Vacuum under WOT?

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Jun 28, 2011 | 02:18 PM

dville_gt

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Vacuum under WOT?

Trying to iron out the bugs and we noticed that during my passes at 100% throttle I am the MAP sensor is showing 91 kPa (should be very close to 100).

I am guessing a lot of this can be attributed to the homemade 3in. pvc intake pipe I built for it so I am going to replace it with a 4 inch aluminum pipe.

Any other reasons that you would show vacuum during WOT? How much h/p would this eat up?

Jun 28, 2011 | 02:51 PM

MeentSS02

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Before you go chasing after the 100 kPa mark, make sure that that's what the ambient conditions actually reflect. I typically see around 96-97 kPa here in Ohio. That said, 91 kPa sounds pretty low, and the first place I'd look is the 3" pipe feeding the engine.

Jun 28, 2011 | 05:06 PM

MontecarloDrag

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Quote:

Originally Posted by dville_gt

The highest MAP value you can see is the atmosferic pressure. Because it's a N/A engine, it can't produce boost, so you will only see vacuum at part throttle and up to atmosferic pressure at wot.

Hook up the scanner and watch the Baro sensor with key open engine not running. That value is the highest MAP you can see at WOT if the engine can breathe freely.

Jun 28, 2011 | 08:02 PM

ShoddyHog

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I had a Volant intake with a MAF...MAP values would drop to 94 kPa. I installed a Svede Speed OTRCAI without a MAF, and now it drops to 97-98.

Jun 29, 2011 | 12:51 PM

redtan

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Quote:

I am guessing a lot of this can be attributed to the homemade 3in. pvc intake pipe

I assume you are not running a 3.8 or so engine? If so that size pipe might be appropriate.

If you are running an LTx/LSx engine then you are chocking the hell out of that engine, so yes a 4" pipe and good filter would alleviate that problem.

Quote:

Any other reasons that you would show vacuum during WOT?

Anything in front of the MAP sensor is what's going to affect the pressure you have in the manifold. From the throttle body forward.

Jun 29, 2011 | 01:13 PM

JonCR96Z

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Yeah it would be nice to know what the engine setup is. If you're running a 408 with an LS1 intake on it it isn't going to matter what size piping that you have because the restriction is going to be the intake in that case.

More details.

Jun 29, 2011 | 05:35 PM

WKMCD

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Not an F-body but my vette would pull down to 91-92 Kpa at full throttle. I went with a 4 inch down tube type setup and now I only loose 1-2 Kpa at WFO. I dont think you can really do much better if you're running an air filter. I had to change the radiator cradle and lay the radiator down to make it work. I also run a 100mm PowrMAF and a 107mm NW TB.