Still waiting to get e-mailed the dyno sheet, but basically I did 150/150 I guess I should be happy for a l24 AFR's were decent, but the SM's are too much in my opinion and the opinion of the race shop I dynoed at. I was barely above 12's and he felt I needed closer to 13's from what they see on NA motors.

What I learned from this experience;

SM needles are too much for the L24 with a mild cam and there is no amount of adjustment that will lean it out on WOT( I tried)Sorry guys, the mixture screws do not effect the entire power band.

The butt dyno is misleading:disappoin

My engine seemed detonation proof(even at 38 full advance)-no signs of it anywhere, either audible or on the dyno sheet-maybe a good motor for turbocharging:cool:

200HP, if I ever make it there, will be lot's of fun.

I will need, and want, to rent time on the dynojet when the Mikuni's are on-I want to be sure.

The dyno shop said that most of the widebands are inaccurate(that they see)

changing timing from 32 to 38 full advance had little effect on HP-in this case

The particulars for those who don't know;

L24-40 over,

early e-88, bigger valves, unshrouded, 9.55 to 1

MSA 6-2 header, dual exhaust

e12-80 ignition, total advance 32-36 -3 runs

SU carbs with SM needles

Cool, always nice to get a baseline for the engine! We'll see what some properly-tuned Mikunis get you, you'll like the triples.

I plan to verify my wideband at my next trip to the dyno, to see how close it is. It's a great instrument to have, even if it's slightly off. You can always scale the numbers once you've verified at the dyno.

Curious point on the mixture screws. They definitely do affect the entire range, but the effect is diminished as the piston rises. They are most sensitive at idle and low speeds/throttle openings, but by the time you're WOT at mid-to-high rpm the effect is small (seemingly undetectable for all intents and purposes). This is why the needle profile must be tailored to the engine, a major pain to do when you get down to the fine details. Triples will be easier!

Thanks for posting the info, Steve! Looking forward to seeing some Mikunis underhood.

I would strongly suggest that if you plan on installing triples and doing other work on the engine, that you dyno the engine and not the car. You will be able to tune the engine to peak performance without any distractions, drive train losses, etc.

More expensive but if you're serious, a better way to go.

If I did the analysis correctly, depending on nozzle adjustment, you should be running between stations 12 and 13 when the piston has maxed out upwards at WOT high RPM. That means that depending on how many turns down you set your nozzle:

The N27 round tops max out at a needle diameter between 0.0710 and 0.0690

While the SM's max out at a needle diameter between 0.0670 and 0.0650.

So I'm not surprised with the results. If you started the day at a full three turns down, the SM's would still be four thousandths richer than stock even if you were to run those nozzles all the way up to dead zero flush with the bridge floor. It doesn't sound like much, but four thousandths is a lot when you look at it in percentages.

Gnose, not that serious, but serious enough to go back with the triples and pay a couple hundred to dynotune while the engine is in the car.

Capt. -I only paid for a baseline run(3 passes), but things were slow so they let me do some adjustments. I wish I has brought my 27's along with me now. I turned my mixtures way in and it only affected the AFR below 3000rpm significantly. So I was taking a chance of running lean there and still be rich. The only real solution was a needle change for my motor. 1.5 turns in amounted to about .1 on the AFR.

The owner thought a full point on the AFR would have been worth maybe 10 HP

This is great information madkaw, and further makes me scratch my head that my SU's with SM needles are making me run lean...

There has to be something up somewhere else.

Anyway, glad to hear your car is running so well. That is awesome! Congrats!!!

The SM needles flatten out as you get towards the tips. The rate of change between stations at the hilt of the SM's is twice the rate of change between stations at the tip. The last half inch or so by the tip is the most gradual changing area of the entire SM needle. So I'm sure you already saw this coming, but that means that 1.5 turns at the hilt has much more impact than 1.5 turns at the tip.

I'm curious as to what kind of numbers you would get with the 27's as well.

Interesting about your numbers though... I suspect ZT wouldn't be thrilled with the results. I don't have the url in hand, but I remember someone else had their car on a dyno with ZT carbs including SM needles, and they were pretty much perfect across the entire operating range. I don't remember the details of the motor, but I'll see if I can dig up that other thread.

makes me scratch my head that my SU's with SM needles are making me run lean...

No.

Kidding.

Also it should be noted that the SM needles are much shorter. Not sure of the impact of that but there has to be some.

I'd love to go back with the 27's , but I'm done with the SU's. I don't mean that in a bad way. I've been sitting on these triples for years- time to move on.

The SU's are a great carb!!

Edited March 22, 201213 yr by madkaw

Also it should be noted that the SM needles are much shorter. Not sure of the impact of that but there has to be some.

Not from what I've found. I've not seen SM's with my own two beady little eyes, but the SU literature says they are the same length as the N27's. Of course, it wouldn't be the first time for documentation to be wrong!

Have you verified that yourself? Because if you have, then that means the SM's are completely out of the nozzle at WOT and there's absolutely no amount of knob diddling that will have any effect on ratio at that point!! :eek:

I can vouch for that Captain. I have both on my bench right now. The SM's are indeed shorter than the OEM N27's.

I will snap a pic for you later today if my test runs this evening show nothing.

Not from what I've found. I've not seen SM's with my own two beady little eyes, but the SU literature says they are the same length as the N27's. Of course, it wouldn't be the first time for documentation to be wrong!

Have you verified that yourself? Because if you have, then that means the SM's are completely out of the nozzle at WOT and there's absolutely no amount of knob diddling that will have any effect on ratio at that point!! :eek:

That was my point. I guess I took for granted you knew that. They are considerably shorter thus making a knob adjustments does nothing for top end AFR. I nthink SM needles should be left to overbored SU carbs and 2.8 or greater engines. Now if I had a crazy cam in my car-but then the SU's would not be the best carb for that.

Sorry guys. I did not know that. I'm at the mercy of documentation, and apparently there's a problem.

I was going by this catalog:

It lists the SM as having fourteen stations:

Being as how the stations are 1/8 inch apart and number one is right where the non-tapered mounting portion of the needle starts, the overall length (of the tapered section) of a fourteen station needle would be very close to 1 5/8".

So you're saying that the tapered section of the SM's are not 1 5/8 inch, but are in fact shorter than that?

Edited March 23, 201213 yr by Captain Obvious
fractions give me trouble :)