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Intake air restriction? 3" vac at WOT, power falls off BAD up top
Have a 12:1 built b20vtec with CNC ported RLZ Head, sk2 pro2’s, etc.
It’s a 68mm TB on a skunk2 pro manifold.
Car peaked 222hp at 7600 and started falling off.
dyno was outdoors, at Bristol dragway, altitude is 1800 ft, but last night the air was acting like were at over 4500ft, was hot and humid.
Noticed it above 7200 it has 2 to 3.2” of vacuum at WOT. Intake pipe is a 3” short ram with 6" velocity Stack. So does that vacuum mean the motor can’t get enough air? Will going to a 70mm TB be enough? Or do I need a skunk2 ultra street and do some light port work, and jump to a billet TB like 74mm?
Re: Intake air restriction? 3" vac at WOT, power falls off BAD up top
3" of draw at higher RPM would indicate some type of inlet restriction. It is possible that the T/B size is partially responsible for this, but there is also something else. Check that the T/B blade is in fact opening fully when the gas pedal is fully depressed. Is the opening in the I/M the same size (or larger) than the T/B ???
Re: Intake air restriction? 3" vac at WOT, power falls off BAD up top
JRCivic1 :
I had the Skunk2 Mani bored to 70mm before i installed the 68mm throttle body, and it does in fact open 100%.
this 2-3" of VAC at WOT has been in my logs for the past year of street tuning (not just on this hot humid evening), only this this weekend on the dyno,did i know it was peaking at 7600, this motor should be peaking much higher, the sk2 pro2's are degree'd to spec as well.
breakdown:
68mm TB, sk2 pro mani, RDX injectors
CNC Ported head from RLZ
Supertech flat valves, springs/retainers
skunk2 Pro 2 cams degree'd to skunk2 spec sheet (cams at (3ex,-1in) 4 degrees separation maintains .047 V2V clearance
11.7:1 84.5MM wisecos on skunk2 rods
B20 block/crank
1320 big tube header, 3in exhaust
Last edited by darrinbrewer; 07-02-2018 at 09:37 AM.
Re: Intake air restriction? 3" vac at WOT, power falls off BAD up top
Alright guys, talked with Luke at 4Piston, he believes it to be a air intake issue as well, pulling 3" of VAC like that under WOT, so I've ordered a CNC Ported Ultra Street Mani, and a skunk2 74mm.
Re: Intake air restriction? 3" vac at WOT, power falls off BAD up top
right now, and in the dyno pull, it was a password JDM 3" short ram with a 6" velocity stack with a new KN filter on that. turned it up toward the sky to get some cooler air on the dyno.
I have 3" aluminum piping and im in the process of building a 3" cold air for it, since the AEM ITR cold air i have wont fit too well with my AC components in the EK.
Re: Intake air restriction? 3" vac at WOT, power falls off BAD up top
Originally Posted by darrinbrewer
right now, and in the dyno pull, it was a password JDM 3" short ram with a 6" velocity stack with a new KN filter on that. turned it up toward the sky to get some cooler air on the dyno.
I have 3" aluminum piping and im in the process of building a 3" cold air for it, since the AEM ITR cold air i have wont fit too well with my AC components in the EK.
The JDM CARBONFIBRE (J's Racing knock-off) "Whale *****?"
Re: Intake air restriction? 3" vac at WOT, power falls off BAD up top
Going back some ten years now, I made 225whp, on my lsv, my buddy made 244whp on his b20v. Same head work, pro2 cams, both of us had 68mm tbodys using 3” Intake and velocity stacks. Cars were tuned by Jeff Evans, he never spoke of intet restriction and they made good power. So if you are indeed having a restriction, your motor is gonna RIP!! And make some really good power!!
Re: Intake air restriction? 3" vac at WOT, power falls off BAD up top
I find it difficult to believe that a 3" tube with a velocity stack/filter on it could make a restriction that would make such a dramatic difference. You should try taking the filter off for a dyno pull, see if it really is the air intake side of things that is choking it.
Re: Intake air restriction? 3" vac at WOT, power falls off BAD up top
QUICK UPDATE
Installed the 74mm TB, and the 4Piston CNC ported Ultra Street.
Been doing some street tuning and logging.
The car richened up in the part throttle map, below 5000 (this mani doesnt really shine down that low) so pulled some fuel, got my part throttle all tuned out.
But up top, from 5000 and above, the car leaned out from a 12.8 to a 13.6, and i had to add a lot more fuel up there, due to this manifold flowing more air.
Vacuum in the higher RPMS dropped form the 3.2" max i was pulling under WOT, to about 2.3" in some spots, but overall it seems to be getting alot more air.
Will have to get back on a dyno and see the difference.
Last edited by darrinbrewer; 07-22-2018 at 09:48 AM.
07-01-2018, 06:33 AM
Intake air restriction? 3" vac at WOT, power falls off BAD up top
