Dynoed my L24 at Zcon

[madkaw]

Well I got my car together just in time to drive down to Zcon. The engine was running really well with about 1000 miles on it. I got outstanding MPG with my SU's (26-28mpg) with my 3.7 LSD. I hadn't even taken the engine beyond 5krpm's till this point. They had a dyno at track days so i thought-what the hell-I'll give it a whirl.

My timing was set conservative at 10 btdc at idle and 35 degrees all in with my zx dizzy. I am running SU's with SM needles. Other specs:

2.4 40 over with eyebrowed cylinder bores

Assembly balanced, new pistons,stock lower end

Compression running 195 across all 6 cylinders

Head is early e-88,, shaved .10 ,semi closed chamber with larger stainless valves,unshrounded to ring on headgasket

Schneider stage 2= 480 lift,270,270

Headers 6-3-2 duals 2" all the way back with crossover

 

As you will notice with the graph I was slightly rich until I started into the power band, then she just fell on her face at 5100 and ran out of gas-basically. The richness issue was the foward SU piston needle beeing to far up-in the piston(figured that out later). The leaness was from improper setting of the float levels(I summized)

 

After getting back from Zcon I when in there and tweeked the floats(big tweek) and noticed a more willing engine to rev, but I believe there is still quite a bit there.I pulled the plugs after the tweeking and the plugs looked about perfect. I was expecting to see more carbon as I made such a large adjustment, but they looked the same as before I adjusted. Do I tweek the floats until she doesn't run well anymore or the plugs change color, or is there something else I can do to fatten her up on the top. I have a set of tripple Mikuni's 40mm sitting on my shelf, but I am holding off putting them on until I have reached the limit on the SU's I have on there. I would like to do a fair comparison of the two set-ups and pick the best for overall satisfaction. I have access to a dyno here locally, but I want to do some butt dyno work before I cough up the 100$ per hour for a real dyno.

Maybe after fattening up the fuel I can work on more timing, but the fear of running lean will keep me where I am at now.

[madkaw]

I guess I should have just asked,"hey dudes-howdoa make my car go faster-dudes", and this would have gotten more responses!

[zack_280]

That car looks a lot like mine. Where are you located? Unfortunately I don't have any pics at the moment. It's in the 'being-worked-on' phase.

[madkaw]

Indianapolis

[blue72]

You could always custom taper your own needles. It takes a bit of dedication and equipment to measure each adjustment though.

[madkaw]

That's certainly an option, but I can't believe the SM's give out at 160hp. I guess I will tweek some more and see what happens.

[WEBEZEEed]

I haven't seen SU,s do that before,mine goe's rich (10.8-11.2 ) at full throttle and I'm at the same power levels you are. SU.s run out of air, there is I would guess 20 more ponies left them, get David Vizard's book Tuning The A Series Engine. He has a very good section on SU modification that wont cost a dime, just your labor. BTW I'm just down the road in Lou.

[madkaw]

Maybe that's what I'm seeing on the graph, I'm running out of air-but guys have seen more hp with SU's. I'm guessing those SU's have been punched out a little to flow more. My timing might have cost me some hp also, since I believe it was set conservative.

With dual 2" pipes this engine might need to breath a little more thru the carbs-I see the mikunis having their day soon

 

What kind of compression are you running and what motor?

Edited August 17, 2010 by madkaw

[30 ounce]

That really looks like your float bowls ran dry or at least low. I was having that problem with my SU's until I got a Holly fuel pump. My carbs were modified by Rebello Racing to flow 360cfm (I think that's what it was) but my 3.0 liter engine could use all the fuel in the bowls in a full throttle 0-60 run. Before you sand those needles make sure you have adequate fuel to the carbs.

[bradyzq]

I would question the dyno in this case.

 

It is VERY odd that you have EXACTLY the same torque on the black run from 2750ish RPM to 5K RPM, flat as a table. It is also very odd that on a carbureted car with a distributor ignition that power peak is at EXACTLY the same RPM on all 3 runs, not even off by 1 RPM. And it is also extremely unusual that it appears the O2 wanders between only 2 readings (10:1 which is probably as rich as the dyno can read and 14.5ish:1). At an honest 10:1 AFR, your car would likely have killed the mosquito population for miles around and been unable to generate the good torque measured.

 

I guess what I'm suggesting is not to put too much faith in that dyno sheet, and before you start changing needles and whatnot, make sure there really is a problem, and that it is as shown on the dyno sheet.

 

Just my $0.02.

[bradyzq]

If the float bowls were emptying due to lack of fuel flow, the AFR wouldn't be able to go from 14.5:1 back to 10:1 in the span of about 250RPM at 5500RPM or so.

 

That dyno sheet just looks wrong.....

[Tony D]

If the float bowls were emptying due to lack of fuel flow, the AFR wouldn't be able to go from 14.5:1 back to 10:1 in the span of about 250RPM at 5500RPM or so.

 

That dyno sheet just looks wrong.....

 

I could if the operator lift throttled and dumped a gob of unburned HC down the pipe... And that is exactly what I would do as a litigation-wary dyno operator when I started seeing the AFR do that kind of thing!

 

Ever watch the AFR on a stock SU car when you drop throttle with and without the throttle closing dashpot on the balance tube? BIG difference in HC jump on drop-throttle above 3K rpms. I'm betting this car does not have AIR Injection or a Throttle Dampening Dashpot installed...

[WEBEZEEed]

You mentioned you wanted to see the limit of your SU,s..... get that book and try his suggestions, I think you like it. I run a stock mechanical fuel pump on mine and have no engine mods save for a header and 2&a half inch ex. and it still went rich even with stock needles. The carbs are 4 screws with a n33 intake. 199K miles running 150-155 psi accross the board. I have improved things a little since my last dyno run, so I'm guessing it's up around 155-160 h.p. and adout that much on torque.( Mustang dyno )

[30 ounce]

The Z Therapy video also has some cool mods to make your SU's flow better. The video quality isn't that great but the info is priceless. I would be wary of switching to tripples. If you can't get 2 throats to work right try 6!! Dave Rebello talked me out of tripples saying a good running pair of SU's will work better for everyday driving than tripples and be almost as good on the track (with his mods of course). Classic motorsports did a comparison on a dyno of Weber DCOE and SU's last month (issue #147 September 2010)and there really isn't much difference.

[bradyzq]

I could if the operator lift throttled and dumped a gob of unburned HC down the pipe... And that is exactly what I would do as a litigation-wary dyno operator when I started seeing the AFR do that kind of thing!

 

Ever watch the AFR on a stock SU car when you drop throttle with and without the throttle closing dashpot on the balance tube? BIG difference in HC jump on drop-throttle above 3K rpms. I'm betting this car does not have AIR Injection or a Throttle Dampening Dashpot installed...

 

Could be, but I still think something's up with the dyno graph. The AFR does the same thing between 3000-3500RPM between the same 2 AFRs on the blue run with no corresponding change in torque. None at all, at least from I can see from the sheet.

 

I've never seen that flat a torque curve, even on a brand new, drive-by-wire, torque-controlled car.

 

My overall message remains that I think madkaw (Steve) should not rely on that dyno sheet nor consider making changes due to it. Everything about it seems odd, and a second set of pulls is cheap insurance compared to having to do and undo changes found to be unnecessary!

[WEBEZEEed]

Madkaw, my motor is the stock 2.4L head never been off. I have done other things like no pollution equipment at all, single row pulley,stock dist. slightly recurved & crane xr 3000 converted, intake has been de-burred and ceramic coated,MSA 6-2-1 ceramic coated header with 2 1|2 ex. stock carb heat shield has been enlarged to try to deflect a little more heat, stock air box is painted with an additive to help insulate,(you can never get enough cold air} the carbs are from a 71 model and have not been bored but are modified per Mr. Vizards book. I run a wide band o2... about 2 years now, the biggest problem I have is going lean on acceleration but goes rich at 3|4 to full throttle. SM needles didn't do much in my case. Needs custom needles but I'll wait. I do get 30-31 mpg at 75 mph, Trans is a close ratio 5 speed with a 3.54 R180 open. Also the metal air horns are gone and replaced with ones a little shorter and a little wider radius ( home made ) I have Pulstar plugs... can;t tell any difference over the E3's I ran which didn't seem any better than the NGK bp6ey,s I ran. I know I'm rambling on here, but I gotta believe that if my motor was built as yours is that h.p. should approach 170 ish and I would think yours would be also if the carbs were modified like mine. What area of Indy you in? i used to go to Greenwood quite often.

[30 ounce]

Madkaw, I think Bradyzq is right about the AFR on that dyno but there is definitely something up at 5250 rpm's. Shouldn't a 10.4:1 air fuel ratio be blubbering rich? You asked about the float setting and they should be set and forget!! www.datsungarage.com has a good trick to set float levels. Once the float levels are set the mixture screws will do the rest. This page has some good info too: www.jetlink.net/~okayfine/sutech.html

Edited August 18, 2010 by 30 ounce

[madkaw]

I appreciate all the replies guys. This is my first dealings with a dyno run and deciphering a dyno graph-so all of you probably know more then me.

 

As to certain aspects of the run;the engine was running rich at the time of the run. The foward SU piston needle was set too far up into the piston creating a rich condition. Rich enough to soot the plugs-so I figure that is what you are seeing with the low AFR. Needle was reset-plugs looked perfect.

The carb floats were set to stock specs at the time of the run, but either my measurements were wrong or the stock specs didn't cut it for this engine. After returning home from ZCON, I adjusted the floats by more then a 1/8" on the tab, and the plugs still look perfect and the engine wasn't as flat on top end-noticable improvement.

As far as the flat toque curve, I'm not sure what the deal is there, but this engine runs like that curve as far as having a very solid torque band across the rpm range. I am impressed how this motor will pull from any rpm.

 

Weebeezeed, I am 15 minutes from greenwood.

 

I will not be making any drastic changes based on this dyno run, but it did pick-up my richness problem, and it did show my leaness issue at the top end, so there is something to go by. I would like to find a point with my carburation that I atleast see some richness on the plugs, that i am making significant changes. As far as the 'set-em, forget-em" theroy, how is that possible. If I just went by the plugs and MPG and wasn't worried about anything else, I would have been happy with this dyno run. Now I have made a huge float adjustment(definetly not spec) and it runs better and still isn't rich. Bruce Palmer was the one to suggest float adjustment. Maybe the it is more then that, maybe the fuel pump is not maintaining the correct setting.

 

An interesting note; the Z before me that had triples on his engine was also showing a very rich condition and making less HP then me. Could it been the suffocating heat that day-95+ degrees and humid?

[Tony D]

At around 10.5:1 AFR you should be getting visible black soot out the tailpipe. It may not produce optimum horsepower, but it won't hurt as much as most think. Running to a 5% HC content gives a very forgiving torque curve and makes the car driveable, though not as economical in fuel mileage. For racing this is not that critical, and the car is far from detonation.

 

The humidity and heat will affect air densities and fuel ratios. Running a chiller box on the fuel line will have similar affects (more dense fuel mix, atomizing and droping air temperatures in the manifold somewhat) but that is way down the line.

 

Really, what you want to do is find a local dyno to do a baseline, and return to it for comparison of changes. If you can swing it, and have all your ducks in a row, renting it for a day for $500 - 800 may sound expensive, but will allow back-to-back comparos of timing, jet movements (needle position changes), float levels, and even Cam Timing. You can really dial it in.

 

Failing that, this is an N/A car and doing this on a deserted level stretch of road is not out of the realm of possiblity. The newer GTECH PASS system will give you repeatable results which you can correleate to most WBO2 dataloggers for pretty accurate front-end comparison and tuning, saving several hours on the dyno.

 

I spent the better part of a month one summer taking suction piston station height readings and comparing to CHT and EGT to get the needle correct on a Turbo Corvair back in the early 80's. You guys have no idea how much easier it is to tune these days with what is available.

 

And how much easier it is to do with EFI!

[madkaw]

I also have ORP less then 5 miles from my house with Friday night drags-30$ for unlimted runs on a premeir 1/4 mile track. I think that will be my dyno for now, and eventually maybe back to the other dyno.

Honestly I have been very gentle with this car waiting for the engine to break in, but now i guess it's time to have some fun. I questioned if my diff would hold up also, because of strange noises, but now I have a spare incase something happens.

I'll post-up if i make over there in the near future.

 

By the way, I saw no black smoke on the dyno run-a little white smoke, but I expected that on a new engine.

 

My next investment is a wideband set-up, I could use it for my car and my daughter's 81zxt.