Ecos

I'm curious if any of you have went with 3" exhaust on an 944s and if so how did it run? I'm assuming it would be a bit large for this car and that the car would perform better with 2 1/2" (correct me if I'm wrong) but does it turn the car into a total dog or just not be quite as torquey?

I'm asking because my exhaust developed a nasty rattle that is driving me nuts and I want to do away with it. I plan on adding boost in the next few months so I don't really want to use a smaller size exhaust and then upgrade it again that soon.


Thanks in advance.

smlporsche

I have a 3" exhaust on my S2 race car.
The dyno results (from this and other changes) shows it's producing quite a bit of power.
I don't know if a 2.5" would be better or not but the 3" works for me.

krystar

if u do plan on having boost, then 3" is a definite.

but if u don't...it'll be kinda loud and a slight decrease in low end. but it's not going to be overly dramatic.

Potomac-Greg

These n/a engines seem to like back pressure. I had modified my exhaust to really open it up; and then to appease the wife, I bought a "stock" cat-back setup with a full muffler.

I put the quieter cat-back on and I was surprised at how much low end torque the car gained. I don't know what I'm giving up on the top end though.

krystar

i wonder how much valve overlap there is on the stock cam. has anyone ever specced it?

halik

Back pressure is a myth on FI cars, exhaust velocity is what matters

Lorax

Uhhh what? You don't think back pressure is related to velocity?

Funn944

I have an '86 N/A, overbored throttle body, adjustable fuel pressure regulator, MSDS headers, 3'" pipe all the way to the rear, Hi flow cat, magnaflow muffler. Maybe lost just a bit of lower end, but not really
noticable. Runs very well, Pulls stronr to rev limiter in MDS ignition, but it is pretty raspy, especially when under full acceleration !

Reimu

Do you lose a fair bit from the bottom end by dropping the cat?

Ecos

How does it sound at idle or cruising speed? I was thinking of going with a high flow cat (right now it has a straight pipe in place of cat) and Magnaflow muffler. I enjoy it noisy at WOT but *if* possible I would like to tone it down at idle and cruising speeds....kinda annoying to scream out your order at Taco Bell, or have the radio blaring just to hear it while going down the expressway. I had a Flowmaster on an old V8 that was ungodly at idle, I switched (to Borla I think) and it was much better...both had nice sound at WOT but the 2nd muffler was a lot better off throttle.

Thanks for the responses.

Also does anyone know offhand what angles the bends are in the exhaust? From pics it appears to be 2 45degree bends and 1 30degree at the front. I will be jacking the car up this weekend to check but thought I would ask just in case people have already found out they are some odd angles or some such.

krystar

yea 2 45's and a 30 in front of the cat is right.

although if u did a tilt angle mount, u'd prob be ok with just one 45 or one 30

Funn944

At idle, or cruising its not really too bad, although definitely louder than stock

harrisonrick

Jesse (jgporsche) dyno'd his S and the results showed that a 2.5 inch exhaust on the 16V S engine was the largest for maximum benefit overall.


I recommend Russell Berry's 944S MAXHp chip too.

halik

You don't want back pressure, that would move the spent fuel back into the cylinder when the piston is moving back down (while the valve is closing). You want change in pressure or exhaust velocity to be high to displace all the exhaust away from the motor and that's a function of the pipe diameter.


longer blurb

roman944

how do you guys loose lower end (torque?) by going catless? I'd think straight pipe would be the best, no?