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Tucson, AZ
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redduk
9/4/2018 8:09pm
9/4/2018 8:09pm
Edited Date/Time
9/8/2018 12:09pm
Bike is my son's stock 2018 yz250f. He likes to run vp t4 for the "extra" power out of turns. The problem is a wicked back fire after jumps. It always happens after he let's off the gas right after leaving the face of a jump. With pump gas the bike runs fine. We messed with different settings with the gytr programmer but usually made the problem worse, that and I don't understand how to use the timing part for performance. Right now he likes the stock setting. Any ideas on using the programmer to eliminate the back fire. Thanks
Are you sure of the age on the T4?
I have checked for leaks in the exhaust system and replaced the exhaust gasket at the last rebuild. We also installed a quick turn throttle tube.
The Shop
Paw Paw
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if there is an option to advance it individually on the top and the bottom, you can do several different tests, but you could try advancing it just on the bottom first. load increases the potential for pinging. there is far less load on an engine in the higher rpm range. advancing timing increases power and throttle response, up until the timing is advance too far, at which point performance will be reduced. Also, the more the timing is advanced, the more fuel is occasionally required although it is a fairly small amount.
also, i would do blind tests so he has no idea what you are doing. all tests need to be done at least twice to have any type of meaningful results.
the ideal thing to do would be to simply put it on a dyno then do the changes on the dyno. you can also test 91 pump gas vs race gas this way. it costs $125.00 for an hour total on the dyno where i am.
I run a mix of 93 and 110 in my yz450. Mostly just to help keep the gas fresh.
Here is a number you can reach a vp tech at.
(951) 696-5100
VP FUEL LIST
https://vpracingfuels.com/master-fuel-table/
Also, their is a large discrepancie between T4's RVP rating on VP's site. The main fuel page lists it as 6.7 while the specific spec page for it lists it as 8.54, therefore, it is always best to call a fuel mfg to determine the correct specs for a fuel if you need them.
If you can get shell v power 93 or 95 octane where you are you could try that also.
If you want to use race gas to get more power. i would call vp and ask them about c10 and u4.4 and the t4 to see what they say and which one they think might be best for your app.
https://motocrossactionmag.com/racers-guide-to-the-hierarchy-of-motocro…
https://www.vitalmx.com/product/feature/Tested-VP-Fuels-Comprison,3212
I also ran sunoco 100 and 105 a few times in the 70's and 80's. .
I also raced the expert vintage 125, 250, open, and over 40 class in 93 and holeshot more races and won more trophies at the years end western regional awards than any other person in vintage racing history, and i did that all with pump gas.
I am hopefully going to get my vintage bike on the dyno in few weeks and i am going to dyno it with a few before and after changes and one of them will be pump gas vs a mix of pump gas and vp's street blaze. granted, their street blaze isn't the best they have but it is oxygenated so i will see what happens, plus it is only around $8.50 a gallon.
I forgot to mention that i nearly holeshot a race at the othg race at perris raceway a few weeks ago on my 38 year old non power valve yz250 with a seriously dented pipe and they all have newer $9,000.00 4 strokes, and most were 450's. I also beat half of them but of course it wasn't in the pro class and i used pump gas with 25% sunoco 100 but i used the sunoco because my bike was pinging horrendously bad at the vintage race 2 weeks before that, however, i found an air leak after that race so that may have contributed to the problem.
With the right map and race gas youll only see benefits in performance. Only drawback is a lighter wallet
2018 kawi 450 is 12.8 and the 2018 husky 450 is 12.6, however, that is irrelevant because those are static/uncorrected figures and the main number that determines what octane level is needed for an engine is the dynamic compression number. You can have an engine with 12.1 static compression and 9.0 dynamic compression, then change the cam to one with longer intake duration and keep the other cam specs the same and it will have less dynamic compression which will require less octane and vice versa. Another factor that determines an engines octane requirement is load. The greater the load, the higher the octane requirement. Load can be reduced by installing numerically higher final drive gears. Another factor is combustion chamber design. Some designs burn the fuel more quickly and engines with "quick burn" combustion chambers require less timing or more octane to prevent the engine from pinging. Some other factors that determine octane needs are ambient air temp, humidity, air density/elevation and so on. The kawi race mechanics had thick notebooks of atmospheric stats and jetting specs they gathered throughout the years at different races and would use those as a guide at each track so they wouldn't have to waste time starting from scratch when jetting for the different tracks.
"These high compression 4 strokes benefit from clean consistent gas."
In general, every engine can benefit from consistent gas, and contrary to many peoples incorrect belief, pump gas is consistent to the point that and difference in it throughout the year is insignificant. The main exceptions to that are states like california and some parts of arizona that oxygenate the fuel and add ethanol to it during certain parts of the year.
"Pump gas these days is loaded with ethanol..."
There is nothing inherently "wrong" or "bad" about ethanol other than it can attract water. Ethanol is alcohol, and the fastest cars in the world run straight alcohol, not gasoline.
"With the right map and race gas youll only see benefits in performance"
You are correct and I have already stated this, but you and some others keep missing that fact.
Pit Row
Also, eddie warren won the amateur championship at loretta lynns around 1984. I went with the race team to an ama 250 national they had the next week that they signed eddie up for. He got lapped by the leaders on a course that was over 2 minutes long and all the race gas in the world would not have prevented that.
Skill is far more important than race gas providing the engine isn't going to blow up from detonation. It's really that simple.
Pump gas quality and consistency has degraded significantly over the years. By any racer's standards, pump gas is not consistent in any state. The inconsistencies in hydrocarbon quality, energy, specific gravity, rvp, ethanol content, water content and actual octane are significant enough to effect engine performance and tuning, both on a dyno and on the track.
Pump gas is loaded with ethanol. While it is not inherently bad in some applications, it is most certainly inherently bad in small displacement 4 stroke and 2 stroke engines, there is a plethora of evidence on this. The ethanol found in pump gas is not the alcohol that the world's fastest cars run. There are many forms and byproducts of alcohol that differ drastically, which are often referred to as alcohol.
There is a measurable gain in throttle response, horsepower and torque to be had by running the correct race fuel in modern day 2 and 4 stroke bikes with stock ignition timing and fuel/carb settings. These gains are amplified when you can tune for the change in fuel, the same way you would when changing any engine component.
I feel the "save your money just twist the throttle more" argument is counter productive in most of these discussions. Would a rider benefit more from spending $1000 training for a few days at a world renowned facility, or on a new exhaust system that had concrete evidence of a hp gain? I think you could form a solid argument for the training over the exhaust in many cases. That doesn't change the fact that the exhaust system will add power to the bike over the stock system.
...and that again proves my point. I can guarantee you with absolute certainty that not a single one of these amateurs could beat a top pro on an identical bike. This means that the amateurs are not using all the power the stock bike has. This means that it is far more intelligent to learn how to ride better instead of increasing the power if one had to choose between one or the other. Also, that $1,000.00 at a training camps is a mere pittance compared to the amount of money one will spend on race gas over pump gas over a years worth of racing etc. There is zero substitute for experience and anyone that thinks there is is not a pro level rider and therefore are unqualified to make that claim.
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