Difference between pcmforless tune and dyno tune
Thread Starter
Instructor
Joined: Jun 2010
Posts: 248
Likes: 2
From: Avon IN
I don't really understand why there is so much question on this thread. Yes alvin does good work, however I have seen the opposite where the tune was too conservative.. it happens. With my 383 build: 1.6 rockers, new valve train, oil pan to manifold rebuild, xfi 268 cam, 32lb injectors, bigger tb, extensive intake work, LT headers, free flowing exhaust, clutch kit, new fuel pump and filter, afpr, air filter, cut airbox, ported heads, bigger valves, new plugs, new wires, new coil should put me where I am now. If all that work just warranted me 50 whp more than stock then something is seriously wrong with the build/setup. I think based on what I have done proves that the tune I got from pcmforless was extremely conservative. I am sure if I datalogged and sent in my chip Alvin would be able to dial it in for me, I just chose to go a different route.
Drifting
Joined: Nov 2009
Posts: 1,341
Likes: 2
From: Perth Western Australia
St. Jude Donor '10
If your fuel pressure was low then that could explain the loss of hp.
Before I did my build I was very disappointed in the top end speed at the track. It just seemed to go flat. Eventually (after I finished my build) I found that I had a fuel leak at the tank on the sending fuel line.
So maybe your new fuel pump and regulator did make the big difference.
Before I did my build I was very disappointed in the top end speed at the track. It just seemed to go flat. Eventually (after I finished my build) I found that I had a fuel leak at the tank on the sending fuel line.
So maybe your new fuel pump and regulator did make the big difference.
Le Mans Master
Joined: Apr 2000
Posts: 5,713
Likes: 105
From: Manassas VA
The power increase is not due to the fuel increase. IMO if it was the AFR would be different between the 2 tunes.
The hp increase at 5000 rpms looks to be about 75hp. I find that hard to believe especially where the AFR never changed.
The hp increase at 5000 rpms looks to be about 75hp. I find that hard to believe especially where the AFR never changed.
Team Owner
Joined: Dec 2000
Posts: 21,094
Likes: 282
From: Phila., PA burbs
I would have liked to do a custom tune for my recent build. The issue I had was that no one in my area (that I'm aware of) tunes OBDI cars anymore and I wasn't interested in learning/buying the equipment needed. So I was left with a mail order tune. I sent PCMforless the details of my build and they sent me out a chip. I then took the car directly to my local dyno for testing. I also bought the stuff to datalog my car. I then sent the datalog and dyno info back to PCMforless with my chip. For the price of shipping they touched up the tune. I went back to the dyno and saw nice gains. It's still not a custom tune, but it was the best I could do without buying the stuff myself.
Race Director
Joined: Apr 2003
Posts: 17,700
Likes: 1,667
From: moraga ca
There are 2 major parameters that go into a tune that determine power; fuel and timing. You are saying that the air fuel ratio was pretty much the same between the two. That leaves a 50 hp increase as a result of a difference in timing. Do you think Alvin's keyboard slipped and he was 10 degrees short at wot? It would be nice to compare spark tables and see what the difference is. Not that hard to do.
Thread Starter
Instructor
Joined: Jun 2010
Posts: 248
Likes: 2
From: Avon IN
There are 2 major parameters that go into a tune that determine power; fuel and timing. You are saying that the air fuel ratio was pretty much the same between the two. That leaves a 50 hp increase as a result of a difference in timing. Do you think Alvin's keyboard slipped and he was 10 degrees short at wot? It would be nice to compare spark tables and see what the difference is. Not that hard to do.
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Thread Starter
Instructor
Joined: Jun 2010
Posts: 248
Likes: 2
From: Avon IN
If your fuel pressure was low then that could explain the loss of hp.
Before I did my build I was very disappointed in the top end speed at the track. It just seemed to go flat. Eventually (after I finished my build) I found that I had a fuel leak at the tank on the sending fuel line.
So maybe your new fuel pump and regulator did make the big difference.
Before I did my build I was very disappointed in the top end speed at the track. It just seemed to go flat. Eventually (after I finished my build) I found that I had a fuel leak at the tank on the sending fuel line.
So maybe your new fuel pump and regulator did make the big difference.
Le Mans Master
Joined: Apr 2000
Posts: 5,713
Likes: 105
From: Manassas VA
There are 2 major parameters that go into a tune that determine power; fuel and timing. You are saying that the air fuel ratio was pretty much the same between the two. That leaves a 50 hp increase as a result of a difference in timing. Do you think Alvin's keyboard slipped and he was 10 degrees short at wot? It would be nice to compare spark tables and see what the difference is. Not that hard to do.
The air fuel ratio is exactly the same. Which if his timing was off it wouldnt be burning as efficiently therefore the AFR would be different. When I look at the table, it looks like a 75hp gain at 5000 rpms.
Thread Starter
Instructor
Joined: Jun 2010
Posts: 248
Likes: 2
From: Avon IN
Here is another more detailed table of the tune before and after. I am running the car tonight so all will be brought to light on whether this tune was fudged or not.. I am doing this for you who question this tune. I drive the car, I know the car, and I believe the numbers that are posted. I will check the plugs for detonation in case there is excessive timing.
Race Director
Joined: Apr 2003
Posts: 17,700
Likes: 1,667
From: moraga ca
Well that explains it. Looking at the afr, they are a whole point different. That could make a big difference. The scale in the original graph needed to be changed. You can't see a 1 point change in afr on a 50 scale.
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
At least part of it anyway. I'd with 383Vett in still wanting to see the spark tables before/after. At least the right-most (heavies load) column anyway.
Suckin' gas, haulin' ass.
Joined: Apr 2010
Posts: 1,100
Likes: 8
From: Newport News Virginia
Your car is spark knocking by the way. See the wavy lines between 4000 and 4700? That's the computer pulling spark advance and then putting it back in when the knocking goes away. I would contribute it to the 13:1 AFR, which is a little too lean in my opinion for a motor like that under a 100% load and WOT. I'm not comfortable with much less than 12.5:1 through the power band.
I would try and get some more fuel put in for that 1000 RPM and get it a little fatter. Eventually, the knock is going to break a ring land and that will make you an unhappy camper. I'd rather lose some power for the sake of reliability, but that's not my car, and I'm not telling you what you should do with it. Just a suggestion is all.
I would try and get some more fuel put in for that 1000 RPM and get it a little fatter. Eventually, the knock is going to break a ring land and that will make you an unhappy camper. I'd rather lose some power for the sake of reliability, but that's not my car, and I'm not telling you what you should do with it. Just a suggestion is all.
Thread Starter
Instructor
Joined: Jun 2010
Posts: 248
Likes: 2
From: Avon IN
Your car is spark knocking by the way. See the wavy lines between 4000 and 4700? That's the computer pulling spark advance and then putting it back in when the knocking goes away. I would contribute it to the 13:1 AFR, which is a little too lean in my opinion for a motor like that under a 100% load and WOT. I'm not comfortable with much less than 12.5:1 through the power band.
I would try and get some more fuel put in for that 1000 RPM and get it a little fatter. Eventually, the knock is going to break a ring land and that will make you an unhappy camper. I'd rather lose some power for the sake of reliability, but that's not my car, and I'm not telling you what you should do with it. Just a suggestion is all.
I would try and get some more fuel put in for that 1000 RPM and get it a little fatter. Eventually, the knock is going to break a ring land and that will make you an unhappy camper. I'd rather lose some power for the sake of reliability, but that's not my car, and I'm not telling you what you should do with it. Just a suggestion is all.
Race Director
Joined: Jun 2004
Posts: 13,961
Likes: 707
From: WI
The dips on the graph do not match the number read out. The graph dips could be scaling factor in the software. If it actually did have knock there (data log!) I would reduce timing rather than add fuel as a first thing to try. I just had my current combo on the dyno and went from 11.9 to 13.2 it picked up 15 HP with no knock. 12.5 can still be very rich for some combos. The point of it is to find where your engine works the best. I'm a little surprised at that fuel read out, there is a pretty large variance in fuel.
Thread Starter
Instructor
Joined: Jun 2010
Posts: 248
Likes: 2
From: Avon IN
Le Mans Master
Joined: Apr 2000
Posts: 5,713
Likes: 105
From: Manassas VA
[ I am running the car tonight so all will be brought to light on whether this tune was fudged or not..
What et and mph were you running before the tune? Are you running on drag radials? Here is a link you may find interesting. It makes it easier to compare the drag slips from different days. http://www.dragtimes.com/da-density-...calculator.php
What et and mph were you running before the tune? Are you running on drag radials? Here is a link you may find interesting. It makes it easier to compare the drag slips from different days. http://www.dragtimes.com/da-density-...calculator.php
Thread Starter
Instructor
Joined: Jun 2010
Posts: 248
Likes: 2
From: Avon IN
[ I am running the car tonight so all will be brought to light on whether this tune was fudged or not..
What et and mph were you running before the tune? Are you running on drag radials? Here is a link you may find interesting. It makes it easier to compare the drag slips from different days. http://www.dragtimes.com/da-density-...calculator.php
What et and mph were you running before the tune? Are you running on drag radials? Here is a link you may find interesting. It makes it easier to compare the drag slips from different days. http://www.dragtimes.com/da-density-...calculator.php
Thanks for the link, very cool.
