What I Call
"Detonation Limited Engines"

Hi Matt -

Thanks for the question - I wish that more dyno owners would think enough to ask! (anybody can purchase the right to be a dyno owner - but you have to earn the right to the title "Tuner"...)

Matt Norton wrote:
Hello Marc:
Ever since I read your email I have had this one thought in my head.  You made this statement below "It's the actual power produced - not silly so-called a/f ratios"  Have you ever seen a situation, with a 4 stroke, where an engine continues to build power ever though it is approaching a dangerous level of operation (i.e. too lean and overheating/detonating)?  Logic would tell me that if it continues to build power then the engine is operating more efficiently which shouldn't be detrimental to the engine.

I need a little clarification on the "build power even though" condition -
If it's too lean to make best power... it won't make best power.... and if it's detonating, it won't make best power and if it's overheating, well, that depends on what you call overheating and if I classify overheating as "the temperature at which the engine makes less power or melts"...... :-)

I can't think of a modern, realistic engine that will make better power when it's too lean, detonating or overheating -

I agree with your thought - if it's making better power with an amount of fuel - then it's a better fuel delivery rate and it IS a more correct mixture.

To be a little less drastic - There are 2 classes of engines:
"Detonation Limited" engines and, well,  "Non-Detonation Limited" engines -

A "Detonation Limited" engine is usually a very high compression engine and will make more hp as the ignition timing is advanced (we will assume that you have fueling perfect for the more retarded timing).
As you advance the ignition timing, power increases. It will increase until you reach an amount of "advance" that causes detonation to occur.
You have a case in that, the more advance you add - the more power you make - UNTIL you reach the amount of advance that caused detonation - When you reach that point - power drops dramatically - and I mean DRAMATICALLY! And it does it in a range of only 1-2 degrees.
You get the feeling that if you added more ignition timing, you'd make more power?
Maybe right, too.
Stop the detonation by increasing the fuel octane and you might be able to add more timing again and power will increase.
Well, until you reach that detonation point again and then any more advance will cause detonation again.
See the "Detonation Limited" engine idea? Advance till it detonates - and up until that point.
If that's the way the engine tunes, well, it's  "Det Limited"

A USA type, high compression (USA legal, leaded fuel allows higher compression) TZ250, of  any V type, with the stock or kit ignition, has an ignition curve that has too much advance in the curve above 12,000 rpm, for the compression that the high lead fuels allow (which SHOULD make more power).
If you start out with retarded from best timing and keep advancing the ignition timing, the power increases everywhere. As you keep adding timing, the engine will eventually reach "too much" advance at 12,500+ and wickedly drop 4-8 hp up there, in as little as a .1mm timing change!
That's kind of a detonation limited engine that's caused by improper ignition curve (yes, yes, yes - I know that the kit ignition allows 6 different curves and that Yamaha made 2 different chips for "leaded" and "unleaded" fuels - but I guess that they did that "leaded" mapping with a low compression engine - as they don't use leaded race fuel and their "leaded fuel" maps are pretty much "non-optimum").
I really tried to get information through about 10 different sources, but...... the closest I got was "What was that ECU part number, again?" "Are you sure?" "Well, I'm new here and I just talked to my supervisor - If that's the part number you have, then you don't have that part....."
I'm not sure who was stonewalling - but - the tz's in the USA could have run a lot better if Yamaha USA or others, would have allowed real ignition tuning -

That happens when power is tested under load - If measuring on a dynojet, it rarely shows up - as the engine load isn't realistic enough and as Champion Spark Plug engineers found a 4&6 Cycle, the dj dyno spark plug them is 300f-400f colder than what is on an EC997 dyno or the real world.

When you reach the point of  "as much advance as the engine can tolerate, - you could go back and add some more fuel (to cool the engine's combustion chamber) - and then advance the timing a bit more - that will help a bit - but - now you are getting into a situation in that you are adding excess fuel (losing power from excessive richness) and gaining power (from adding ignition advance).  I prefer to not get into that situation........... Those engines are more likely to do bad things to themselves.....

Better to have a little less compression and have the "right fuel for power" and the "best timing for power".
Easy on the engine - easy to tune on a day to day basis - Easier on pistons, rings, rods, etc...

A Non-Detonation limited engine will let you advance timing, improving power to Best Power and then, be able to advance the timing a bit too much and then simply lose a little power, like only 1% or 2% for a couple degrees too much from Best Power timing setting. No dramatic hp loss -
(yes, yes, we are assuming that you have already gotten the fuel rate to deliver Best Power - not silly a/f ratios)
These are all streetbikes, dirt bikes, 2 strokes and 4 strokes as delivered by the major manufacturers, including Aprilia and most of the Ducati's.

As far as AMA racebikes - all the Supersport bikes and the overwhelming majority of  the old Formula Extreme 1000's were Non-Dets.....

Marc Salvisberg

----- Original Message -----
Sent: Sunday, August 29, 2004 6:28 PM
Subject: Re: a couple of questions concerning CRB-S36-2.0-APK kit


Hi Matt -

Hope it's not as hot up there as it is here .......

OK -

Matt Norton wrote:

Hello there:
I race a 2001 SV650S and I have installed one of your CRB-S36-2.0-APK kits along with a Two Brothers full racing exhaust system (no other modifications to the engine). 
My questions are:
1.  What is the reasoning for having the main jet size on the front cylinder 2.5 points more than the rear when the OEM configuration is the same jet size for both cylinders?

A good tuner with a good dyno (not a dealership level dyno) can see the difference in power produced by changing one jet in one carb -
So - if the engine makes better power with the gets staggered  -  then, so be it - the jets should be staggered - It's the actual power produced - not silly so-called a/f ratios...........
I've fixed all sorts of carburetion problems that the original manufactures couldn't figure out - for example - the Kawasaki zx6r, 95-97, the zx9's, 00-01 and the yzf750, 93-96, the Yamaha R6's the Belgarda Yamaha raced, Muzzy's zx6's, Vance and Hines yzf650's and Yoshimura's gsxr750's -
Essentially - I don't really care what the manufacturer did -  :-)


2.  In the instructions, one of the line items that can be adjusted are the "fuel screws".  I'm assuming that the "fuel screws" are actually the "idle FUEL mixture screws" as shown on your website towards the bottom of this page.

They are also the "only" screws that control fuel in the carb - so - that's why I don't write it - Also - If I write that they are the "idle" fuel screws, that infers that they are only for idle and have no other effect - and they actually do help control the fueling at cruise and part throttle / high rpm..........
So - better that I write "fuel screws" and not mislead people -

 3.  On this same page below the "idle fuel mixture screws" diagram, there is a picture of the "main air jet".  Can you explain to me why you would want to change this jet vs. just changing the main fuel jets to have an optimum WOT setting?

The main jet "offsets" the fuel delivery curve and the "main air jet" controls the shape of the fuel delivery curve from about the torque peak till redline -
You can't even begin to see that on a dynojet or any other dyno using an O2 sensor for socalled a/f ratio and it's also generally impossible to see in a sweep test - but it's the reason why we are able to fix things and diagnose things that most people can't -

Most of the people with our EC997 dyne systems can do the same kind of work -

As far as what's written on the SV's on the internet - it's pretty poor science and there's been a lot of effort spent in trying to update it - but - at this date - it's still the same old misleading information -

Best regards -


Thanks very much for your time.
Matt Norton
Lethbridge, Alberta - Canada