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Discussion Starter #1
Guys,

I found this very interesting today. I installed a new ZZ4 shortblock in my 63 in May this year with a STOCK front sump oil pump and Pan. At first start up when engine not warm I would get 35-40 pounds oil pressure at 800 rpm idle. When the car got good and warm around 190 degrees and running for 20 plus minutes under driving conditions the oil pressure droped to 7-8 pounds ONLY AT IDLE but goes right back up to 20-40 pounds when engine rpms increase so I always have at leat 10 pounds per 1,000 rpms once past idle.

I have called GM and 3 certified GM Dealers who tell me this is NORMAL! They actually have some ZZ4's that are running 3-4 pounds at idle. Said that as long as the oil pressure is increasing with engine rpm up to 25-40 pounds based on rpm range that all is fine! Good rule of thumb is 10 psi per 1,000 rpm...above idle.

This very much surprised me to learn that they are seeing engines actually have 3 pounds of oil pressure at idle!
 

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It's been my experience that the front sump pumps don't hold the hot oil pressure as good as the rear sump pumps but that does seem odd to have that much difference between hot and cold pressure. Maybe some GM mechanics on this site will have some input.
 

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I have the fastburn crate engine I"m using the oilpump that came with it and holds 60 lbs hot and 25 to 30 at idle, I use a 1/8 copper oil line on my gauge because I think they response to the decrease and increase pressure alot better than the smaller lines.


Norm
 

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oil pressure

:cool: hey bucs01,i rebuilt my 355ci almost 8 months ago ,been doing a lot of hot rodding ,it holds 50 to 60 lbs when cold at ldle,but once warmed up at idle about 20lbs ,in gear maybe 5lbs ,i've had no problems at all in this time ,and i haven't been easy on it ,you'll be ok , :)
 

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The oil pressure on mine goes down to about 5 or 6 psi in gear (rebuilt 350 with front sump). That worried me quite a bit until my neighbour checked up for me and said that is about normal for a SBC. I haven't had any problems so far, but then again it has only been on the road for over three months now.

Perhaps those with a high volume pump (not availale for front sump applications I've read) would have higher pressures.
 

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I'm reading a lot of low oil PSI with front sump pans.
Could there be a leak in that long tube between the pick-up, and the pump? Possibly sucking air? Just a thought. :confused:
BTY, my rear sump 327 has 20lbs at hot idle.
 

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The oil pump for the front sump pans is smaller than the standard rear sump oil pump and pumps less oil.
 

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Discussion Starter #8
Thanks for the feedback, guys. I switched from a rear pump/pan on my old engine with a high volume pump and was used to getting 30 pounds or so at idle and 40-60 when driving. Seeing the low readings in this front pump/pan combo on the zz4 just surprised me.

All I do it put around or drive to cruises and get on it once in a great while so I am sure it will be fine, like you said.

I am going to take my Nova to the local Chevy dealer just to have them document that I did bring it up.......and have a receipt. Just in case something goes wrong even after my warranty is up! ;)
 

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I have a high volume high pressure pump on my 327. Cold it idles with around 60 psi and as high as 95 psi at high rpms. Hot has 50 psi at idle and about 75 psi at 6000 rpm. I don't especially like it so high but the motor has been in the car for two years with no probs and I do run the car pretty hard some times. Next motor will not have a high pressure pump because I am worried about the distributor gear wear and I think it robs power to turn the pump. I think a high volume pump with a lower pressure spring would be ideal.
 

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No oil pressure!!

I installed a new stock type oil pump when I switched to a rear sump pan in my 66. Does the pump have to be primed? I did install the pump shaft, and there is oil in it. I don't build any pressure while cranking like I did before (the gauge reads zero), and there isn't any oil coming out from the top of the rockers. Help!!!
Grant
 

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Did you use the same oil pump shaft from the front sump pan? The front sump one is shorter in length.

It wouldn't be a bad idea to prime the pump.
 

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get youself a oil priming tool that goes in the distributor and you spin with a drill. spin it up, you should have resistance and check oil pressure. try that before replacing anything. if for some reason its not long enough... then you will have to start taking things apart. you need either the oil pump primer, old distributor body or something to spin it, i recommend the tool

http://store.summitracing.com/partdetail.asp?part=11010
 

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If you used the Chevy II shaft it's too short to engage the rear sump pump.
The Chevy II front sump pump is shorter to clear the crossmember.
I just happen to have both a Chevy II front sump drive and a Milodon rear sump drive on my desk.
The unique Chevy II drive shaft is about 5.3" without the sleeve. An aftermarket drive is about a 1/2" longer or 6" with the sleeve.

You'll have to remove the pan and pump to change it. The retainer sleeve won't pass through the hole. I'd recommend using an aftermarket steel sleeve shaft. The nylon sleeve that is used with the stock Chevy II shaft could fail causing a catestrophic loss of oil pressure.

Which reminds me I have to check with the machine shop on the status of my front sump drives.
 

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Thanks everyone. I thought I knew most of the things that made our Chevy II's unique, I guess I found another one! I can't understand why the shaft would be shorter, the distance from the top of the pump to the distributor is the same :confused: . Oh well. It snowed here last night, so I'm in no hurry to get the beast on the road anyway.
Grant
 

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No quick fix. You have to use the correct shaft. Sounds like you have all winter to get it fixed. Hope you have a heated garage.
 

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all the advice you received i agree with, in regards to the adapter and pump gaskets... i also agree with the heavier duty pump shaft with the metal collar.

there was a thread a while back posted by Paul Wright, he showed very convincing proof why the metal shaft should be used.

just like the ol' Fram commercial... "you can pay me now (cheap) or pay me later (tons)


john ( better safe ) than sorry :)
 
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