I have a 1990 with short ram intake, 4-2-1 header and now I have 2.25" exhaust from the catback with flowmaster muffler. I don't think this is my imagination, but after adding the 2.25 exhaust my RPMs dropped 200. RPMs went from like 4000 to 3800 at 80 miles an hour. Does this make sense??? I have the stock motor, plan on doing the minime here soon. Did anyone notice thier rpms lower after going to a larger dia. exhaust?? It is louder by all means, but my car did pass emissions
thanks for the input.

laters,
Elmerfudd

 

it's your imagination

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sporkcrx &raquo;</TD></TR><TR><TD CLASS="quote">it's your imagination</TD></TR></TABLE>

I'll agree.

 

Only gearing changes can change RPMs.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by StorminMatt &raquo;</TD></TR><TR><TD CLASS="quote">Only gearing changes can change RPMs.</TD></TR></TABLE>

there is no possible way that having a more open exhaust can make your gearing change! The only think I noticed when I have my silencer out vs silencer in on my exhaust(4-1, 2.25" full, test pipe, straight through muffler) is that I have a drop in low rpm power with it out.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by elmerfudd &raquo;</TD></TR><TR><TD CLASS="quote">RPMs went from like 4000 to 3800 at 80 miles an hour. </TD></TR></TABLE>

You mean it USED to be 4k RPM when going 80mph and now it's 3.8k RPM when going 80mph?

Well you can't predict land speed (mph) by RPM only. There are too many variables in the equation (i.e. road conditions, weather, engine power output @ xRPMs). Maybe your motor simply makes more power earlier in the RPM band since you put on the exhaust? I don't know. Or maybe you just had more traction that day. Or less wind-resistance. Or maybe you lost some weight, or maybe your car lost some weight. A hypothetical example: Take your car and drive it on the road and note the speed at 2nd gear redline. Then take the same car on the same tires and drive it on some ice- A glacier or something. Note the speed at 2nd gear redline...and it'll be different; obviously. RPM alone does not determine mph.

But it could be your imagination too.

 

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

You mean it USED to be 4k RPM when going 80mph and now it's 3.8k RPM when going 80mph?

Well you can't predict land speed (mph) by RPM only. There are too many variables in the equation (i.e. road conditions, weather, engine power output @ xRPMs). Maybe your motor simply makes more power earlier in the RPM band since you put on the exhaust? I don't know. Or maybe you just had more traction that day. Or less wind-resistance. Or maybe you lost some weight, or maybe your car lost some weight. A hypothetical example: Take your car and drive it on the road and note the speed at 2nd gear redline. Then take the same car on the same tires and drive it on some ice- A glacier or something. Note the speed at 2nd gear redline...and it'll be different; obviously. RPM alone does not determine mph.

But it could be your imagination too.</TD></TR></TABLE>

Besides gearing, the only other thing that changes the RPM vs speed relationship is overall wheel diameter. All the other stuff (power curve, torque curve, wind resistance, traction, etc.) doesn't make a difference. It can affect how fast the car will accelerate or travel. But not the number of RPMs required to attain a given speed.