HP Cost of KPA Restriction
HP Cost of KPA Restriction When you see a KPA drop in the intake vs ambient at WOT how much is that worth in horsepower?
Let's say 94 KPA dropping from 101 KPA ambient?
Can too small of cylinder heads also cause a vacuum, or is it limited to filter, intake tube, throttle body, and intake itself.
Let's say 94 KPA dropping from 101 KPA ambient?
Can too small of cylinder heads also cause a vacuum, or is it limited to filter, intake tube, throttle body, and intake itself.
TECH Senior Member
Joined: Jun 2016
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From: Central Cal.
If you are showing vacuum in the intake manifold at WOT, the restriction is at the TB or before, like intake plumbing, the MAF, or air filter itself. "Small" heads restrict past the intake manifold, so would not increase pressure drop
Can't it also be insufficient plenum volume?
TECH Senior Member
Joined: Jun 2016
Posts: 22,303
Likes: 3,619
From: Central Cal.
I have seen a kPa drop at high rpm as many have but...on the dyno I removed the intake piping before the throttle body and actually saw a loss. On another setup, I used a ported tbss intake manifold that showed higher kPa map readings than an unported unit, but the unported unit made more rwhp and did better at the track. Sometimes data from sensors isn't everything if it doesn't translate to better acceleration/power gains, kind of like huge flow bench cfm results not actually translating to a power gain in all situations.
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When I still lived in Phoenix, I had 94 kpa with the maf and 97 kpa without the maf, which is why I tell people chasing big power to ditch the maf on a f car. I did not get a direct before and after dyno but it registered on the butt dyno.
And that was a 4" CAI with a 100 mm maf
And that was a 4" CAI with a 100 mm maf
Agreed with Darth. On my 01 SS I was at 96kpa WOT I believe. Ditched the MAF and went straight 4" tube from the SLP lid (lid neck is 4") to the NW92mm TB and that fixed the issue. was at 100kpa for WOT after that. Netted me 9/7 I believe... Went from 451 to 460hp and 413 to 420tq.
This was done on the dyno.... took about 10 minutes to swap.
This was done on the dyno.... took about 10 minutes to swap.
Spanks13, Excellent thread! I've wondered about the same question too.
My 416, 100mm MAF, 104 lid 102 TB, 102 LSXR w / ported runners: At 2500 rpm the MAP was 98 Kpa and dropped to 95-96 at 6200 rpm. Showed 97 Kpa at 6350 rpm.
Would ditching the MAF and gaining ~ 3 KPA usually be worth about ~ 8 whp in most cases?
Do we know if certain specific air filters are better or worse for this?
Doesn't seem like it dropped much.
Is 95-98 Kpa a decent valve for that range of rpm?
My 416, 100mm MAF, 104 lid 102 TB, 102 LSXR w / ported runners: At 2500 rpm the MAP was 98 Kpa and dropped to 95-96 at 6200 rpm. Showed 97 Kpa at 6350 rpm.
Would ditching the MAF and gaining ~ 3 KPA usually be worth about ~ 8 whp in most cases?
Do we know if certain specific air filters are better or worse for this?
Doesn't seem like it dropped much.
Is 95-98 Kpa a decent valve for that range of rpm?
Spanks13, Excellent thread! I've wondered about the same question too.
My 416, 100mm MAF, 104 lid 102 TB, 102 LSXR w / ported runners: At 2500 rpm the MAP was 98 Kpa and dropped to 95-96 at 6200 rpm. Showed 97 Kpa at 6350 rpm.
Would ditching the MAF and gaining ~ 3 KPA usually be worth about ~ 8 whp in most cases?
Do we know if certain specific air filters are better or worse for this?
Doesn't seem like it dropped much.
Is 95-98 Kpa a decent valve for that range of rpm?
My 416, 100mm MAF, 104 lid 102 TB, 102 LSXR w / ported runners: At 2500 rpm the MAP was 98 Kpa and dropped to 95-96 at 6200 rpm. Showed 97 Kpa at 6350 rpm.
Would ditching the MAF and gaining ~ 3 KPA usually be worth about ~ 8 whp in most cases?
Do we know if certain specific air filters are better or worse for this?
Doesn't seem like it dropped much.
Is 95-98 Kpa a decent valve for that range of rpm?
The SD tune definitely felt a bit more snappy though.
What air filter are you running? I ran a K&N and loved it. I'm not sure if Green Filter makes a panel filter for F-Body's but they flow like nobody's business and filter amazingly well.
Yes, the tune is dialed in. I need to plan to revisit the dyno and pull the MAF using the Green filter instead of the current WIX air filter. Definitely going to do that in the spring.
Thank you for the Green prescription Dr. Wigham
Thank you for the Green prescription Dr. Wigham
I think The card filter hurts the F body most. Because that card is right in front of the throttle. Now on something where the maf is further upstream it may not matter as much. On a f car though, you may as well only open the throttle 80%
I'd still run it like that. Clamp down the lid and let her eat 
That was always one of the biggest complaints with the K&N; the lack of sealing from the airbox to the lid. That looks substantially thicker.
That was always one of the biggest complaints with the K&N; the lack of sealing from the airbox to the lid. That looks substantially thicker.
