructions called for seems to have made a tremendous difference. If I need them possibly I can move them to another program that will allow me to manipulate them.

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