[RamAir6]

I needed an engine to race with this year (since I havent complete my pontiac yet) I put together a small block chevy 400 with some used parts I had laying around the garage. Here's the problem, I notice when I had it on the dyno that it oil pressure was fluctuating alot. I just wanted to know if anybody know's what causes this?? It has a standard volume/pressure oil pump. I ran 20w50 Valvoline race oil. The clearances are .003 on the mains and .0025 on the rods. Im attaching a copy of the dyno sheet so you can look at different oil pressures at the different rpm. The only things that I have come up with is that the pump is possibly cavitating or the pressure relief valve in the pump is slaming back and forth. If anyone has an idea please let me know.
Thanks
Jason Dammen

[RamAir6]

I needed an engine to race with this year (since I havent complete my pontiac yet) I put together a small block chevy 400 with some used parts I had laying around the garage. Here's the problem, I notice when I had it on the dyno that it oil pressure was fluctuating alot. I just wanted to know if anybody know's what causes this?? It has a standard volume/pressure oil pump. I ran 20w50 Valvoline race oil. The clearances are .003 on the mains and .0025 on the rods. Im attaching a copy of the dyno sheet so you can look at different oil pressures at the different rpm. The only things that I have come up with is that the pump is possibly cavitating or the pressure relief valve in the pump is slaming back and forth. If anyone has an idea please let me know.
Thanks
Jason Dammen

[Tom Vaught]

Look pretty normal to me when the crank is orbiting around in the mains. P Dude may have a
better idea on SB Chevys as I am no expert on them. Tom V.

[PONTIAC DUDE]

I agree. Looks normal to me.

Depends also on how fast they brought up the rpms.
That 63 looks like a fluke reading.
Remember that 100 rpms in that short a time period. If there was a problem, then the pressure would show a constant loss and they would have shut er down.
Or a loss and then build back up over a longer rpm range.

Pan capacity?

Oil Filter?

Did you pull the bypass out of the oil filter adapter in the block and plug it with a pipe plug? A must for racing as that bypass open around 65psi or so and then your bypasing the filter.
Same deal as the Pontiac. I always plug the bypass on Race stuff.
[img]/infopop/emoticons/icon_wink.gif[/img]

Build it fast, build it right, build a Pontiac.
http://PontiacDude.cc

[RamAir6]

P. Dude,
The engine has a 6 quart pan and also has the bypass blocked. I wasn't really worried about the oil pressure, I just wanted to see if anyone knew why it jumped around. I just hope this doesn't become an issue in the middle of the season. [img]/infopop/emoticons/icon_frown.gif[/img]
thanks again
Jason Dammen

BTW You can tell this is a real small block chevy dyno sheet, if you notice where it is stating the specs of the engine when it gets to oil it says "on floor". [img]/infopop/emoticons/icon_wink.gif[/img] (had a small problem with the rear main seal) oh well fixed now...

[rpmalone]

Just a thought, maybe the variation is with the oil pressure sensor. You might ask to see oil pressure data from other engines recently dyno'd?

I agree that the variation looks small and the numbers overall look good (including TQ/HP)

About 6 months ago I built and dyno'd a 406 SBC for a local oval track A-Body and although the engine was quite different from yours I did go back and look at the oil pressure data and it was pretty linear (.5 to .8 psi incr per 100 rpm).

This was on a fairly new dyno so maybe it's the instrumentation.

[RamAir6]

We dyno'd a friends engine the same day that I did mine and his oil pressure was real consistant. Im not sure what to do... I'm thinkin that I might replace the pump since I am going to dyno another engine in about 6 weeks and I could bring this one with for some more tuning. The oil leak was making such a mess the last time I was there I didn't tune it as much as I would have liked. [img]/infopop/emoticons/icon_frown.gif[/img]

[rpmalone]

Well that seems to rule out the measuring device as culprit. Some other ideas... filter differences (some filters have internal bypasses)...pickup design (I've read that the larger circular stock type pickups are more prone to generating vortexes and sucking air if the level drops too much) though you're using a 6qt pan and std vol pump so that doesn't seem too likely.

If you do choose to replace the pump, here's what I used on the SBC oval track engine I refered to and it seemed to work out great;

Melling M55A - this is their equivalent to the Z28 pump. $30 thru Jegs. Melling tech says its good for about 10% more volume and pressure than the standard pump. On the dyno it produced very consistent pressure and the bypass appears to open at about 80 to 85 psi (85 when oil was 180deg, 80 when oil was 220).

I was using Valvoline VR1 20W50 with a blocked bypass, bearing clearances were .0025, NAPA Gold 1061 filters (used for 3 seasons of oval track with no problems - changed after each race of course), Moroso 6qt road race pan #21900 and pickup #24170.

The only change I made to the pump aside from disassembly/inspect/clean was to set the clearance between gears and cover to .oo3 by sanding base cover and gears on a flat plate with 400/1200 grit.

btw - what heads, cam and intake did you use on the engine? - you got great results!

[RamAir6]

Silver,
Thanks for your input, I will consider it when I decide what I want to do.

The engine combo is as follows:
Block: 1976 .060 over 400 block thats been filled with spayed caps.
Crank: Summit proline 3.75 stroke
Rods: Eagle 3-D 6.0"
Pistons: Custom Ross +5cc net dome
Cam: Comp Cam Mech. Roller @.050 276/284 107LC .630 valve lift in/exh
Timing set: Comp Cams external belt drive
Rocker arms: Comp pro-magnum 1.6's
Heads: Brodix -11 race ported by ron's porting service
Intake: Brodix HV1000 also ported by ron's
Carb: 1050 pro-systems Dominator using a 2" adaptor to bolt it to the 4150 flange intake.

The dyno sheet I posted was with the Dominator, the engine made 627hp with a 926cfm Carb Shop Holley and 1" blended spacer.

Just in case your wondering, I really did have most of this laying around the garage. I had to get the rods and pistons to complete the engine and I was surprized to see the HP numbers this thing produced. [img]/infopop/emoticons/icon_smile.gif[/img] My dyno operator told me that the Dominator carb and my engine want to be boyfriend girlfriend since it picked up almost 40hp and it was tuned for my brothers 700hp 469ci Pontiac. I think with some more time I could have tuned the thing to make somewhere in the 680hp range. Maybe we will find out when I make it back there. Let me know if what to know anything else.
Thanks Again
Jason

[rpmalone]

Thanks for all the specs Jason. I can only dream of a day when those kind of parts can be found sitting around my garage.

[Taff]

Ramair6, did you block off most of the oil return holes in the lifter valley? I suspect that with the bearing clearances you have your oil pump is sucking the pan dry momentarily. Try adding another quart or two of oil to see if it makes a difference.

[RamAir6]

Taff,
It has the lifter valley vents that are about 1 1/2" tall so it can still breath but doesn't allow the oil to fall down on the crank. I had six quarts in the engine so I hope it isn't starving the pump, but I suppose anything is possible. Might have to try add some if it continues the next time I'm there.