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Old 04-07-2012, 08:06 PM
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326 pontiac engine low compression

Is 120 psi across on all 8 cylinders to low, engine smells of oil at 3000 rpm and lacks power, thinking of engine swap either ponti 400, 350 chev or ls which is best ? currently turbo 350 RHD 67 firebird

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Old 04-07-2012, 09:37 PM
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Quote:
Originally Posted by Jellyfish1968
Is 120 psi across on all 8 cylinders to low, engine smells of oil at 3000 rpm and lacks power, thinking of engine swap either ponti 400, 350 chev or ls which is best ? currently turbo 350 RHD 67 firebird
120 psi is low if the cam is stock and the timing chain wear hasn't let the cam timing get retarded.

You can get an idea of how bad the timing chain is stretched by making a temporary timing tape (or buy one).

Remove the plugs (what do they look like, oily, fouled?) and by hand rotate the engine backwards (CCW as viewed from in front of the car) until you feel the slack has been taken out of the chain. Mark the damper at the TDC line of the timing scale on the cover (or any easy to see stationary point on the engine).

Then rotate the engine CW and stop as soon as you feel the added resistance when the slack in the timing chain has been taken up. Mark the damper a second time to your reference point. The distance between the two lines is how much slack there is. You can do this several times to get a feel for it.

You can also estimate the slack w/o a timing tape by comparing the distance between the lines to the timing scale. If the timing scale shows that 10 degrees = 0.6" (which is what it will be if the damper is 6.8" diameter), use that to tell how many degrees of slop there is in the chain.

If the low compression readings are from wear, then it's most likely time for a rebuild. You can do the compression test over, except this time squirt some motor oil through the plug holes before running the compression test. If the readings increase, the rings are shot. If not it's bad valve seal.

BTW, if you still have a points ignition, it's time to add a conversion to get rid of them or add an HEI distributor.

A 400 or 455 Pontiac would be my choice if the engine was going to be replaced. Pontiac info and sites HERE.
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Old 04-07-2012, 09:42 PM
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How did you do the test? The correct procedure is remove all the spark plugs, disconnect the coil wire so it cannot start and block the throttle to it's wide open position. If the test was performed with the throttle closed it can't get much air and the readings will be on the low side. How many miles are on this engine? If it's got high miles there's a pretty good bet it needs a rebuild. Being you already have a Poncho engine in the car then I would think the easiest bolt in and go route would be to drop in another Poncho engine.
If the bellhousing on the trans only accepts a Poncho engine then it would be easier to leave it in rather than remove it also. Poncho 400's seem to be pretty good engines, however if your looking for performance the smogger years were not very good to them, many came from the factory with 7.5:1 compression ratio which is dirt low. If you looked around you maybe able to find one from the early 70's and some of these came with decent horsepower numbers and some really nice torque figures. But that's not to say you couldn't find a smogger Poncho 400 and do some performance mods to it.
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Old 04-08-2012, 02:39 AM
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Thanks Fellas

I will find a 455 crate engine and have it shipped to oz, so far it looks about $5500 plus $1000 for freight. Will the turbo 350 handle 500hp ?
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Old 04-08-2012, 08:22 AM
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A stock turbo 400 would be cheaper than a built 350.A 350 can be toughened up but the difference in cost for hard parts and such makes the 400 a better choice for strength verses cost .
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Old 04-09-2012, 03:13 AM
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are tuff dawg engines ok

Looking at this engine on e bay, has anyone heard or recieved one of these engines?

(PONTIAC 455/500HP CRATE ENGINE BY TUFF DAWG ENGINES #160777014149)
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Old 04-09-2012, 01:01 PM
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Quote:
Originally Posted by Jellyfish1968
Looking at this engine on e bay, has anyone heard or recieved one of these engines?
(PONTIAC 455/500HP CRATE ENGINE BY TUFF DAWG ENGINES #160777014149)
That is D&J Machine in Phoenix. I've read both good and bad about them. I would want to know the brand names of some of the internal componants, so it would take a phone call or two. It might be a great street engine, but you wouldn't know unless you talk to someone that has one.

Bill
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Old 04-09-2012, 06:21 PM
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Exactly what level of performance are you looking for from your Firebird?

There is "no such thing" as a true Pontiac "crate engine". That term implies "brand new". Pontiac blocks and heads haven't been made since 1978. There ARE aftermarket blocks and heads, of course. A "crate" engine like that from Butler or The Dude would cost around $16K. We, too, put them in crates...

A 455 is not the better choice these days. If building a hot rod, use a 400 block and "stroke" it, if you MUST have the larger cubes. 400 blocks are physically stronger than any of the "large journal" blocks. The better 400 blocks were made between '67 and mid '75. Blocks with "557" as the last three digits of the casting number should be avoided for a hot build. They're fine for 400 HP.

I would highly recommend you look into Pontiac builders, rather than an E-bay or "bargain" rebuilder. Do it right the first time, and you don't have to do it a second.

Keeping your Pontiac "Pontiac" is a major deal to some car people. Since the NMCA started racing muscle cars, Pontiac parts have been forth-coming. We're now on a level field up to 500 CID, and may actually have an "edge" where "pump gas" is concerned.

Jim
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Old 04-09-2012, 07:32 PM
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If you plan on installing a engine with a true rating of 500 horsepower then you have some work to do. Number 1 is the fuel system. a large cube engine with 500 horses is hungry, and it'll want at least 3/8 fuel line front to back. You will also need some sub frame connectors to stiffen the unibody up otherwise it's asking it to twist the body which will cause all kinds of problems.
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