TR6 TR6 carb tuning vs. HP

[BryanC]

In the thread on ignition systems there was a link to a GRM article on tuning:

https://www.grmotorsports.com/backissues/mg-dyno.php

In the article, they say that tuning the carbs made no measurable difference in peak hp.

"This car has SU carbs, so mixture is adjustable throughout the operating range. We were surprised to find that while an overly lean or overly rich mixture made the car run poorly, power was not affected in any measurable way."

That seems a little strange to me. Does anyone have any experience with carb tuning and real dyno results on a TR6?

Bryan

 

[Brosky]

Bryan,

I went through a complete dyno session on my TR6 and I walked away convinced by the dyno shop that performance was hampered by my carbs being too lean on the low end and too rich on the high end.

I have since installed an air fuel ratio meter and re-tuned the engine. I have not returned for another set of pull tests, but I plan to this spring at the next club session.

After tweaking the carbs, i find a bit more power on the high end and a much smoother idle on the low end. Another factor is that I boosted my compression by swapping to a shaved head after the dyno testing, so it will be interesting to see what a difference everything made.

 

[BryanC]

I would expect that the work you've done with the new head will give a good improvement. That's what makes this question hard to get an answer to. Most of the time, people make other changes and it's hard to tell which one did what. It seems hard to find someone that has done back-to-back testing. The article on the MG test was interesting in that they did just that. I was just surprised by their answer. I wouldn't expect a huge difference from carb tuning - maybe 4 or 5 hp over the range - but zero seems low.

Bryan

 

[Tinster]

See Bryan?? Tinster knows zip about engines but
he knows who does!

Good Morning, Paul!!
Hope ya had a good night's sleep.

D

BTW- not stealing this thread, please no replies.

Paul, did I ever tell you about all the very happy
joyful little things in the Christmas culture here
on the island? They instantly make folks cheerful.
No? Well, maybe I will. /bcforum/images/%%GRAEMLIN_URL%%/angel.gif

felicidades a todos

d

 

[Brosky]

Bryan,

I did the carb adjustments before the head replacement so as to keep things somewhat separated, but I did not go to the dyno shop before doing the head, so the change will be the result of a combination of work performed.

 

[PeterK]

"We were surprised to find that while an overly lean or overly rich mixture made the car run poorly, power was not affected in any measurable way."
Bryan

Actually that's not surprising since the only thing they did was tune the carbs. Granted, it would run better, possibly smoother as in Paul's case.

But the same carbs, no engine mods to take advantage of a better air/fuel mixture. Now if you help it breath better, work on the combustion chambers, improve the spark, then yes, untuned carbs would be less likely to be about to take advantage of the changes, and when tuned may produce a speck more HP on the dyno.

Of course, the easiest and cheapest way to make your car quicker is to lighten it up, especially unsprung weight, lighter wheels, lighter tires, lighter seats, remove the bling chrome, clean out the junk in your trunk, go on a diet, i.e. anything to reduce the weight.

 

[Darrell_Walker]

Of course, the easiest and cheapest way to make your car quicker is to lighten it up, especially unsprung weight, lighter wheels, lighter tires, lighter seats, remove the bling chrome, clean out the junk in your trunk, go on a diet, i.e. anything to reduce the weight.

I wish I could find the page I saw a few years ago. Basically they took a plain econobox, and started stripping it down and seeing how fast they could make it. In the beginning it was pretty simple stuff like interior, but by the end most of the outside sheet metal was gone!

 

[Brosky]

Take a look at some of the old pictures of the early 60's Super Stock Plymouth's and Ford's with the aluminum front ends and bumpers. They had two bucket seats, no heaters and nothing on the dash.

 

[TR3driver]

Of course, the easiest and cheapest way to make your car quicker is to lighten it up,

Don't forget rotational inertia in the drivetrain; especially anything in front of the gearbox (that has to be accelerated 5 times instead of just once).

Along those lines, I believe Joe Alexander is planning to offer lightweight steel flywheels in the near future. TRactor motor at first, but likely the TR6 will follow.

 

[DNK]

Per Randall's remarks.Do you think an aluminum or a well lightened drive shaft makes much difference?

 

[Brosky]

The driveshaft's are not all that heavy Don. Hmmm, maybe a bad statement.

Well, let me clarify that. After picking up the ones that I used to carry in the 70's, they don't seem to be that heavy, but it's probably relative to the shorter length and my poor memory.

I will defer to a smarter source that can verify the actual weight and what it would be "ideally" with a lighter unit.

 

[BryanC]

A lighter driveshaft wouldn't hurt but its effect would be small compared to the flywheel. The key is the rotational inertia - as Randall said. The rotational moment of inertia depends on the radius squared. So for a small tube like the driveshaft, the inertia is small. The flywheel is much larger in radius (and turns faster since it's before the gearbox) so it has a much larger effect.

Bryan

 

[Monkeywrench]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]This car has SU carbs, so mixture is adjustable throughout the operating range. We were surprised to find that while an overly lean or overly rich mixture made the car run poorly, power was not affected in any measurable way.[/QUOTE]

I don't have experience with stock motors, but from knowing full tilt race motors, mixture makes a HUGE difference.

As it has been discussed, lower rotating mass (actually mass in general) and drag will effect acceleration in a great way. Besides what has been listed, you may consider the following..

use synthetic fluids throughout the driveline
check to see if the wheels are all square to each other
make sure your brakes aren't dragging.
use good high temp. synthetic grease in the wheel bearings
alignment, tire pressures, sizes, and compounds will all have an effect.
Not all tires weigh the same. Some are heavier than others.
Ideally chose a wheel that has most of it's weight concentrated towards the center. The closer the better (though it's not exactly ideal for the street)

.. that should be about it for now.