2.9 Losing boost...out of ideas - video inside

[badmpg03]

Can’t figure this out - been going on for over a year now see this vid - boost falls 5-6lbs in upper RPMs:
Blower seems fine after I sent it back and Whipple inspected it.

Shop doing my work is top notch and been building/tuning cobras for 20 years.

It’s not belt slip - have had belts on so tight broke pulley’s & 3 alternators

Assuming not the motor - I had the exact same symptoms when I was on stock motor and then again when on the full built motor. I had weak cylinders on stock motor and actually thought boost drop was the motor was letting go...and why I built it to start.

Shop doing the work has been working cobras 20 years, probably built 100 engines. I used best stuff - stock crank - .020 bore - JE pistons/oliver rods 10:1 comp - ported heads / cams, ID 1050x, FORE fuel, crusher inlet..

Shop did a smoke test for leaks - nothing found. Then we monitored bypass valve with a camera under boost - it is working properly

Before we pull the Whipple and put my old KB back on to see what happens....just seeing if you guys have any ideas what else we can check for.

I’m open ears to suggestions please
Thanks for any help

 

[FJohnny]

I'm guessing you have already checked the boost gauge fittings. Have you tried hooking up a different boost gauge? Maybe blowing past a seal in the gauge at high boost and slipping a bit of air. Easier than pulling stuff apart if it can be traced to just a bad fitting or gauge.

PS Great looking car. Definitely not losing boost from having too dirty an engine compartment!

 

[Weather Man]

Does the dyno trace reflect the lost boost?

 

[badmpg03]

I'm guessing you have already checked the boost gauge fittings. Have you tried hooking up a different boost gauge? Maybe blowing past a seal in the gauge at high boost and slipping a bit of air. Easier than pulling stuff apart if it can be traced to just a bad fitting or gauge.

PS Great looking car. Definitely not losing boost from having too dirty an engine compartment!

Thanks for replies should have put that in post. Its not gauge, have tried a couple and car is down on power
Making 660-680 at end of pull like 14 psi or so
Trying for more like 750-800 at 20-21 psi. You can see numbers fall off

 

[MG0h3]

That is odd. Just some background info; what RPM did you start the pull at? My 2.9 standard shoots to 18/19 as soon as I hit WOT and creeps to 20 the last 1500/2k rpm. I won’t really stab it under 2500 though. You almost sounded bogged there. Is it possible there is some kind of restriction in the inlet and as RPMs go up your engine starts sucking the intake dry? Sure you would see a collapsing intake. Throttle blade not opening all the way?


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[badmpg03]

That is odd. Just some background info; what RPM did you start the pull at? My 2.9 standard shoots to 18/19 as soon as I hit WOT and creeps to 20 the last 1500/2k rpm. I won’t really stab it under 2500 though. You almost sounded bogged there. Is it possible there is some kind of restriction in the inlet and as RPMs go up your engine starts sucking the intake dry? Sure you would see a collapsing intake. Throttle blade not opening all the way?


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I had same thoughts and thought it was bad to get into boost hard below 3k...but it is how the tuner does pulls. He is on dyno there

Throttle b sticks open. We have had the Whipple on/off car 3 times, also sent back to Whipple for inspection / new seals. I don’t think there would be anything in there.

I was originally running DW injectors as well. We switched to ID’s and it helped tune idle a lot - although still not perfect. Also was supposed to help tune at higher rpm over DW

 

[MG0h3]

Man that is odd. Whipple says it’s good to go so we’ll go with that.

Either the air is going somewhere or you can’t get enough in. I’ve never even had the blower off my car to see the path but could it be back feeding through the EGR?


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[Bdubbs]

Op I'd assume you've replaced the intercooler o-rings? Thought I've heard those can go bad and create boost loss.

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[MG0h3]

Op I'd assume you've replaced the intercooler o-rings? Thought I've heard those can go bad and create boost loss.

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Thought about that too but he should be blowing coolant out the IC Rez if so. Or creating a leak somewhere I’d think.


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[Bdubbs]

Thought about that too but he should be blowing coolant out the IC Rez if so. Or creating a leak somewhere I’d think.


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Not necessarily. It can pressurize the ic tank. If you take the cap off and notice pressure that's likely where it's going.

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[MG0h3]

Not necessarily. It can pressurize the ic tank. If you take the cap off and notice pressure that's likely where it's going.

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Could be but damn that’s got to be a decent amount of air for the boost to fall off like that.


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[Bdubbs]

Could be but damn that’s got to be a decent amount of air for the boost to fall off like that.


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Yes. Just throwing out ideas. I recall some members on here losing 3-4 psi because of this.

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[01blckcobra]

What valve springs?

 

[01blckcobra]

Have you tried vht or adhesive spray on the belt just to make sure? Seems like belt slip.

 

[Goose17]

I am by no means a tuner and kinda just “thinking out loud here.” When you had the car on the dyno, did you data-log your throttle position as well as commanded air/fuel vs. actual air/fuel? If your fuel delivery is not quite up to snuff, your tune may be closing the throttle a bit as rpms increase if there is a mismatch between commanded air/fuel and actual air/fuel... the tune could be closing the throttle a bit to keep the engine from running super lean. I would expect boost to drop off if that was the case. Again, no tuner here... just taking a guess.

 

[railroad]

I did not read all the replies in detail and not a lot of experience with all performance options, but is it possible on either end of the engine, intake or exhaust is reaching max flow limits. The boost could flash to max boost, but as either end of the air flow maxes out, it reaches its continuous flow limit. Clear as mud, huh.
I guess to test, you need to remove or enlarge the air filter, then the exhaust.

 

[DSG2003Mach1]

I am by no means a tuner and kinda just “thinking out loud here.” When you had the car on the dyno, did you data-log your throttle position as well as commanded air/fuel vs. actual air/fuel? If your fuel delivery is not quite up to snuff, your tune may be closing the throttle a bit as rpms increase if there is a mismatch between commanded air/fuel and actual air/fuel... the tune could be closing the throttle a bit to keep the engine from running super lean. I would expect boost to drop off if that was the case. Again, no tuner here... just taking a guess.

terminators have a cable directly from pedal to TB, the computer cannot intervene

 

[whitedevil95]

I had a friend with the Exact same problem. His throttle body was not opening all the way. Its been a somewhat common problem on the crusher kits for some reason. He chased his tail around for months until he figured it out. Give that a look for sure!

 

[badmpg03]

Op I'd assume you've replaced the intercooler o-rings? Thought I've heard those can go bad and create boost loss.


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Will check on this. Not sure what shape they are in or if have been replaced.

My coolant overflow box is always very hot if that would be any sign.

What valve springs?

Not sure but did Ferrea valves and built the heads, I don’t think it’s springs purely because stock motor had same problems. Will ask though

Have you tried vht or adhesive spray on the belt just to make sure? Seems like belt slip.

I suggested this to tuner just to cover the base I don’t know if he ever did. I have had belt slip on Eaton/KB and this just doesn’t sound like it,too consistent on boost drop and too much, belt has been cranked hard and is in perfect shape after 1000 miles of this, and put on thump billet tensioner. Might bring this back up before we pull blower though

Man that is odd. Whipple says it’s good to go so we’ll go with that.


Either the air is going somewhere or you can’t get enough in. I’ve never even had the blower off my car to see the path but could it be back feeding through the EGR?



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I believe EGR was deleted. That’s what I can’t figure is where all that air is going so consistently

I did not read all the replies in detail and not a lot of experience with all performance options, but is it possible on either end of the engine, intake or exhaust is reaching max flow limits. The boost could flash to max boost, but as either end of the air flow maxes out, it reaches its continuous flow limit. Clear as mud, huh.

I guess to test, you need to remove or enlarge the air filter, then the exhaust.

Running crusher inlet, 5” filter and 1 7/8 ARH headers thinking not intake/ex problem

I had a friend with the Exact same problem. His throttle body was not opening all the way. Its been a somewhat common problem on the crusher kits for some reason. He chased his tail around for months until he figured it out. Give that a look for sure!

Man I don’t know if we have actually pulled filter off and made sure blade is open 100 percent. Will do this, would be funny if it was that simple

Thanks guys for some ideas

 

[Soap]

Man I don’t know if we have actually pulled filter off and made sure blade is open 100 percent. Will do this, would be funny if it was that simple

Don't need to remove filter, just look at the TPS counts on your datalog.

--Joe