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Backpressure issues?

1045 Views 5 Replies 4 Participants Last post by  RadioFlyer90
I use my '90 pickup to commute down to town each day, and the drive involves a 5-7% grade several miles long. The truck is high geared, which makes for great gas mileage, but doesn't help much when climbing the hill. It's also carbureted, which means it has less power to begin with. I suppose I could downshift, but but the engine really has to wind up to reach even 50 mph in third (It's a 4-speed). I have been looking at my tiny exhaust pipe and thinking that it probably is not helping anything to have such small exhaust. I checked into getting dual exhaust but the guy at the muffler shop told me that the 22R needs a certain amount of backpressure to run properly and so I shouldn't attempt to increase the exhaust flow. Is this true? Could I get away with running a bit larger pipe and perhaps a less restrictive muffler and still give the engine the backpressure it needs (if it needs it)? Or should I just drop it in third and let the engine scream away and hope that Japanese engines really do have a high redline?
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smaller tires might be in order....

but i wouldn't see a problem with running 50mph in 3rd, i do it in my 5spd all the time....

when in doubt, ream it!
You technically do need the backpressure, but thats up to you. If you want a good exhasut that will give you power instead of take away from it just get a catback for the time being from one of the better manufacturers. I wouldn't go above 2.25" though, because then you could lose some backpressure. Leaving it in lower gears while going up a hill or incline is ok. Higher gears are for straight shots anyway, lower gears are for the pulling, inclines, etc. Redline for these trucks is around 5500. If you don't have a tach, just feel it out. You'll know when you're going to fast for that gear.
with a 3:58 rear end and 195/70/14 tires my truck turns 3200 rpm @50mph in 3rd gear...

it turns the same in 5th @ 75 mph....
The engine is an inline four. No way does it need dual exhaust. You only have one header, so dual would just give the exhaust gas more places to go before leaving the pipes. If I were you, I would keep everything single side ehaust. I would go with a nice sized straight pipe (2 1/4 or so...) then I would install a high flow cat, all new piping back to the muffler, and a high flow muffler. That will really open her up.
5500 rpm?! Wow! I didn't really know I could run it up that high. Even 3200 rpm is higher than what I am used to. My old truck that I used to commute with has a flathead inline-6: it reaches its peak torque at 1800 rpm and I set its redline at 2500 rpm. As for the smaller tires, it makes practical sense as far as the final drive ratio goes. However, the people who design the exits from parking lots around here seem to think that everyone has the ground clearance of a 4X4- I have stock tires on it now and I'm surprised that I haven't knocked my rear bumper off!
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