Quiz for Bench Racers

[Koncretekid]

Here's a sort of quiz for all bench racers to consider:

In 2012 I managed 137 mph maximum speed at BUBs, 134mph record.  For 2013, I increased my maximum speed to 145mph, new record at 143.  I made no internal changes to the motor other than to touch up the exhaust valve, which I believe was damaged either during a dyno session or at Loring, ME after the 2012 run.  But I did make a few minor changes as follows:

1.) Replaced spoke wheels, front and rear, with newer cast aluminum ones.
2.) Made full circle rim enclosing covers for the rear wheel (flat)
3.) Lengthened the intake manifold by 3 inches
4.) Leaned out the carburetor from a 152.5 to 147.5 main jet on a Mikuni HSR42, because after changing intake manifold, it was running rich
5.) Shortened the exhaust by 1 inch
6.) Changed breather on crankcase from a disc valve (PCV valve) to a reed valve, and connected it to an extractor tube in the exhaust
7.) Retarded the ignition timing from about 28 degrees to something like 20 degrees (accidently), but I can't give you exact numbers
8.) I increased the lift on the intake valve from .400" to .450" with a revised ratio rocker arm
9.) Rebuilt the frame on account of finding two broken tubes and 5 other cracks
10.) Found and re-donned my lucky "biker shorts"

A dyno run subsequent to the 2013 run showed only about a 1 hp increase over 2012.  My bike is very consistent, with all runs on any given year within a few mph of each other.

So the question is, which changes were significant and which ones were not?

[Stainless1]

Evidently you went in the right direction with the minor changes you made... but what were the course and wind conditions from one record to another...

[Jessechop]

Wind has been a killer for me at Loring. I have seen a 130mph bike run 121 because of wind.....


With that said, if conditions were "the same" I would guess the rear wheel disc was the big help

[bak189]

Number 3 and number 4..........................long live BSA

[Sumner]

Number 3 and number 4..........................long live BSA

Since you obviously know more about the motor part than I do  I won't touch that but if that isn't it or in conjunction with it I'd say 1 and 2 but I'm unsure about 1 if it didn't also get a full cover,

Sum

[Rex Schimmer]

Tom,
Do you think that you may have gotten a performance boost when you retarded the timing from 28 to 20 degrees? If you did this is a comment on the efficiency of your combustion chamber/piston design. Most hemi combustion chambers like lots of lead because they have poor combustion but you have added a squish band that may have helped yours. Steve Nelson, V4FL number 221, has an early Ford with a DOHC conversion that is hemi in configuration and he also has a piston design that incorporates a squish ban, we all thought that it should like 34-36 degree of lead but on the dyno best power was made at around 25-26 degrees.

Actually I vote for No. 10 as we all know that "lucky biker shorts" rule!!!!

Rex

[RansomT]

Typically in the sport bike area, lengthening the intake (velocity stacks)  moves the TQ curve down the curve while increasing the intake lift (with a good designed/ported head) moves the TQ curve higher. Probably negated one another.

[runt13]

the changes you made were significant!

the ones you didn't get to make were not!

[lsrjunkie]

I'm a superstitious kind of guy. I'd say it was the shorts. 

[makr]

I vote shorts.


Also the salt was pretty good last year.

[Milwaukee Midget]

Tom - this is all a huge success.

Okay, 1 hp increase - but what did the powerband and torque curve look like in comparison?  And did you dyno with the entire exhaust in place?  The additional lift under the curve with the extra rocker ratio would have opened the valve up faster with better low lift flow.

But realistically, the best way to figure this out would be to bring all the old parts back to Bonneville and start replacing the good guy parts with the slow parts and see which ones slow you down the most.

Although I think I wouldn't re-crack the frame - then you would need to replace your "Lucky Biker Shorts".

It's good to know why you are successful, but sometimes you just have to accept the fact that you are.

 

[tauruck]

When changing so many things you never really know do you?.

I'd opt for 1 and 2.

The shorts just add weight!.

[Koncretekid]

Summary:
Conditions were better for me in 2013 with Density Altitudes of around 5900, temperature around 70 degrees F, and 0 to 6mph winds, compared to 6300, 77 degrees, and winds from 7mph head to 11mph tail, so this probably helped.  As far a Dyno runs go, they were a disappointment, as the read-outs contained missing data, so I do not put much stock in them.  According to my data, I would have needed an increase of 9 hp to go 9 mph faster, or a commensurate decrease in coefficient of friction.

So I believe that I did achieve a lower Cd plus an increase in hp.  The longer intake, when on a dyno back East, showed a substantial increase in torque and hp at lower RPM, but no increase at the top.  I put some credence in the reduced timing as well for maximum rpm. So another plus is a better acceleration when in top gear trying to get those last few mph.

We live with the fact that we only get to race once or twice a year so we have to make multiple changes or we won't live long enough to get them all in.  Ideally, we would make a bunch of dyno runs to test each change, but I don't have one near enough to my build site, so that isn't an option.  In the end, the lucky biker shorts win.

Tom

[Stainless1]

The difference in density altitude between Oct and Aug put 5MPH on the lakester with the 1 liter NA motor when Pork Pie set his record.  Ran the same AFR at both meets, more air, more fuel, more power.

[TheBaron]

Better Aero-Aero-Aero !

An 8 mph gain is enormous  !

Robert