<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nowtype &raquo;</TD></TR><TR><TD CLASS="quote">

No. Look at sport bike engines. Many have over 100% VE. I'm fairly sure our 20mm 600cc restricted engine on our FSAE car has over 100%. You can get over 100% VE without a compressor. It requires compression in the intake manifold, but you don't need a compressor to do such a thing. Talking to the head of our engine team its about intake manifold pulse tuning. As the valves shut it it pressurizes the intake manifold a small amount and there is your "compressor". Again, over 100% VE is possible on a naturally asperated engine. I'll have more data in a few months as things move along.</TD></TR></TABLE>

Indeed it is possible.. It is all about the reflection of the pressure wave hitting the valve then reflecting from pressure differences or hitting the intake plenum and reflecting back, you want the wave to come back to the valve in perfect timing when the valve opens again, = boost of air, boost, whatever.. can cause over 100% VE.

 

Most street motors run anywhere around 65-70%, performance motors run around 100%, Nascar runs 115%, drag 120-125%. Cosworth actually has a bike that runs at 145%

Just to give you an idea of how much air is actually drawn in from pressure differential....I've flown heads on the flow bench before....walked all the way across the room a good 15-20ft away. While the machine was running I just barely tapped the tip on a can of black spray paint for two seconds and had a guy turn the machine off one or two seconds later. The port had black streaks inside....totally blew my mind

 

So, the D series motor in question (with a stock head, intake and exhaust) would most likely have no boost and if a manifold pressure guage were used - it would show negative pressure @ 7,000 rpm/rbm???

This engine would be a long way fron an F1 engine.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by purpleh22 &raquo;</TD></TR><TR><TD CLASS="quote">So, the D series motor in question (with a stock head, intake and exhaust) would most likely have no boost and if a manifold pressure guage were used - it would show negative pressure @ 7,000 rpm/rbm???

This engine would be a long way from an F1 engine.</TD></TR></TABLE>The second you open up the throttle it should go to zero yes.

 

yes i get it now . thanks alot
i asked that question because i read in some post someone say : ( (under normal running operations, naturally Aspirated engine, the normal boost is between 0.8~0.9 bar = 10~13 psi)

and i told him that is very wrong info

but i wanted to be sure from you
anyway thanks alot

 

He is correct... although "boost" is not the best word to use...

Atmospheric conditions are +/- 14.5 psi MSL making 10-13psi about right on a NA motor given the VE's of 70%-90%.

Boost, as most FI people tend to refere to it, of 10-13psi would be an absolute pressure of 14.5 + 10-13psi or 24.5-27.5psi.

I think you and your friend are engaged in a discussion of semantics pertaining to the word "boost".

 

I have seen positive pressure on 2x 2.0L 13:1 CR with skunk Stage 2 cams. This was between 2000-3000 rpm 1-1.5psi of boost.

 

Unless your pressure tap is at the intake valve I doubt that. You probably just have a gauge that isn't very accurate.

Intake harmonics will create a pressure pulse... But not in the intake plenum.

 

very good discussion