I've been tinkering with tuning for a little over a year now. My truck runs a whole lot better now than when I started, but I think there is more that I can get out of it. I've decided to take it to a dyno and there will be someone there to assist me since I've never tuned with one.

What can I expect while I'm there? Any tools that I should bring? How do you tune with a dyno? I'm sure I will find out more, but I don't want to go into this shop of professionals looking like a complete idiot. I assume you start with the lower RPM stuff, but what about high loads? Do you tune for 1600 RPM @ 60 map, then move onto the next square or do you go somewhere else? Do you tune ALL fuel first, then move onto the timing?

I just want to go there and use my time as efficiently as possible since it isn't exactly cheap. I beleive the tune is a little more refined than "roughed in", so I hope I don't have to completely start over.

 

If you have a "real time" editor, then you should adjust your fueling to obtain approximately 12.8:1 +/-.2 (which ever gets the max TQ/HP) with the spark advance that doesn't cause knock to occur and yields max TQ/HP too. That will give you the most efficient use of your dyno time.

If you do not have real time, then you will need to take time between runs to modify the bin and do another run. This is more "trial and error" and will require you to keep modifying fuel and spark until you obtain max TQ/HP. Usually, due to the cost, you only do a couple and "live with the best you could get". Work on the Fueling for AF ratio I mention and then adjust the spark.

But, from what you can gather, a real-time editor is really the best way to do this.

 

Find out before hand what type of dyno it is. Many chassis dyno's only allow a "run" to be made. They won't hold a speed/load. With this they are best utilized for WOT tuning.

With lightly to moderately modified vehicles 99% of the fueling can be refined by driving around. On-ramps and getting up to highway speed is good for checking this at higher loads/RPM.

Then once at the dyno, seat-belt the laptop in (they rarely survive a trip through the rollers). Data log every run.

First run, double check the AFR. Then work on the spark timing. Note that as the RPM increases the MAP will be decreasing. Note what area of the SA table this is. It may not be 100 KPa through out the run.

Once you have a baseline pull 2 degrees of timing and make another run. Did the power improve or drop off? Note what areas of the RPM curve changed. Some may be better, some may be worse.

Adjust the spark timing accordingly and make another run. If the power dropped off with the 2 degreees less timing, then add 4 back in to give 2 degrees more then the basline. You can make small adjustments to the AFR as the best power spark advance is found.

RBob.

 

RBob,

Should you look to completely eliminate any Spark Knock when tuning for WOT? Some people seem to think that you should have some in order to know that your taking advantage of as much SA as possible for power.

Secondly, you hear stories about how a particular tuner can get an addtional 10-20rwhp. Maybe I haven't done this enough, but if you have the AFR pretty well dialed in and the SA is setup to avoid KR but gain torque/hp, what else can you do to maximize power?

 

I have the an Autoprom, so I'm good with the emulator. This is a truck, so I've heard to aim more towards 12.3:1; does that sound about right?

This dyno will do loads, so that will be nice. It's actually a shop that does turbos, so they were a little confused as to why I want it done there.

Rbob, you said to double check my AFR. I am using OL only, and using the original open loop coolant vs AFR table that was set in EBL. Do you mean to check it against these values? I drove around for 3 hours on Saturday doing numerous VE learns, so the VE tables look great.

One other thing, if the VE tables are in line for the amount of timing I have and I adjust the timing a few degrees, how much does that actually affect the fueling? 10%???

 

To me it would depend upon whether it is a race motor or a street motor. Bill Jenkins would run his engines on the verge of all out detonation. Just for the extra power it gave. He also went to great lengths to equalize the temperature of the heads and chambers.

To me for a street engine, nope, not worth it. Then again in todays world a 'street' engine may come out every winter for a freshen up. It all depends upon the wallet vs. the gains.

RBob.

 

As for AFR the folks at the dyno shop should be able to help. What I mean by this is what to target. The biggest issue with AFR today is the WB units and the fuel mix. Some WB units report 14.7:1 at stoich, others 14.5:1 at stoich. WB sensors are accurate at stoich, so no matter what AFR they report at that AFR it doesn't matter what fuel is being run.

Once the exhaust AFR moves from stoich, so does the WB sensor calibration. If the dyno shop has a good WB setup and they understand todays fuels, that will help.

What I mean by double checking the AFR is that it may move as the spark timing is changed. Just keep it on the rich side and don't go for max lean power. It is a street vehicle (am I correct?), and if so then max rich power is where you want it to be under WOT.

For a street vehicle a safe tune is better then a lean max power tune. Save the lean tune for drag racing. Street engiens need the extra fuel for engine cooling. They can easily be under heavy load for more then a 1/4 mile at a time.

At the same time you may want to change the targeted AFR. This would be the OL AFR table (CTS vs VAC).

I hope this helps and doesn't confuse you more. Part of the reason is that last week I did a bunch of work on what todays fuels are. True stoich isn't 14.7:1 anymore. And 93 octane vs. 89 octane has a lower AFR for stoich. Then add in some ethanol and the stoich AFR is even lower.

RBob.

{edit: just to be sure, if you do try to 'tune on the fly' while the vehicle is under load on the dyno. Be absolutely sure of what you are typing in. One mis-type or one mis-think and valves can end up in the mufflers and the pistons in the oil pan. I rank this kind of stuff right up there with having a WB adjusting the AFR as the car traverses the 1/4 mile. . . }

 

As RBob mentioned, you will only be tuning WOT when you are on a dyno. I personally think you should get a GOOD "part throttle" tune done as a "good base" before you do ANY dyno tune.

If you don't have a "good base", then you'll just be adjusting P/E Tables based on WOT reaings on a "poor base". Should you later make any future changes (which is highly likely if you have a poor base) then those future changes to the "base tables" will make your "dyno tune" obsolete and require another tune again.

As RBob said, 99.9% of your tuning can be done without a Dyno Tune, especially if you have a Wide Band O2 Sensor. In fact, some would argue that tuning by a Wide Band O2 Sensor makes a Dyno Tune meaningless and any "adjustments" may actually be anomolies as a Dyno Tune only measures HP at under a very limited circumstance. In a Dyno, you don't have air resistance and drag. Also, you won't get a chance to tune under a wider variety of circumstances like different elevation, temperature and humdity.

So, I would say the Dyno Tune should be the LAST thing you ever do AND if you did enough "real world" tuning with a WB, the Dyno should be ONLY to measure your HP and NOT for actual tuning.

 

Thanks for the warning. I actually mis-typed last week and luckily the only consequence was that it ran like crap.

The dyno place charges $45 for using their WB, so maybe I should do that to see how far off mine is.

The vehicle is a street vehicle and the engine is new, so I will keep it on the safe side.

Now this is something I haven't really thought about until now. If the targeted AFR is say 14:1 at a given CTS and VAC, when you tune the VE table, you are tuning for 14:1, right? What if you change the 14:1 target to 14.7:1? Is the AFR still tuned for 14:1 until you readjust the VE table?

 

Well I think I have a good base tune, but I'm not sure if my timing at lower RPMs (non-PE) is where it should be. The fuel looks great and it runs smooth, but I figured a dyno might help me with the timing for most of the driving I do. Tuning the timing by just driving around doesn't work real good for me. My butt dyno is horribly inaccurate.

So you think tuning for WOT is a waste unless my base tune is perfect? What if the base tune just needs finessing?

 

Well, the closer the better ... but it's a "nice to have", NOT a necessity.

On a "basically stock" engine, the stock tables are far from perfect and it would be better if the person tuned the tables first before doing a Dyno Tune. BUT, I would also say it would NOT be a waste of time either to do a Dyno Tune with the tables "as is" from an stock eprom on a basically stock engine. However, if the engine was modified to any degree, then I would say "tune the part-throttle first" then the Dyno Tune.

Does that give you a "reasonable guideline" to work with?

 

If you tuned in "Open Loop", then yes, the tables would be setup for 14:1 NOT 14.7:1. In fact, a lot of guys do that for that very reason...most find a slightly richer "base" AFR makes for a better running engine "overall".

Some even tune with ONE TABLE! With Wide Band and running "Open Loop" then use just one main VE Table and tune it to correspond to what they want. They know that in certain kpa/rpms, the engine is idling and they run a AFR they like (say 13.5). Then in another area, they run 14:1, in the area where they run "on the highway", they may go leaner to 15 or 16:1 and the area where they are basically WOT, they tune for 12.8-13.0:1.

It's quite possible and some swear by it as the BEST WAY to tune. I personally prefer to tune as the way GM designed it with a Main Table and separate tables for Highway Mode, P/E and Cold Start - but I live in a mountainous area and I find this makes tuning simpler with better driveability.

But, if I lived in a flater region with steady elevation, a single table would make things simpler to tune. I guess a person needs to try both and determine what THEY prefer. There is a lot to be said for simplicity with just one table - especially if you have a big solid roller cam.

 

I was thinking about this just the other day and how the whole "tuning" thing started. Today, we go out looking for the 128 BLM Holy Grail but I recall Grumpy describing how he started. With nothing more than a tach and Vacuum gauge, he'd add or subtract fuel and timing based on getting the best vacuum for a given rpm. So as he got the tune better and better, the actual MAP would drop. So he chased the tune down the MAP table until MAP started to go back up. Then he would take a step back. So he really wasn't tuning for 128. That's why he always said to "give motor what it wants". That's how he started.

 

You may find that their WB units reported AFR doesn't match your WB units reported AFR. And most likely won't. A good shop will have a WB setup that can be calibrated for different fuels. An example is that premium unleaded with 10% ethanol has a stoich of 13.8:1.

A regular run-of-the-mill WB unit will report that as 14.7:1 (stoich). Where a WB unit that can be calibrated for different fuels will report 13.8:1 at stoich.

I guess this goes back to your previous post about using 12.3:1 as a good power AFR. For a regular WB unit and todays fuels it is a safe AFR to target.


When the AFR target is 14.0:1 and the VE is adjusted to provide that in the exhaust, changing the target to another AFR will have the PW also change. So no additional changes to the VE table are required. The targeted AFR is part of the calculation for the injector PW.

However, that is in a perfect world, as non-linearalities always creep in. So some minor changes in the VE may be required.


On the dyno I would at a minimum get the WOT spark timing set up for decent power. Then, since they can hold a speed/load, see if you can hit some points at various RPM and loads. Maybe even get a log prior to going of the RPM/load range for a freeway merge.

Then use that path through the SA table(s) for the dyno testing. Just be careful if you do max power timing at lower RPMs. As this gets into driveability in traffic crawl. And best power timing can make a vehicle difficult to drive smoothly at low speeds.

RBob.

 

As always, great advise from you guys.

It will be interesting to see how close the tune is already during WOT. I have the AFR nuts-on at 12.3 up to about 5K RPM and the max timing is set at 28. Everything I've read said that the best timing for the vortec heads is 28, and from what I could tell, I lose some power at anything above or below it, and the same goes for the AFR. It will be nice to see if I'm right or not.

When I was doing my initial tune for WOT, I tried changing the PE AFR table around and it didn't seem to do much so I ended up adjusting the VE table to make up for it. Any idea what could cause that?

Having said that, maybe my WB is off. I will definitely rent theirs.

 

Well, it's done. It didn't go quite like I had hoped. To my surprise, the first run the person running the dyno took one look at the cruise and lower RPM areas and said "well everything looks real good here" without making any adjustments at all. He said he might try adding a few degrees here and there, but said it looked good where it was at. The shop was busy and they specialize in installing and tuning turbos, so I'm not sure how much I buy into it, but the guy did seem to know what he was doing. I think he may have had bigger fish to fry though.

Then came the WOT tuning. 12 runs up to 5500 RPM only to discover that my tune at WOT was already so close I only gained 6 HP and 3 ft.lbs of torque in the end. What a waste of $400. Aside from that, I'm fairly disappointed that with all the money I've spent on this engine so far, what I got is as good as it's going to get without spending a lot more. I was hoping (and told) to get around 330 at the crank which would be about 250 at the wheels. I only got 220 at the wheels which would be about 275 at the crank. 50 HP off of what I thought I would get. The engine stock was rated at 200 HP. I replaced it with a new crate engine, vortec heads, mild hydraulic roller cam (instead of flat tappet), K&N intake, 3" exhaust, bigger TBI, and this is all I ended up with? That really sucks.

Now, before the dyno session, I did some datalogs at WOT. My WB said it was right on at 12.3:1. When I brought the truck in today, they were supposed to weld in another bung so I could compare a "professional" WB setup to my own. Well, they didn't have any lifts open, so we had to remove mine and install theirs in it's place, so in my datalogs, I have no WB readings. This also sucks. As expected, there is a huge difference between the two. My WB readings were a consistant 12.3:1 and theirs showed 11:1. He never saw any readings with my WB and I didn't offer any information, but as he was removing it he said this particular brand tends to read three-quarters of a point leaner than what's really there. I didn't tell him in this case, it's more like 1.3 points leaner.

Here's where it gets a little interesting. The reason I got 12 runs was because he said that 11:1 is way to rich so he kept pulling fuel. For some reason, this engine likes to be pig rich because every run that he pulled fuel from, it lost power. Every time he gave it what he thought it needed (instead of listening to the engine and giving it what it actually needed; RIP Grumpy) it lost power. He even pulled another guy over to take a look at the runs, then they changed their sensor out and the readings didn't change. So this thing looks like a diesel at WOT, but that's where it's happy.

Anyone else seen that before?

 

What kind of WBO2 sensor do you have? I scanned back through the
thread and didn't see mention of what it is.

 

It's an Innovate LC-1. There might be 2K miles on the sensor and I just recalibrated it.

 

I figured you were going to say that, I have the same one.

 

It's supposed to be a good WB for the price. I kind of wonder if there was a problem with theirs. They tune race cars all the time and the lead in the fuel is hard on sensors, or so I've read. They were literally pushing a twin-turbo charged dragster off the dyno right after I got there.

I also wonder about their accuracy with multiple fuel types running past the same sensor.

 

im kind of suprised by your hp numbers, it does seem low. what kind of torque did it make, and at what rpm was peak torque. what kind of shorty headers are you running? and what y-pipe are you using? i wonder if you are losing some power there? the factory y-pipe on that truck is really restrictive. my stock 95 truck has an 1-7/8" y-pipe into a 3" from the factory. im wanting to replace that with something like 2-1/2" y-pipe. to hopefully get some more power. your set-up seems solid. i would have guessed 350 horse and like 400 lb/ft torque. but i can only guess. i havnt been to the dyno myself.

 

im kind of suprised by your hp numbers, it does seem low. what kind of torque did it make, and at what rpm was peak torque. what kind of shorty headers are you running? and what y-pipe are you using? i wonder if you are losing some power there? the factory y-pipe on that truck is really restrictive. my stock 95 truck has an 1-7/8" y-pipe into a 3" from the factory. im wanting to replace that with something like 2-1/2" y-pipe. to hopefully get some more power. your set-up seems solid. i would have guessed 350 horse and like 400 lb/ft torque. but i can only guess. i havnt been to the dyno myself.

 

Pre-tuner, how much "playing" did you do with your AFR and spark advance? Sometimes, you can add a bit more spark with a little extra fuel and get a bit more HP. Usually you can do this more at the "top end" and extend you usable RPM range.

 

I'm using some cheap Pacesetter shortie headers with the factory Y-pipe. When I had the rest of the exhaust done, I asked the guy doing it if he thought it was restictive and he said no, so I didn't bother having it replaced. I think it's probably 1 7/8" like yours.

Here is a pic of the dynoslip. The torque curve is pretty flat (to me anyway) and it looks like the peak is at about 3800rpm. Peak HP is all the way up at 4700rpm. Seems high to me.


http://i64.photobucket.com/albums/h1...h/dynoslip.jpg

There were about 4 runs wasted on chasing the lower AFR, and everything else was dialing the AFR in. It doesn't show in the picture, but the peak AFR is at about 12:1 @ 3500rpm and continues down from there through 5K rpm. We increased the timing by 1 degree from where I had it and it lost power. That was about all the chasing we did. The timing is the same from about 3200 on up.

 

well, from the things ive read about our stock exhaust, and how restrictive it is, id say that the y-pipe and maybe the shortie headers are bottlenecking your setup, just like its doing to mine. the y-pipe alone might be worth 25 hp.

 

What? How can an 1 7/8 pipe that feeds half of the engine be restictive when the whole engine runs into a 3" pipe? I'm not saying you're wrong, I just don't get how that works.

The reason I went with the short tube headers is because they are supposed to be better for torque and the long tubes are more for higher RPM's. I've been wanting some headers with the Jet coating since the painted ones look so bad. Do you think the short headers are a problem or the brand (or features) of headers I have.

My supercharged '99 has some Banks short headers. Maybe I should swap them.

 

The shorty headers are terrible for torque, longer primary tubes to a point will make more torque at a lower rpm. The 1 7/8" pipe can be a restriction because two 1 7/8" pipes do not have neary the area of a single 3" pipe. In fact it takes 2 x 2 1/4" pipes to equal the area of a single 3" pipe.

 

I'll look into some long tubes then. I didn't come this far to give in now.

Any idea why it likes so much fuel? Wrong cam?

 

Brian at TBIchips did some dyno testing before and after exhaust modifications with his "Black Magic" and "Blue Whale" projects. The conclusion was the factory setup is very restrictive: http://www.tbichips.com/blackmagic.htm. He pulled another 40 rwhp and 50 rwft-lbs by changing to a 2-1/2" y-pipe. From the text, it sounds like he was using shorty headers and a 3" Magnaflow cat in both dyno runs. The results are mainly from the y-pipe change. Interesting, hey?

I would try a new y-pipe since it would be relatively cheap to fab up compared to buying/installing long-tubes and an entire new exhaust. For $180, you can get a mandrel-bent tube from Edelbrock that's a direct fit for your truck: http://store.summitracing.com/partde...5&autoview=sku. It was designed for lowered trucks (1.675" more clearance), but it will bolt right up to the factory manifolds or direct replacement shorty headers. I actually have a brand-new Magnaflow cat that has never been used that was hacked off a direct-fit y-pipe for the 88-94 C1500. You can take it off my hands for $50 + shipping. Just weld it on and go. PM me if you are interested.

 

Interesting article. If nothing else, you all have helped me see the light and I really need to get that Y-pipe changed out. Hopefully it will fix the problem, but it will definitely get me some more HP. I haven't decided yet if I'm going to replace the headers also. The Thorley's come with a Y-pipe and I can get away from the cheapies I got on there. I'll keep everyone posted.

 

Pre-Tuner, did you disable the "Knock Retard" feature? The reason I say this, is if you allow the eprom to retard the timing (as it does stock), the slightest amount of knock (which may not show up) can cause you to lose MORE TIMING than you added. I call this the "one step forward and two steps back".

Guys who just "twist the distributor to add timing" often encounter this when you finally show them a real-time reading.

If you have a well tuned eprom, I often find it better to limit the Spark Retard when in WOT to the smallest setting (so you can see it) and control the spark curve manually. If the "knock retard" starts to retard the timing, the havoc it causes with the spark curve causes the amount of timing the engine to handle is much less than if you control the curve yourself.

But, if you lost power with a 1 degree add of timing, it strikes me that you have the "knock retard" functioning - and that can be a major source of trouble when tuning yourself. I do let the "knock retard" work in "part-throttle" just incase, but only in part-throttle.

 

It is enabled, but I use the EBL and the timing shows up as being exactly what it's supposed to be. I also don't see any counts in the dump log.

So you're saying I could have knock that doesn't show up but the ECM will make corrections anyway? I'll disable it next time and see if it helps me any.

 

Real interesting. Let me know if I correct understand:
Say I have a timing table with 30 deg total timing at wot. It made 300 HP.
I try to add 2 deg of timing (total timing = 32).
Run at the Dyno: 290 HP.
The knock tables are not reduced and during the dyno session the knock sensor sense a knock and continue to detect knock. The total timing removed are 5 deg. The engine is running at 27 deg. At 27 the hp went from 300 to 290.

Now with the Knock table at only 1 deg, when the engine knock it remove only 1 deg. (It is running at 31 deg-with some detonation).
The HP with 31 deg total timing are 310.

So adding timing you think you loose power. And this is not true.
In real, you are gaining power. (you need only to add premium) gas
-Beppe-

 

Problem fixed! I haven't been to the dyno yet, so I don't have firm numbers, but it's definitely better. I ended up changing the headers to ceramic coated Doug Thorley Tri-Y's (mid length) and it came with a 2.5" Y-Pipe. Now she can breathe! It sounds better, pulls better, and gets up to speed faster! I'm not sure how Brian got 40HP at the wheels, but I might have gained 40HP at the crank. It is definitely noticeable, even with the roughed-in tune I have now.

 

Everyone should run a PROPER set of headers. Tri-Ys are the only way to fly in a truck application as far as I am concerned.

 

No kidding. I always thought the header style didn't matter as long as the exaust could get out. Boy was I uneducated.

 

Overall matchup of components is VERY important. My 305 TPI is a perfect example of that. It pulls hard, EVERYWHERE in the power band, and gets good fuel mileage. What is not readily apparent in the picture is just how large in diameter the header pipes are. From the ports they are a good 1 3/4", then step up to 2 1/4" at the first merges then run into 2 1/2" collectors. When I first installed them on my TBI engine with ported vortecs and a custom grind cam, the strong scavenging, ported exhaust head ports, and the extra exhaust duration on the cam would actually pull the incoming air/fuel charge into the exhaust. I had to change cams to keep it from happening.



http://s243.photobucket.com/albums/f...t=101_1403.flv

 

How did you ever figure that out?