Hey guys, im getting ready to put a 355 engine into my car. We had it built by a local shop, it's 10.5:1 compression, making 310hp and 330 ft/lbs of torque. It's coming with a set of good flowing heads ported and everything by the shop just for my motor. I'll be putting an edelbrock performer intake on it, with a edelbrock 600cfm performer carburetor, and some ceramic (not sure what brand) headers. My tranny is a built 700r4 with a b&m shift kit and my rear end is a positraction (not sure on gear ratio). Now, what my main concern is, is that my exhaust system after the aftermarket headers, is still the stock y-pipe with the cat and it goes back into an 80 series flowmaster with dual outs. Is the exhaust gonna hinder my performance? Is it a realistic expectation to hope for close to 300HP at the rear wheels with my setup? Any advice is greatly appreciate guys!!! Thanks

BTW: my block is 4 bolt main...not that that really matters, but oh well.

 

If your Y-pipe has a smoother transition into the "y" shape and not the way the factory designed them, you should be ok.

as for pipe size;

If you have at least a 2 1/2" before the Y junction and 2 1/2 after, you should be fine.

Dunno if you have a Cataletic converter still, but I would assume not.

 

Yea, ive still got the cat on it. I hope it won't suffocate the engine. Also, what kind of power should i be expecting at the rear wheels? Is 300ish a decent expectation with my setup i listed in my first post?

 

Any more advice guys??

 

A stock T-type Y pipe would cut power a lot for sure, and if the engine only make 310HP on dyno I would expect to see at least a 50-70 HP loss at the rear wheels with a automatic.

 

i honestly dont see the point in getting headers (especially big buck ceramic ones) without doing further exhaust mods. i am pretty sure that the facory y pipe and cat would be the bottleneck instead of the headers. so i am going to say that it will hurt you.

 

I honestly know exactly what you mean about the headers, but they came on the car. It never made sense to me either why they would buy good headers and a flowmaster muffler, and have intentions of racing this car but leaving the stock y-pipe and all that crap. Now, that i have to pay for the motor and the accessories for it, and i have to get a new windshield in my car, my money is pretty much gone, so i can't do anything with the exhaust for now. I was afraid i was gonna suffer a pretty big loss in HP to the rear wheels, but i'll just have to live with it for now. 250-260rwhp isn't too bad for a street car.....is it?

 

250 - 260 hp is a lot more then stock. I'm guessing my car was about 170 - 180 hp when I got it. It should be enogh power to put a smile on your face.

 

Yea, that's what I was thinking. I mean, i have a stock '84 z28 with the lg4 prolly making 110rwhp (150 "raw") and my '83 z28, even with the 355 that's in it now, thats all worn down, the difference in performance from each of the cars is daylight and dark. The '83 would kill the '84 all day long prolly even running on only 6 or 7 cylinders.
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By the way guys, the exhaust problem probably isn't going to last for more than a year, cuz next summer my plan for the car is to either get new hooker headers with the hooker y-pipe or have a shop make me an x pipe true dual exhaust. But, it'll be alright for now, i just have to get some more money saved up.