Author Topic: Turbo question  (Read 1040 times)

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Offline Shimy87

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Turbo question
« on: February 10 2021, 03:33:18 PM »
Thinking about "handing down" the turbo in my car ( 5931) to my sons and putting larger one in mine. Questions, dont plan on running more than the 24 lbs I run now, so is boost boost? Is a larger turbo at 24 going to make any more power? This one spools quickly so I assume a larger one might be slower spooling.

Looking for guidance here. I have run my current combo to death and cant get into the 11's  :icon_eyes: and been reading lots of threads and seems a 6262 is a really common choice.
87 GN, K&N cold air, gutted cat, TT 5.7 chip, AFPR, 340 Walbro w/ hotwire, 60 LBS injectors, 981 valve springs, 206/206 Cam, RJC Powerplate, LS1 MAF & translator, Vacuum brakes, Hellwig rear sway bar, Energy suspension poly bushings, Razors Alky, Pypes exhaust, 5931 turbo, CK9.5 converter

Offline nocooler

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Re: Turbo question
« Reply #1 on: February 10 2021, 05:03:39 PM »
Bigger wheel should move more air mass at similar boost levels, unless itís way out in no mans land on the compressor map. 
Iíd think any upgraded turbo should hit 11s - the turbo might not be the issue with the combo if itís not performing like it should. 
IhaveaV8

Offline Steve Wood

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Re: Turbo question
« Reply #2 on: February 10 2021, 05:35:50 PM »
To expand a bit on what Jeremy just posted-

Boost is a bit meaningless but is is somewhat relevant when boost is the only thing in the equation that changes.

Boost is the resistance to flow rather than a measure of flow.  If we put a given turbo on a stock engine with stock ports, cam, etc., as we increase boost the hotter the air temperature will become as it enters the engine.  The hotter the air temp, the less dense the air charge will be.  The less dense it is, the less air molecules there are going into the cylinder.

If we use a turbo with a larger wheel, it will heat the air less and will put more molecules of air into the cylinder for a more dense mixture and the car will make more power at the same boost.

Now, the 6262 seems to be a "magic bullet" when matched with a converter that matches up with it, but, as Jeremy says, the car should be capable of running solidly into the elevens with the existing turbo.  Something is not quite right with the drive train and I don't recall how the mph matches with the rpm, etc. on your runs, etc.
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Offline ULYCYC

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Re: Turbo question
« Reply #3 on: February 10 2021, 06:26:23 PM »
You should be deep into the 11's with your combo, Unless your existing turbo is bad the new one wont make much difference.
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Offline Shimy87

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Re: Turbo question
« Reply #4 on: February 10 2021, 11:12:21 PM »
If memory serves I cross the line at 5300ish at 108ish. I was running a 26 inch drag radial and had 60 ft times in the 1.6 area, went to a 28 inch to try to get it to mph out the back.....60 fts went to 1.8ish and mph stayed the same??? Best run was a 12.2. 24 lbs of boost, no knock and 790ish lowest reading. Any lower and I started to see knock. Maybe it's the converter but Chris said it would be really good for my setup???
87 GN, K&N cold air, gutted cat, TT 5.7 chip, AFPR, 340 Walbro w/ hotwire, 60 LBS injectors, 981 valve springs, 206/206 Cam, RJC Powerplate, LS1 MAF & translator, Vacuum brakes, Hellwig rear sway bar, Energy suspension poly bushings, Razors Alky, Pypes exhaust, 5931 turbo, CK9.5 converter

Offline ULYCYC

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Re: Turbo question
« Reply #5 on: February 11 2021, 07:07:19 AM »
Your 60 ft's need to be 1.60 or better to hit the 11's with your combo. Too many things can cause your issue.  I would start with compression check, bad tune setup, crack header, slow spool due to tune or bad turbo, trans and or converter issues. Get some powerlogger readings to post.
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Offline Shimy87

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Re: Turbo question
« Reply #6 on: February 11 2021, 08:43:59 AM »
Thanks, its -21 here today in WI so wont have pl readings for months. No header cracks, compression is good. It spools quickly and no oil in up pipe. Turbo should be fine. Bought it new, maybe has 5000 miles on it.. car shifts good in normal driving and on track.

I dont know how to confirm good or bad tune. I have Eric's tt chip, I leave timing alone, adjust fuel in each parameter to get lowest af without knock. Dont think there is much more to turning that I can improve but that's why I'm asking.

My original goal was a nice street car that could run 11's, my suspicion is this converter is not a good match to my set up but again, dont know enough to figure it out.

Thanks sgain
87 GN, K&N cold air, gutted cat, TT 5.7 chip, AFPR, 340 Walbro w/ hotwire, 60 LBS injectors, 981 valve springs, 206/206 Cam, RJC Powerplate, LS1 MAF & translator, Vacuum brakes, Hellwig rear sway bar, Energy suspension poly bushings, Razors Alky, Pypes exhaust, 5931 turbo, CK9.5 converter

Offline ULYCYC

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Re: Turbo question
« Reply #7 on: February 11 2021, 09:21:09 AM »
What stall speed is the converter advertised at?  What is you footbrake stall rpm's. But before you blame the converter, the engine has to be running correct.  A weak cylinder won't allow good converter test results.
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Offline Shimy87

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Re: Turbo question
« Reply #8 on: February 11 2021, 10:06:56 AM »
2800 stall. I dont have the numbers anymore but I did have 1 cylinder that was down about 6 lbs from the rest...didnt think that would be significant enough to matter but maybe.
87 GN, K&N cold air, gutted cat, TT 5.7 chip, AFPR, 340 Walbro w/ hotwire, 60 LBS injectors, 981 valve springs, 206/206 Cam, RJC Powerplate, LS1 MAF & translator, Vacuum brakes, Hellwig rear sway bar, Energy suspension poly bushings, Razors Alky, Pypes exhaust, 5931 turbo, CK9.5 converter

Offline Steve Wood

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Re: Turbo question
« Reply #9 on: February 11 2021, 11:09:34 AM »
It really does not add up to me.  If it is capable of 1.6 short times, it should have no problem going into the elevens from what I have seen.

I am a bit surprised that it is not capable of turning 28" tires as easily as it does 26"--certainly not 2 tenths slower.

108 mph is slow for the combo.  I thought maybe the converter was very inefficient but, 5300 rpm is around 11% slip which is not very much for a lock up converter which is not being Locked...Note that I am assuming you are not locking the converter and that 5300 is indeed close to what you were seeing at the top end of third gear crossing the line.

With the 206 cam, I would expect you to be shifting around 5600 rpm and crossing the line about the same (5600)

Without any other evidence to the contrary, I would wonder about how strong the valve springs are after a few miles have been put on them.  Comps have been known to go soft at times.  I would like to see a PL log graph of the acceleration in third gear to see if it slows down notably in third on the top end.

Would not hurt to also look at bottom of the lifters to see if any are "scrubbed".

The older I get, the less crucial tuning seems to be on a car that is in good condition.  Unless something is way out of whack, fine tuning is often less than a tenth difference on these cars.  Yeah, I know that is heresy...

BTW, what IC are you running?  Stock downpipe?
« Last Edit: February 11 2021, 02:24:49 PM by Steve Wood »
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Offline Shimy87

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Re: Turbo question
« Reply #10 on: February 11 2021, 04:37:06 PM »
Found an old post with info from 2017

Car ran ok 12.1 was best. Too many cars showed up so only 4 runs. I think my tire height is holding me back but wanted to ask here. All 4 runs were 107.69 to 107.80 MPH and the times were 12.3, 12.1, 12.3 12.2.  short times were best of 1.6 worst of 1.8.

So question is what is the ideal tire height for the 1/4 mile? I'm crossing the line at 3rd at 54XX RPM

My third run I tried leaving it in OD and as you see, same MPH and time but crossed the line at 47XX RPM. Felt like is shifted with about 100 FT left to the line.

running a 3 inch down pipe and stock intercooler.
87 GN, K&N cold air, gutted cat, TT 5.7 chip, AFPR, 340 Walbro w/ hotwire, 60 LBS injectors, 981 valve springs, 206/206 Cam, RJC Powerplate, LS1 MAF & translator, Vacuum brakes, Hellwig rear sway bar, Energy suspension poly bushings, Razors Alky, Pypes exhaust, 5931 turbo, CK9.5 converter

Offline Steve Wood

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Re: Turbo question
« Reply #11 on: February 11 2021, 05:31:57 PM »
I greatly prefer 28" tires.  They provide more contact patch at launch and increase the mph at a given rpm on top end by about 8%.

I would rather run them, increase first gear timing by two or three degrees and spray a little more alky all the way thru the run.

I still wonder if the valve springs are adequate in third gear to counter the boost at higher rpm.  I have noticed over the years that more and more guys are running about 105 psi springs on the seats.  Brad may have run a bit more with the Pioneer springs he liked.

The stock intercooler is very restrictive and you are probably putting 30 psi of boost into the inlet side to get 24 psi in the plenum.  I suspect that is pretty inefficient at high rpm and the air charge is pretty hot even with alky hence my comment about more alky (more cooling).  Many don't understand that higher rpm's really increase the strain on turbo output.

I greatly prefer stock location intercoolers and a number of people are knocking on the doors of the 8's with stock location units these days.  The problem with them is that most are pretty restrictive on the inlet side which increase pressure drop across the core and the really quick guys are porting heck out of the inlet ala Melissa/Russ Merritt, Rob Ortoski, etc.  Sorry, Rob, I forgot to look up the correct spelling of your name before typing this. Still they are knocking on the 8's with much larger turbos, etc.

Most people have figured out that the intercoolers are simply heat sinks and that not much cooling by airflow happens on a run.  In fact, a couple of people have demonstrated such by plugging the air intake inlet with a towel and running the same times.

I think the aftermarket slic favorite is by far the PTE in spite of the inlet restriction.  Dan (Grumpy) might have additional info on the inlet porting done by Russ/Melissa.

Another question, what was your 1/8th mile speed?
« Last Edit: February 11 2021, 11:13:10 PM by Steve Wood »
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Offline ULYCYC

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Re: Turbo question
« Reply #12 on: February 12 2021, 07:17:58 AM »
A 35yr old stock tired intercooler as Steve mentioned could be half your problem. New one could knock off 4-5 tenths off your et.
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Offline Shimy87

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Re: Turbo question
« Reply #13 on: February 12 2021, 01:06:19 PM »
 I researched and GN1 sells a SLIC for $699, PTE asks $1179. I called PTE and asked whats better about theirs....he looked it up and said looks like they copied us, its probably made in China so thats the difference. I'm all about buy American but almost twice the price, ouch!!

I do have 28 inch M&H racemasters on car now, last track day car still ran 108 around 12.3, but 60 foot sucked at 1.9.....I probably just need to learn how to launch the car with these.

For sure I think I'm going to replace the valve springs, cheap and not that difficult.

Considering IC purchase, maybe I can find a used PTE??

Scoob was convinced the converter is crap and its killing me. I called and talked to Art Carr, after a long conversation he agreed ( not shocking, he sells converters) and strongly recomended a 19930 code O......$899. He said he had same converter in a daily driver and was very streetable, drove it to work every day for years but its parked now. Side note on this CK converter. On the freeway at 65 I turn about 2500RPM, Art said his converter will be closer to 2100 and that would be great.

87 GN, K&N cold air, gutted cat, TT 5.7 chip, AFPR, 340 Walbro w/ hotwire, 60 LBS injectors, 981 valve springs, 206/206 Cam, RJC Powerplate, LS1 MAF & translator, Vacuum brakes, Hellwig rear sway bar, Energy suspension poly bushings, Razors Alky, Pypes exhaust, 5931 turbo, CK9.5 converter

Offline reality

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Re: Turbo question
« Reply #14 on: February 12 2021, 02:13:57 PM »
I third the converter is the problem.
The whole  time slip numbers would help though.
« Last Edit: February 12 2021, 02:18:59 PM by reality »