What to do, what to do...

[Lewis]

Hey guys, this has been on my mind for a while now, when I take apart my sled for repairs etc... What should I do about the engine? I was contemplating boring it out to something, and getting some performance Wiseco pistons, what size would be best to bore to? It is a 750 atm. And what other mods would NEED to be done for this to work properly?
Would it even be worth it in the end? And last but not least what would it cost approx. (I'm not talking about sending it to Hauck for a 3 grand job though).
Thanks again, Lewis
P.S. Dean send me a PM about contributions to the site. :)
:urock:

[Skinner]

Save you're money, forget the boring, nickesil cylinders ( to expensive to have redone and very little gain, as long as the walls are in good shape, keep the stock pistons, And by all means

READ THE POSTS ON THIS SITE

Tons of good info,IE: gasket squish, clutching, jetting, gears etc.
You do NOT need to reinvent the wheel unless you want to spend a gazillion dollars, these things were fast to start with. Spend your energy, not your dollars and study the mods that have already been proven.
Yammiegod, Toydoc, VVmax, racer7X, MOF, Jminor, Rules and many not mentioned can all help you out with tech advice. You need to decide what you really want to use the sled for, not just to haul ass.
Hope this helps ya

Skinner:homework:

[Lewis]

Hey Skinner, I was thinking more about just boring to a 800, or 791cc to be exact, I don't need to go all out, no point, but do you still think this would be overkill?
Thanks Lewis

[Master of Faster]

What Skinner is telling you is that there is alot of effort in boring these cylinders with little gain.

If you want to build a performance engine, you need to look into the things he suggested, head mods, port timing, and so on.

750cc's is plenty to get the job done.

Alot of people think to BIG BORE a motor is the ulitmate performance mod, but that really isn't so.

[Skinner]

AMEN, MOF

[mattman]

Lewis,

As stated by MOF and Skinner (and many others on this site - just not directly on this post) your 750 is plenty strong and IMO, you can make it faster than an 800 given the same mods to both sleds.

Regardless of what people think - 800 vs 750 in terms of ultimate sled for power, speed, drags etc. your 750 can get the job done and more.

So, IMO (as some others have posted already) the overbore is not worth it (if it can be done to the 750) for the amount of $$ it would cost to get the negligible performance increase.

Spend your $$ wisely. CLUTCHING, clutching, clutching - is very important as many have posted already. Wake up the "beast" from within and use all the HP that it is currently making and ensure that you can hook up - suspension adjustments and track - to put all the power to the ground instead of spinning.

Well that's my $.02

Let it SNOW!

[Lewis]

Man I'm getting these weird vibes saying I shouldn't waste time or money on boring it out, strange huh?
Well then, since boring is excluded, which I guess is a good thing (costs a lot)
in more detail, what are the more rewarding mods that I can do? I have a set of quads coming in the mail, so that is taken care of, I understand that I need to weld the crank for these, are performance wiseco's worth it though?
I think this post will be useful to more then just me... ANY info, ideas, much appreciated:urock:
:fishing:
Thanks, Lewis

[Master of Faster]

What quads did you buy, welding a 750 crank is only necessary if your spinning 9000+ rpm.

Other than that, the first thing that comes to mind would be to get thicker base gaskets to raise the timing and have the heads cut.

[Lewis]

Bought a set of 750 PSI's, I think they are Trailblasters but I'm not sure.
Would I need to bring my heads to a specialist or could I cut the heads myself?
Thanks

[Master of Faster]

If you're a machinist I suppose you could do it yourself, but a fair machine shop should be able to do it for under $75.

The purpose is to bring compression back after raising the cylinders.

With PSI quads there is no need to weld the crank, they spin at 8350 rpm just like stock.

[Lewis]

Okay, so I could cut the heads, and get thicker base gaskets, also I was reading about taking away a head gasket also, all these three raise the compression right?
So those are the main three? Then it's all up to jetting and clutch?
Lewis

[Lewis]

And for a new CDI, would an 800 unit work just as well as an aftermarket version?
Thanks
-I know I've posted a lot on this thread :)

[Master of Faster]

The thicker base gasket will raise your port timing, giving you somewhere around and extra 10+ hp I believe, lowering your compression at the same time. Cutting your heads will bring back the compression you lost. Removing a layer of headgasket is the cheap way of raising compression, cutting the heads is the proper way so you should just cut your heads to where they need to be and use a normal gasket. I believe you will end up cutting about .030" of the heads but after installing the thicker base gasket you can check your squish to determine exactly how much you can cut from the heads.

This is a 750 motor right? So no reason to use anything but the 750 CDI since your running stock r's.

After that, clutch, clutch, and clutch it again.

[Lewis]

Thank you very much MOF, you seem to be the only one willing to explain this stuff to me :D, so are you saying that you either cut the head or remove a gasket? Can you not do both and gain that much more compression? Also what about boring the port hole, as I see IZZ has done?
Sry if I'm being a bother, just can't help it, knowledge from school is one thing engines is another :D:D
:banana_1: :banana_1:
Lewis

[Master of Faster]

Don't worry about it, I'm happy to answer questions until my fingers hurt, lol.

Cutting the heads and removing a layer of gasket do basically the same thing, it in essence makes the combustion chamber smaller to increase compression.

Now you can only increase your compression so far until you experience pre-ignition/detonation and toast your motor, that is when the air/fuel mix is compressed so far and heated so much that it ignites before the spark plug ignites it. That causes two flamefronts which then crash into each other causing a pinging sound and eroding the top of your piston away.


So say removing a layer of gasket removed .005" and your cut the head .025" removing .030" total which (in this example) is the max you can remove. You might as well just cut .030" from the head right from the get go and not screw around with the gasket, get it?

Cutting or enlarging the holes in a piston can give you some power but can also be detrimental to your motor if not done correctly. You can easily hurt the strength of the skirt of the piston, and if the skirt breaks bad things result. So if that is something you want to do, give IZZ a PM and get some details about how he sucessfully did his.

[Lewis]

MOF you are too good to me :urock: :goodp:
Thank you very much, Lewis
-Although, when the sled comes apart the questions will flow...

[Lewis]

This thought just came to me, what about with higher compression pistons? I understand that most AF pistons do increase compression slightly, wiseco for example. If I were to take off 0.30 from the head, would I get the pre-detonation problem with new pistons?
Lewis

[Master of Faster]

Not common practice on 2-strokers. Mostly used on 4-strokes because its easier to raise compression with piston than to cut heads and have to deal with valve clearance, adjustments, and so on.

Good question, but once again, I'd have to say stick with whats proven and what works. Cut the heads;)

[Lewis]

Oh okay, so newer pistons would just be lighter etc... I was just wondering if there would be an issue of too high of a compression resulted from new pistons, was not implying to resort to new pistons instead of cutting the heads for the extra little p o w e r.
Thanks once again, Lewis

[Master of Faster]

Gotcha, shouldn't be a problem. Depends on what kind of pistons you were to go with as to whether they'd be lighter or not. In alot of applications it is hard to beat the oems.

[IZZ]

Well dude I just wrote you a very long detailed reply and it disapeared when I hit submit! Thats the third time its happened to me.

Ill try to recap:
I agree with all the above. Dont waste time on boring over - IMO its silly. (and Im more power crazed)
Mattman hits the nail on the head -
wake up the beast from within
750,s ROCK
in other words you have a screaming demon under that hood that just needs a few simple cheap do it yourself mods to awaken. Mattmans right on again when he says
CLUTCHING - CLUTCHING - CLUTCHING.
Thats the boat Im in now - Dialing it all in. The mods are simple enough with the right tools and alot of time but thats only half the battle.

Those pipes youve got coming will blow youre wig! Youre talking 20+ HP man! Bolt on! just get youre jetting and clutches set right which will be a no brainer using this site. Theres info eveywhere from everyone on clutching and jetting a stock 750 with PSI quads.

Now if you go through with the efficiency mods on top of the pipes you might be in the same boat as I. Youre gonna find that theres not to many people that run exactly the same sled with the same mods with the same pipes at the same elevation for the same applications as you. So youre gonna be on youre own at least a little - (youre never completly on youre own when you ride a Vmax 4 - brother) :bowdown:

Now I dont mean to discourage Ya from doing the mods, just realize what youre gettin into.
Youre gonna want to: 1.raise youre cylinders (Im not sure how high on a 750) - Dont do what someone tells you they did to theyre 800 because I know you can only cut youre 750 heads so much (not as much as an 800)
Ask Ken. He has done some awesome posts on these mods for the 750 (unfortunatly theyre lost in space somewhere) He can probably save you alot of headaches and time by giving you some pretty straight forward specs to go from (and you can trust him)

2.cut youre head (and use a stock gasket) - because you see the single layer head gasket compression boost is sort of a quick and easy way to bump youre compression up, for example if you dont want to remove youre cylinders and get into the cylinder lift or changing pistons and stuff. Its a fast easy way to gain some compression. but if youre raising youre cylinders - youve got to cut your heads to match and then some if possible, to get some more compression. Again my advice is to ask Ken as this goes hand in hand with the cylinder lift.

3.Drill a boost port hole. Youre 92's pistons dont have one if theyre stock anyway. Yamaha started drilling a hole in the intake side of the piston skirt in 93 I believe, called a boost port - it lets more intake charge fill the crankcase as the piston blocks the intake port. You can drill these holes oversize up to 3/4" but thats walking the line, like Master said this can and will weaken youre piston skirt. I think most people only drill them to 1/2" or 5/8". IMO what you should do if youre doing all this is get new pistons and rings for a 93 or 94 that already have the small boost port in them. This will give you a place to drill from. Otherwise youll have to get the measurements on the stock holes from a 93 and mark that on youre 92 pistons so you know where to drill. Now the thing with drilling that hole is to use a drill press and a step drill bit, make yourself up some kind of a jig to hold the piston firmly where you want it, and you want it so that when you drill the hole out you leave the bottom of the stock hole to be the bottom of the new oversized hole. In other words you dont drill the oversized hole on center of the stock hole, youre center of the oversized hole will be at or towards the top of the stock hole. Dont ask me why, I didnt write the book on this, I assume its to avoid weakening the skirt to much at the bottom there. Again Ken and some other guys (sorry I cant remember who all) had some great pics detailing the procedure in a great post on the mod, but that was a long time ago in a galaxy, far, far away.............................................. ..........................................:xmas-smil BEST OF LUCK AND A MERRY CHRISTMAS TO YA!

[MadMax-4]

Hey all,
Sorry to budd in boy's, just a quike question,
what would be the total HP gain after all the mods???
MadMax-4

[IZZ]

Madmax 4, I wish I knew! My guess is between 10-20 hp. But theres so many variables to consider, like how far you lift the cylinders, how much you cut the heads (or what your final compression comes out to be), the size and shape of the boost port hole, whether or not your talking a 750 or 800 even.
Im not one to stretch the truth and would rather under rate my sleds #'s than exagerate, that being said I would feel vey comfortable saying my 750 was in the 175 -180 HP range if I did all the mentioned mods, was running PSI quads and had the jetting dead on with premium fuel.

But Id like to hear from people who have done testing! Anyone?

[Lewis]

:urock: :urock: :goodp:
This post is coming alive :) Thanks IZZ for the long explanation, although I would need to get some good pics and have my engine apart to totally understand the boost hole, or port hole, or whatever it was called, but I will understand it soon,
And thank you again
Lewis

[Lewis]

KEN! Where are YA! hahaha

[MadMax-4]

Hey Lewis
I think the photos below are a part of what IZZ is talking about.
Later
MadMax-4

[IZZ]

WOW!!!
Check them bad boys out!!!
I cant imagine doing that yourself, at least not freehand with a roto tool!

[IZZ]

O.K. I dug deep and found these pics of mine

Picture of piston in the cylinder with oversized 3/4" hole
Picture of piston on bench with stock boost port hole

[IZZ]

Wow , Madmax 4 thats something to look at in comparison to your pistons with a view there! and to think I was scared I was walking the line with my puny little 3/4" holes!

[Lewis]

Those are some beastly looking holes :O :D
Don't really understand it though, I haven't done almost any work on 2-strokes, mostly car engines so... Hopefully it will make more sense when my engine comes apart. One question though, way would you drill a hole in the piston so that your intake can go underneath the combustion area? How does this make sense? I can see drilling a bigger intake to let more in but well whatever.
Thanks Lewis

[Lewis]

Also, I was reading the tech articles and I saw the one about the Bender and RPC oil injection, what does this do? The sled is already oil injected. And the one about the pressure changes under the hood, because of the vent hoses, give me your thoughts.
Thanks Lewis

[Master of Faster]

Lewis on a two stroke motor the intake of air/enters underneath the piston where it lubes the crank and then it is pull/pushed through the trasfer ports and enters the combustion chamber. That's about as simple as I can put it, so the hole in the piston essentially just allows for more flow.

[MadMax-4]

Hey lewis

Check out the link below it will give you a realy good idea on how a 2 stroke engine works in detail, scrole down to the near bottom of the page and watch the engine move, let the page load up all the way.

http://www.mts.net/~ghygaard/sp12.htm (http://www.mts.net/~ghygaard/sp12.htm)

MadMax-4

[toydoc]

Madmax 4, I wish I knew! My guess is between 10-20 hp. But theres so many variables to consider, like how far you lift the cylinders, how much you cut the heads (or what your final compression comes out to be), the size and shape of the boost port hole, whether or not your talking a 750 or 800 even.
Im not one to stretch the truth and would rather under rate my sleds #'s than exagerate, that being said I would feel vey comfortable saying my 750 was in the 175 -180 HP range if I did all the mentioned mods, was running PSI quads and had the jetting dead on with premium fuel.

But Id like to hear from people who have done testing! Anyone?

This is the 750 on the dyno with all the above mods, psi quads and a 800 cdi box.

[IZZ]

Wow Toydoc, I feel like an idiot. Thank you so much for posting that!
So you dont gain much if anything from those mods? according to the dyno tech data on the stock 93 with psi quads they pulled 160 with 145 mains! and like bruce pointed out in that article following the graph he was convinced the sled woulve developed more hp with leaner (and still safe) main jetting.
What do ya think gives with that?

[Ken]

KEN! Where are YA! hahaha

I'll work on redoing the post that I did on doing a cylinder lift.

Ken

[racer7x]

I'll work on redoing the post that I did on doing a cylinder lift.

Ken
I will save it this time. :frech32:

[Ken]

Dean,

Can we do the hidden forum again so I can work on the post as time permits?

Thanks,

Ken

[racer7x]

Just did, PM you the link in 1 minute. LOL :)

[Lewis]

Haha, thanks Ken, just hope Dean finds it :D , okay thank MOF, once again, I was thinking about that last night, and figured it must be something like that.
It seems hard to believe those mods wouldn't increase HP at all... Whatever, I don't give a 'sheep', I'll do em anyway, there must be some increase.
Thanks Lewis

[toydoc]

Wow Toydoc, I feel like an idiot. Thank you so much for posting that!
So you dont gain much if anything from those mods? according to the dyno tech data on the stock 93 with psi quads they pulled 160 with 145 mains! and like bruce pointed out in that article following the graph he was convinced the sled woulve developed more hp with leaner (and still safe) main jetting.
What do ya think gives with that?

Your no idiot IZZ. Thats not why I posted. It does add power you can feel, more so if your clutching is right on. The power up kit that most people sold was just what you listed, .039 base, one head gasket, cut head, window piston with a 6~8hp gain. Thats right what I ended up with. Also Carls dyno is known to be one of the better ones, no fluff numbers. Plus the 750 made over 105lbs of torque under 8000rpm. For a true pump gas 750cc sled the numbers are very good.

[Lewis]

Thanks Mad-max4, makes perfect sense now, but does anyone have any comments on the direct oil injection articles, worth doing or not?
Thanks very much, Lewis

[Lewis]

Hate to be a bother but slight confusion, if I raise the cylinders 0.039 over stock, why is it I can only cut the head 0.030, could I not cut it 0.039, because I would be losing compression then would I not?
Hahahah, Lewis

[IZZ]

Lewis, The stock gasket is .019 (or something like that) - so your only raising the cylinders around .020 with a .039 gasket.

So... if you cut .030 off the head your going to be taking an extra .010 off, since you only need to take .020 off to come out even.

[Lewis]

Thanks IZZ, I got a set of .051 Hauck gaskets, are these worth using? I got them for free, so it doesn't matter if they aren't worth using.
Lewis

[Ken]

Lewis have a look at this thread.

http://www.vmax4.com/vbulletin/showthread.php?t=790


Ken

[Lewis]

Wow! Thanks very much Ken, got a deticated member here :)
So I take it that if I decide on the .051" base gasket, I would need to cut the heads (how much is the most I could do?) along with removing a head gasket?
Also, just to clarify, is re-chambering the head cutting the 'dome' of the head more, to gain back what you lost in cutting? And what do you mean by "squish"? Is this how much the gaskets get compressed when you tighten the bolts? Might sound like a dumb question, I just want to make sure I get all the terminology right, not to confuse something with something different.
This is becoming a long thread, thanks again to all of you who have suffered my constant posting/questions.
Lewis

[Ken]

You might want to double check your gasket thickness I don't think that Hauck makes a .051" gasket.

What year is your sled?

Squish is the band around the outside of the head where top of the piston and head actually end up quite close to each other. This area serves a purpose, it increases the velocity of the fuel charge as the piston reaches TDC. But if it is too tight the piston can contact the head, if it is too large then you can lose power due to a greater volume of late burning fuel in the squish band.

In my opinion you shouldn't cut the heads on a 750 any more than .020" without rechambering (reshaping the squish band and possibly the dome). But you need a machinist that knows what he is doing, and you need to know what final squish and head volume you want to end up with.

If you have any doubts then Hauck still offers their power up kit, send them your heads and pistons and they do the mods.

(Anyone else out there can feel free to chime in or disagree, I'm no expert)

[Ken]

Lewis,

I just noticed that you are only 15 and that your sled is a 92. My advice to you would be to take the conservative approach. A couple of extra HP isn't worth a trashed motor, there are a lot of us who are a bit older who have stories of our screw ups. It's a lot more fun having a sled to ride than a story to tell.

If you really want to mod your sled then I would recommend that you get a couple of Hauck .039" base gaskets or you can double up on the stock gaskets. Have your heads cut just to the squish band, probably in the area of .020". Use a 93/94 head gasket, it's only 2 layers vs the 92 which is 3 layers. You could also consider having your pistons windowed but don't go too big on the windows, I'd say .5" maximum and you'd probably be safer with .375".

Ken

[VMAX80096]

If you have a 92 750 or 800 raise the cylinders and put a bigger hole in the piston. If you have a 93/94 750 do just the hole and remove 1 layer of the head gasket....raising the cylinders on this year doesn't help...you might gain some on the top end but will lose on the bottom...they already have good port timing....the 92 and 95 up don't.

[IZZ]

Here ya go lewis. Sorry it took so long. Theres probably a hundred ways to do this, the concept is to just vent the carbs to an area where theres a constant and consistent supply of ambient air ( the same air as far as pressure goes that the mouths of the carbs are exposed to) I found some brass fittings at the parts store and attached them to the airbox with a nut on the backside. I also T'd each carbs lines together. This makes your jetting more consistent. Read the vent tube article for an excellent rationalization. One thing to keep in mind is did the manufacturer take this high speed enrichment effect into consideration when they chose the main jets for the carbs? (hard to imagine they did because its not a consistent enrichment depending on which way the winds blowing) I dont look at it as a performance mod, more like adding consistency and predictability to your machine for easier tuning. So when you do your WOT run to check your plugs and piston wash, it will read the same whether your riding against the wind or with the wind!

[Lewis]

Awesome, thanks IZZ, great photos, just need one thing clarified though, what exactly does WOT mean, I understand the concept, if you can call it that, of it, I just want to know what the words for the acronym are.
Thanks Lewis

[IZZ]

Wide Open Throttle - The concept of it on a Vmax 4 is....Fast as Hell!!!! LOL!

[Lewis]

Hahaha, thanks IZZ, knew it had to do with passing all the other sleds out there.....:D:D:D
Lewis