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Discussion Starter · #1 ·
Hey guys im new to the site , have been checking the site out for a while but just now registered as im in a bind.

OK i recently finsihed building my poncho 400 bored 040 forged pistons 6x heads shaved to 9.2CR , Perf RPM dual plane intake , lunati 233/241 503/527 110lsa cam , scorpion roller rockers etc.

I have never built a pontiac before only chevy's and i have never used oil pump gaskets, well i didnt use one on this Pontiac either.
I was talking to a friend who told me that Pontiacs require a gasket on the oil pump....

When i finished the motor after cam break in , i noticed that once it warms up to 190 oil pressure drops to ZERO on my auto meter 200ps gauge that was in the car , so i went and bough a cheap sunpro oil pressure gauge and its reading 55lbs on start up , once warm and in gear 20lbs at idle , if i bump the throttle it flys up to 60lbs.

Just trying to figure out if i need to lift the motor and drop the pan to put this gasket on the oil pump... Or if pontiacs are like Chevys where they will be ok without them .... I used the melling high volume pump.
 

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Grumpy Old Goat Herder
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I have always used a gasket between the pump and the block. I don't know if it won't work without one, but as long as you have sufficiant oil pressure, you should be okay.

Bill

 

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WFO
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I always use a gasket. Paper is OK but IIRC Melling has a copper one that's nice. Pumps are usually very flat but the block is another matter. I wouldn't risk not using a gasket.
 

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Faith - Respect - Trust
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Agreed with all above, I've built many a Pontiac motor and always use the gasket. Don't know if you'll be OK or not but, I do agree that if you have sufficient oil pressure chances are you haven't done damage.

Rule of thumb in the future, if a buddy says you don't need something, but, whatever he says you don't need to put on doesn't take a pile of time, you already have it, and it won't stop your car from going fast...put it on.

Just sucks that you may need to pull the pan.
 

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Discussion Starter · #5 ·
Thanks guys figure i better pull the pan....
Im sure it did no damage as it has enough oil pressure for the few test drives i took .....

I appreciate the quick replys.
 

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Discussion Starter · #6 ·
Quick question.
Since im pulling the oil pan and taking off the oil pump its a Melling 60psi MEL-54DS the stock replacment.

They make the MEL-54F which is a 80psi pump which would raise the pressure 30%.

My question is if i went to this 80psi pump is there any bad it could cause?
They say its for 455 motors but the 400 is basicly the same block.....

Just trying to get all my ducks in a row before i lift the motor and pull the pan.

Advice? Thanks
 

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Grumpy Old Goat Herder
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You don't need an 80# pump unless you are running a 421, 428, or 455 block, 3.25" mains, with lots of bearing clearance. The RA IV (60#) pump is optimum for all other applications.

Bill

 

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Faith - Respect - Trust
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A 60 pound pump is all your going to need. Unless you have everything upgraded to handle the extra pressure I wouldn't use it and again, looking at the parts you have installed stick with what you have.
 

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Discussion Starter · #16 ·
Yes but correct me if im wrong 15-20 @ hot idle is low?

See the thing is the machine shop told me he likes to set clearnaces loose for drag racing but i told him i will only use it as a street/drag , im wondering if he did not set the clearances loose and a higher psi would compinsate.....
 

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Regular production engine rebuilders and prefer to set the bearing clearances on the loose side because they do not want any "come-backs" due to wiped or spun bearings. That is because the machine shop does not know how the engine is going to be used, no matter what the car owner tells them.

Regular production rebuilt engines will have just enough oil pressure at idle to keep the lifters quiet. Most automobile owners who buy regular production rebuilt engines do not have an oil pressure gauge. The idiot light is caliibrated at the factory to illuminate at 7 lb. at 600 RPM.
 

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As Bill and 69 pointed out, those are perfectly normal readings for a 400 Pontiac. Added pressure in the Pontiac is counter-productive as it "heats" the oil more. The big mains in the Pontiac heat the oil enough, thank you... Wayne Hoehns (built the most powerful Buick 231s in the "Busch" days) once told me never put an oil temp guage in a circle track Pontiac or 351 Windsor (both 3" mains). "You don't wanna know..."

What MouseFink says about shops "adding" clearance is sorta true. That is, we allow engines "out the door" with more clearance than factory "tolerances" listed. Partly because of just what he says. Customers don't always end up using the engines for exactly what they say, and we have to "build in" some flexibility. We have SOME customers we "tighten things up" for because we KNOW what they're up to. But it's a common misconception that "tighter is better". As long as there's enough oil to keep the crankshaft "floating", it's all good. "Tighter" will actually add heat to the oil, too.

Aother reason engines are "looser" than original is the parts themeselves. Bearings are now designed such that, when the crank is in the "middle" of the tolerance, clearance will be near the "high lmit". Performance applications typically grind the cranks to the "low limit". That, combined with the "high limit" clearance bearings, an additional .0005-.001" OVER the high limit is seen. This is when oil pressure can degrade at low RPM.

FWIW

Jim
 

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Discussion Starter · #20 ·
Thanks for the info guys. I remember him telling me he likes to set clearances loose for drag applications and i told him it would be a street/strip motor.. He line bored it and set the crank and main bearings.
I was going to but when i checked it the clearances were so tight , i just went ahead and dropped the block and crank off to the machine shop that cut the crank. I set up the pistons and rod bearings.

Im thinking he set the clearnaces a lil loose because i said strip.
That would surely explain the pressure.
I ran it today and all is good , once it warms up im showing 20-25 @ hot idle in gear!


My pnocho had 50 pound pressure at idle. 20 is to low for new engine, install the gasket. Careful to get the pump rod square away properly on install.

Larger pump should not be an issue once the new gaskets installed. Melon high volume was all i had. High pressure pumps usally require some machine work on the blocks oil passages.

Always install all the funny gaskets on pontiacs!!! Most important part of poncho build.

MY MOTOR HAS 50-60PSI IN PARK , ONCE I DROP IT INTO DRIVE WITH THE MOTOR @190 DEGREES IS WHEN THE PRESSURE DROPS TO 20LBS....
 
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