Two questions

FlyingLow

FlyingLow

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1. In dealing with turbos which is better for response time. To downshift to a lower gear while driving therefore creating a larger vacuum and high RPM's or just leave it in gear with low RPM's and go WOT?

2. What is the best and worst speeds for QC's to do roll racing? Does this change with FI?
 
Wish I could help, but :dontknow: Howya doing Scott :D :rock:
 
I'm tempted to agree with D and say "How's it goin' ", but I'll try to answer.

If the turbos can generate enough boost, keep the RPMs down. A QC is heavy, so low RPM and high boost should fit perfectly.

Sorry, I forgot the question and where I was going with this.:dontknow:
 
I'm doing pretty good these days.

What I'm trying to get at was about roll racing. Seems like it takes a while for the turbo to spool up. So if I downshift I'm at high RPMs but like -20 Vacuum. Once I floor it I have to go from the negative vacuum to positive boost. That takes a little while. I can alleviate that problem if I ride the brake and give it some gas, but that is not really the best option. So I'm basically trying to figure out the best way to roll race.
 
FlyingLow said:
I'm doing pretty good these days.

What I'm trying to get at was about roll racing. Seems like it takes a while for the turbo to spool up. So if I downshift I'm at high RPMs but like -20 Vacuum. Once I floor it I have to go from the negative vacuum to positive boost. That takes a little while. I can alleviate that problem if I ride the brake and give it some gas, but that is not really the best option. So I'm basically trying to figure out the best way to roll race.
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What speed, gear, rpm, etc are you generally roll racing from ? and what rpm does your turbo spool up the best at ? Probably dumb questions, but I drive a stock stick ok :D
 
I think I get where you are going, with a turbo you need to build boost to have it instantaneous, that is why it works good when you apply brake , it puts pressure on the engine thus creating vaccum thus boost.

You're best bet is try dropping a gear , or goin into tow haul mode, not sure on yours, mine builds kinda at around 3500 or so, but if you are around 3000rpms and youare not "coastin" you should have a quicker boost time without much lag.

Really not sure with the STS, you may have to play with it a little, but if you are rolling around 30mph a touch of pressure on the brake will get you to boost quicker, it will just take some finess:D
 
Heres the story on the STS kits from what Ive seen. My friend Joe Donovan has tuned several of these on camaros, vettes, etc. He noticed that they would wander all over the place on power. Being a very good tuner, he tries to get everything back to the same basic temp before the next pull is made, ices the intake, all the fans blowing on the car, etc. I argued that he should hot lap the car, and I guaranteed it would make more power on the dyno, and it did, by over 50HP, and even more under the curve. Heres why: turbos take energy (heat) to spool. This is the reason a little 1.3L rotary can spin up a 88+MM turbo, because of the huge amount of heat created. The turbo is so far back on an STS system that it very quickly losses all its heat, and therefore has alot of lag because it takes a while to build it back up. For roll racing with your truck, you would want the RPM's up high, and brake boosting (holding the brake down and the gas at the same time to build boost) will make a huge difference if done correctly, especially on a huge turbo setup or an STS because of the distance. Brake boosting is not easy on transmissions or brakes, so use caution and common sense, trans temps can rise very fast under a loaded situation like that. Hope this helps,
Justin
 
i've only dealt with turbos on the srt-4 and shelby cars, but i've never seen any turbo setup be on the vac side while applying the gas going down the road. seems it should only be in the vac when you let off the accelerator, but the second your on the gas it should "start" building boost. i'm not sure how you have it set up, but maybe the distance away is why you have so much lag. so what i would do is find a gear/mph combo that atleast lets you start out at 0 vac/boost and try wot from there. that way you arent trying to come from the negative side and your turbo is at the point where it is ready to start making boost when you do go wot.
 
FlyingLow said:
WTF? I know you don't like STS but if your info can help me out then post it up.
Click to expand...

What I had to say Scott was not as much a help, as a warning.

In my opinion using Power Braking, be it while stopped or moving is dangerous with this system. The back pressure caused by this system builds up heat in the engine which causes failures. Hell, any back pressure will cause this. Remember the few members that lost engines due to clogged cats? Well that is what the STS does.

Like I have said, I just hate to see you loose an engine.:(
 
On mine if I punch it the tranny downshifts to a lower gear and the turbo spools instantly. If I was going to race somebody I would downshift manually before because it takes the truck a second to do it on its own.
 
The turbo is turned by exhaust flow. The more exhaust flow you have the faster the turbo turns. Vacuum and boost pressure are controlled by the combination of throttle plate position and turbo speed. If I were racing from a roll I would have the engine turning from 3500 to 4000 rpm. "Spooling up a turbo" is what they call it when you hold the brake and mash the throttle thereby increasing exhaust flow and boost.It eliminates turbo lag when launching from a dead stop. That is where a belt driven supercharger has an advantage, no lag waiting for boost,it is there when you ask for it. Of course you have parasitic H.P. loss with a belt driven supercharger. That is the reason high horsepower diesels have gone to a dual turbo setup. A smaller turbo boost the larger turbo which gives you quicker boost and a cooler intake charge.
 
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