Author Topic: Turbo question  (Read 1041 times)

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Offline ULYCYC

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Re: Turbo question
« Reply #30 on: February 13 2021, 02:59:04 PM »
Missing 100hp or $100 for makeup for a 60yr old women.  Spending it in the kitchen would get better results...
new springs, converter and chips won't find the missing 100hp if basic issues aren't  found and repaired as Steve mentioned
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Offline Shimy87

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Re: Turbo question
« Reply #31 on: February 13 2021, 03:34:03 PM »
I can get a leakdown tester on amazon for $35. I could roll her into the heated shop and check on the items mentioned. No way to run a log for quite a while but I will

Dont i have to pull the intake to check lifters and lobes?

The last run numbers I gave you were with 28 inch tire and it did cross the line between 5400 and 5450. When I had the 26 inch tires it ran the same mph but I can't find any post where I gave the rpm.
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 #32 on: February 13 2021, 03:47:12 PM »
That's about 18% then with 28" tires.  That is way too much, obviously.  Don't know if you converter will hold up to being locked or not, but, we really need that log to see how much it slipped in first and second since the 1/8th was slow mph as well.  Third puts more load on it so I would expect it to slip more in third.  We also don't know what the slip was right after the shift...I would expect more.

Yes, you have to pull the intake but you are a pro at that!
« Last Edit: February 13 2021, 04:02:18 PM by Steve Wood »
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Offline ULYCYC

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Re: Turbo question
« Reply #33 on: February 13 2021, 03:56:24 PM »
Dont  have to pull the intake. Pull off rocker arm assemblies and and check with a dial indicator. Put a pushrod on the shoulder of the lifter and measure total lift of each int and ext. If any are out of wack with the others that's your problem. It could be a lifter, lobe or valve problem. At that point you would have to pull the intake and inspect.
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Offline Steve Wood

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Re: Turbo question
« Reply #34 on: February 13 2021, 04:03:00 PM »
yep
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Offline reality

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Re: Turbo question
« Reply #35 on: February 13 2021, 04:14:38 PM »
I have to ask, how is your TV cable and is it adjusted properly?

Offline Shimy87

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Re: Turbo question
« Reply #36 on: February 13 2021, 04:33:08 PM »
I will get a dial indicator also....really dont want to pull intake....goin g to be pissed if cam has a bad lobe, was very careful with breakin and always used good oil and zinc additive

The tv cable is set correctly..

I dont know how you do the math but what is acceptable converter slip.....and can you mathematically determine what it would be running with an acceptable slippage number?
« Last Edit: February 13 2021, 05:05:58 PM by Shimy87 »
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 Shimy87

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Re: Turbo question
« Reply #37 on: February 13 2021, 06:04:17 PM »
Got out laptop and found an old log I saved of a test on the street before a track day if that shows you anything....problem is I have no idea when this was
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 #38 on: February 13 2021, 06:14:12 PM »
This is a complicated subject.  Would you believe that?

Before I try to get into that, do you know what your rpm is when you sit in the car, put it in drive, foot on the brake of course, and ease down on the gas until the boost gauge is reading zero (point between vacuum and boost)?  I am guessing with that turbo it should be around 2600-2700 rpm.  Again, notice that I am asking for the rpm at zero boost, not the rpm when the turbo is making max boost against the foot brake. :)

Okay, slippage is a bit tricky because it can vary.  What I am calling slippage in the case is the percentage at the finish line.  This is calculated by computing the theoretical rpm required to go (in your case) to go 108 mph as compared to the actual rpm that you saw (say 5425 rpm).

If we have a 28" tire, we can compute circumference which is about 88", and the final gear ratio of the transmission plus the rear diff ratio 3.42, and either mph or rpm we can compute either mph or rpm.

In our case we have both mph and actual rpm so we can calculate, using the mph, what the rpm should be to go that fast and call that theoretical.  Then we can compare that to the rpm we actually recorded to go that fast and figure how much we were slipping compared to the theoretical.

Because I am old and lazy, I did not want to do the calculations on a calculator so I used the wallace racing calculators  http://www.wallaceracing.com/converter-slip.php   and some others from Wallace http://www.wallaceracing.com/calc-gear-tire-rpm-mph.php    
I should have done one by hand to verify the correctness of the Wallace apps but I knew it was in the ballpark from just looking at your numbers.

Now, again, this is the slip at the line, it does not tell us how much it slipped on the shifts where it will often be larger because of the "hit" the converter takes when the load of the next gear hits.  The "tighter" the converter, the more the rpm drops on the shift.  A loose converter will hardly show a rpm drop on the shift whereas a tighter converter may drop 800 rpm or so.  I would say I probably expect 400-700 rpm drop.

Turbo cars are difficult to nail down because the more boost/power you make, the looser the converter will be when looking at it's performance.

Okay, using the first Wallace app above, I calculated the slip to be 17.75% at 5425 rpm, 28" tire (88" circumference), etc..

Now, if I go to the second link, and use the mph calculator, and put in 5425, 28" tire, and no slip, I calculated about 132 mph theoretical top speed.

If I put in 12% slip, I get 118 mph as compared to your actual 108 mph.

If I use the data we think we know and change the slip to 22% instead of the 18% the first app gave me.  Something is a bit off in their calculations but again, I ain't doing it by hand.  There are other apps online that one could use.  It seems obvious that the converter is slipping a ton on top end no matter what.

Now, like I said, we really need to see what it does all the way thru the run, that's why we use Powerlogger to analyze things,.

How much should a converter provide?  How much money can you spend.  Really high dollar ones from ATI or such probably provide maybe five% (is that right, Ed?).  Lock up converters that are not locked might be more like 14-15%?  Lock up converters that are locked should be somwhat less than 10% while they last.  Reasonable priced non lock up converters are maybe 10-12%  I guessing from a foggy memory.

Some lock up converters endure more abuse than cheaper ones.

I think your car, if mechanically sound, should be in the elevens as it sits and it will pick up a few tenths with a better IC.  IF MECHANICALLY SOUND.....

Again, see if you get an opportunity to see what rpm the car is running in drive, foot on the brake, boost gauge  showing zero.






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Offline Steve Wood

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Re: Turbo question
« Reply #39 on: February 13 2021, 06:21:49 PM »
that file showed 97 mph so I guess it was an early one.
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Offline reality

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Re: Turbo question
« Reply #40 on: February 13 2021, 06:30:15 PM »
I think it would be interesting to do the same kind of calculations using the ET to compare.

 picking up 20 mph in the back half and 7.8s in the 1/8.

 Something sure don't add up.

Offline Shimy87

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Re: Turbo question
« Reply #41 on: February 13 2021, 06:52:49 PM »
I read Steve's post several times. My boost gauge doesn't show vacume, just boost. I can do the test and see when the gauge starts to move.

That log was not a full 1/4 mile pull. When I test on the street I only run it up to 100 mph.

From everything guys have posted, if I understand, it's not terrible in the 1/8 but falls apart in the second half of the track. With the slip am I blowing thru the converter in the second half?


The file said saved in 2018 so that a run with 28 inch tires, and pretty much as it sits now, didn't run much last summer so that's a current situation log

On the log how does the rpm look at the shifts?

Sorry if I'm not following you here, trying to understand it
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 #42 on: February 13 2021, 10:12:10 PM »
I don't know anything about that log...what tires, what converter.  Assuming it is a 26 tire and the mph is right on it, it looks like it would be about 5250 rpm at a projected 108.

go ahead and creep upon the boost until you see the needle start to move and see what that rpm is as soon as it moves.

I don't know how anyone knows what shape the engine is in without vacuum info.  I use that as one of my main guide lines :)
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Offline Shimy87

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Re: Turbo question
« Reply #43 on: February 14 2021, 08:43:44 AM »
28 inch tire, test pull on the street to 100 mph, not a full 1/4 mile run, all parts are in my signature.

I will try to do the boost test this week.

Got the gauges before I knew better, story of this car, hahaha
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 #44 on: February 14 2021, 09:34:14 AM »
So do you have the right gear in the transmission to match up with 28" tires????

In other words, when the speedometer reads 97 mph is that for 26" tires or is that 97 mph with 28" tires?  IF you did not change the gear in the transmission, that 97 would be 105 with the taller tire on it.
Steve Wood

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A lot of broken parts does not make you a racer; it makes you a slow learner.