wasp

well i have to add a cat or i wont pass inspection, right now i have 2.25" y pipe and 2.25" all the way back to a flowmaster , no cat..........................i was going to have them change it to 3" after the y pipe, with a catco cat and a hooker aero chamber, think this is money well spent or should i just have em throw a 2.25" cat in?

wasp

well a summit tech told me he wouldnt go any bigger than 2.50 " on a 305 cube motor...................he said id lose alot of scavenging with 3" which isnt good............you guys agree?

onebad84z28

bull ,i just went from a dynomax 2.5 cat back to a 3 " banks and change my hedman y pipe to 3 where the pipes come together to the cat and let me tell you what a differnce. i had a bog off the line i couldnt tune out now with the 3" no more bog and more throttle responce and power. took me and my friend about 2 hours to do the job at his shop. i would have the shop do the same to your y pipe.

1bdbrd

iTrader: (1)

you have a modded 305 with better induction. he has what i would assume is a bone stock 305 tbi. its not like it exactly moves a lot of air compared to yours.

original poster: depending on what your future mods are, a 2.25 y pipe will be the restriction before even a 2.5 inch catback would be. if its cheaper by any substantial amount to go 2.5 inch for the rest of the ehxuast i woudl do that unless you have honest plans for bigger cubes or a better top end for the 305.

wasp

well first off my motor isnt stock , ive done everything cept cam and heads.................ill list later....................my y pipe im going to leave 2.25 because i was having a scraping issue and i dont want to have it again, so i was only going to change from the y pipe down to bigger, 3 or 2.5............................

msd 6a box
accell coil
accell plugs
msd wires
dual snorkel with k&n ( ran both hoses down into the air dam)
edelbrock tbi intake
flow matched injectors
injector spacer
tb spacer
adjustable fuel pressure reg (running 16 psi)
crane 1.5 roller rockers
griffin radiator
be cool tranny cooler with fan
tranny rebuilt by level 10 in nj
aluminum tranny pan
helwig sway bars front and back
3.73 precision gears with auburn posi
aluminum driveshaft built by dennys driveshafts
kyb shocks and struts
panhard bar
hooker 2138 headers (1.5 primaries into 2.25 y pipe)
accell heated o2 sensor


i may have missed something, the bottom end hasnt been touched yet but i do have an slp cam (51002), i just havent had the money to get edelbrock e-tec 170 heads and a different manifold( different bolt pattern , name escapes me now)

but the summit tech said no matter what i do to a 305 3" is too big.................

ScottyRS

iTrader: (2)

But think ahead a few years...when the 305 quits, you're gonna have to drop in a bigger motor, and the 3" would be nice to have. Also, cheaper than a 2.5" and then a 3" exhaust. And if for no other reason: why not?

(Besides, the guy is just trying to sell you a crate engine)

Air_Adam

Two 2.25" pipes flow the same amount of air as a single 3" pipe, from what I've read from past discussions. So, when your 3" single becomes a restriction, your 2.25" Y-pipe will at more-or-less the same time.

a 3" DUAL exhaust is way too big for a 305, and even some big blocks... a 3" single exhaust system is roughly the same as using a 2.25" dual exhaust system, which is just about right for a decent 305 or 350.

wasp

ah , so the 2.25 y flows almost the same as the single 3? well it does go into a single 2.25 pipe for about 10" or so............perhaps 3" is the way to go then

v8nate92RS

Go 3", as long as you have stock manifolds and y-pipe going 3" with the cat and cat-back won't hurt you at all. I did this, I have stock manifolds and y-pipe going into a 3" Catco direct-fit and a 3" Flowmaster American Thunder. It sounds bad *** and it did not hurt performance at all. The mods you have right now are more than justified for a 3" cat-back.

CamarosRUS

i have that same issue, no cat but my headman 1 5/8 headers came with a small y pipe and i have a 3" mandrel exhaust the rest of the way back. i know the y pipe is holding me back and because its so small compared to the rest of the piping it is a crappy job trying to get the two to meet together

wasp

i have headers vnate.................camaro.............dont they make 3" to 2.25" reducers? how else would the shop do it?

onebad84z28

What we did to my y pipe was cut it where they merge into one and weld a 90 degree and 45 degree bend cut to fit and mig weld it together,now i have two 2 1/4 into a 3" pipe instead of going into a 2 1/2 pipe. i am sure a shop could do the same to yours.

wasp

i was looking at reducers on summit, none go from 2.25 to 3 , but they have a 2.25 to 2.5 and a 2.5 to 3..................should i get these when i order the muffler and cat? cant the shop just widen the end of the pipe on the machine? or not that much

v8nate92RS

Any good exhaust shop should be able to make or find a reducer to put from the 2 1/4 Y-pipe to the 3" Cat. That's how mine is set up and they did a dang good job welding the reducer in. I'll have to take some pics when the rain stops.

wasp

what about from the catback? im going to purchase a hooker aero chamber muffler, i have a flowmaster now and wana try something different......................should i buy a cat back system or let the shop make it, which do you think would be cheaper?

Vader

"Summit tech" - Isn't that a contradiction of terms? An oxymoron, if you will?

He probably wouldn't go any larger on a 305 since they didn't have a larger one in stock, would be more my guess. He gets no commission on a no-sale.

wasp

well i see what your saying but the tech line is different from sales, he said hed change to 2.5 but not 3 as the motor would be pushing the exhaust more than the pipe helping to pull it, he mentioned a few different types of pulses...........