Question to you guys.

My 355+847+LE2 setup is underway and im looking forward to when its actually time to put the motor in. My car is lowered and ground clearance is an issue out here where i live. I already have problems banging on stuff with stock exhaust. I know there are even more clearance issues with LTs. I have heard good things about Mac mids, However I dont want to build this heavy breathing engine and then choke it with some poor flowing headers.

Will I lose a lot of power if i go with mids instead of LTs?

My car is a 97 and the way they have the tubing routed in the dual cat 96/97 Mac mid setup is funky, So i have been thinking that a 94/95 set of Mac mids with a custom Y might be the better way to go.

What do you guys think?

Oh i would also be using a cutout most likely.

Thanks
Steve

 

If the macs are 1 5/8 primaries there is room for improvement. A 1/34 primary tube is better. I believe the slp and AS&M headers are mid-lengths with 1 3/4 primaries. I couldn't give you an exact number for what the power difference would be between 1 5/8 and 1 3/4 but I would guess a solid 10 hp over what you have now. I would think the more power you add the greater the effect of having the larger primaries would be so maybe the HP numbers will be greater than 10 HP

 

Well, that's a tough one. You are on the breaking point where 1 5/8" primaries stop performing as well as 1 3/4" primaries. If you look at the cars that are dynoed over at www.advancedinduction.com you will see that guys with MAC mids are putting down 400 rwhp just like the guys with 1 3/4" long tubes. That's with the same heads/cam combo. In my opinion though, if ever want to go for more HP the MAC's will start to hold you back. The nice thing about the 1 5/8" primary is that the low end TQ is great, because they help keep exhaust velocity high even at low RPM's, which helps to scavenge that old fuel/air charge out of the cylinder and suck in the new fresh air.

I don't recommend LT's or 1 3/4" mids very often, but in this case it might be worthwile. Do NOT get the '96-'97 style headers. Go with a midlength or Long Tube for sure.

Dan

 

I've got a '93 Z with a 96,000 mile stock bottom end/CC305/ported LT1 heads. I've went 12.05 @ 112 MPH with a set of MAC headers.

I'm building a new 6" rod/847 cammed 355. I can't see any reason to not reuse my MAC's.

Frank

 

This is what I always thought (smaller diameter gives greater pressure, and thus greater exhaust exit force), but then lately I've been seeing guys on the boards saying just the opposite...that larger diameter long-tubes give better low-end torque...and the kicker here is that they give the very same reasoning...the larger diameter, straighter tubes allow for greater exhaust velocity... So who is right here?

 

Larger diameters have WORSE low RPM TQ. Smaller diameter primaries have better low RPM TQ. Don't believe otherwise.

Longer primaries help with low RPM TQ. Shorter primaries help with high RPM TQ.


Dan

 

Right on. At least give them a shot before automatically switching to LT's. I've always thought you've had awesome times with the setup you have.

Dan

 

Well there were a couple variables when i tested my 2 sets of headers......
But I had SLP 1 3/4 primary headers on a 220/230 CC305 cam and full bolt ons... and the car ran 104.9 mph..
At the time the car was pulling 5-15 degrees of timing and i did not know this... so probably would have ran 107mph or so..
Then i went with Long tubes with high flow cats and picked up 2mph. THe computer was still pulling timing and i did not know it. And that Day it was 95 degrees out. The night i ran the 104.9's it was about 80 degrees. Now maybe the timing wasnt pulling as much that?? who knows..

But my butt was telling me it was faster with long tubes.

Go with jet hot hooker long tubes is my opinion..

 

Only problem with the long tubes is that I would have serious clearance issues with my lowered car. If im not gonna lost much power (5hp or so) then ill just stick with the midlength setup and maintain atleast some driveable clearance.

Steve

 

well 2mph in the 1/4 is more like 20 horsepower.

But putting long tubes on a lowered car... I wouldnt do it. No speed bumps for u.