had a speed shop install my MAC mid length's and ORY pipe w/O2 sims along w/new plugs and Taylort 10.4 wires....car doesnt seem very quick like i expected...weird...i was expecting a beast and the car, to me, felt stronger before....there is a slight exhaust leak at the end of the Y pipe where the MAC end is bigger (im getting that tac-welded tomorrow) but still it doesnt feel right...sounds mean but feels slower...any suggestions...here are my current mods...

98Z28 Arctic white M6
SLP Lid w/K&N
SLP MAF 85MM
Shaner S2 T.B
T.B bypass
MAC headers w/ORY pipe
Taylor 10.4MM wires
Pro 5.0 shifter
Flowmaster 80series

 

my car was SOTP faster and gained 4 mph in the 1/4 mile....

 

That is interesting. A very knowledgable guy on the CSSOA website told me that when you install headers and the O2 Simms, that you might need to check the air/fuel ratio for a lean or rich condition. I am looking at doing the exact same setup on my SS, so we will see in about a month what it does?? Maybe your brain was expecting too much and it just seems slower? Kind of a hard subject to cipher out. You should have an reasonable gain like Eric said.

 

Your Flowmaster muffler is probably more restrictive than your stock muffler. Get a cutout or a catback and toss the Flowmaster. There in lies your problem. What good does letting the exhaust flow in the headers and ORY Pipe do if it all ends up choking up in the muffler. Your best bet is a cutout.

Also you would have seen much better gains with Long Tube headers. IMO if you cant afford them wait to do headers. Midlengths wont get you nearly as much gains as LTs.

 

get a maft it usually has to be played with to get the hp increase

 

Interesting..... He clearly stated he has a 80 series Flowmaster muffler.... In case you didn't know people who just swapped that were gaining about 8 horses over the stock muffler on a dynojet. This isn't the same muffler thats included in the catback kit no one likes.


But yes... a cutout would flow better.... you could say that about a cutout over any muffler. Heck why should he choke the car by not running open headers.


Sure he won't gain as much under the curve, but the Mac's are as bad as you think they are... I gained 4 mph no other mods, yet one of my friends who go the SLP longtubes gained like 2.5 mph... Maybe I just got lucky or his SLP's sucked who knows. The mac's aren't a bad header.


Eric

 

Yeah I'm confused too. Macs DO NOT make 40 hp and that's what it takes to increase 4 mph in the quarter. There must have been other contributing factors. Maybe weather or other mods? Now I'm not saying that you didn't go 4 mph faster I'm just saying that something else came into play to help you out.
Heck on a stock motor you'd be hard pressed to get 40 hp out of long tubes running open headers More like 32-35hp
But you are right Mac mids are way better than people give them credit for. I know a guy with a heads cam setup that has run 10.6s at 125+ thru Macs.

 

Well, those MACs may have given him 4 mph, but he's still only running 110 mph. So, does that mean 106 mph with only the other mods he has? It's a pretty safe bet to assume he has a lid and catback. Maybe his sig hasn't been updated. 322 rwhp? My '98 ran as quick/fast as his '99, but without headers.

I've always thought that a lid/catback/headers/ORY/tuning combo was good for 350 rwhp and 113 mph traps with an M6. That's just typically what I see.

 

The 322 RWHP was with a lid, flowmaster 80 series muffler, and maf ends. Not too shabby i think. the 12.9 Was on street tires.. I'm not running DR's until I save up enough for a new rear .


Oh Al,

Don't ask me.. I was expecting like 108-109 as my trap speed.... not 110.5... Before the headers i was running 105-106.5 mph. Closing my cutout dropped me down to 109.5, and that was in very hot weather. I honestly am amazed at the difference they made, but then again, those stock manifolds on the 99's suck. A lot of the guys over at LS1.com (i haven't dyno'd since the headers so im going on that) dyno'd 20-25 rwhp increases with the macs. They aren't perfect, but i got them so cheap i figured what the hell.

Eric

 

OK, so to clarify: the 322 rwhp was before the MACs. The 12.9 @110 mph was after the MACs.

You were running 105-106 with 322 rwhp?

I ran 12.8s and 12.9s @110-111 on street meats...323 rwhp.

 

different dynos read different... remember that.