Measured Backpressure on the Vette - Page 2 - Motorgen - Automotive Events, Meets, Cruises and Forums

BRIAN · 04-12-2010, 02:34 PM

Awesome, now I just have to wait for you to uprade your exhaust and dyno again

94cobra69ss396 · 04-12-2010, 02:58 PM

I'd like to see that too. I've had some discussions about the negetive effects of backpressure and I would love to remeasure the backpressure on your Vette after the upgrades and then see what the difference is on the dyno.

Vettezuki · 04-12-2010, 04:02 PM

Quote:

Originally Posted by 94cobra69ss396

I'd like to see that too. I've had some discussions about the negetive effects of backpressure and I would love to remeasure the backpressure on your Vette after the upgrades and then see what the difference is on the dyno.

I want to do it for sure, but new headers, cats, replumbed exhaust and new tune is going to be well over a grand and probably closer to two. I'll be putting that into the project car first. But I will get to this. Not quite sure how best to do it to isolate the effects of back pressure. Just inserting some hi-flow cats in place of the stock cats, measuring back pressure, and if essentially gone, dynoing might be the best way. Changing to LT headers, new injectors and tune, etc., there's just too many contributing factors to increased power.

94cobra69ss396 · 04-12-2010, 04:11 PM

Quote:

Originally Posted by Vettezuki

I want to do it for sure, but new headers, cats, replumbed exhaust and new tune is going to be well over a grand and probably closer to two. I'll be putting that into the project car first. But I will get to this. Not quite sure how best to do it to isolate the effects of back pressure. Just inserting some hi-flow cats in place of the stock cats, measuring back pressure, and if essentially gone, dynoing might be the best way. Changing to LT headers, new injectors and tune, etc., there's just too many contributing factors to increased power.

I agree. Just because there is no longer back pressure doesn't mean that the flow is optimum. Are your cats bolted in between the exhaust manifold and the aftercat or is it welded? If it is just bolted we could probably make a test pipe to replace the cat and then measure the back pressure again.

Vettezuki · 04-12-2010, 04:40 PM

Quote:

Originally Posted by 94cobra69ss396

I agree. Just because there is no longer back pressure doesn't mean that the flow is optimum. Are your cats bolted in between the exhaust manifold and the aftercat or is it welded? If it is just bolted we could probably make a test pipe to replace the cat and then measure the back pressure again.

They're bolted. Pretty easy to remove actually. Good idea.

94cobra69ss396 · 04-12-2010, 04:54 PM

Quote:

Originally Posted by Vettezuki

They're bolted. Pretty easy to remove actually. Good idea.

Is it a straight shot? If so, it would be really easy to make them. Just go to Autozone and pick up some tube.

BRIAN · 04-12-2010, 10:13 PM

If I may hypothesize here, the torque curve will simply shift to the right on the dyno graph with only an exhaust size upgrade with no tune or cam replacement in mind.

edit: wait wait....if I have this right in my head, increasing the exhaust size too much would cause the curve to move to the right (RPM range). Why? Well I figure too large of an exhaust would take a higher amount of exhaust pressure to create velocity, in other words higher RPM's needed. Too small an exhaust we have a restriction of the velocity trying to release.

94cobra69ss396 · 04-12-2010, 10:34 PM

Quote:

Originally Posted by BRIAN

If I may hypothesize here, the torque curve will simply shift to the right on the dyno graph with only an exhaust size upgrade with no tune or cam replacement in mind.

I don't think so. If anything he'll see an increase across the entire range that the dyno sheet shows but mostly in the upper rpms. Remember that he already has a restriction that even at idle is creating 1 psi of pressure in the system and 3 psi with just a rev. I had a plugged cat on my Suburban and it didn't even have back pressure at an idle. It did however have 3 psi on a rev but only on one side.

BRIAN · 04-12-2010, 11:03 PM

Hmmmm I have my head rapped around this now. Need to find something else to occupy my time haha. We'll leave it up to the dyno

edit: YA! Without using any formulas and just winging it, anywhere between 2.5" and 2.75" should yield a better power curve. ^^^^This guys is right!! As I said though I think too large and the gains will only show on the top end. I don't know why I'm bringing all this up, it just snapped into my head this whole exhaust theory ordeal I heard about.

enkeivette · 04-12-2010, 11:14 PM

You do realize that your car is already really fast don't you?