It all depends on the bearing clearances in the engine. High volume oil pumps create additional strain on the pump drive mechanism and the weakest link is the distributor drive gear, especially if it hasn't been replaced. Even if it has sometimes the roll pin which holds the gear onto the shaft will shear. So, if you run your main & rod bearing clearance on the tight side then you will run the risk of drive gear/roll pin failure.

Bearing clearances for the 351M/400 are .0008-.0026 for the mains & rods. If you're going to run a high volume pump I'd run them on the high side of those specs.

 

I was told not to due to it would pump the pan dry, oil could possibly not drain back fast enough in certain circumstances. I'm almost burrying the needle on the gauge with a stock replacement on my rebuild, I need to get a good manual gauge to pin down the exact psi that it's pushing at.

 

I really believe the correct clearence is the key. In our project engine, we had a stock volume pump and it idled at 30-40 lbs with the oil hot. We did do some extra restricting, but when it comes to the clearence you have to really watch what you are doing. If you just go according to the books suggestions, t doesn't take much to get some tolerance stack and now the engine is to loose. What I thinkis the ultimate is to finish the block main bores and finish the rods. Install the bearings and grind the crankshaft according to your readings. I have noticed that if I grind a shaft to the normall mid- spec, it is usually looser than I like. I usually end up over the high end of the spec.

I think restricting the front main helps alot also. We just purchased a different piece of equipment called a Simtest. We are able to spin the engine over and allow it to pump oil and see where it goes. No valve cover, intake or oil pan. I will take a video of the amount of oil and try to get it posted.

 

Tim, see if you can set up that block to completely plug that extra passage at the #1 we talked about for a nice visual test.

Another thing to watch is the #1 cam bearing installation depth. There is a big leak path there if it is not installed correctly.

 

FYI the last 3 engines we have built, we have pluged the passage off completely, and redrilled the cam supply line 5/16 just to the depth of the big main feed line.

We also have a new oil pump that we want to test before we decide to sell it. A vendor of ours has gone to the same manufacture who make oil pumps for Catapillar. They are making oil pumps with much tighter tolerences, which they claim to boost low rpm pressure quit a bit.

 

Good to hear about that port being plugged. I think the #1 main passageway from the main gallery as machined is really large enough, no need to drill it out bigger.

If someone would make a crescent internal gear pump it would help to boost pump efficiency also. Excessive clearances really eat into pump flow and efficiency especially with an ordinary spur gear pump.

 

a lot of dizzy gear failures are being blamed on the HV pump when the real reason they're failing is because aftermarket distributor manufacturers can't get the gear set to the correct depth on the shaft. if the gear is set too deep into the engine, the gear will be forced down onto the thrust surface cast into the block. it looks like MSD has made an attempt to remedy the problem by making the shaft in 2 pieces with a slip joint in the middle. this modification will elimnate the possibility of the hold down clamp compressing the dizzy and shaft to the block. i just recently found that my unilite was jamming the gear down, the dizzy gear and the gear on the cam are both ground up nasty. by drilling a new hole in the new gear i was able to raise the gear up on the shaft and i now have clearance between the bottom of the gear and the block. the gear is free to contact the block but it is not held by force in contact. if you can't get a feeler gauge between the bottom of the gear and the block while the dizzy is clamped down you have a problem, it must be checked! mine broke at least 3 roll pins before enough metal was ground off that it stopped. i blamed it on the HV pump and heavy oil at the time but i'm sure it would never have broken a single pin if the gear was not being jammed down. and i'd still have a good cam too.

like Tim says, if your crank is at mid-spec, the clearance will likely be on the big side. i wouldn't hesitate to run a HV pump under those circumstances, as long as the gear is riding free.

 

With the engine closed up it is difficult to tell where the gear rides. Shim washers adhered to the bottom of the shaft and close observation (measurement) of the distributor height when installed can produce an approximation of the gear spacing. Spacers cut from shim stock can be used to adjust the distributor height for gear spacing instead of drilling a second hole in the shaft and weakening it.

Also if the gear has been jammed against the block the bearings in the distributor have been ruined. Replace the distributor bearings or distributor.

pssst- remember to remove the adhesive from the distributor gear... -And keep a magnetic retriever handy in case Murphy visits and the unthinkable happens.

 

yeah it's pretty hard to see without the timing cover off, but if you do have the timing cover off for whatever reason, don't forget to check it out! one suggestion was to use plasti-gage to see if the pasti-gage was being completely smashed. if the dizzy is set in carefully it might work? or if enough plasti-gage is used the weight of the shaft won't smash the plasti-gage until you clamp the hold down?

 

Make sure you get the bearings in that dizzy replaced.

Plasti-gage might work well also.

 

i hadn't given any thought to the dizzy getting damaged, while working on the gear i didn't notice any problem but next time i have it out the bushings and shaft will get a good going over.

 

You guys are frightening me...

I'm running a High volume Dynagear/Clevite/Dana/Whatever they are called now, with a Mallory Unilite....No problems yet...

 

Here's the problem that can happen when you start adding volume to increase the pressure, instead of correct clearence. More oil is being "slung" out of the crankshaft, making the oil rings work harder. High pressure pump cost some HP, and pumping more oil will start to raise oil temps. The list could go on. Again if you have a choice, get the clearence correct the first time.

 

I emphatically agree with Tim.

My understanding of the bearing tolerance numbers are that these are the published service limits. They will never get tighter as the engine is run. So, if one is building an engine for maximum service life, building as close to the tightest service limit would seem to be the object of the game. This situation does not require nor desire a HV pump.

IMHO, the only time a HV pump needs to be used in a working truck engine, is when the engine is at or over its service life, or it was not initially built to the proper tolerance.

Go with the stock pump but also discuss with your builder where your bearing tolerances will be and why, and what you will accept or refuse as far as the machined toleraces. GL