Polishing the Plenum
Polishing the Plenum
Does any one really see any advantage in polishing the plenum and intake pipes (what are these things called) on a box stock Q45? I know that air will flow a little better but is it really worth the time? Has any one done this?
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Air flow restriction is a top rpm down phenomena. The most restriction is at 6900-7300 rpm where it might be 83% higher than say at 4,000 rpm.
http://www.modernperformance.com/dcx/ex ... achine.htm
The torque curve shows you the efficiency fall off caused by the air flow dropping in relation to filing time. As the rpm increases the 248 degrees of intake open time gets faster and faster so the air speed has to get faster and faster to fill the cylinder ...friction is a function of air speed on the walls of the runners. The air travels faster in the center of the runner.
When you extrude hone the interior of the plenum/runners you are increasing the inside diameter ever so slightly so you move the tuning point up a few hundred rpm which has the effect of increasing HP 1-1.5% at best at 6000-6300 rpm. There are increases all the way to redline of a similar amount.
You have to weigh the cost per horsepower increase after an ecu upgrade and very loud exhausts, the cost gets higher and higher with each fine tuning per HP found.
At one time you could get bored out and hand massaged throttle bodies which added 3 HP for $600 exchanged and a full PRECISION HONE was $1000 for upper and lower runners.
If you want a massaged [tuliped shaft and knife edge shape leading edge] throttle body I can make one for you for $450 if you want me to flow bench it that would add another $200 [what they charge me].... 3 HP
Is $200-$300 per each extra HP worth it ?
When you have a fine tuned motor to begin with it gets hard.
http://www.modernperformance.com/dcx/ex ... achine.htm
The torque curve shows you the efficiency fall off caused by the air flow dropping in relation to filing time. As the rpm increases the 248 degrees of intake open time gets faster and faster so the air speed has to get faster and faster to fill the cylinder ...friction is a function of air speed on the walls of the runners. The air travels faster in the center of the runner.
When you extrude hone the interior of the plenum/runners you are increasing the inside diameter ever so slightly so you move the tuning point up a few hundred rpm which has the effect of increasing HP 1-1.5% at best at 6000-6300 rpm. There are increases all the way to redline of a similar amount.
You have to weigh the cost per horsepower increase after an ecu upgrade and very loud exhausts, the cost gets higher and higher with each fine tuning per HP found.
At one time you could get bored out and hand massaged throttle bodies which added 3 HP for $600 exchanged and a full PRECISION HONE was $1000 for upper and lower runners.
If you want a massaged [tuliped shaft and knife edge shape leading edge] throttle body I can make one for you for $450 if you want me to flow bench it that would add another $200 [what they charge me].... 3 HP
Is $200-$300 per each extra HP worth it ?
When you have a fine tuned motor to begin with it gets hard.
-
Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
The 94 engine is a little different in that earlier designs had a fuel puddling problem when you closed the throttle from WOT which caused emissions to be a little higher than one would want considering the requirements of 1996.So they went to what is called a high head port design. Instead of 4" separate runners [for each intake valve] in the head they continued the single oval runner with a notch for the fuel spray 2" down into the head....this left no place for the fuel to puddle but changed the tuning to lower the rpm ......so the HP dropped to not exceed the published spec 276 HP and the peak torque declined from 307-303 to 292-295lb/ft......they just used up a little of the built in margin. So the car lost a tenth of a second from this change.
This was pretty common across the board for Nissan [and others]with the 90-93 G20/Q/300zx engines being stronger than the 94 and above.
Because of the VVT they did not change Q cams from 90-95 [like they did in G20], the 96 has a milder [middle of the road] cam without VVT.
The point being is that some very fine tuning of the heads might yield a little more flow but it's not a one way street, you have to accept low rpm reversion [during overlap idle -2500 rpm before the velocity gets high enough to make sure the exhaust gases don't contaminate the incoming charge].
The 90-93 heads had a directional bump [funnel] just inside whereas the 94 did not.
This was pretty common across the board for Nissan [and others]with the 90-93 G20/Q/300zx engines being stronger than the 94 and above.
Because of the VVT they did not change Q cams from 90-95 [like they did in G20], the 96 has a milder [middle of the road] cam without VVT.
The point being is that some very fine tuning of the heads might yield a little more flow but it's not a one way street, you have to accept low rpm reversion [during overlap idle -2500 rpm before the velocity gets high enough to make sure the exhaust gases don't contaminate the incoming charge].
The 90-93 heads had a directional bump [funnel] just inside whereas the 94 did not.