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post #16 of 35 (permalink) Old 10-30-2014, 09:40 PM Thread Starter
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i bet you have a lot of power left on the table there; have you checked your AFR with a wideband?
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post #17 of 35 (permalink) Old 10-30-2014, 10:23 PM
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i bet you have a lot of power left on the table there; have you checked your AFR with a wideband?
AFR is 12.2 to 12.9.

What makes you say that? Just curious.

I know my exhaust is pretty restrictive (a single 2.75" pipe over the axle is a hell of a choke point for my car). And my TB and Intake Manifold are untouched. But where in the tune do you see potential for more. I'm all for making more power!


1995 Camaro Z28 LT1 LE2 355 w/ forged pistons/rods, 230/238 .565/.565" 110+6, 1.6:1 SA RR, LT Headers with ORY, T-56 (rebuilt w/ some upgrades), McLeod Street Twin, Lowered 1.25" (Stagg Shocks and Summit Springs) LCA Relocation brackets, Adj Panhard Bar, Poly suspension bushings, STB , CAI, !emissions crap, Magna Flow Cat Back. 146,xxx miles. Purchased Feb 7, 2012 (168K) 414rwhp
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post #18 of 35 (permalink) Old 10-31-2014, 12:11 AM Thread Starter
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What makes you say that? Just curious.
your timing map is bone stock where it matters (heavy load, wot.)

for that kind of cam, WOT timing should look way different than a stock cam ...

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AFR is 12.2 to 12.9.
max power on fast burning aluminum heads like this is found more high 12s to low 13s. you should head a bit leaner and see how it behaves.

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a single 2.75" pipe over the axle is a hell of a choke point for my car
why is that? you're only 1/4" under a 3" exhaust. a single 2.75" isn't actually that bad for this kind of car, in fact it can promote velocity of exhaust gasses within the operating range of the engine to create more useable power in normal driving ranges. it might choke it out at very high rpm, but not much.
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post #19 of 35 (permalink) Old 10-31-2014, 03:30 AM
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your timing map is bone stock where it matters (heavy load, wot.)

for that kind of cam, WOT timing should look way different than a stock cam ...
This is what the build liked. As you can see this is the 16th Tune file for my car, and each file has been adjusted multiple times. I've done less timing and more timing. This is where it ended up. It is close to stock, but it's where it ended up. My dyno tuner isn't what I would call well versed on LT1's. LOL.



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max power on fast burning aluminum heads like this is found more high 12s to low 13s. you should head a bit leaner and see how it behaves.
It could use a little more leaning out. But, at 12.9:1 AFR at max VE and a little richer down low I'm o.k with it. Here's my last dyno chart. The AFR line is at the bottom and peaks at 12.9:1 at about 5400RPMs.

I did find a place 5 minutes from my house that will rent me their Mustang Dyno for $100/hr. But, I want to get some other mods (like the exhaust) done before I dyno tune it again. I can play with AFR and Spark timing (I want to play with injector timing too) more then.



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Originally Posted by steveo
why is that? you're only 1/4" under a 3" exhaust. a single 2.75" isn't actually that bad for this kind of car, in fact it can promote velocity of exhaust gasses within the operating range of the engine to create more useable power in normal driving ranges. it might choke it out at very high rpm, but not much.
I understand exhaust gas velocities, but at my power level a 2.75" pipe (and a single 3") is a pretty good restriction to power. Optimally I should be at about 3.5" single at my dyno powered. But, that will go up as I open the exhaust. And it'll rise more with future mods too.

The further away from the engine the smaller the pipes need to be due to cooling, but with my engine VE exceeding 100% and pushing 6600 rpm (going to be 7K in the future) the math shows the 2.75" diameter over axle pipe is too small. And to that you should never reduce exhaust size down stream as it introduces a restriction. Even if it's set up to go from 3" to 3.5" to 3" again it's losing power. Once the exhaust pipe goes to a certain size it should stay there or get bigger only, never smaller.

Here the math. A straight pipe will flow ~115 CFM per square inch of cross-sectional flow area.

At 6100 my VE table is maxed out in the tune (tuner pro RT won't let me go any higher than 99.61%) and my AFR is ~12.5:1. Extrapolating the data from my PE AFR correction tables and the data log AFR on the dyno chart I can conclude that at 6100 RPMs my engine is at 106% VE.

At 6100 RPMs and 106% VE the engine is pulling in 664CFM of cool air, but pushing out about 970CFM of burned air and fuel. I need 115CFM per square inch of cross sectional straight pipe to match my 970CFM of exhaust gases. Of course the pipes are not straight, but it doesn't have to be perfect just close. It is a DD after all. My engine at 6100RPMs needs a 3.40" diameter single pipe exhaust, straight (using .060" for wall thickness). At 7K (assuming 100% VE, a 6% drop from 6100RPMs) I need a 3.53" diameter exhaust, straight piped. In either case they are both about 3.5".

At lower RPMs I will lose some scavenging, but it actually won't be too noticeable from where I am at now due to my LT headers and Y-Pipe and VE chart. To that point, my VE tables at my cruising speeds are ~50%, that would mean that optimally a single straight 1.5" exhaust pipe is optimal. I'm well over that, going even larger will have nil an effect at those engine speeds from where I currently sit.

This is all taking into account my engine as it sits. The TB will get done along with the Intake in time. The exhaust right now is about 65% the size it should be, so it's a restriction and a pretty good one at that. My current exhaust flows a max of 624CFM before it represents a restriction (and that's straight with no bends), I need 970CFM or 55% more cross-sectional area.

Most guys go with 2.2CFM per HP and 115CFM per sq inch of exhaust pipe cross section. That's 2.2CFM per flywheel horsepower. That puts me at about 1071CFM needed or just over 3.5" diameter single straight pipe as I sit.

No matter how I cut the math it points to a single 3.5" pipe straight (or 3/4" larger than where I am now). Remember that area grows at double the rate than diameter when it comes to a circles. Doubling the diameter will quadruple the area. The 3.5" exhaust is 27% larger in diameter, but 65% larger in cross-sectional area. A 3" diameter exhaust is only 1/4" (9%) larger than 2.75", but it's 20% larger in cross-sectional area. These numbers seem slightly off because I'm accounting for the .060" wall thickness.

Taking all that into account I've decided to shoot for a 4" Single exhaust with dual bullet mufflers (in series one on the I pipe and one right before the exhaust tip). That should support about 525rwhp without any losses in power, keep the exhaust tone low and at a decent dbl and like running Open headers.

That lets me upgrade the TB and intake manifold and still have room for some juice down the road with out ever having to change my exhaust again. And in the interim it wont effect driveability noticeably either.


1995 Camaro Z28 LT1 LE2 355 w/ forged pistons/rods, 230/238 .565/.565" 110+6, 1.6:1 SA RR, LT Headers with ORY, T-56 (rebuilt w/ some upgrades), McLeod Street Twin, Lowered 1.25" (Stagg Shocks and Summit Springs) LCA Relocation brackets, Adj Panhard Bar, Poly suspension bushings, STB , CAI, !emissions crap, Magna Flow Cat Back. 146,xxx miles. Purchased Feb 7, 2012 (168K) 414rwhp
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post #20 of 35 (permalink) Old 10-31-2014, 08:23 AM Thread Starter
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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.

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It could use a little more leaning out. But, at 12.9:1 AFR at max VE and a little richer down low I'm o.k with it. Here's my last dyno chart. The AFR line is at the bottom and peaks at 12.9:1 at about 5400RPMs.
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.

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This is what the build liked. As you can see this is the 16th Tune file for my car, and each file has been adjusted multiple times. I've done less timing and more timing. This is where it ended up. It is close to stock, but it's where it ended up. My dyno tuner isn't what I would call well versed on LT1's. LOL.
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'.

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(I want to play with injector timing too)
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.
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post #21 of 35 (permalink) Old 10-31-2014, 04:10 PM
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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.

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Originally Posted by steveo
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).


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Originally Posted by steveo
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.


Quote:
Originally Posted by steveo
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!


1995 Camaro Z28 LT1 LE2 355 w/ forged pistons/rods, 230/238 .565/.565" 110+6, 1.6:1 SA RR, LT Headers with ORY, T-56 (rebuilt w/ some upgrades), McLeod Street Twin, Lowered 1.25" (Stagg Shocks and Summit Springs) LCA Relocation brackets, Adj Panhard Bar, Poly suspension bushings, STB , CAI, !emissions crap, Magna Flow Cat Back. 146,xxx miles. Purchased Feb 7, 2012 (168K) 414rwhp
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post #22 of 35 (permalink) Old 10-31-2014, 04:42 PM
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post #23 of 35 (permalink) Old 10-31-2014, 05:05 PM Thread Starter
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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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post #24 of 35 (permalink) Old 10-31-2014, 06:57 PM
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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 timing at WOT. I'll data log it once I get my clutch installed.


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post #25 of 35 (permalink) Old 10-31-2014, 07:19 PM
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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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post #26 of 35 (permalink) Old 10-31-2014, 08:15 PM Thread Starter
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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.

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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.


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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 WOT timing from 3200rpm to peak RPMs, but logs 37 actual. It holds 36 timing at WOT from 3700 to 5300 then 37 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 advanced. So the spark timing is actually closer than stock to valve timing.


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post #28 of 35 (permalink) Old 11-01-2014, 12:37 AM Thread Starter
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My tables were set at 33 WOT timing from 3200rpm to peak RPMs, but logs 37 actual. It holds 36 timing at WOT from 3700 to 5300 then 37 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.

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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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post #29 of 35 (permalink) Old 11-01-2014, 12:46 AM
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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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Last edited by hrcslam; 11-01-2014 at 04:23 AM.
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post #30 of 35 (permalink) Old 11-01-2014, 10:07 AM Thread Starter
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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.

Last edited by steveo; 11-01-2014 at 10:09 AM.
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