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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.
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.

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.

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.
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:
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'.
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.

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. :D


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.
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!
 

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Discussion Starter #23 (Edited)
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.
ah.. i dont think so

your VE table is off by 8-10% at high RPM and high MAP too.

how do i know that? i have your PE targets vs your actual wideband readings on the dyno.

first off your total added percentage of fuel between the two tables should probably be about 13% to hit a 12.9:1 average, and it's not. it's WAY higher, meaning your ve tables are fairly lean under high load.

furthermore you can determine that it's -probably- not a constant that's off, your PE RPM tables are so friggn crooked but they result in a fairly consistent AFR.

if you had an accurate VE table, you should be able to ZERO the RPM table and afr should be fairly constant from 1000rpm right through to 7000rpm.

so i doubt your maf is less acurate than your VE tables are right now..

it's easy to fix your maf scaling if it starts to skew at high rpm. just install a wideband, set it to open loop 13.5:1, do a half a dozen pulls of various loads. your AFGS vs wideband afr will show you exactly how much various parts of your maf table are out.
 

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ah.. i dont think so

your VE table is off by 8-10% at high RPM and high MAP too.

how do i know that? i have your PE targets vs your actual wideband readings on the dyno.

first off your total added percentage of fuel between the two tables should probably be about 13% to hit a 12.9:1 average, and it's not. it's WAY higher, meaning your ve tables are fairly lean under high load.

furthermore you can determine that it's -probably- not a constant that's off, your PE RPM tables are so friggn crooked but they result in a fairly consistent AFR.

if you had an accurate VE table, you should be able to ZERO the RPM table and afr should be fairly constant from 1000rpm right through to 7000rpm.

so i doubt your maf is less acurate than your VE tables are right now..

it's easy to fix your maf scaling if it starts to skew at high rpm. just install a wideband, set it to open loop 13.5:1, do a half a dozen pulls of various loads. your AFGS vs wideband afr will show you exactly how much various parts of your maf table are out.
I got 6% off (low) at 6100RPMs. AFR Target is 14.7:1. PE Coolant Corr is 12.11, PE RPM Corr is 12.11 over 5200 RPMs. With my VE table at 99.61% and using those correction factors actual AFR should be 11.83:1, but logged AFR was ~12.5. So 12.5/11.83=~106% at 6100RPMs. At 5400RPMs (about where AFR peaks) I get about 109%.

But, I can't go any higher in the VE tables so it's been adjusted with the PE tables. That is why the PE tables are the way they are. They were adjusted with a wideband on the dyno to get the ~12.5:1 AFR. I can mess with the PE tables to lean it out a bit, but I'll be doing it blindly without a wideband. Dammit I really need one of those! Money is stupid tight right now so it'll be January before I can buy one.

I'm still interested on where you think my Spark Timing Tables should be. Reading my plugs the spark timing is right where it should be. If I lean out my AFR's I should be able to pull a little bit more timing at WOT than I have. But daily driving, in the cruising and decel areas, what should it look like?

EDIT: I've updated my PE RPM correction tables to read about 12.7-12.9:1 now (Thanks to MS Excel). I also pulled 1掳 timing at WOT. I'll data log it once I get my clutch installed.
 

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3" true duals 馃檴:D

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I've contemplated this, but it's actually even more piping than a single 4" set up (about 580rwhp without losses). I'd need an X-pipe to get the advantage of a single exhaust Y-pipe scavenging set up, still have less exhaust gas velocities, and it'll take up more space.
 

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Discussion Starter #26 (Edited)
But, I can't go any higher in the VE tables so it's been adjusted with the PE tables.
that's the point when i'd just fudge the cylinder volume or something to get more headroom. just scale cylinder volume and ve table by the same percentage to get more overhead in the ve table.

Reading my plugs the spark timing is right where it should be.
reading the ground strap? you have way better tools than that.

with timing in cruising range, you're generally trying to reach peak vacuum without going over at all. the second vacuum stops increasing as you add timing, you've gone too far

with timing at WOT, of course, you're trying to maximize power without detonation. this usually looks like a slight upwards incline from whatever base timing, increasing towards your torque peak and then leveling off (unfortunately the LT1 is some kind of timing mutant that never ends up looking that way...)
 

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that's the point when i'd just fudge the cylinder volume or something to get more headroom. just scale cylinder volume and ve table by the same percentage to get more overhead in the ve table.
I thought about doing it that way. I'd have to change the VE tables and the volume constant. But, it would require a complete re-tune on the dyno for PE tables. The way it's set now works pretty good I'd say.


steveo said:
reading the ground strap? you have way better tools than that.

with timing in cruising range, you're generally trying to reach peak vacuum without going over at all. the second vacuum stops increasing as you add timing, you've gone too far

with timing at WOT, of course, you're trying to maximize power without detonation. this usually looks like a slight upwards incline from whatever base timing, increasing towards your torque peak and then leveling off (unfortunately the LT1 is some kind of timing mutant that never ends up looking that way...)
Yes, I read the sparkplugs and my data logs.

I didn't know about the vacuum thing at cruise timing, thanks! I'm gonna do that once my car is back on the road.

I feel you on the WOT timing. What the tables show and what actual timing is are two different things. My tables were set at 33掳 WOT timing from 3200rpm to peak RPMs, but logs 37掳 actual. It holds 36掳 timing at WOT from 3700 to 5300 then 37掳 from 5300 to peak RPM on the data logs (87kPa, 98% TPS).

IIRC, these heads are pretty quick burn heads right? If so the timing being where it's at (close to stock) would make sense considering the cam is ground 6掳 advanced. So the spark timing is actually closer than stock to valve timing.
 

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Discussion Starter #28
My tables were set at 33掳 WOT timing from 3200rpm to peak RPMs, but logs 37掳 actual. It holds 36掳 timing at WOT from 3700 to 5300 then 37掳 from 5300 to peak RPM on the data logs (87kPa, 98% TPS).
this is something i'm working on. im hoping soon i'll be able to provide a patch for EE that provides 'honest timing'. for some reason, my tunes never end up adding much timing at WOT, but some others add anywhere from 3 to 6 degrees? right now its a mystery.

I thought about doing it that way. I'd have to change the VE tables and the volume constant. But, it would require a complete re-tune on the dyno for PE tables. The way it's set now works pretty good I'd say.
it shouldn't require any re-tuning if you just increase cylinder volume and decrease VE by the same percentage. you should end up with the same VE table but have room to move.

but also keep in mind that when an engine starts making over 100% VE, that's usually a sign that a constant is a bit off in the first place.
 

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this is something i'm working on. im hoping soon i'll be able to provide a patch for EE that provides 'honest timing'. for some reason, my tunes never end up adding much timing at WOT, but some others add anywhere from 3 to 6 degrees? right now its a mystery.



it shouldn't require any re-tuning if you just increase cylinder volume and decrease VE by the same percentage. you should end up with the same VE table but have room to move.

but also keep in mind that when an engine starts making over 100% VE, that's usually a sign that a constant is a bit off in the first place.
What do you mean the constant is a bit off? How can they be off a bit?

EDIT: Ahh I see. My actual displacement is .0013% larger than what my tune shows. I wouldn't think that would change what my VE is reading though.
 

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Discussion Starter #30 (Edited)
what i meant was more along the lines of it's rare to actually achieve over 100% VE in an n/a engine. and if you do, it wont be by much.

so really if you need more headroom, just take something linear in the airflow calc (cylinder volume is convenient), multiply it by 1.10, and then multiply your VE table by 0.90. that'll give you a bias of 10% in the VE table (well..and any other table that uses cyl. volume), so you can work with an engine up to 110% VE.

there's a guy working on dissecting the fueling calculations a bit better right now. im not entirely sure how cylinder volume is used while in MAF mode. it might also jack up something else that i'm not aware of. but last time i did this it worked fine.
 

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what i meant was more along the lines of it's rare to actually achieve over 100% VE in an n/a engine. and if you do, it wont be by much.

so really if you need more headroom, just take something linear in the airflow calc (cylinder volume is convenient), multiply it by 1.10, and then multiply your VE table by 0.90. that'll give you a bias of 10% in the VE table (well..and any other table that uses cyl. volume), so you can work with an engine up to 110% VE.

there's a guy working on dissecting the fueling calculations a bit better right now. im not entirely sure how cylinder volume is used while in MAF mode. it might also jack up something else that i'm not aware of. but last time i did this it worked fine.
I agree with all of this. I've triple checked all the constants and they are as advertised; 36# injectors (P/N:0280155737) @3 bar (44PSI), 355CID. I can bring the injector constant down or the CID up. But in either case, because I'm SD, I need to rebuild my VE tables after I drop them down in all areas above max VE. I need a wideband to do that. Even if I went back to MAF mode I'd need a wideband.

Basically I need a wideband. Come January I should have some wiggle room again in the budget. So it'll have to wait until then.
 

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Discussion Starter #32
i doubt you'd have to redo your VE tables. the cylinder volume is a linear constant that is a base airflow calculation. increasing it by 10% should allow you to scale the ve table down by 10% and land you exactly where you were before.

you can use narrowband trims to determine a linear inaccuracy in that change as well (check your trims before and after the change)

i wouldn't change your injector constant (a fuel calculation) to jack up VE (an airflow calculation) (although it would work).
 

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i doubt you'd have to redo your VE tables. the cylinder volume is a linear constant that is a base airflow calculation. increasing it by 10% should allow you to scale the ve table down by 10% and land you exactly where you were before.

you can use narrowband trims to determine a linear inaccuracy in that change as well (check your trims before and after the change)

i wouldn't change your injector constant (a fuel calculation) to jack up VE (an airflow calculation) (although it would work).
The problem with the VE tables is that right now everything at WOT over 3K RPMs is off the chart (along with other area's under WOT but still in PE mode cells). So I have nothing to multiply/divide to get the values right in each cell (every cell over 100%).

Also I can't go based on my narrow bands as they do nothing for me in the cells I need to adjust because I'll be in PE mode. If I turn off PE mode I run the risk of detonation (which I can pull timing for but that'll throw off burn rates and O2 readings under actual WOT conditions), but could get close to the VE curve on the tables.

I wouldn't change my injector constants either, but it is one way some tuners go about doing it. My reason is that if I ever decide to replace my injectors with different ones in the future I only have to adjust that one constant and everything else will run the same.


Basically, I'm stuck where I'm set at until I get a wideband O2 set up going. But, I like your idea of increasing the CID constant by 10% and decreasing the VE tables by 10%. Then using the wideband to tune the VE tables back up to where they need to be with the PE tables set to a constant.
 

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people have been asking me a lot to do some basic tunes for silly things like EGR deletes, or whatever, so i've decided to create a robotic auto-tuning service that generates a bin based on your particular needs.

this should be good for people that aren't comfortable tuning their own cars.

here it is: http://fbodytech.com/autotune.html

the tunes generated are nothing special, just the dead basic tunes to make your car run right. it's likely paying for a tune-by-mail tune may gain you a bit of performance over these, and for cammed out hopped up nos monster track queens, they definitely are not the tune you're looking for.

.. but that's what you get for zero dollars, so enjoy.

i will add more tuning options in my free time or as requested.
Is this still a thing? I'd like to generate a base tune for a friends car that i'm fixing up.
 
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