Boost leaks with MAP sensors, and why you should check for them

[jspaeth]

Just thought I might be able to help some people out here, with something I just fixed on my own car.

I had a GT2871R with stock motor for a while, car felt great, but over time, seemed to lose its response just a bit.


About 8 months ago, I installed 264 cams and built the head, and put on a Greddy Intake Manifold....my expectations were that naturally, I would lose some spool up, but see a big increase in top end.

Well, that is exactly what happened. However, when getting tuned, power was VERY slow to come on (full boost around 4300-4400 RPM) and boost was tapering off from 18 psi at 5700 RPM off to around 14 psi at 7500 RPM.


I just figured the boost controller needed to be reconfigured to deal with the additional flow and pressure on the wastegate flapper.....

So over the past few months, I have been running around with the solenoid duty of the boost controller ramped up in the high RPMs, in an attempt to keep boost at 18 psi to redline...


Welllllll (yeah, weak), yesterday, I was giving my car a "look over" and discovered that a hotpipe intercooler coupler had a gash (from rubbing on the chassis) about 2 inches long that I could put my finger right through.


Now, I have had boost leaks before, and usually the car just drives like shit.....but that was on MAF....

With a MAP sensor, as long as the leak is not HUGE, the car will run JUST FINE.

Essentially, I was probably overworking the turbo a bit....it tires to spool to target boost, but some of the air never reaches the intake manifold....


.................................................. ................................................

Anyway, I have since fixed the coupler, and sure as shit, I feel like it's a whole new car! Spool up in any scenario is WAY faster, especially half throttle or 2nd/3rd/4th/5th gear at like 2500-3500 RPM....

4th gear, flooring it from 2500 RPM, I see full boost (18 psi) by 3800 RPM, and I am able to hold full boost out to redline without having to drastically ramp up the boost controller duty at high RPMs.


I dynoed 350 whp and 285 ft-lbs @ 6500 RPM, but then the boost was dropping like a rock after that.

At 7000 RPM, I was at 340 whp, 260 ft-lbs.....however, this was with the boost dropping all the way down to like 14-15 psi.

I figure an extra 4-5 psi at 7000 RPM is good for at LEAST 30-40 ft-lbs.

300 ft-lbs @ 7000 RPM is good for ~400 whp, which is what you would expect out of a GT2871R SR with big cams.



Moral of the story:

ESPECIALLY if you are on a MAP sensor, spend the hour or two to go over all of your couplers in fine detail to make sure nothing is leaking ANYWHERE.


With the size of the gash I found, I am amazed the car even dynoed what it did....

And I ran a 13.1 @ 112 with a SHIT 2.3 60' with a HUGE boost leak hahahahahahaha

[eklips3]

wow , i never thought a gm map sensor would not notice s boost leak of that size .

thanks for the heads up man

[tinys s14]

you can do a leak down test to see if you cooler pipes or coupleers have any small leaks too

[jspaeth]

you can do a leak down test to see if you cooler pipes or coupleers have any small leaks too


True.

Never was able to understand how this works tho....

Care to explain to me? If you pressure everything, won't air just go out the intake or into the motor?

How do you seal things off?

[hobag]

I made a leak tester that went over the intake of the turbo and had a fitting for an air compressor. I filled it to 20psi and used a spray bottle with soapy water over every connection. If you have a leak it will bubble :D

[jspaeth]

I made a leak tester that went over the intake of the turbo and had a fitting for an air compressor. I filled it to 20psi and used a spray bottle with soapy water over every connection. If you have a leak it will bubble :D


Ok and what did you do to prevent the compressed air from coming out of the air filter end?

I understand how it works, but just wonder from a practical standpoint, how people seal the ends.

[slider2828]

Doesn't Everything eventually lead back to the air intake? Cause you want to test your intercooler too... Siliconintakes.com have a fitting for the intake pipe side....

[bb4_96]

You put the tester on the hot pipe where you would hook it up to the compressor outlet. That would let you test all the connections that see boost. turn you motor to close the intake valves. Then pressurize and spay with the soapy. Also check you setup on 5psi over what boost you plan on running to make sure you don't blow any couplers if you boost a little higher than expected.

I'm confused you have a standalone that usies a map sensor? You should check for boost leaks regardless maf or map although on maf system the missing air will be more easily noticed.

Where was it rubbing the chassis at?

[slider2828]

Yeah PowerFC D-Jetro uses a map sensor... so does haltech and AEM... they all can be map sensor... With a map sensor it doesn't directly meter airflow, therefore any air introduced into the system is taken into account... Basically.

[jspaeth]

You put the tester on the hot pipe where you would hook it up to the compressor outlet. That would let you test all the connections that see boost. turn you motor to close the intake valves. Then pressurize and spay with the soapy. Also check you setup on 5psi over what boost you plan on running to make sure you don't blow any couplers if you boost a little higher than expected.

I'm confused you have a standalone that usies a map sensor? You should check for boost leaks regardless maf or map although on maf system the missing air will be more easily noticed.

Where was it rubbing the chassis at?

Was rubbing on the chassis cut-out on the hotpipe side behind the headlight and next to the coolant overflow (S14) where you have to cut the sheet metal....it's a greddy kit.


Ohhhh I see now, okay, so you are pressurizing from the compressor outlet all the way to the head, with the valves shut.

[mattsil80wis]

i know cody and i replace the maf with a connector with a truck tire valve on it that fits into the coupler...we than pressure the system...air doesnt go through the motor cuz the valve in throttle body is closed...(tried to find a pic of it on cody's site but couldnt)...its a great way to find leaks...you could also use a smoke machine, but ive heard good and bad things about this (damage to the motor because of the smoke, but finds leaks you wouldnt normally)....using a water spray over the couplers is good, but doesnt allow you to really see under the coupler (depending on position)...best way to see is to fully take off each coupler and inspect them

speaking of which im gonna have to do this just to make sure everything looks good on my car

ps...nice meeting you on sunday

[jspaeth]

i know cody and i replace the maf with a connector with a truck tire valve on it that fits into the coupler...we than pressure the system...air doesnt go through the motor cuz the valve in throttle body is closed...(tried to find a pic of it on cody's site but couldnt)...its a great way to find leaks...you could also use a smoke machine, but ive heard good and bad things about this (damage to the motor because of the smoke, but finds leaks you wouldnt normally)....using a water spray over the couplers is good, but doesnt allow you to really see under the coupler (depending on position)...best way to see is to fully take off each coupler and inspect them

speaking of which im gonna have to do this just to make sure everything looks good on my car

ps...nice meeting you on sunday

Matt, nice to meet you as well.

I am not sure how this would work tho.....you have air going INTo the turbo at high pressure (okay), so it comes out the turbo outlet (fine) and through the IC to the throttle body.

The throttle body is NOT air tight (can't be right, because with no pedal depression it is still open a BIT, and even still, it is not an AIR-tight seal even if it were closed all the way).

I bet that when you guys did this, you had the crank properly position so that the intake valves were all closed.

This isn't WRONG...you just more out of the check than you think! This shows that your TB gasket and intake manifold gasket are all sealed well, as well as that your valves are seating nicely!

[96Turbo]

That's the cool thing about MAP sensors over MAF. Even if you blow a coupler completely off, you'll be able to drive it just fine (with no boost) to at least get you home/to the shop. You can also run any kind of blow off valve, wherever you want it.

But that also means you gotta be extra careful checking for boost leaks

I'm surprised you didn't hear it. I bet there was quite a bit of air rushing out...

[mattsil80wis]

Matt, nice to meet you as well.

I am not sure how this would work tho.....you have air going INTo the turbo at high pressure (okay), so it comes out the turbo outlet (fine) and through the IC to the throttle body.

The throttle body is NOT air tight (can't be right, because with no pedal depression it is still open a BIT, and even still, it is not an AIR-tight seal even if it were closed all the way).

I bet that when you guys did this, you had the crank properly position so that the intake valves were all closed.

This isn't WRONG...you just more out of the check than you think! This shows that your TB gasket and intake manifold gasket are all sealed well, as well as that your valves are seating nicely!


i know its not air tight but its not going to let a massive amount of air to leak through at a fast rate...it will allow you enough time to find a leak....but than again we do it multiple times to check everywhere

[SHINCHU]

ah thanks man. i am running almost the exact same setup (264 cams with greddy FMIC and t518z turbine) with PFC D-Jetro. when i install my stuff in my new car i will be sur eto line the chassis cutouts with smome door protector.
pretty sure my old japanese s14 had that also. great way to prevent the sliced couplers.

(this stuff Edge Trim™ Flexible Edge Molding - TRIT560SERIES (http://www.autobarn.net/edge-trim.html?site=google_base))