Dyno time!!!
- Thread starter erlrich
- Start date
Andy Bettencourt
Super Moderator
1. Do 3-5 pulls. Make sure all your fluids (tranny and diff) are up to temp.
2. I would adjust FP in bigger chunks or you could be doing 20 pulls getting it right. Maybe 5lbs at a time and then tweak when you see a decrease. Make sure you keep the A/F on the rich side of the line. Going lean may result in a failure. I like to use about 13.8 to 14.1 while in the power band.
3. If you have a stock bottom end, did you calculate the amount you took off your head based on a future .020 or .040 overbore? If you maxed it out, you may end up with more than the legal 1/2 point max in compression bump when you increase your bore. Hopefully someone went over that with you.
4. I would be careful on ignition timing. Go up in 1 or 2 degree incraments. You don't want to overshoot this and get too much advance. In order to really get your timing down with a fuel change, you will need to drain the tank for the new fuel. If you can't do that at the dyno shop, drain now and start with the gas you intend to run.
Have fun! Remember, dyno number differ so much so your job isn't to match 'marketing' numbers, it's to maximize your personal set-up.
AB
2. I would adjust FP in bigger chunks or you could be doing 20 pulls getting it right. Maybe 5lbs at a time and then tweak when you see a decrease. Make sure you keep the A/F on the rich side of the line. Going lean may result in a failure. I like to use about 13.8 to 14.1 while in the power band.
3. If you have a stock bottom end, did you calculate the amount you took off your head based on a future .020 or .040 overbore? If you maxed it out, you may end up with more than the legal 1/2 point max in compression bump when you increase your bore. Hopefully someone went over that with you.
4. I would be careful on ignition timing. Go up in 1 or 2 degree incraments. You don't want to overshoot this and get too much advance. In order to really get your timing down with a fuel change, you will need to drain the tank for the new fuel. If you can't do that at the dyno shop, drain now and start with the gas you intend to run.
Have fun! Remember, dyno number differ so much so your job isn't to match 'marketing' numbers, it's to maximize your personal set-up.
AB
Just out of curiosity, how do you plan to do cam timing adjustments?
Listen to what the guy running the dyno has to say too. He may not know about your specific car, but he will know things like what Andy is saying about increments of change. Also, if for nothing else, he'll tend to help you more if you don't treat him like he's never done it before.
Have fun.
Listen to what the guy running the dyno has to say too. He may not know about your specific car, but he will know things like what Andy is saying about increments of change. Also, if for nothing else, he'll tend to help you more if you don't treat him like he's never done it before.
Have fun.
erlrich
Super Moderator
Thanks guys, I really appreciate the tips.
Andy, as far as the head, I know .023 sounds like alot, but both I and my engine guy did the math and even with a .020 over bore and the oem flat top pistons I'm going to be hard pressed to get much, if any, above the stated factory compression numbers. Don't know if I was blessed with overly generous combustion chambers, or if maybe Nissan just got really conservative with their later engines, but as best I can figure my compression had to have been .2 to .3 below spec to begin with.
M, I'm using the cam gear with the offset bushings to return timing to stock.
I'll let you know how it goes.
Andy, as far as the head, I know .023 sounds like alot, but both I and my engine guy did the math and even with a .020 over bore and the oem flat top pistons I'm going to be hard pressed to get much, if any, above the stated factory compression numbers. Don't know if I was blessed with overly generous combustion chambers, or if maybe Nissan just got really conservative with their later engines, but as best I can figure my compression had to have been .2 to .3 below spec to begin with.
M, I'm using the cam gear with the offset bushings to return timing to stock.
I'll let you know how it goes.
erlrich
Super Moderator
Hey guys,
Aside from the fact that the numbers were truely disappointing, and the car didn't seem to respond much to any of the changes I made, I was very concerned that the A/F mixture in the lower rpm range (< 3500) was really lean - like off the scale lean. I realized we don't spend much, if any, time in the lower rpms, but I was wondering if this is typical with this car, or if this is something I need to look into. I've attached a copy of one of the pulls; they were pretty much all the same as far as the A/F curve is concerned. The fuel pressure for this pull was set at 33/41psi, cam and ignition timing were spec.
[attachmentid=627]
Aside from the fact that the numbers were truely disappointing, and the car didn't seem to respond much to any of the changes I made, I was very concerned that the A/F mixture in the lower rpm range (< 3500) was really lean - like off the scale lean. I realized we don't spend much, if any, time in the lower rpms, but I was wondering if this is typical with this car, or if this is something I need to look into. I've attached a copy of one of the pulls; they were pretty much all the same as far as the A/F curve is concerned. The fuel pressure for this pull was set at 33/41psi, cam and ignition timing were spec.
[attachmentid=627]
Glad you posted the plot. For your build the numbers do seem off. Seems like the engine is not running right or something is choking you down. Do you have the secondary intake butterflies removed from the intake manifold? Did you do a coolant bypass on the manifold/TB? (doubt this makes a difference but just wondering). Stock intake? What are the compression numbers? Balanced and blueprinted injectors?
Not sure what but something is up. Below is a dyno of 2 different motors for comparison's sake.
The red line is a junkyard motor that wasn't cracked open. The S&S header on this car was badly dented where it bends to go under the car. Exhaust wasn't the greatest work but flowed well i guess. Compression test was 175, 180, 175, 175. So, it was a very nice junkyard motor.
The blue line is actually a built motor. Shaved head, decked block (for the +.5 CR increase), valve job, new valves, pistons, balanced, etc. Goes to show it takes a lot to beat the factory numbers sometimes. Compression test was 180 across the board. We had dyno'd it with a JWT ecu also, but the peak numbers didn't change. There was an increase in power from 2k - 4500 rpm (which we don't use anyways) and after that it was the same as the stock ecu. With the JWT, after 5500 rpm the a/f dropped to 11.5:1, but the power was the same.
Both cars had balanced and blueprinted injectors, which we have found "regained" a lot of power. To me it's a must for cars this old.
Send me the .drf file and I can add it over the 2 plots below and post another with all 3. Could be interesting.
[attachmentid=631]
Hope that helps some.
s
erlrich
Super Moderator
Steve - yes on the butterflies (for those wagging fingers it was explained to me that once I had the (legal) port matching done these butterfiles no longer seat properly and must be removed), no on the bypass, yes on the stock intake(other than the port matching). Compression numbers are a little low, but consistent; 165 - 170. Leakdown was under 2% across the board. I already knew the compression was going to be low - when I had the head done my engine guy calculated my new compression to be around 8.7, and my own calculations had it at 8.8. And that was after the head was shaved .023". The injectors were cleaned and flow-tested last year; they were flowing between 260 - 264 cc/min at 43 psi (I believe they're rated at 270cc?).
There may be a couple of things there - I'm still using the S&S header in its 'street' configuration. I know several guys have mentioned there are gains to be found by opening up the exhaust, so that will be one of my next projects. Also, I did everything with the JWT ECU in the car - in hindsight I wish I had tried at least 2 - 3 pulls with the stock ECU. The only other thing I can think of is that maybe I plugged a vacuum line I shouldn't have when I pulled the EGR & AIV systems. I'll have to go back and look at that.
Anyway, I'll be doing a complete rebuild over the winter, including boring .020 over and going to the flat-top pistons. In the mean time I'll go over everything else and see if we can't do a little better next time.
Thanks again.
erlrich
Super Moderator
Gary, you're absolutely correct, there's nothing in the ITCS that specifically allows the removal of the butterflies. What the ITCS does explicitly permit is "manifold and cylinder head port matching". What it does not say is "manifold and cylinder head port matching is permitted unless it requires the removal of the butterflies to do so". To quote the second-most uttered mantra of IT (right after IIDSYCYC), "If it says you can, then you bloody well can".
Now, I have one favor to ask of everyone; if we decide to turn this into a 20-page debate about the legality of removing butterflies, could we please start a new thread? Pretty please? I was really just trying to figure out what's wrong with my car here.
[/b]
ITCS 17.1.4.D
Exhaust emission control air pumps, associated lines, nozzles, and electrical/mechanical EGR devices may be removed. If such items are not removed, they shall not be modified in any way. If EGR devices/nozzles are removed from a cylinder head or manifold, any holes remaining shall be completely plugged. Water to an intake manifold may be blocked or removed as part of the emission system.
In the factory Nissan service manual those butterflies are specifically called out as part of an EGR device.
...back on topic please.s
Hmmmm. You've got me stumped. You're compression numbers are good, new head, good injectors, A/F is ok. You SHOULD be making more power, easily in the high 130 range. Something still isn't right. I don't know what to tell you though, really odd. I would go thru everything again. Do you have spares of things like fuel rail, fpr, distributor, coil, etc? I wouldn't wanna buy that stuff but try swapping in different things and see if that helps. How do your plugs look? Post a pic. Cause the overall A/F might be good but there may be 1 cylinder running really rich and another really lean and the overall A/F could be fine but in actuality the motor isn't running at peak and you're losing power.
Yes, you could get more power with a bigger collector, but you've still got some issue with your current setup. You should have seen the S&S header on the junkyard motor car that pulled 138, it was really dented badly and the exhaust setup was a 2.5" crush bent. Nothing spectacular at all. That was on a stock ECU. I would leave timing at the stock 15 degrees until you're at a point where you need to maximize power. At this point you just need to "find" the stock power. I know power numbers do vary from dyno to dyno, but I think we can rule that out in this big of a difference. And we've dyno'd several cars at this dyno and they are inline with power numbers from other dynojets in the area.
Just make sure to dyno the new setup before hitting the track. If the current problem has something to do with the setup you have in regards to the engine and such, you could run into the same problem with the new build. Because you'll be swapping over all the electronics and manifolds etc. Don't want to have the same problem with a brand new motor. Sucks to spend all that money to make the same power.
s
erlrich
Super Moderator
Jim - I actually remembered you telling me that in a previous conversation, and just to check I did a run with timing at 10 degrees. It was one of the few times I saw noticeable results - unfortunately in the wrong direction. I am starting to believe though that whatever the problem is, once I get it figured out I will be pretty much starting from scratch, so I won't rule that out just yet.
Steve, I don't keep much in the way of spares for the ignition/fuel systems. I was considering replacing the coil and maybe picking up a used distributor just to see if the issue was ignition related. As far as the fuel system, the filter & fpr are new, injectors should be in good shape, so the only thing there might be the pump. I will probably go ahead a replace that just to eliminate one more variable from the equation.
Oh well, what fun would this be if it were easy
lateapex31
New member
I bet the wideband o2 sensor on the dyno used a probe for the tailpipe. The lean condition at low RPMs is a result of insufficient exhaust gas volume flowing through the small diameter probe which shows as lean (high 02 content).
Also keep in mind different dynos, different days, different weather etc has a huge impact on dyno numbers. You can take that very same car back on another day and make 10HP +/-
Also keep in mind different dynos, different days, different weather etc has a huge impact on dyno numbers. You can take that very same car back on another day and make 10HP +/-
erlrich
Super Moderator
Yes, it did.
Thanks - that makes me feel a little better. I'm still pretty sure the low hp/tq numbers are for real though; at MARRS IX those damn RX7s were walking away from me on the straights, even though I was getting good runs on them through the corners! Oh the shame...
timrogers
New member
That is possible, but I've seen tons of dyno sheets where the A/Fs are correct from low to high RPMs.
Are you sure you were getting full advance throughout the rev range at full throttle?
I was wondering that because if the A/F on the sheet is correct and you are so bloody lean in the bottom end that your motor is knocking and this is being picked up by the knock sensor. The ECU will in turn pull massive amounts (try 20 degrees) of timing from the motor to try to stop the knock. New input from the knock sensor is ignored by the ECU above +/- 4000 RPMs but if the last info the computer had was that there was knock detected, the timing stays pulled back and your power suffers.
I have had a similar issue on my road car (I think its due to a knock sensor going soft) and didn't realize what was going on until i used the Nissan DataScan software on my laptop with a Consult cable hooked up to the diagnostic port while I drove on the highway.