I'm not expecting a huge jump in power. There's a couple guys right around my power range with the Magnaflow cat back that dyno'd 15-17rwhp more with cutouts open. I won't be running cut outs, but should be damn close to the same with 4" exhaust. I expect some where between 7 and 15 HP or round abouts. What I like about it is that it'll no longer be a restriction as I increase power. I will say that I am still considering a single 3.5" set up too.i understand the numbers and how they always push towards giant pipes, but in practice, i think you'll notice very little gain from going larger than 3" exhaust in that ~500hp range.
i betcha if you ran open headers right now with your 'restrictive' 2.75" pipe you'd gain like 8rwhp.
exhaust cfm is one area where the "ideal" math and reality don't quite match well.
guys with cutouts in front of a decent 3" system without a lot of muffler on it have proven that, the gain isn't gigantic.
i've also never heard a 4" single exhaust system with a gas engine sound very good.
not trying to talk you out of it specifically, just don't see the need to go bigger than 3". i dont think your numbers reflect an exhaust system that's robbing you of any power.
Plus I love the deep deep tone. And a single pipe out the right adds to the unassuming look my car has right now. On the street most people don't realize it's my car loping. They think it's a V6.
I'd actually like to go back to a MAF tune, but I think it's calibration is way off at high RPMs. My data logs show 289afgs max at 6275 rpms (last I did pulls with the MAF) at a relative density of about 79.3% (using the MAP and IAT readings). That's only 597CFM when it should be reading about 664CFM. That's more than a 10% difference at WOT. I'm not happy enough with my tuner to go back again for a MAF tune so I'm going to wait until I get my exhaust done and hit up the tuner rental down the street from me, or until I get a W/B O2 mounted and hit up the track (ideal).steveo said:if it likes that AFR, definitely keep it, especially if it's a street car. safe is good. the difference between ~12.9 and ~13.2 for example is fairly small.
i was about to ask how the hell you ended up at that AFR, but then i realized you're running speed density, so never mind.
Interesting. I'd like to see what you'd target for spark timing with my cam. Also, I'm an M6 with 3.42 stock gearing too. So my cruising RPM's are lower than you might expect with this cam. At 65 I'm in 6th at 1450RPMs. At 45 I'm in 5th at 1500RPMs. And on my daily commute I rarely exceed 3000RPM's.steveo said:i'd be interested to see what he tried, and why it failed. it's by far the weakest spark table for a cam that size on an lt1 i've ever seen, it's 99% stock.
im also suprised driveability doesn't suck in a lot of areas with a timing map like that. if it's driving good, awesome. most people don't get that lucky.
keep in mind that with a stock cam, the two left hand columns are decel, the next couple are cruising on a flat road. with your cam, the first six columns of your timing map are likely just decel.
the stock timing table is set up for a cam that makes a realistic torque peak of like 2 grand and makes a ton of vacuum, and likes a whole lot of timing at very low rpm cruising range.
your setup is so far off of that. this is not something that will show up on a dyno or matter for a track car, where pretty much only the right hand two columns of the spark table are used, but more so with street tuning and aiming for 'smoothness'.
I'm down if you want to set the timing up how you'd think it should be and I'll load it and data log it and get that back to you. I'd like to see if things could improve too.
I really want to do this and I certainly need a dyno for this one. I want to see how much timing the injectors would improve not just power, but also emissions. I'd love to get my build to pass emissions. Not likely, but it'd be fun to try!steveo said:now that's something i've never had the chance to play around with, with a cam that size where it'd make much difference. i'd be very interested to see what you come up with for sure; i bet there's quite a bit to be gained.