Dirt racer needs help

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Racer26

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Nov 15, 2007
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South Texas
I race a modified on dirt. I've had a lot of bad luck breaking oil pumps and screens due to harmonics issues on a 383 stroker. I now run a 355 and recently had another oil pump failure. I now have a custom built pick up tube that's 3/8" off the bottom of the pan and is welded to the pump. I just recently installed a special order oil pump that has been machined to take out high rpm harmonics issues. I've been told I am running to heavy an oil (Valvoline racing 50wt) even though I'm in deep south Texas where it's almost always HOT. This motor runs on Methanol and I change the oil every three race nights. Is this frequency OK?

If it makes any difference the 355 has a scat crank, eagle rods, SRP flat top pistons. The heads are Bowtie 205 angle plug that have been angle cut with the tallest edelbrock intake available. Hydraulic cam with solid lift and roller rockers. I was running the Fram HP4 filter but I am now changing over to the WIX racing filter.

Any help would be appreciated.
 
I used to formulate for dirt track racers running methanol and would recommend 20W50 synths or blends and most ran 355's but there are a couple of questions to be answered.

What is your fuel pump pressure and oil temps and what kind of oil pump/screen setup are the other racers using?

What are your peak rpms; what is the top rpm the pump was designed for? Is the oil

As far as your OCI, only a Used Oil Analysis can help you determine that. I have seen so much methanol in the oil after one race that it diluted the oil to a low 30 weight. What's the appearance of the crank bearings?

Where is the pump breaking?
 
What make/model of oil pump/screen? Why are you getting harmonics large enough in amplitude to tear up pumps/pickup screens? Are you by chance using a RH kickout with some sort of extended pickup? If you have the misfortune to have a late model Melling pump, I can understand the frustration.
 
I have been running the Melling pumps all along. Yes it's a RH kickout pan with an extended pickup. The pump in the 355 broke a rotor inside the pump(very rare). That's where the oil being to thick came from. I also just started running the Lucas oil additive but from what i've seen on here I shouldn't run it due to adding air in the oil????? The 383 pumps where breaking due to items vibrating loose. From what I've been told the 383 is hard to get balanced. I have a new motor builder that's working on that issue now. Not sure on oil temp but fuel pressure is around 4 lbs at idle and 6 lbs at 7000 RPM. I try not to run the 383 over 7000 rpm. How can I locate the closest oil sample facility in my area to get an analysis ran to determine intervals on my changes. I would really like to know exactly how much alcohol is getting in my oil.
 
Terry Dyson of Dyson Analysis is in Greenville, TX. You can order a kit from his website. Turnaround has always been good for me. I don't know how close you are to him. He will also provide a "read" or interpretation of your oil sample.
 
If you were running a straight 50 weight with Lucas then your oilmay be very thick.

Again, a synth or blend 20W50 seems to be the best choice for modified dirt racing using 355's.

It would seem to me that oscillations would break the dist. shaft rather than the rotor.

My experience is that distributor shafts and dist. gears break more often than oil pumps.
 
The later Melling pumps are using powdered metal gears/rotors instead of billet. They have been having problems with the gears breaking, excessive vibration/gear chatter, and pump body breakage problems. Melling lightened the body castings so you have more flex to contend with. Most racers not running drysumps moved to Milodon pumps.

We have had wierdness in the past with pickups and vibration. Extended pickups need to be braced to something besides the pump housing. You can run a brace from the pickup screen to one of the windage tray/main studs to keep the shake down. We had one bright guy who tacked a thick washer to the top of the pickup screen to change the resonant frequency of the tube assm.
 
Originally Posted By: punisher
The later Melling pumps are using powdered metal gears/rotors instead of billet. They have been having problems with the gears breaking, excessive vibration/gear chatter, and pump body breakage problems. Melling lightened the body castings so you have more flex to contend with.
Awesome!
That's really crummy. When did they start doing this?
 
"We had one bright guy who tacked a thick washer to the top of the pickup screen to change the resonant frequency of the tube assm."

Makes sense, since more mass would lower frequency. Anything with a moment arm and mass would tend to shake in sympathy with engine pulses/vibrations.

I think you have three choices, go with a dry sump system, find a pump with forged gears, or go with an electric pump with sump tube/screen tied down at least three places.
 
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