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Converter or clutch needs upgraded.
I’m to lazy to read all the stuff about valve springs or turbos being the object of confession.
Since it is a chassis dyno, this is a possibility. What does the rpm graph look like? Does it blow right through what should be peak hp? How does it drive? What is noteworthy?

The OP is dead set it seems that he has checked all engine possibilities and all of it checks out. If that is the case, it has to be turbo's or drivetrain I'm guessing.
Were there any significant changes to the IAT's between the old and new turbos? Confident that the boost readings are accurate and consistent between the two engines? If the air quality and pressure are similar, there should be no HP difference from the turbo's.
Possible that the dyno is at fault? Again, you ought to be able to feel the difference on a drive.
 

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Discussion Starter #22
Leakdown tested the engine, it's at 5-10%, compression is 160-165(9.2:1 c/r). Checked valve spring pressure, 220 lbs on the seat. As far as changes to the engine, heads have been changed, still have a 225 cc runner, but intake flow went from 246 @.600 to 300 @ 600. Turbos are t4 flange, 67/66 billet wheel. Old turbos were t3 flange, 61 mm. I've heard it brought up that it might have lost velocity through the heads, even though it's laggy and all, it still made boost, so shouldn't it have made better power with better flowing heads?
 

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Discussion Starter #23
Since it is a chassis dyno, this is a possibility. What does the rpm graph look like? Does it blow right through what should be peak hp? How does it drive? What is noteworthy?

The OP is dead set it seems that he has checked all engine possibilities and all of it checks out. If that is the case, it has to be turbo's or drivetrain I'm guessing.
Were there any significant changes to the IAT's between the old and new turbos? Confident that the boost readings are accurate and consistent between the two engines? If the air quality and pressure are similar, there should be no HP difference from the turbo's.
Possible that the dyno is at fault? Again, you ought to be able to feel the difference on a drive.
Took the car to the track, and was a dog. At low boost (6 psi) ran 11.9, old combination at that level would've been mid/low 10's. It feels laggy, and doesn't make explosive power like it used to. Iat on the dyno was 118° this is the holley data log from one of the dyno runs.
IMG_20200202_184643.jpg
 

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Well I think we can agree that something is wrong!
if it isn’t cam timing, I would expect something with the turbos or the tune. Laggy for sure. Did you try throwing more fuel at it? Taking away? You verified no leaks for sure? Maybe the bigger turbos, bigger ports made it more converter sensitive. But I’m stuck on turbos or fuel. Fuel pressure where it should be?
 

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Discussion Starter #26
My tun
Well I think we can agree that something is wrong!
if it isn’t cam timing, I would expect something with the turbos or the tune. Laggy for sure. Did you try throwing more fuel at it? Taking away? You verified no leaks for sure? Maybe the bigger turbos, bigger ports made it more converter sensitive. But I’m stuck on turbos or fuel. Fuel pressure where it should be?
my tuner thinks that the turbos are too big, but they are only 66/67 twins. Viren says that he sells a bunch of them for 5.3's/ls engine, and they light off at 3500. I would think a 383 sbc should be able to use them. I just talked to the dyno operator as well, and said that it's making 14 psi at 5800, so shouldn't the power jump at that point and match at least what I had? He said no, that power on a Dyno just doesn't go up in a straight line, that it's a ramp that builds. But I just don't get how these turbos can work on a 5.3, but not a 383?
 

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Discussion Starter #27
Well I think we can agree that something is wrong!
if it isn’t cam timing, I would expect something with the turbos or the tune. Laggy for sure. Did you try throwing more fuel at it? Taking away? You verified no leaks for sure? Maybe the bigger turbos, bigger ports made it more converter sensitive. But I’m stuck on turbos or fuel. Fuel pressure where it should be?
Fuel pressure is set to 60, and holds it, even data logged it, and it maintains 11.5 on both widebands. Here's the turbos on the car right now.
Screenshot_20200203-111754.png
 

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Might be a little big for instant light off. But it shouldn’t do this. I have been know to say f-it and ignore the plugs and o2 and just throw fuel at it to see what it does. Hell even just turning up the fuel pressure 10-15 psi would tell you if that’s it or not. Maybe even go the other way if it gets worse
 

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Do you know if the head port area changed at all? I know you say they both are 225cc but do you know the cross sectional area and valve sizes? Just curious, i dont think it would be a problem. Atleast not be as bad as what you are seeing now, something seems very off for this to be that drastic of a difference.
Those turbos arent huge by anymeans for a 383 so shouldnt have problem spooling. Larger exhaust side i think the cam could open exhaust earlier with more split on duration but it shouldnt kill the combo
 

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Discussion Starter #32
I talked to brodix, the track 1's were around 221 cc, the Dragonslayers are 225. Supposed to be a similar port configuration. My old turbos (61's) had a .63 ar, and lit off almost immediately, and made 850 rwhp, at 16 psi, but were probably maxed out. These turbos have a .96 ar, and this is a twin application
 

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Was the cam a 4/7 swap? BOV leaking or adjusted too loose (if you have one), wastegate/s leaking?
 

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Discussion Starter #34
Was the cam a 4/7 swap? BOV leaking or adjusted too loose (if you have one), wastegate/s leaking?
I masking taped the wastegate discharge tubes closed, and disconnected the control hoses and drove the car, ran it and accidentally spiked it to 25 psi. Never blew the tape open on the tubes. Cam is a bullet solid roller, standard Firing order. Same cam that was in the car before. And in the video the whole system was pressurized to 10 psi, and only leaks were the throttle shaft bushings. I'm just starting to think that these turbos are too big.
 

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Is the car auto or stick? And when I switched from an 80mm to a 91mm it didn’t make the same power the 80 did at lower boost but once I got into the 20’s it really came alive
 

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Discussion Starter #36
Is the car auto or stick? And when I switched from an 80mm to a 91mm it didn’t make the same power the 80 did at lower boost but once I got into the 20’s it really came alive
It's a 4l80, 3400 stall
 

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Idk what others are making with those turbos but i had a mild 400” sbc with 60/65 master powers, 195 cc head 233 deg hyd roller. Th400. Made 640 on 12.5 psi mustang dyno. Trapped 139 1/4 at 3700 lbs roughly with no boost footbrake leave 1.50’s 60 ft. Went to 70/65 masters and car slowed down, spool was slower. Took 17 psi to go 140 again.

Changed bigged heads cam with the 70/65’s with .96 housings. Made ~700 whp on about 15 ish psi. 790 on 17.5-18 psi. 1009 on 24.5. Trapped 145 3750 lbs with transbrake boosted leave on 15 psi.

I honestly don’t understand how you did 850 with that setup on small t3 61’s. But is what it is lol. The vs racing 67’s i cant imagine being worse than masterpowers but maybe they could be turds and dont flow until they get more boost? I have heard vs 7875’s need boost aka pressure ratio before those wheels really flow mass.
 

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Discussion Starter #38
Idk what others are making with those turbos but i had a mild 400” sbc with 60/65 master powers, 195 cc head 233 deg hyd roller. Th400. Made 640 on 12.5 psi mustang dyno. Trapped 139 1/4 at 3700 lbs roughly with no boost footbrake leave 1.50’s 60 ft. Went to 70/65 masters and car slowed down, spool was slower. Took 17 psi to go 140 again.

Changed bigged heads cam with the 70/65’s with .96 housings. Made ~700 whp on about 15 ish psi. 790 on 17.5-18 psi. 1009 on 24.5. Trapped 145 3750 lbs with transbrake boosted leave on 15 psi.

I honestly don’t understand how you did 850 with that setup on small t3 61’s. But is what it is lol. The vs racing 67’s i cant imagine being worse than masterpowers but maybe they could be turds and dont flow until they get more boost? I have heard vs 7875’s need boost aka pressure ratio before those wheels really flow mass.
Old combination ran 1.4 60, 9.62/147 mph, at 3950.lbs
 

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Discussion Starter #39
A
Idk what others are making with those turbos but i had a mild 400” sbc with 60/65 master powers, 195 cc head 233 deg hyd roller. Th400. Made 640 on 12.5 psi mustang dyno. Trapped 139 1/4 at 3700 lbs roughly with no boost footbrake leave 1.50’s 60 ft. Went to 70/65 masters and car slowed down, spool was slower. Took 17 psi to go 140 again.

Changed bigged heads cam with the 70/65’s with .96 housings. Made ~700 whp on about 15 ish psi. 790 on 17.5-18 psi. 1009 on 24.5. Trapped 145 3750 lbs with transbrake boosted leave on 15 psi.

I honestly don’t understand how you did 850 with that setup on small t3 61’s. But is what it is lol. The vs racing 67’s i cant imagine being worse than masterpowers but maybe they could be turds and dont flow until they get more boost? I have heard vs 7875’s need boost aka pressure ratio before those wheels really flow mass.
And that was footbrake at 16 psi, with the cx racing 61's
 

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Only thing left is the turbos. Will Viren test them for you?
I know a lot of people have good luck with the Ching Chong turbos but I would try the Borg s366 and not look back. If everything else checks out what else could it be?
 
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