Fine Dyno tuning

[sierra4000]

Hello,
Exist some old tricks - recommendations for quick changes during fine dyno tuning to maximize power ??
(racing old style engine)

for example:
different fuel
carb. height change (differet spacer)
antireverse plate
exhaust tailpipe diameter change
etc
etc

Thanks for any tips

Radek

 

[lucky-guesser]

Without knowing anything about your current set up other than it is a carb, its hard to make many (meaningful) recommendations.

different fuel --> depends what you are running now. Perhaps a higher octane but I don't know your abilities to modify your ignition timing or what your compression ratio is.

carb. height change (differet spacer) --> More spacer is better on the engines that I am used to, but idk what you have so idk how valid that is in your case.

antireverse plate --> no experience with these but from some quick reading it looks like they are highly dependent on your exhaust set up and cam timing.

exhaust tailpipe diameter change --> 1) diameter change is hardly a quick thing to just casually do on the dyno. 2) You are always going to want a large diameter pipe, as few bends and excess routing as you can get away with, low restriction (no cats, muffler, resonator), and a shorter length if possible. Highly modified high HP cars will often dump out to the side or below the car, as to shorten travel distance all the way out the back.

I struggle to come up with anything along the lines of what you are asking, as most of the major gains will come from larger modifications, which will be done in the shop. Not last minute at the dyno. That is where you get fuel and spark dialed in, that's about it.

 

[sierra4000]

Compression ratio is around 11.5
310 degree camshaft
ported heads
open/ optimized exhaust by computer program

I saw gains (peak HP) with 100 octane fuel from a different brand
I saw gains (area under the TQ curve) with just a change (reduction) in the diameter of the exhaust end

and you see, you still told me something, and that changing the height of the carburetor can be beneficial, thanks for that.

 

[kjoiner]

I'm far from an expert but you might want to check out the show "Engine Masters". It was on Motor Trend but you can probably find it on Youtube. The reason I mention it is because they did several episodes where they tested those very changes. One episode focused on exhaust system variables (header diameters, pipe length etc.), another one focused on intake manifolds and spacers. They performed dyno runs on each variable and compared the results. There was also another show "Engine Power" but it mostly focused on engine builds and not testing as many variables as Engine Masters.

Kyle

 

[BrianPetersen]

There's scientific method, and there's cut-and-try, and there's a scale in between.

When you change something and it has an effect, do you understand WHY it had an effect?

In this day and age, no serious dyno testing should be done without instrumentation. The more, the merrier. Coolant temperature (possibly at multiple locations - not just at the waterpump or thermostat housing). Oil temperature (same). Oil pressure. Exhaust-gas temperature, preferably at each cylinder as close to the exhaust port as possible. Lambda, preferably for each cylinder. If you have the ability to measure real-time cylinder pressure, fantastic, that's a real help for optimising ignition timing. If it's sensitive enough, that can tell you if the intake is restrictive or the exhaust is restrictive or if pressure-wave effects are helping or hindering.

If you haven't the instrumentation, you're just guessing ... cut-and-try.

I've seen the shows like Engine Masters. The bits you see on youtube etc are the showy parts where it looks like they're doing something. They don't show the underlying design and mathematics and simulation that went into the design of the various bits and pieces that they're showing being tested on the dyno. The grunt work that really counts behind the scenes, is boring to watch.

 

[dtimberlake]

In the olden days motorcycle carburetors had small hoses on the bowl vent.
Gently sucking or blowing on the vent hose could suggest whether richer or leaner jetting should be tried next.

 

[Lou Scannon]

In the olden days motorcycle carburetors had small hoses on the bowl vent.
Gently sucking or blowing on the vent hose could suggest whether richer or leaner jetting should be tried next.

At WOT under load?!!

 

[BrianPetersen]

Lambda measurement (whether gauge or datalogging) will turn that up without question, and it works fine on old skool carbureted engines just as well as with EFI, and it also gives an indication of "how much" something needs to be changed, so that you can zero in a lot quicker. I have a lambda gauge installed on my race bike (which has EFI). It has been useful for at-the-track mapping changes. Data-logging would be better, but that's above my pay grade.

The whole carb-spacer thing is foreign to me, though. Everything I've ever worked on, whether carb or EFI, uses a separate throttle body or carburetor per cylinder, which is part of the tuned-length intake runner for that cylinder, and makes cylinder-to-cylinder fuel maldistribution some combination of a non-issue and a foreign concept. I know OF the fuel-distribution problem (and fuel drop-out and puddling) that single-point EFI or carb systems can have, but I've never had to mess with it. Some of the old V8 intake manifolds had an exhaust cross-over passage between left and right banks that went through the intake manifold, presumably to apply heat to strategic places to improve fuel vapourisation. The Chrysler Slant Six had the exhaust and intake manifolds bolted together underneath the carb so as to create a hot-spot to hopefully vapourise any fuel that dropped out of suspension underneath the carb. The "log" intake manifolds on other carbureted inline sixes were horrible. All this supports having separate lambda measurement per cylinder if you're serious about this.