Bracket Racing and Viscosity Index

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RDY4WAR

RDY4WAR

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When it comes to bracket racing, I'm always seeking ways to make the car more consistent and predictable. With the car put away for the winter after a disappointing season, I'm researching ways to improve it for next year. Viscosity index is one thing I'm looking at closely since a higher VI means less viscosity change with temperature which may mean better consistency if the oil temp is slightly off from ideal from one round to the next. If I'm wrong in that theory, please advise.

I'm currently running Amsoil Dominator 5w-20 which has a VI of 158. I'm looking closely at Eneos Racing 0w-20 which has a VI of 239. Is this something worth pursuing or would it just be sisyphean labor? Are there other parameters I should be looking at instead?
 
I drag race myself and can tell you coolant temp is far more important then what oil is going to do for you.
 
Originally Posted by RazorsEdge
I drag race myself and can tell you coolant temp is far more important then what oil is going to do for you.


I seem to be able to control the coolant temp easier than the oil temp. I usually roll into the 2nd beam with the coolant temp at 165*F and oil temp at 140*F. I've had cases when forced to "hot lap" with short turn arounds between rounds where the oil temp is 150-160*F and it has thrown the ET off slightly. (by .02, but enough to break me out after 3 back to back 13.62 runs) The trans temp I can manage to keep at around 180*F. I monitor density altitude, wind speed and direction, ambient temperature, barometric pressure, and humidity carefully and can predict it fairly well. I've had times where I was burned down before and it cost me.

The footbrake class at my local track gets competitive. A few weeks ago, I cut a .008 light and went 13.631 on a 13.62 dial-in and lost.
 
I think at the typical engine operating temperatures, or in that such a small operating window (temp wise), the viscosity delta can't be that significant going from one vi to another. That part of the curve (at or near operating temps) are not that steep so not a huge change in cSt.

maybe any cSt change no matter how small can impact race car performance ... idk!

I think if you are chasing lower cSt that bad, you may stick with very thin oils. But thin oil and racing who knows what's going to happen!
If you are chasing the flatter viscosity cure by going to much higher vi, it doesn't seem like that it would make that much difference (cSt) in those parts of the curve between let's say 0wx20 vs 5wx20.

Ping @Shannow ... he should be able to help. He is the viscosity curve master!
shocked2.gif


Edit:
I noticed you had defined some temp range (150-160) which is much lower than I was expecting or used to.
 
Last edited:
What's it running in ?

The Amsoil has an HTHS of 3.1...HTHS is the viscometric appropriate for bearing surfaces (like pistons and bearings and the like)...the Eneos is 2.7, very much lighter.

HTHS is what is protecting your bearings, and 3.1 for the Amsoil is in the range of a typical 30 (ILSAC) grade.

You'll get more power from the ENEOs (by a couple of hp), and you are right that there'll be less variance.

I can't believe that you can measure the difference in ET between a 5-8C change in oil temperature, and that it's 0.02 sec (don't take it the wrong way, I'm struggling with the consistency of the other processes that you can identify that)

If that's the case, I'd try something first before chasing VI.

If you have that much better control over the coolant temperature, I'd put a thermal blanket over the sump (to keep the heat in), and if that provides more consistency in temperature (no random loss out the sump, the heat has to go through walls and water), then I'd drop the volume by a quart (less mass to control - less windage too maybe).

Last point is why I'm interested in the vehicle and engine.
 
I probably have no clue of what I'm talking about but I would think the HTHS of 3.1 (at 150C) is hurting your ET's at your 140F oil temp.
 
Originally Posted by ka9mnx
I probably have no clue of what I'm talking about but I would think the HTHS of 3.1 (at 150C) is hurting your ET's at your 140F oil temp.


I'd agree...but it's consistency the OP is after.
 
The car is a 1993 Camaro with a completely stock LT1 5.7L V8, 160*F thermostat, and TH350 transmission with a FTI 4000 stall converter. 5 quart oil capacity. It has reverse cooling if that makes any difference. (cools the heads first) I bring the footbrake up to 2200 rpm at the line to launch, it flashes to 4200 rpm off the launch and shifts at 5800 rpm. It crosses the 1/4 mile at 5600 rpm in 3rd.

Total run time from startup to shutoff is less than 2 minutes. I'll idle it a little in the lanes beforehand if the ambient temperature is a bit cold. To keep things consistent, I try to keep coolant temp just off the thermostat at 165*F, the oil temp after the burnout and staging at 140*F, and transmission temp at 180*F. I keep exactly 30 psi air pressure in the front tires so they measure the same rollout breaking the beams pass after pass. I stage it the same way every pass, easing forward until I just break the 2nd beam, come up on the rpm when the first yellow comes on, release the brake on the 3rd yellow, and let the car do the rest from there.

I aim for oil temp staged at 140*F (+/- 1-2*F) to keep it consistent as possible. The oil temp is usually around 170*F after the run. I've never seen it exceed 180*F.

I chose Amsoil Dominator 5w-20 for the high HTHS. (for a 20 grade) It shocks me as well that a 10 degrees difference would make such a difference. There was only a 1 degree difference in ambient temp that afternoon from the previous round, no change in wind, density altitude was still within 10 ft of before, followed the same procedure but got held up by a track official before bumping into the staging beams for about 45 seconds while they investigated possible debris on the track. Meanwhile, I was sitting there idling and watching the oil temps creep up. It's the only variable that was off from the norm. The coolant and trans temp is regulated by the fans. The oil is not. I've considered adding an oil cooler with a fan hooked to a switch that I can kick on in such situations. That or bring the oil temp up closer to coolant temp before staging.
 
I would be running a 195F thermostat (first choice) or one of the 0W-5 racing oils (not first choice). Your starting oil temps are too cool (unofficial view).
 
Why was the season disappointing? I watch the drags a couple times a year and in my opinion drag racing is just plain brutal..
 
It had the 160*F thermostat when I bought it. I just haven't messed with it besides lowering the fan cut on temp. Do you think it would help consistency to go to a higher coolant temp?

The car doesn't see any street use. It's track only, trailered back and forth. I change the oil at the beginning of the season and again halfway through the season (February and July) which ends up being around 50-60 passes.
 
Originally Posted by CT8
Why was the season disappointing? I watch the drags a couple times a year and in my opinion drag racing is just plain brutal..


Broke the original 4L60 transmission back in the spring (replaced it with the TH350) and kept shooting myself in the foot. Made it to the semi-finals 3 times and lost all 3; one because I went -.001 red (made me mad), another when the transmission broke 3rd gear, and the last time when I got burned down at the line and broke out. I also had 3 first round losses.
 
With your dial-in so close to what the car will do, it's a knife edge. I might try bringing up the engine op temp with a 180* T-stat. If that seems better, go up another notch. Do you have a pan blanket? Yes, I'd run an oil cooler you can control.

Next issue, how close are your battery voltages on each run? With fans on and off, unless you are running a really big deep cycle, you will get some variation.

Locked ignition timing, or running advance(s)? I have seen ignitions be slightly inconsistent unless they are really pampered ...
 
You want your engine, consistently, up to operating temps (100c) at each pass to get consistent results. With all his racing and dyno testing Smokey Yunik said the engines performed best and most consistent when at operating temp. The cold engine guys are trying to keep intake air and fuel temps as cold as possible. There are other ways to achieve that goal. The LT1 was designed for a 195F thermostat.
 
I'll put a stock thermostat back in it. With the oil temps being higher, I'll probably step up to a 10w30 oil as well.

Originally Posted by BrocLuno
With your dial-in so close to what the car will do, it's a knife edge. I might try bringing up the engine op temp with a 180* T-stat. If that seems better, go up another notch. Do you have a pan blanket? Yes, I'd run an oil cooler you can control.

Next issue, how close are your battery voltages on each run? With fans on and off, unless you are running a really big deep cycle, you will get some variation.

Locked ignition timing, or running advance(s)? I have seen ignitions be slightly inconsistent unless they are really pampered ...


Yes, I have an engine diaper. I'll probably add an oil cooler.

I ensure all fans are switched off before I bump into the 2nd beams. Voltage stays pretty steady at 14.0-14.2 volts.

OEM spark curve +2 degrees globally.
 
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