Boost Drop at High RPM

[robvas]

755 on pump sounds abnormal

They say in the article it made 423 without the blower, so maybe the dyno was a little happy, or the car was a bit of a ringer, STD vs SAE.... They also spun it out to 8k where the graph you posted stops at 7k

680...maybe that dyno reads low? Regardless the boost shouldn't fall off like that, if you look at almost every other whipple graph.

Here's a Wengerd tuned Whipple that made 735 on 93

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[Autopart101]

They say in the article it made 423 without the blower, so maybe the dyno was a little happy, or the car was a bit of a ringer, STD vs SAE.... They also spun it out to 8k where the graph you posted stops at 7k

680...maybe that dyno reads low? Regardless the boost shouldn't fall off like that, if you look at almost every other whipple graph.

Here's a Wengerd tuned Whipple that made 735 on 93

Maybe the dyno reads low. It's Beefcakes Dyno. The video shows 714 once SAE is applied.

 

[Autopart101]

This pull was 775@7500rpm. The IAT2s never got over 138. Not sure what the boost reading is. Looks like almost 21 degrees of timing never pulled up top. I can not attach the file.

 

[Angrey]

If there's a restriction on the uptake side (either the intake tube or the TB) it will eventually show up as the blower being less efficient at drawing enough air in to compress or pump to get a pressure buildup in front of the cylinders.

I have probably one of the highest flowing setups around (ported GT350 heads, 2" long tube primaries and a 150 mm TB/Tube) and my dyno pulls are an initial jump to 16 psi, then it gradually creeps to 19 psi by about 5k rpms and then holds steady and never "catches" the motor to create more all the way through 8500 rpm.

If the blower is getting significant fluid friction at higher flows to draw the necessary volume/flow of air, it might show itself as a slight drop in boost pressure.

It could also be belt slip (or both) but given the OP's setup, that's unlikely. It's probably just the restriction that's not allowing it to keep pace with the increasing flow of the motor as it revs on the top end.

I'm betting if you were to open up the uptake side you'd see that dip either improve or go away.

Also keep in mind that boost pressure is a counter-intuitive thing sometimes. You need air to back up (restriction) in order to create boost, so just because it's making more boost doesn't mean it's necessarily an improvement in flow.

Two cars, one that flows very well and one that doesn't, can make similar power but the better flowing motor is less boost pressure (simply because it's moving volume better and doesn't need the same density to match the total flow). That's mainly on the blow side (heads through to the exhaust). If you're getting restrictions on the uptake, the blower is struggling to suck enough air through a straw to keep up. (or to be more precise, it isn't able to create enough pressure drop for the ambient air to push through to balance the pressure).

Sometimes you can make more power on less boost if improve the blow side flow.

 

[engineermike]

Just FYI, this is how Roush limits boost with charge temp:

I think they run around 1.6 load stock, depending on ambient air density, so it would start limiting throttle above 155-160 deg charge temp.

Roush starts pulling borderline timing at 122 deg charge temp:

This number is multiplied by another as a function of engine load, generally time .15 so at 151 deg it's pulling about 9 deg timing. Keep in mind this assumes you aren't riding the knock sensors. I don't know about the Mustang but the F150 Roush was tuned to not ride the knock sensors.

 

[Autopart101]

If I'm reading vcm scanner correctly. My 2.7 pulley was seeing MAP at 28.9 psi at 7500rpm. I also have a dyno pull with the stock pulley. 3.0 pulley was 2-2.5 psi less the entire pull.

 

[Pistol_91]

138 degrees IATs are wild.

 

[Autopart101]

138 degrees IATs are wild.

That's why I now have an Interchiller.

 

[engineermike]

138 degrees IATs are wild.

Yes and the weird thing about Roush is that they’ll run 140+ cruising down the road never even in boost!

 

[Autopart101]

Yes and the weird thing about Roush is that they’ll run 140+ cruising down the road never even in boost!
[/QUOTE

Yes and the weird thing about Roush is that they’ll run 140+ cruising down the road never even in boost!

 

[Pistol_91]

Yes and the weird thing about Roush is that they’ll run 140+ cruising down the road never even in boost!

I knew they get hot but didn't realize how hot they run on a normal day. It's insane. Imagine how much power they'd actually make with cooler air. In Florida, I would never run a PD blower just because of temps.

 

[Autopart101]

I knew they get hot but didn't realize how hot they run on a normal day. It's insane. Imagine how much power they'd actually make with cooler air. In Florida, I would never run a PD blower just because of temps.

With the interchiller installed. It runs 87 degrees in the summer. I picked up .25 60-130 with just the interchiller. If I could do this all over. I would go with a centrifugal blower.

 

[engineermike]

I honestly think with a bigger tb and e85, the Roush will make the same power as all the other blowers until you’re limited by pulley size.

 

[Autopart101]

I honestly think with a bigger tb and e85, the Roush will make the same power as all the other blowers until you’re limited by pulley size.

Are the Roush 2650s geared differently than other 2650s? I also can't find a rear overdrive balancer. I did see one that was 5% over stock coyote. I think the Roush is already overdriven at 7 inches.

 

[hlfbkd420]

Yes and the weird thing about Roush is that they’ll run 140+ cruising down the road never even in boost!

I can look at my car some days and she warms up.

Honestly though, I can start the car after sitting all day in the summer sun and it's already heat-soaked. Covered parking doesn't help much either.

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