Can oil pressure effect amount valves open?

I've noticed on my stoker motor that it seems to have more power when the oil is cool. The reason I'm thinking this is because at startup when the engine is cool it has great power...once the engine is warm i.e. in about 10 minutes, it still has great power but at this time the oil pressure is still high leading me to believe the oil hasn't yet warmed up completely. Once the oil pressure comes down after driving about 15 minutes the engine doesn't feel as strong.

I'm running Mopar performance valve springs with a comp cam 68-231-4 and stock issue lifters.

My oil pressure at startup is 50 psi at idle and about 75 over 2000 rpm.
Fully warmed up my oil pressure is 20-23 at idle and approx 50-55 over 2000 rpm.

I'm currently running a 10W40 oil dino.

The engine has 6k miles on it but has had this problem the entire time.

Is it possible that the stock lifters can't handle the valve springs once the oil warms up and becomes thinner?

Highly unlikely.

It is possible that the lifters bleed down when the oil is hot. It would likely have little to do with oil pressure and more with oil temp and more directly oil thickness. An easy thing to try would be running 20W50 or even straight 40 weight and see if anything changes. I actually think it is a long shot but is a possibility. Do you know your stock spring's open and closed pressures and that of the new ones.

When I put in a my Crane fireball cam the lifters were identicle to stock in every way.

B-loose

First off it helps if you list the year and vehicle info.:soapbox:

When a Renix based engine is started, it runs using a preprogrammed set of fuel curves until it reaches operating temperature, at which time it starts taking the various sensors into account in setting the fuel air ratio.

What injectors are you using? Are they the original ones? Either way, the computer is reading things and setting it to be too lean, most probably. Adding a MAP adjuster will let you set the fuel air ratio to what ever you need. If you are running the stock injectors, some people have not had good luck trying to get a lot more fuel through them. That is why a lot of people go with 24# injectors. You could also be fighting a fuel charge temp sensor problem. That is one very few people ever think of. If it is reading wrong, it can effect the ratios as much as the MAP. The combination of the two are the early equivelent of the mass air flow sensor on newer engines.

Yup it's Renix based.

1988

24# injectors
Map adjusted to 5.4 volts
No intake work
Stock 52mm throttle body...I'm working on getting a larger unit.

Bender said:

I've noticed on my stoker motor that it seems to have more power when the oil is cool. The reason I'm thinking this is because at startup when the engine is cool it has great power...once the engine is warm i.e. in about 10 minutes, it still has great power but at this time the oil pressure is still high leading me to believe the oil hasn't yet warmed up completely. Once the oil pressure comes down after driving about 15 minutes the engine doesn't feel as strong.

I'm running Mopar performance valve springs with a comp cam 68-231-4 and stock issue lifters.

My oil pressure at startup is 50 psi at idle and about 75 over 2000 rpm.
Fully warmed up my oil pressure is 20-23 at idle and approx 50-55 over 2000 rpm.

I'm currently running a 10W40 oil dino.

The engine has 6k miles on it but has had this problem the entire time.

Is it possible that the stock lifters can't handle the valve springs once the oil warms up and becomes thinner?

Click to expand...

The lifters don't need much oil pressure to pump up so once they've done that, they stay pumped up as long as oil is circulating through them. Therefore it's highly unlikely that the slight loss of power when the engine's hot could be due to the lifters.
It's far more likely that your engine could simply be getting heat-soaked, so the IAT sensor is reading high manifold temps. and retarding the timing. Do you have a cold air intake or is the filter breathing hot underhood air? That can make quite a difference.
I don't think your engine's running too lean with the MAP at 5.4v though it could be a remote possibility. I have the MAP set at 5.9v on my stroker but then mine is HO-based with a ported head and Mustang 65mm TB. I also have Ford 24lb injectors and I think I've got it just at the lean end of stoichiometric.
____________________________________________________________
1992 XJ Laredo 4-dr - 4.6L I6 HO Stroker - 176k miles - AX15, NP231, D35c, D30
Estimated 263hp/323lbft, best 1/4 mile [email protected] before stroker install
Websites - Jeep 4.0 Performance, 4.6L Stroker Build-Up, Dino's Jeep Tricks

Hey, Dyno, what cam are you running. Its interesting you are running lean while I was running rich with the same injectors. I guess maybe the difference is in the computers. You are also running a larger bore TB, but mine was rich even at an idle.

I'm using the Crane 753905 cam (204/216 duration @ 0.050). I think the difference might be my ported HO head. If your head is still a stock Renix, mine will far outflow yours so that may be why my engine needs more fuel. My larger bore TB will also make a difference. I have the stock HO computer with JET Stage 2, Robertshaw 180* t'stat, and IAT sensor relocated to my homebrew FIPK so it reads ambient temp. all the time.

The actual cam timing can have an effect on idle richness..if the cam is too far retarded, intake reversion will over enrichen the incoming charge...more common with camshafts that run large overlap events.

One thing for sure...I agree that the engine is slightly lean when hot.

I also think the loss of lift theory is very highly unlikely.

MudDawg said:

One thing for sure...I agree that the engine is slightly lean when hot.

Click to expand...

If the engine's running too lean, it will also run hot. Since I increased the MAP voltage on my stroker, the engine's been running cooler. My oil temp. used to max out at 225*F in traffic but now it'll barely reach 210. It's also lower in highway driving (185*F now, 195*F before).

I'm reluctant to increase my MAP voltage anymore as my exhaust at first startup has a the scent of richness...also the idle is a little loppy compared to the MAP at 5.0V so I'm guessing I'm on the rich side at first startup.

I am currently sucking in quite a bit of hot air into my airbox as the front is currently a large 4" hole. I have it setup to plug it since I have a custom snorkle that feeds from the cowl at the bottom of the windshield. I used to have my IAT at the airbox when I ran the plain 4.0L but moved it back to the intake manifold as I figured the 24# injectors would make the mixture plenty rich without a relocated IAT. Perhaps I'll put it back to the airbox and plum my intake tube so it gets fresh cool air.

What else could reduce performance when the engine is hot? My current performance decrease when hot can easily be felt by the @ss dyno so I think my issues go further than just requiring cooler intake air.

So, I've moved the IAT and have noticed a slight difference...it's a bit better. I still feel the power loss when the engine warms up.

Any other suggestions?

Cooler intake air will help a lot. Underhood air can reach 170*F on a 115*F day so it would make a tremendous difference if you could get the intake to breathe in ambient air. The IAT will also read a lower temp. and allow a bit more ignition advance for more performance.

I'd consider tight bearing clearance since the motor was recently built, has high oil pressure and has had the problem from the git-go.

Max...

Wouldn't tight clearances lead to unusually high oil pressures? Mine seem to be right in the correct range.