Checking your engine performance on a chassis dyno?

[Jerry Clayton]

OK Mark, I see that thats a dynojet---I also see that it was above 16-1 afr---He was probably checking the oil pressure while the engine was running super lean---

[tnewland]

STL Mark
Thank you for posting the graph, I will try and post one of the printouts when I get home tonight.

[tnewland]

Here is a printout of the final pull on the dyno. As per the particulars of the engine it had an original GT 40 steel race crank, carillo rods, arias pistons, HV (blue printed) oil pump with a high capacity aviad oil pan, stock dual point ignition, roller valve train and weber carbs, heavily modified stock iron heads and an iron block.

[eschaider]

tnewland,

I tend to come down on Jerry's side of this argument. The dyno operator is operating the dyno that your car is running on. His job is to use the tool correctly and that requires his attention.

A 6500 rpm pull for a 289 is a walk in the park unless your internals are not up to it - and then you shouldn't be at the dyno! I think you would have to work very hard to make them that weak. What I mean by internals not being 'up to it' is like Jerry said OEM rods, or small capacity oil pan with a high capacity pump etc. Even OEM rods are amazingly good. I remember during the 60's more than a few of our friends 289's that consistently shifted with ease and repeatability at 7500+ rpm with "OEM" rods.

I think your component failure problem is attributable to the lean period when the engine went above a 16:1 AFR and probably an oiling shortcoming attributable to parts selection or assembly during the build phase. A !6:1 AFR under load is damagingly lean. At the very least it will detonate (which kills rod bearings) and with only a little luck you can burn a piston if you are persistent.

Like someone else said previously, you don't need a dyno pull to diagnose a distributor whoops. You can do that on a distributor machine without even starting the car. Another observation is that when you go to the dyno to do a pull, 150 mph is a walk in the park or a 3 inch stroke engine - so is 7000 or so rpm. Even more significant is the fact that the MPH is not a real consideration. What you are trying to do is cycle your engine through its entire operating range, in high gear, to begin the process of optimizing your tune (assuming you're not there for bragging rights). Wherever the MPH goes it goes! Frankly I don't believe I have seen a dyno that would not accommodate 200 MPH but again the real issue is exercising the engine through the entire operating range in high gear to begin the optimization of the tune.

If I were you I would begin trying to figure out how I got to a 16:1 AFR and fix that problem first so it doesn't happen again. With respect to the crank it is most probably repairable. If not then a modern day replacement is readily obtainable from FRPP. If you are one of those guys who like near bullet proof strength in their pieces have one of the crank grinders cut you a billet shaft.

As a general rule of thumb you do not want to use vintage components with high valuations that are difficult to replace. They are valuable museum pieces today that remind us of how it was during those halcyon years of the 60's when all this magic came into being. They should be on display as historical artifacts to be looked at but not operated.

Just my $.02 - well maybe $.15 (extra words)

Ed

[eschaider]

Just looked at your dyno sheet. Nice shape and numbers. The wiggling at the top of the pull that is bothering you is nothing significant. It could be spark blowout because it wants a little more electrical oomph at the plug in that power range. There are any number of "incidental issues" that could produce that wiggling. The really important question for you about that is, how much time do you spend driving you cobra in that RPM range? That, is what will determine how important the fix is.

On the other hand I'll bet you spend a lot of time driving your Cobra in the range that you have a 16:1 AFR. This is a problem - that need fixing!


Ed

[Jerry Clayton]

Ed---the 16-1 was on StLMark deal

Tnewland---whats the blank square at the top of the graph?? is it something that just didn't come thru on the scan??

With your crank--was it by any chance undersized seeing as how old it was???and what bearings did you have and oil pan????

[eschaider]

Duplicate message deleted by author

[eschaider]

You're right Jerry. My bad.

tnewland, I would begin looking for an oiling system problem.

Ed

[tnewland]

I added that I have an aviad high capacity oil pan with the propper pick-up. The crank was standard on the mains and .020 on the rods (i am not sure what bearings the builder used). The blanked out part on the upper left is the dyno operators business information. Oil presure before the dyno run had always been 80-90psi at idle cold and 23psi when warm, driving was around 70psi. As far as using vintage parts go, unlike some of the people tathave these cars I like to have the driving sensation as close to what the real cars represented rather than the modern incarnations of today. This was the whole idea of keeping the RPM level within a SAFE area of operation and not causing undo stress to the drivetrain.

[Jerry Clayton]

.020 on the rods? there aren't many of the high quality bearings in the .020 undersize-

thats a lot of pressure drop from cold to hot on the oil--I assume probably that you don't have a cooler? and or you are using light viscosity oil?

I don't see any a/f ratios on your graph and also noted that the devisions of the graph are pretty weird---they evidently have hp graphed from 0-650 to come up with those divisions-makes it hard to tell hp/tq at a glance compared to a graph that is divisable by 10---example 0-500 --each line would be 50 hp instead of 65 and you could tell where you were--well that isn't relavent in your case but I try to always get the dyno operators to scale the graph so that it not only is easy to read, but they have a consistant look between cars and tests

I'm leaving at 5 am tomorrow for the London Cobra show but am ancious to get back Sunday to see more on this

[tnewland]

I have an oil cooler with a 180 degree thermostat. The engine builder recommended 20/50 viscosity oil. The A/F ratio at 7300 RPM on one pull was 12.6 and on the second pull at 7500 RPM was 13.0, lean! The A/F at 6500 RPM was 13.2 and 13.2 during both pulls, so the engine was running lean during both full pulls with a max A/F of 13.9 at 5100 RPM during both pulls.

[STL Mark]

I wonder why they would do full pulls with lean conditions.

Also, the chart looks a little ragged at 6500 RPM - but its a little hard to tell.

[tnewland]

STL Mark
I agree, specially when the operator is supposed to be watching for irregularities!

[tnewland]

Here is a photo of the A/F, HP and TQ printout from the second pull:

[eschaider]

Originally Posted by tnewland

I have an oil cooler with a 180 degree thermostat. The engine builder recommended 20/50 viscosity oil. The A/F ratio at 7300 RPM on one pull was 12.6 and on the second pull at 7500 RPM was 13.0, lean! The A/F at 6500 RPM was 13.2 and 13.2 during both pulls, so the engine was running lean during both full pulls with a max A/F of 13.9 at 5100 RPM during both pulls.

Your engine had a relatively broad rpm range that it exhibited the mid to high 12.x to 13.x:1 AFR over. You have a legitimate complaint with your dyno operator. He shoud be monitoring the AFR during the pull and be prepared to abort the pull if the AFR numbers go the wrong way. To do a second pull without correcting the AFR problem is difficult to understand.

A 13.x:1 AFR is not good for your engine. I don't know how to reasonably set your expectations for potential damage. My expectations for damage at a 13.x:1 AFR would suggest the damage would be proportional to the duration of time under load at that AFR and how often you did it. Repeated abuse (detonation) could eventually get a rod bearing. Occasional occurrences would probably limit the damage to the rings and potentially the leanest pistons.

Your oil system sounds like it should be adequate. Having said that, it is always worth the effort, after one of these failures, to take a careful second look to make sure all the "stuff" is assembled correctly and in working order. I know this next comment sounds dumb but don't forget to be sure the engine had/has enough oil in the pan for the modified, increased capacity oil system.

Ed

p.s. An afterthought: As some others have already observed, your oil pressure appears to have some fairly large swings from hot to cold. While cold engines normally have high oil pressure, engines at operating temperature do not typically loose as much pressure as yours does. Sometimes when you see these types of swings in oil pressure the engine is telling you it has a hurt rod bearing (or very large oil clearances). There is the possibility the insert was already toast when you got to the dyno. A potentially bad insert not withstanding the two pulls at better than 13:1 AFR did nothing to help.

[DAVID GAGNARD]

Oil presure before the dyno run had always been 80-90psi at idle cold and 23psi when warm, driving was around 70psi

I think that you cold idle oil pressure is way to high at 80/90 ps...you'll see most engines of similar components is the 35 to 45 cold psi range........

hot oil pressure at 23 psi is o-k,at high rpms, 70 psi is what i would consider the max, anything from 50 to 60 would just fine......

Also, way too much differential between the cold/hot readings, as someone already said, you may have already had bearing problems.......

to compare, my 331 race engine running 15/50 Mobil 1, cold idle,just a tad under 40 psi, hot idle, just a tad over 30 psi, at anything above 2000 rpms, from 50 to 60 psi max........7000 rpm chip in the MSD box......

David

[tnewland]

I believe the rule of thumb for oil presure is 10 psi for every 1000 RPM at operating tempeature. As previously stated the engine builder recommended a high grade 20/50 conventional motor oil.