Question on dyno and gas

[TAC]

I'm getting my '87 TT dyno'd next week. It's going to be done on a dyno I don't know much about. They jack the car up, remove the rear wheels and bolt on a water cooled hydraulic pump gizmo. They use hydraulics to control the pressure. It's kind of weird looking but it allows the operator to actually control the engine speed while I keep the throttle at WOT. We are going to be doing quite a lot of pulls and I'm a little worried about the stress on the engine. I've asked for several additional fans to keep things cool and the shop has offered a tank of high-performance gas.

My questions are about this gas. Should I use this gas straight...not mixed with 92 octane? Does the high-po gas cause more stress or does it allow the engine to run cooler? The shop says it will help control heat and detonation. Is this type of gas unleaded? I was thinking maybe a 50-50 split w/regular gas or maybe just use good old 92 octane Chevron. What do you think?

As long as we're on the subject I'm not sure how to tell the shop to safely jack the car. I know there are jacking points along the side of the car but I doubt the shop's jack fits into that slot. I didn't really see any way to jack under the rear end because my Y-pipe with crossover pipe blocks that effectively. Can I have them use a floor jack and put it under the X-brace (it's a convertible) right where the brace attaches to the body? Is that strong enough to be a jacking point?

Any help is appreciated.

TAC

 

[TAC]

A quick follow up question. What's the redline on my engine? What RPM level should I not go past? Thx.

 

[8388]

if your car is still stock, then 91 or 93 pump will be fine. If you still have the cats, leaded fuel will kill them, and cause serious problems. If the gas is unleaded and you want to add some ( a few gallons)to the tank because it's got a higher octane rating then that would be fine. Keeping it cool is the main deal. dynos are actually less stressful than doing the same on the road. I would make sure they have am A/F meter hooked up. that way you can see how rich or lean it is and where. If it's stock anything over 5300 rpms would be a waste of time.

 

[*89x2*]

Don't forget, Leaded fuel will also contaminate the o2 sensor as well, causing a (rough) driveability issue down the road.


I would be most concerned of the intercooler heat over engine heat - fans will take care of the engine but WOW :eek those intercoolers could fry an egg after repeated hard pulls

 

[90Callaway]

What Sam and Chris said is good advise. My car makes more power and does not knock on 93 octane pump gas. And I have an extra point of compression and slightly higher than stock boost. If you can't get 93 you could add 2-3 gallons of 100 octane unleaded race gas... the key being UNLEADED.

Absolutely yes to the A/F ratio with a wide band O2 or you're basically wasting your time. You might be suprised what you find. You want to maintain in the range of 11.5-12 to 1 across the pull. (Someone feel free to correct me if you think that's not optimal.) That is a little "fat" but a good safe ratio for a twin turbo. Anything over about 5000rpms will not yield any meaningful data on a stock TT. 5300 as Sam stated would be max.

It's a little tough trying to get a decent start to a pull on these cars because it's hard to get the turbos spooled at a lower RPM in 4th gear. That's the gear they will use for the pull because it's the 1 to 1 ratio.

Please post your results! Good luck and have fun!

 

[90Callaway]

Oh, and as Chris mentioned... don't touch the intercoolers. Those babies will be smokin' hot! Unfortunately, that kills power.

 

[TAC]

Thanks for all the replies. I have been assured the race gas will be unleaded. I'm looking to put 10 gallons into a half full tank. They have a wideband sensor that will hook into the bung hole in my front y-pipe. We may end up doing a little boost tuning while on the rack. It's been so long since I've turned a wrench on the wastegates...I'm not sure how what does what. If I back out the nuts toward the end of the bolt shank doesn't that tone the boost down? Screwing it in towards the wastegate body ramps it up, correct? Yes, I know to adjust each turbo by the exact same amount. It's pretty smooth right now and I don't want to mess it up.

BTW...anyone ever here of this kind of dyno? It's called a DynaPack. How do the results compare to a Dynajet? On a Dynajet I maxed out at 289 rwhp and 436 lb ft torque @2700, iirc. The first run's the best.

 

[90Callaway]

If you mean a DynOjet that is an inertia dyno. You basically use the rear wheels of the car to accelerate a big heavy drum in the floor. Or sometimes they are platform mounted. The rate at which the car accelerates the mass of the wheel is used to calculate HP and TQ. One of it's flaws is potential wheel spin. Another is no ability to place actual load on the vehicle.

The Dynapack as you mentioned is hub mounted. Therefore, no wheel spin. It also uses hydraulic brakes to load the drivetrain of the car. It could place enough load on the car to actually pull your engine down from redline and stall it.

The Dynapack should be more accurate because it is measuring actual work performed by the engine rather than estimating it with a calculation. I've never used the DynaPack so no first hand experience.

Dynapack USA has a website if you want to research before you go.

 

[SurfnSun]

Like has been said above. Unless you are cranking the boost up, running straight race gas will be a waste of time and will bring your power down. It burns too slowly, run a few gallons as a safety net but thats about it.

Yes, youve got the correct method for adjusting boost.

Kevin, when we finally got my car tuned it was to 11.5:1 all the way across the board. I wouldn't worry too much about wheel spin yet, there are alot of guys making 800+rwtq that haven't spun on the dyno.

FWIW the air temps directly over my motor after a few pulls was guessed to be above 150 degrees! You'll have a nice set of interheaters when youre done pulling. My first pulls were usually the worst even tho the ICs were cool. I have thought about taking a bag or two of ice to wanna cool them down between runs....or maybe a fire extinguisher filled with pure C02. I think rwhp would come up by at least 20.

 

[TAC]

Like has been said above. Unless you are cranking the boost up, running straight race gas will be a waste of time and will bring your power down. It burns too slowly, run a few gallons as a safety net but thats about it.

Yes, youve got the correct method for adjusting boost.

Josh: Thanks for the help. In my case I'm not doing the dyno to check the power level. We're using the race gas to help keep the engine cool and thus out of danger from the dyno pulls. This type of dyno (as pointed out above) actually can put quite a load on the driveline and can actually stall the car. It seems to me this could conceivably be harmful to the engine. Thus we'll be watching AF ratio quite closely.

So, given the above, what ratio of race gas to normal gas should I use to give a good mix of performance vs safety? Sounds like the higher the better since it burns slower, reducing the chance of detonation. Correct?

 

[SurfnSun]

well 2 gallons of 93 + 1 gall of 100 will give you ~ 95 octane...that will be plenty Id guess. when I fill up I usually go 10gal of 93 and then fill er up with 100.

Yes basically the gas burns slower to keep it from igniting before the piston reaches the top of the cylinder.

Why are you dynoing if you're not looking for power numbers? Is the car running bad or anything? just wondering.

 

[8388]

Tac, I don't really think the strain will be more than if the car was actually on the road, unless the operators of the dyno are not up to the task. If you decide to do this have a big fan directly infront on the car, and another aimed towards the intercoolers. After each pull put your hands on the intercooler, if it's too hot for the touch, I would wait for them to cool down before the next. Like I said before, keeping the heat down is the main deal. Also keep an eye on the voltage. Too much heat ruins the alt. Low voltage, if it goes unnoticed can be detrimental to your engine. Low voltage = lean condition due to injectors /fuel pump running under powered.

 

[Aurora40]

Tac, I don't really think the strain will be more than if the car was actually on the road, unless the operators of the dyno are not up to the task.

Just a quick thought, but on the road, if you apply large amounts of force to the driveline, the wheels will typically break loose and thus relieve it, only causing damage to the tires. If this is hub mounted, the driveline will always be taking the brunt of it unless the dyno thing has some threshold setting where it just lets it spin. Just a random thought is all, I know nothing about that particular dyno...

 

[8388]

Dyno pulls are usually short bursts. All I can say is when I'm on the road its much harder on everything, as I'm using all of the gears, not just 4th.

 

[TAC]

well 2 gallons of 93 + 1 gall of 100 will give you ~ 95 octane...that will be plenty Id guess. when I fill up I usually go 10gal of 93 and then fill er up with 100.

Yes basically the gas burns slower to keep it from igniting before the piston reaches the top of the cylinder.

Why are you dynoing if you're not looking for power numbers? Is the car running bad or anything? just wondering.

I can't go into any detail but I can say I am working with a software company in designing a soon to be announced game. After it's announceed I can say more.

These dyno runs will not be typical. The car will be on the dyno and then run at WOT. The dyno operator will induce power to hold the driveline and thus the engine at a fixed RPM level for 30-60 seconds and then we shut down. The idea is to produce the sound of the TT under load at a fixed RPM. I am not really sure how the turbos/microfueler are going to react under those circumstances so I am trying to be very careful. I'm hoping a good high octane fuel will help keep heat down but I don't want to go tooo far so that's why I'm thinking 50/50 with my 92 Chevron. We don't have 93 here.

8388: Good point on the voltage, I will definitely keep my eye on that too. I'll be watching all guages...temp...boost...A/F to make sure nothing's up. If things get too hot or just doesn't "feel" right we'll shut it down. I've seen the drill done with a friend's ZR-1 with no problem but the nuances of the turbos and microfueler have me a little concerned.

I'm not quite sure how instant the "braking effect" is applied by the dyno. It's definitely not that I go WOT and hit redline and then they clamp it on so I drop to 2kRPM or anything like that. They program in the desired RPM range and the dyno ramps up the braking in line with the engine's acceleration and stops it at the desired RPM. They seemed very knowledgeable about the process when I was there last and hope they'll keep me safe.

 

[SurfnSun]

TAC, send them my way if they want some numbers on a wonderbar/exhaust car