Tips for Drag Racing Tuning Prep?

VMAX  Forum

Help Support VMAX Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Lotsokids

Well-Known Member
Joined
Jul 17, 2009
Messages
565
Reaction score
12
Location
Memphis, TN
I found a local place to rent a trailer to bring the V-Max to the drag strip 4.5 hours away. So this will allow me to do some tuning prior to going, without worrying about "streetability."

1. I have a custom VERY free-flowing exhaust, which is extremely loud. I understand the combination to use with this is free-flow air cleaner and an appropriate jet kit. I can get a good air cleaner, but I need suggestions for a jet kit. I'm thinking stage 7?

2. Fuel in Hungary is a choice of 95 or 100 octane. I remember someone here suggested to NOT use 100 since it carbons up the heads. I've been using "95 Super" from Shell here for daily use. Would it help to use the 100 only for the track, or would this hurt my times?

Three racing events there in 2016. I'm really excited. Racing here in Hungary is simple and cheap. I just sign 2 waiver forms and race on the track all weekend for about $23.
Try to do THAT in the U.S. :confused2:
 
The higher octane fuel is better if you decide to go higher in compression, either with only Pistons/rods or charger/turbo. Higher octane prevents detonation which is fuel igniting prior to spark timing. Just like on a Diesel engine.
 
As far as jet kits....there are 2 main ones out there. Stage 7 and Sean's. I'm more partial to Sean's because you keep the bottom of the factory air box. ..so you keep the velocity stacks for good torque down low and midrange. Tuning for both is very similar.....and there are great threads on here showing people's experience with both.

Sent from my SCH-R890 using Tapatalk
 
Not sure if the octane ratings are the same here as they are there?

Unless you engine is built to take advantage of the higher octane you won't make more power with 100.

As Eric said, Sean's muscle jet kit or Stage 7 is the way to go. Sean's kit is a bit cheaper, similar top end HP and more mid. Winner IMO.
 
The octane ratings are the same you get better quality and higher octane at the pump across the pond.
 
Thanks Dennis, A man at scottish fuels told me the only difference was the price.:ummm:
 
$5.71 a gallon
If you have been to the UK and gassed up a vehicle I've noticed the difference in the smell. It reminded me of the '60's and '70's gas we used to get.
 
I wish that I could see the shape of the needles, that will determine how well the bike will run at part throttle. It also says air box modification.....what exactly is that? To get good hp out of a Vmax....you will need to move a bit more air....so you will need to either significantly grind on the airbox lid opening (under the Y) or switch to pod filters. Because your now letting in that much air, then you need air correctors...etc.

My initial feeling looking at that kit, is that it is similar to a stage 1 kit by dyno jet. On the ebay page....it talks about the bike running sluggish, because its Too LEAN. Actually from the factory the Vmax is RICH.....and if you richen it up, it will fall flat on its face. The stage 1 kit can be made to run decently, if you take the directions....and throw them out of the window, and tune to the motorcycle.

If money is an issue, a "stock" Vmax can be made to run very well and put out in the neighborhood of 110-115 hp. I would first say, new spark plugs gapped to .035. Dropping the main jets from 152.5's to 150's with stock exhaust, with aftermarket exhaust, drop mains to 147.5's, and put a .020 shim under the needle. Make certain that the float height is set at 17 mm. If the carbs still have the brass plugs for the A/F screws in them, drill those out, and then turn all of the A/F screws to 2.5 to MAYBE 3 turns out. That will richen you up in the 0-4000 range where you will piddle around town in.

I'm not trying to talk you out of spending money....I just dont want to see you wasting money. All of that can be done for under 40 dollars....probably 30.

If you have more money.....stage 7, or Seans kit is where the money is at....plus enough people have dyno'd on this site with both kits, there are recipes out there just waiting to be used.

EDIT*** One more thing....they talk about a lean engine "hurting the engine" Ive been on the dyno, and an A/F around 16 to 1 at part throttle around 3000 rpm. The Vmax will surge and buck a bit....and will let you know that it doesnt like being that lean, and the engine still isnt hurt. For best HP on a Vmax your looking for an A/F of 13.5-13.6 to 14.0. The Vmax likes a leaner topend.
 
I'd stay away from a no-name jet kit and brass.

If you don't want to spend a few hundred on a STG7 or Muscle Jet kit, stick with stock. Just buy smaller mains and needle shims. Play around to get it just right. A well tuned stock setup is going to be within a few HP of a bike with a full blown jet kit.
 
...Dropping the main jets from 152.5's to 150's with stock exhaust, with aftermarket exhaust, drop mains to 147.5's, and put a .020 shim under the needle...

I thought a larger number for the jets would equal more fuel. Am I wrong? I do have modified exhaust (nearly zero back pressure, extremely loud).

And if possible, could you please explain the .020 shim under the needle. I'm only familiar with clipping in different notches.

That's a lot of information - I appreciate it.
 
The stock American Vmax needles don't have clip notches. So many of us put a shim in to pull the needle outward. .020 to .035 seems to be the average thicknesses used. A #10 washer rubbed down to the correct size works. You can gain some hp trimming the Y and shimming it up with plastic bushings and longer screws. This works well on a budget. Sean's kit or stage 7 is going to cost a little more. The stage 7 filters are over $100. Making your own crankcase breather set up can work well too.
 
I thought a larger number for the jets would equal more fuel. Am I wrong? I do have modified exhaust (nearly zero back pressure, extremely loud).

And if possible, could you please explain the .020 shim under the needle. I'm only familiar with clipping in different notches.

That's a lot of information - I appreciate it.

Ok.....do you remember high school geometry....and how you said that you would never use it in "real" life.....well now you will.

On the Vmax, the needle doesnt sit down into the main jet, but it fits close enough that it causes an obstruction.

Now these are made up numbers....strictly used for illustration purposes. So, you have a main jet, and it has an inside diameter of 4 (see geometry) and the needle fits down in there, and it has an outside area of 2, so that gives you an effective area of 2....for fuel to flow thru. But lets say that you have a bigger jet, and a fatter needle. The inside area of the jet is 5, and the outside diameter of the needle is 3, so it actually gives you the same area to flow fuel, like the other jet. An area of 2.

Something else to think about.....that is only at a certain RPM. At a higher rpm, the engine needs more fuel, so at higher rpm, the needle gets pulled out more, and so will allow more fuel to go thru the main jets.

This is a simplistic view of it....because there are different circuits, and different parts of the carb control fuel at different times....but this should help you to understand how needles work, and below there is a pic that shows the 4 main needles that you can use. Stock, stage 1, stage 7 and factory pro. Thats why I was curious what SHAPE were the needles in the sigma kit.

Next question.....have you ever dealt with the carbs on cars? They will flow a set about of air all of the time. A carb rated for 600 will flow 600 cfm all of the time (again a simplified view). The carbs on a Vmax are called CV carbs....constant velocity carbs. So they will always try to match the amount of fuel, with the amount of air flowing thru them.

Here is where the exhaust comes into play. An aftermarket exhaust flows more air out....right? And because of that....it will inturn PULL more air in, and with the extra air.....it will pull more more fuel with it as well...which makes you TOO RICH. Thats why with an aftermarket exhaust...to DROP to 147's to lean the carbs back out. It looks like you have cobras....which are just slip ons. No performance increase. So drop to the 150's....maybe 147's if you need to. With an aftermarket exhaust.....you would definitely need to drop to the 147's...they flow so much better.

Now then......020 spacer. Unless your running a stage 7 kit with aftermarket pod air filters.....or Seans muscle jet kit, you can really only use the stage 1 needles, or stock needles. (most people dont like the stage 1 needles.....remember when I said throw the directions out the window?) So.....with the stock needles, and an aftermarket exhaust...you need just a bit more fuel when the needles start coming in, so you can do that by raising them .020, and give yourself a bit more fuel in the midrange.

For Vmax purposes, you either have a stock exhaust, slip ons (slip on mufflers....like I said....no performance increase) or a full aftermarket exhaust.

Hope this helps.
 

Attachments

  • FP needles.JPG
    FP needles.JPG
    41.5 KB · Views: 13
...It looks like you have cobras....which are just slip ons. No performance increase. So drop to the 150's....maybe 147's if you need to. With an aftermarket exhaust.....you would definitely need to drop to the 147's...they flow so much better.

Yes, I have Cobras for daily use. BUT I have custom pipes that were installed when I bought the bike. I install them back on when I run at the track. I'm also running true 4-into-4. I cut and blocked the crossover tube. For whatever that is worth for this subject.

Here's a video from when I first got the bike, but the sound doesn't do it justice. I like loud exhaust, but this is very much "in your face" obnoxious. Especially in the morning when I roll through my little Hungarian village to go to work. That's the main reason why I bought the Cobras.

http://vid5.photobucket.com/albums/y177/Lotsokids/V-Max/New%20VMax/VMax_Rev_zpsfync447v.mp4




Thank you again. Much info to digest. I'm not much of a carb guy.
 
Yes, I have Cobras for daily use. BUT I have custom pipes that were installed when I bought the bike. I install them back on when I run at the track. I'm also running true 4-into-4. I cut and blocked the crossover tube. For whatever that is worth for this subject.

Here's a video from when I first got the bike, but the sound doesn't do it justice. I like loud exhaust, but this is very much "in your face" obnoxious. Especially in the morning when I roll through my little Hungarian village to go to work. That's the main reason why I bought the Cobras.


Thank you again. Much info to digest. I'm not much of a carb guy.

Yes it is a lot of info....and you can be a carb guy, it just takes time, patience....and a willingness to tinker until things are right. With the other exhaust, are they aftermarket head pipes as well, or just slip ons like the cobras? In the pic the head pipes look to be aftermarket. The stock ones are double walled.

Great sounding bike as always.
 
Yes, I have Cobras for daily use. BUT I have custom pipes that were installed when I bought the bike. I install them back on when I run at the track. I'm also running true 4-into-4. I cut and blocked the crossover tube. For whatever that is worth for this subject.

Here's a video from when I first got the bike, but the sound doesn't do it justice. I like loud exhaust, but this is very much "in your face" obnoxious. Especially in the morning when I roll through my little Hungarian village to go to work. That's the main reason why I bought the Cobras.

http://vid5.photobucket.com/albums/y177/Lotsokids/V-Max/New%20VMax/VMax_Rev_zpsfync447v.mp4




Thank you again. Much info to digest. I'm not much of a carb guy.
What was your reason for cutting the crossover tube?
 
Those look like stock headers to me.
Notice the chrome trim piece just before the slip on mufflers and the stock rear pipe covers at the manifold.
Unless you get a Full aftermarket exhaust system (not slip-ons), a Jet kit will be a waste of money.
Jetting down from stock mains (152.5) to 150's or even 147.5's may help slightly but you won't see much gain in HP with the stock headers as they are the most restrictive part of the exhaust system.
 

Latest posts

Back
Top