TheViper

will reducing back pressure by putting headers on make me loose any low end trq?

AJ_92RS

No

rx7speed

don't make me start on this again please!!!!!


the reduction of back pressure will give you torque

when you reduce backpressure you make it easier for the motor to push out your exhuast gasses giving you less of a pumping loss

also when there is less of a restriction your exhuast gas will move faster creating a lower pressure area behind it inside the cyl
now remember the high pressure zone likes to move to the low pressure zone to equal out there pressure.
the greater the difference the faster it happens

and you have 14.7 pounds of pressure in the atmosphere so the lower the pressure you cna get in the cyl before the intake valvle opens the better this way you suck in more air

hope that works for ya

rx7speed

hey aj I find offence to your "import" thing in your sig man


first off the honda has more displacement then I do
and secondly it looks like a r<x>icer to me not a real import

AJ_92RS

Hey I know........

I'm gonna go to every Import message board (even though I don't own one) and tell them I'm offended that they think domestics suck!!

If you don't like it, don't look at it!!!

rx7speed

but's it's so false




sounds more like your talking about r<x>ice... not imports

Mark A Shields

stop your whining

AJ_92RS

I'd put **** if it didn't get ****ed out!!!

Wait...... you just wrote it and it didn't.

Anyway...... it is referring to rycers not imports in general. Maybe I'll change it to "Hondas" just for you.

FYI, I do own an import, and it's a Mazda. 1993 MX6 LS. I don't have a V-Tec system, but I do have a VRIS.

Variable Resonance Induction System. It's like a dual-dual plane setup, sorta.

rx7speed

I can swear as well on the boards

but yes this honda trend sucks really bad with all the people going about with there 50 foot wings and cans bigger then the rest of the car stupid s<x>hit like that pisses me of man. why in the world would someone want to f<x>uck that s<x>hit up? oh well who knows. oh and your mazda with the vris I think they could have found a better name for it since it sounds like something nasty and not good forthe car. just curious though you know where I can find some info on that thing?

mikobu3

**** is not what you drive
its what you eat

Mark A Shields

Gee, I wonder how in the ri<x>ce you do that

rx7speed

you don't own an import how are you doing it???

oh wait you own a ford



so what did you change your aim name or something?

rx7speed

amen to that

five7kid

iTrader: (14)

Boys, boys, boys. If you don't start playing nice, we're going to send you to the principal's office and send you home with a note pinned onto your collar...

Let's answer the original question. Backpressure is not the issue, it's the exhaust velocity. The problem is typically caused by putting too large of primary tube headers on too small an engine. For instance, 2" primaries on a stock 305 will kill low end torque - not because of of reduction of back pressure, but because the exhaust pulse enters that big cavern after the exhaust port and no longer needs to move as fast. When the next pulse comes, it won't be dragged along by the previous pulse, which is what happens when the primary size (and tube length) is matched to the engine size and RPM operating range (typically called "cylinder scavaging").

Putting 1-3/4" primary headers on a 283 will kill low end torque. To make it up, you'd have to put in a wild high-RPM cam and a very loose torque converter. For the engine described in your sig, 1-1/2" primary tubes would be a good bet to balance low-RPM torque and high-RPM power.

Wishmaster's87IROC

iTrader: (4)

When I went and had my CAT checked out..he drilled a hole in the pipe right before the CAT and checked the pressure, if I can remember correctly the meter read "0" is that good? He had someone get in the car and rev it to a certain RPM when he checked it. So what you saying is, for the 305 we should get 1 5/8 primaries and what size collectors? 2 1/2 or 3"?

Mark A Shields

nope, real busy lately.

five7kid

iTrader: (14)

Sounds like a differential pressure check from the cat inlet to outlet. "Zero" is good, although it probably wasn't really zero, just below what the gage would read (which is fine).

1-5/8" primaries and 2-1/2" collectors are fine for a healthy 305. A factory stock LG4 or LO3 would be okay with 1-1/2" primaries.