Tuning the twin turbo

There is so much emphasis on the top HP/TQ numbers. What a ~~~~ show.

Ken, does the car feel as you want it too? If so, sounds like a successful project. You have a one of a kind, beautifully cared for SC. Congratulations.

I think I'm going to troll this place when my SVO project is done and never post dyno numbers.

The tubo setup was to be a fast spooling turbo. I should sneeze and the turbos should start spooling. I went backwards in the power curve. If I cant leave the starting line as fast as a supercharged car than one needs to have an advantage in HP & TQ to run the competition down and win the race. Hence the emphasis on HP & TQ The intention was alway to have a faster car than before. Now having said that I beleive the setup can be improved on but nobody is giving me a direction to begin tinkering with change.

Ken

PS Thanks for the kudos
 
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Well if the bov and wg are working properly, the tune is on, no boost/exhaust leaks etc, I dont think there will be any tweaks that cause a major change, just some fine tuning. This might just be how a rear turbo car is, theres just so much plumbing in both directions. If thats the case and you're unhappy, Ill do anything I can to help you stick those things under the hood.
 
Ken, you are in unchartered territory running rear mount twins on this platform. As long as you are happy with the performance it makes that is all that matters. Imo 450rwhp is very respectful.

Speaking my opinion on it (not that it matters) I would have expected more power at 20+ psi and quicker spool out of this combo. I don't see how it's taking almost 3000rpm to spool 48mm turbos. A few things stand out to me as possible causes. It could be wastegate issues, boost leak (I don't run any type of bov btw), mismatch of turbo wheels, great volume of piping, or maybe just the nature of the beast. I don't think anything is wrong with your converter except maybe on the tight side.

On the street where is the converter flashing to? Once it builds boost does immediately flash the converter or is it taking time to get to the flash stall? I think getting the right converter behind this setup will do you wonders. I think this setup has a lot of potential and it's just a matter of getting everything working together.
 
Well if the bov and wg are working properly, the tune is on, no boost/exhaust leaks etc, I dont think there will be any tweaks that cause a major change, just some fine tuning. This might just be how a rear turbo car is, theres just so much plumbing in both directions. If thats the case and you're unhappy, Ill do anything I can to help you stick those things under the hood.


Great post! This is what it's about.
 
I have been talking to STS turbo, they are going to think it through and offering suggestions, best I can expect. They feel the turbos should spool a lot faster and the power level is low. I am not happy with the performance so I need to work on it and figure it out.

Ken
 
not so here..

Ken, you are in unchartered territory running rear mount twins on this platform. As long as you are happy with the performance it makes that is all that matters. Imo 450rwhp is very respectful.

There was a guy, Sir Walter, I think was his name that had a pair of rear mounts. He was somebody from the other SC group from the St Louis area... Someone from there might be able to add some light to this for you.. Otherwise Ken you still have a great looking car.. I have been staying out of this as I know very little about this kind of a set up. The only thing that I can add is the lag may very well be from all the pipe you need to fill before you get this thing spooled up. This I know from my diesel trucks and that is about all I know.. Just an idea, could there be a blockage of some kind on the pressure side?? Good luck and hope you find the issue and get it to the shoot out.....Rich
 
I skipped over a bunch of stuff so sorry if I repeat something someone else said. Dave's right, it isn't the converter. That will have a percentage difference compared to a stick car, but that this isn't a power level where engines can blow through a converter. There are plenty of 6-7 second quarter mile cars that dyno 900hp and make 1400 crank hp, but that's for completely different reasons that nobody is running into at these power levels. Much too technical and lengthy to get into at the moment, though.

A disadvantage of running a rear-mounted turbo setup is that the length of added pipe increases the amount of time it takes for the hot side to create the pressures necessary for spooling. That negatively effects the boost ramping that Binks mentioned. Your motor spools the turbos pretty well, but if it was a short, underhood setup then as soon as it hits about 8-10psi it would have a steep boost ramp resulting in a quicker full boost event. This is a small issue, though. You need to adjust the converter to take advantage of your boost curve. If you're complaining about spool with an auto car you have the wrong gearing and converter.

Another thing, the most important information we can get is what the turbos are telling us. Turbos are mostly limited to their turbine housing. Excessive exhaust pressure can cause this. You should be targeting exhaust pressure anywhere from 1.25-1.75 times your boost level. It will still make power lower than that range, but spooling will suffer and it indicates your A/R is too large. If it is higher than that range then you have an A/R problem unless it's a large A/R, then you have the most underestimated problem with turbo sizing; the size of the exhaust wheel's exducer (the 66 part of a "6266" turbo for example) is too small for the engine. If the pressure fall in that range and you cannot gain power from increasing boost, the compressors are off of their maps and you need a larger/more efficient compressor side(s).

I would suggest getting a full datalog of your hotside. I don't know if you're logging boost in BE or not, but if you are, I would adapt a line to your hotside to get a datalog of it.
 
Well as I continue to track down the gremlins in the car. I gave a lot of thought to what could be a problem. After a lot of thought and advice from other sources I felt the waste gates were the logical problem. If they were opening and bleeding off pressure that would make for lazy spooling. I decided to take the boost controller off line and run the waste gates on springs only, (21lbers) with a boost reference source. took it for a spin right after the change. Spin being the exact words as the tires cant keep traction. Spooling is almost instant and it feels like someone strapped a rocket to the rear end. Due to rain coming in I had almost no time to play with it. I need to focus on when boost is all in. I was so happy the other day all I could think of was wow. Now I have to focus and get it ready for the shootout. Might have something competive to race after all

Ken
 
Great news Ken!!! Thanks for staying after it and keeping us informed and allowing us to sharing with us and allowing us to share in the highs and lows.
 
Good deal! You could always compare load curves to see the improvement in data terms. The load curve will most of the time reflect tq curve on a dyno also where peak boost comes in. This makes it hard to tell where full spool is when running a non locked converter like we are.
 
took it for a spin right after the change. Spin being the exact words as the tires cant keep traction. Spooling is almost instant and it feels like someone strapped a rocket to the rear end.

Ken

Sounds like your set-up is coming together Ken, good luck on a new personal best at the track................:)
 
Well as I continue to track down the gremlins in the car. I gave a lot of thought to what could be a problem. After a lot of thought and advice from other sources I felt the waste gates were the logical problem. If they were opening and bleeding off pressure that would make for lazy spooling. I decided to take the boost controller off line and run the waste gates on springs only, (21lbers) with a boost reference source. took it for a spin right after the change. Spin being the exact words as the tires cant keep traction. Spooling is almost instant and it feels like someone strapped a rocket to the rear end. Due to rain coming in I had almost no time to play with it. I need to focus on when boost is all in. I was so happy the other day all I could think of was wow. Now I have to focus and get it ready for the shootout. Might have something competive to race after all

Ken

Make sure you bring some spare half shafts.
 
That's got to put a smile on your face!!!!

This morning I ran it up the street a few times. Tried to power brake it. At 2500 rpm tires broke loose so I let off the brake soon after that. Boost comes on real fast and hit 18lbs of boost around 4500. At that point tires were spinning so hard the rear was kicking out and I let out of it. I have not gone past that at the moment as my AFR gauge decided to quit. I am trying to get some time on the dyno to recheck the AFR and see how the numbers have changed. I am running out of time quick. The car is filth dirty and need to be buffed out and waxed. This year is going just to fast. The power is far more violent than the whipple once boost is hit. Will be interesting what it feel like at 6300 rpm. Yes I am smiling now

Ken
 
Ken,

Looking forward to seeing you and the car at the Shootout next month. I'm sure it will look and run great.

David

Will be limited to 18lbs of boost which it is making on the street. The shootout will give me an oppertunity to see how poor it launches or good. I can than decided on how to work on that. Looks like my options are the manual valve body you told me about. A two step setup to launch and of course a working boost controller to dial up the boost. But for now I want to just have some fun having a running car to race and hang out with the crowd. Got to get off my duff and register tonight

Ken
 
I'll be doing my shake down passes at the shootout too Ken so there will be two guys at least more worried about dialing in than winning races lol
 
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