WOT Tuning

[Tyler Townsley]

Originally Posted by Jerry#397

Tyler,

If I read your reply correctly it seems to me that one could "plug" the bypass line and remove the thermostat?

Thanks,
Jerry

Yes, but.

http://deliquescence.net/~tyler/misc/zr1waterflow.jpg

As I said earlier Lane tried this on his 90 at one point and found the water did not cool because it flows through the radiator too quickly to cool the water.

A little more discussion. Lotus speced the LT 5 pump at 25 gpm flow per 1000 rpm. The stock radiator was not reliable over about 100+_ gpm so the bypass was developed to avoid having to source another radiator. GM felt most owners would not operate the motor over 5500 rpm for any length of time so there would not be threat to any long term operations.

Once you start competing with the car you find you spend a lot of time over 5k which will stress the cooling system but the above must be taken in consideration when makeing any changes.

Tyler

[Jerry#397]

Tyler,

Talked with Randy Woods today about his thermostats and the testing that he has done, VERY interesting. I purchased a 165F heavy duty thermostat from him. He stated that he recommends the 165F as it is the best of both worlds (160F vs 170F) and that the 165F heavy duty is built to his specs after much testing; it begins to open at 165F and is fully open at 180F. He went on to say that his fans are set to "both" kick on at 190F and shut off at 180F.

We talked about the "bypass" and he validated what you and Fast Lane had said about keeping some water flow thru the bypass.

Hopefully he will post some of his testing results.

Again want to thank you for sharing all the "nuggets" of info on the cooling system and the oil cooling system.

Jerry

[tomtom72]

Tyler, I would like to add my thanks also for your sharing the light about the cooling systems, both water & oil.

At 25 gpm flow/1k rpms, would that be a constant multiplier? So that at 7k rpms the flow is 175 gpm?......in theory only, minus the reducing effects of pump cavitation on flow. I guess what I'm trying to figure out is what to ask of an aftermarket radiator mfg'er with reguards to burst pressure of the tanks and the core tubes. I've seen in the past that aftermarket radiators have suffered ruptured core tubes when T-stats were miss boxed.

Also, I'm sure that I'm not seeing the answer to this next Q in the system diagram, but what about flow to the heater core? Is that part not subject to seeing the same flow & pressure as the radiator?

TIA

Tom

[Tyler Townsley]

One thing to remember is that pump 'pulls' water in at the same speed it pumps it out so just what pressure the heater system sees may be different than what we expect. I once knew the name of the engineer who designed the system but time has put too many other things in and I cannot get it out. LOL Lotus spected the pump to put out 25 gpm at 1000 and 100+- gpm at 4k. To my knowledge I have not heard any Grant radiators failing and I talked to Dewit when he was developing his replacement radiator and was under the impression it was capable of ZR-1 water flows but you might call and ask him. I am using a fluidine as Hib H worked with them to make sure they understood the demands placed on the unit and Dewit did not have a replacement unit at the time.

Tyler

[tomtom72]

Tyler, thank you very much for sharing your info with us!

I apologize to Mr. XFire for doing a hi-jack job on your thread.
It's just that this whole cooling system issue is making me think twice about what wisdom GM brought to the table.......most Z owners certianly do exceede 5k rpms with their cars I would think.....or at least I know I do when I'm doing the twisties with mine....again I apologize for the hi-jack.


Tom

[XfireZ51]

Originally Posted by tomtom72

Tyler, thank you very much for sharing your info with us!

I apologize to Mr. XFire for doing a hi-jack job on your thread.
It's just that this whole cooling system issue is making me think twice about what wisdom GM brought to the table.......most Z owners certianly do exceede 5k rpms with their cars I would think.....or at least I know I do when I'm doing the twisties with mine....again I apologize for the hi-jack.


Tom

Tom,
No worries. if this thread has coaxed some nuggets from Tyler, then its worth it.
In the meantime, I've installed my WB O2 in the car but now the weather isn't cooperating. I'd like to compare what my WB says to the one at the dyno.

[mrand]

Originally Posted by tomtom72

It's just that this whole cooling system issue is making me think twice about what wisdom GM brought to the table.......most Z owners certianly do exceede 5k rpms with their cars I would think.....or at least I know I do when I'm doing the twisties with mine....again I apologize for the hi-jack.

Howdy Tom,

Note that Tyler said "GM felt most owners would not operate the motor over 5500 rpm for any length of time so there would not be threat to any long term operations." I think this statement is correct. GM sold these as street cars, and high speed blasts on the highway or deserted roads certainly isn't a problem. Drag racing isn't a problem. Even SCCA racing with them isn't a problem. Only the few owners that take their ZR-1's to a high speed road course and manage to sustain high RPM operation would see this problem.

Engineering is about lowest cost for your target market, and I'm sure that sustained high speed road course operation wasn't in the design goals.

Have fun,

Marc

[Paul Workman]

Originally Posted by Tyler Townsley

Lane Goldstein (Fastlane) used a switch in the cockpit to turn on his fans with engine off to cool down his motor between runs. You can do the same thing by turning off the motor but leave the ignition on and turning on the A/C both fans should come on.

Tyler

Fascinating thread! Whenever this topic comes up (not just with LT5s exclusively) it occurs to me that unless one also had an electric water pump, there wouldn't be much (or any) significant water circulation thru the radiator when the engine was not running. So, running the fans would only cool that slug of water in the radiator, and except possibly for miniscule(?) flow due to convection currents (cold sinking, hot rising, etc), there would be little cooling of the engine itself, no? And, once the temp of the thermostat was reached, even convection current would be cut off when it closes.

Just thinking out loud here -- I suppose with continued cooling, the slug in the radiator could eventually sink to ambient temp, so when the engine is re-fired, there would be a sudden overall temp drop as the cool slug from the radiator is mixed with the water that remained in the engine's water jacket; how much the temp would drop would depend on the temp differentials (radiator vs. block) and the proportions of hot and "cold" water being mixed.

Ignorance is bliss, or in my case, makes me dubious; re cooling fans significantly cooling the engine at shut-down, especially w/o an electric water pump. But, then again...I could be "all wet". If time is of the essence, every little bit (of cooling) helps, I suppose.

I think I'm saying that unless there is a water pump involved, running the fans is not going to be nearly very effective in a short time. In the absence of an electric pump, I suppose the engine could be fired for a few seconds to force an new slug of (hot) water from the jacket into the radiator, thus expediting the cooling. (Kinda makes one ponder getting an electric water pump, huh?)

P.

[tomtom72]

Mr. XFire thanks! Good luck with your new diagnostic/research equipment! I will look forward to your findings, which I hope you share with us!


Marc, I guess I should have phrased "doubting the wisdom that GM brought..."
in a different way. I wasn't trying to be insulting to GM, et al.
........But I'm guilty as charged with the 5k rpm thing....I guess I get carried away with corners all strung together. I know I can "see" the spike in temps after awhile, water goes up and then the oil starts to climb if you're too high in the rpm band for too long. I notice it if I'm using 2nd & 3rd more than 3rd & 4th for more than 15 mins..... you keep bumping up against that 'circulation/by-pass limit'. I know the easy answer.... don't do it at all. It just seems to me that it's such a waste to have all that "room" on the tach, a balanced forged crank & rods, and No Push Rods!.....and not being allowed to use it.......for very long periods of time....it's just not fair!


Tom

[mrand]

Originally Posted by tomtom72

Mr. XFire thanks! Good luck with your new diagnostic/research equipment! I will look forward to your findings, which I hope you share with us!


Marc, I guess I should have phrased "doubting the wisdom that GM brought..."
in a different way. I wasn't trying to be insulting to GM, et al.
........But I'm guilty as charged with the 5k rpm thing....I guess I get carried away with corners all strung together. I know I can "see" the spike in temps after awhile, water goes up and then the oil starts to climb if you're too high in the rpm band for too long. I notice it if I'm using 2nd & 3rd more than 3rd & 4th for more than 15 mins..... you keep bumping up against that 'circulation/by-pass limit'. I know the easy answer.... don't do it at all. It just seems to me that it's such a waste to have all that "room" on the tach, a balanced forged crank & rods, and No Push Rods!.....and not being allowed to use it.......for very long periods of time....it's just not fair!

Howdy Tom,

Certainly not going to disagree with you. I've seen the temps climb several times as well on the track. It sure would have been nice if they'd put more money and effort into the cooling!

Marc