Lotus Elan

Dry Sumped Racing Engine ideal oil pressure

PostPost by: SJ Lambert » Tue May 24, 2011 10:28 am

What oil pressure do you guys look to make in dry sumped racing engines?

By way of benchmark figure - Miles Wilkins reckoned in his T/C book that the Cosworth HC pumps gave 65 pounds hot pressure in wet sumps in engines aimed at track work back in the day.
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PostPost by: rgh0 » Tue May 24, 2011 11:55 am

50 to 60 psi when hot for a 20W50 synthetic is plenty and produces the required flow for any race twin cam with in spec tolerances on bearing clearances. Flow needs to be up about 30% versus the standard pump and this flow requires this sort of pressure.

Flow is whats important not pressure and pressure to get required flow will vary depending on oil visocsity and tmeperature and bearing clearances.

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PostPost by: cabc26b » Tue May 24, 2011 1:49 pm

To Rohan's point the subject of oiling encompasses more than just pressure -

There's a fair amount of work you can do in the passages, jack shafts etc. type of drilling in the cranks is also a factor. In some people's minds there is justification for oiling from the other-side of the block.

On the pressure question , I had this discussion as my engine was going up on the dyno , and it was insisted that we changed over to a high pressure spring ( which on a johnson pump is 60lbs) no matter what manufacture said ( Johnson sail it could run a lot lower) because of my clearances and crank being cross-drilled .

Before the wet-sump motor , I ran a dry sump setup that was a constant 60lbs + hot with mobil1 for years with out issues.

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PostPost by: SJ Lambert » Wed May 25, 2011 10:25 am

Thanks guys.

How about a short stroke 5 bearing 120E block (an iron head screamer) revving to 9000 or even a bit more?

Some guys with their dry sumped T/Cs are saying that they are looking to make 70 or 80 pounds and that 60 or 65 is marginal. Is there a requirement for increased pressure beyond 8000 revs?

It certainly makes sense that it's all about flow - either a bearing is being lubricated or it's not!

Oils and bearings are getting better too aren't they?!!!

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PostPost by: GrUmPyBoDgEr » Wed May 25, 2011 10:58 am

For what it's worth; I ran a 1650cc pre-crossflow fitted with a Lazenby dry sump pump & the hot running pressure was around 65 lbf.
Not a "screamer" of course
Another engine I built was a 1300cc Twincam with a Cosworth dry sump pump & that revved up to 11k in a 23b & from memory also had about 65 lbf hot.
Unfortunately I never got the chance to use it in anger, so cannot confirm that to be the right or wrong pressure, but I guess it would have been OK.

Cross flow or non-cross flow Fords will have lower internal losses than the Twincam which has to lubricate 3 camshafts!

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PostPost by: cabc26b » Wed May 25, 2011 12:24 pm

How about a short stroke 5 bearing 120E block (an iron head screamer) revving to 9000 or even a bit more?


between 60-70lbs on gear drive. non-crossflow , holbay front mounted pump . ISKY cam and mae "high" rocker assembly -

BTW I find is odd that the modern valve gear is breaking over here with regularity . just saw a trashed non crosflow motor that had a cam beak into 3 pieces at 8500 RPM ....
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PostPost by: SJ Lambert » Thu May 26, 2011 10:14 am

Got advice today that 60 to 65 lbs is fine. 70 is ideal. 80 could be headed too high even at 9000 rpm.
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PostPost by: rgh0 » Thu May 26, 2011 11:07 am

70 psi ideal - nice simple answer - but - at what temperature and bearing clearances, oil viscosity and resultant flow rates I would still ask. Pump pressure is the outcome of a complex lubricant flow situation, pressure on its own is not the answer just one dependent variable.

70 psi will not hurt and may be the right outcome but every other element needs to be matched also and you dont actually need 70 psi to get it to work right. I can get 70 psi out of the standard pump on a standard engine with cold thick oil and / or close bearing clearances and putting some washers under the relief spring but your bearings may not last to long in a race situation despite you having the ideal pressure.

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PostPost by: SJ Lambert » Thu May 26, 2011 12:53 pm

I'm as toey as a Roman sandal about it all - machining firm who did the work on the actual crank in question have made those remarks. Their work includes Coventry Climax FPFs, Repco Brabham V8s.

I for one, reckon that there's nothing wrong with 60 psi with engine assembled to correct tolerances - my problem is that I'm a luddite as far as these things are concerned. Dad, who back in the day had a fair bit to do with race motors of this type, is concerned that figures approaching 80 psi are on the high side too - he never had any oiling problems back then - so if his memory is reliable then we're going great guns if we're on Castor Oil!!

I imagine, without knowing, that modern oils may flow better and not need high pressure to acheive flow rates.......

Too high a pressure could presumeably lead to cavitation or other maladies???

I guess that if one was to err, it would be better to err on the high side - bearings are cheaper than motors who's connecting rods have made bold bids for freedom!!!
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PostPost by: rgh0 » Fri May 27, 2011 10:58 am

The major potential problem with going to high apart from greater risk of leaks will be getting to much oil up in the head. If your cam bearing clearances are good you should be ok even at 70 psi or you can put in a restrictor plug in the feed gallery to the head as people do - probably because they run to high oil pressure !!!

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PostPost by: jkolb » Mon Jun 06, 2011 2:01 pm

Johnson Pump Question

I have a Johnson pump (Mick) installed and just had a complete failure of oil pressure on start-up. Jackshaft is intact (engine ran until I shut it down), tank is full of oil, and I had not broken any of the line connections since the previous time the engine had run (7 days previous). Only about 25 minutes of time on the engine, none at high load. Engine is running 20-50 wt Valvoline racing oil and the oil was preheated to 120F.

Any thoughts? I have verified that the gauge is operating and am about to pull the pump which, as you can imagine, is no fun!

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PostPost by: cabc26b » Tue Jun 07, 2011 10:39 pm

Jerry,

I run a Johnson pump on one of my elans - it's configured for "wet sump" though. I assume yours is dry sump B/C
tank is full of oil
. here are my other assumptions , Your other time on the engine is with the Johnson pump, you checked and or installed the medium or high pressure springs you got with the pump at time of installation, you have/had oil pressure when you crank the motor on the starter.

If the above is correct , and this is a guess at this point , check out your scavenge line, I have heard that the Johnson pump can collapse a typical scavenge hose , and that you need to accommodate that contingency in your plumping. I run what amounts to a hard line from my pan to the suction side of the pump by bridging a couple or -10 AN fittings with a section of aeroquip , the unsupported length is less than an inch.

let me know

George
Last edited by cabc26b on Wed Jun 08, 2011 11:55 am, edited 1 time in total.
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PostPost by: StressCraxx » Wed Jun 08, 2011 4:18 am

I have been lurking in the background with the posts on this thread.

I am not racing a Twink, only a humble Kent pushrod motor in a Formula Ford, but its almost the same bottom end, bearings, side mount Titan oil pump and drysump pan. I only spin it to 7K on purpose, sometimes a bit more by enthusiasm or by missed shift.

Oil pressure in my Zink FF and in my road Elan is 35psig at 4K rpm and above with 5w-30 synthetic race oil at 180F. High pressure is not vital. Oil Flow is vital. The oil is as much a coolant as it is a lubricant. The bearings need the presence of oil to work. The rotation of the shaft within the bearing forms a hydrodynamic 'wedge' that supports the shaft in the bearing. The oil flow provides heat transfer medium to remove the heat generated by shear generated by the journal in the bearing. I can get more pressure if I want, but I have the pressure adjusting screw set for 35psig.

Ask your engine builder. 20W-50 oil at 70 PSI, 120F is quite heavy and costs you significant power. Its easy to do a dyno pull with one grade of oil and temperature, then drain and fill with a lighter grade, higher temp and lower pressure. My engine builder found 4 HP just by changing oil to 5w-30 racing synthetic and raising the oil temp from 55 to 95C. If you can increase the scavenge vacuum and improve the scraper, still more power is available from the crankcase by reducing parasitic drag if you have the time and inclination.

My FF Kent motor has over 50 hours of club racing on the bottom end. It will be time for a freshening this winter at 70 hours, mostly due to the pounding of the rings in the piston lands and a freshening of the head. YMMV.

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PostPost by: SJ Lambert » Sun Jun 19, 2011 10:31 am

Thanks for your thoughts Dan (and everyone else). Our twink still has it's original Cosworth side mounted pump and our Holbay "Screamer" 5 bearing pushrod motor has a front mounted Holbay pump. Both are adjustable for pressure. Cosworth one has yet to be opened up for inspection.

I think we've certainly got scope to increase oil temp with the Holbay motor as we can blank oil cooler and even water radiator to increase temps if necesssary. Engine is in a sports racer (no fan). We have not had any high temperature problems to date, if anything, we're still working on getting temps up.

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PostPost by: s4elan » Fri Jun 24, 2011 8:14 pm

My racing twincam runs about 45psi hot with Redline 20x50. I shift at 9k. It is dry sumped with a Pace 5 port pump. I was initially concerned until I watched the flow volume into the sump tank. It moves lots of oil. I also have the restriction plug in the block to head oil passage. Never had any kind of oiling issues and the crank/rods/cam bearing surfaces are still std after 8 years.

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