Carbed 2 stroke turbo guy's !!!

[Spaarky]

I dont know if this applies the carb end of turbo's, but i will throw this in there.... I am running a carb turbo... and always lookin for the little extra here and there to squeze out of it...

How much affect does the pipe have on the HP(speaking twin). All of my teachings are that the back pressure virtually doesnt matter. If the stock pipe is empty you are good to go? Typically everyone(that I know of) has ran a stock pipe.

I know Speedworx is making one for the Cats and now SLP/OVS/Kirk Williamson have one for the Polaris's(EFI and CFI's). Can this really help? Worth the money? or just a gimic. I dont know how(not a pipe expert) a person can get better flow?

 

[mattymac]

I remember seeing somewhere that pipe mfg's were claiming that an aftermarket turbo pipe was making the same HP @ 8 lbs of boost that the same motor (M8T) made @ 12 lbs of boost with the stock pipe.... COUGH COUGH BULLCHIT!!!!

So lets say 7 hp per lb of boost, 4 PSI diffrence X 7 HP per lb = 28hp... I myself am thinkin this is a bit of a stretch!

On my CPI turbo pipe on my cat the volume "looks" to be more than a stock pipe, and the outlet itself is bigger, the welds are better, thicker gauge material, doubled up spring tabs and a more forward design to fit the turbo itself better, A sweet pipe but HP gains like that??? NO WAY!

 

[triple7]

Hey guys, I have a ?? about plenum area at the carbs. Everyone seems to be using a pressurized box that hooks to the carbs. What is the reasoning behind this?? Is a plenum area necessary or just the simple way of getting the job done??

 

[gus bohne]

1.does the pipe design play a part when under boost?

YES, Please do not forget this is still a 2 stroke regardless of turbo .

2. how much can it be worth ?

In virtually all cases, a pipe, when tuned to broaden the peak will show very good gains on your turbo. Larger center cans ( dwell) produce torque, this is a common way to see a stronger pull under boost and will offset the loss OFF boost caused by the larger stinger and LOST backpressure.

3. most run the stock pipe.

Typically we do as it is cost effective and is of lesser concern than getting the sled out and tuned and running good.


Like porting for a turbo, turbo specific exhaust is an ''extra'' item that is not really mandatory for wicked performance and long life,.
The heavier materail of the stocker holds heat in much better than the lighter aftermarket pipes that are NOT turbo specific.


4. Plenum volume,,, is it needed or easy build.....

Intake design and plenum sizing are TOOLS to tune the shape and efficiency of your system. Plenum volumes at sea level will be larger than at altitude, plenum volumes for drag racing vs for lower rpm transient throttle operations again will be different but STILL based on engine cc and gulp factor..

Too small a plenum will make for poor balance and attomization . When the rear wall is too close to the carb bell, reversion will get you chasing your *** in circles ,, you will have rich spots that transition to deadly lean spots.

Excessive intake heat and poor fuel/air distribution are common in small plenum boxs..
I will skip the pages we could write on the differences in bowl vent signal seen in too small a box.


Gus

 

[ExtremB]

interesting but explain to me what is plenum volume?

 

[triple7]

Plenum volume is the amount of open area or volume between charge tube and carb throat.

Gus, if I heard you correctly what you are saying is that there is a need for some plenum area?? More so than say directly hooked charge tubes??

 

[gus bohne]

Yup,, you got it Jake.

The rule of thumb in blowthru carb set ups has been 2 times the carb throat diameter for a distance to back wall fiqure..

40mm carb = 80mm box depth ,, so take it from there.

Jim Howard did try using pvc tube as you said directly to each carb NO box or plenum..

POOR to say the least,, not that it couldn't be made to work just was not convenient at the time..

Think of it as if there were no turbo, would the engine like running with this configuration ???
if not ,, then 9 out of 10 times it won't like it under boost.


kinda like a sucthru system,,, they just suuccckkk and backfire and bog and load the engine and load the charge tube and THEN THEY GO !!!



Gus
also known as lancelot link,, secret agent chimp !!

 

[ExtremB]

Ok perfect the plenum volume is a equaliser presure for the carburator .

 

[triple7]

I see. So there needs to be plenum volume. And plenum depth should be twice that of carb throat diameter, or atleast use that for a good starting point.

Now, does it matter much where the charge box is fed from? I would think ideally would be directly behind the carbs, dead center of the box. But, if my idea has to use a box, and I dont really have the ability to feed the box from the center from any angle, can I feed it from the end and be ok??

 

[gus bohne]

Yes you can Jake,
just try to make the entry as far from a carb opening as possible,, and definatly not toward either entry.. at a 90 to the carb entry.

If you have to be closer than say,,,,,60mm from the bell edge to the inlet of box . I would want a hook deflector in the entry to roll the draft away from the bell.


Gus

Its not so much an equalizer as a common bowl of cereal to eat form....

 

[DWHalverson]

Good thing for me then. My charge box is 80mm deep.

Charge tube lenth on our XP kits is 28''. Can't remember some of the others but the looked long. After a couple tries I finally got this one trimmed and fished in there.

Dave

 

[triple7]

Perfect! Thanks for the info Gus! I will probably send you some pictures when I get a little further on the design of this thing. Just to clarify this is not my entirely own system. This will be an addition to Dave's kit.

Dave, the idea we discussed is in the design process. It will fit, it is drawn up and I think this is going to work well. If I can get within a couple inches of 28'' I am going to be happy with it. How high is the turbo mounted from the bottom of the sled??

Thanks a hole bunch!!

 

[turboxp]

turbo

i can understand we all want to learn i was in the same position as you.If you want to learn about turbo systems with out making the same as some elses read the book Boost it was put out by the turbo master himself Corky Bell it will give you a pile of stuff that is way over my head but alot of it is in terms that the average guy can grasp.That is how i built the turbo system for my xp and also a rev.It is a lot of fun and you will have good days and bad the guys who sell the kits have had a few of them i'm sure.

 

[triple7]

Thanks for the info. Just ordered it. If you dont mind me asking, what kind of a turbo setup are you using turboxp?

 

[DWHalverson]

I think turboxp is Dave Bell from Idaho, correct me if I'm wrong. He was useing the Garrett and looked to be having good luck with it. Looked like a solid kit.

Dave

Thanks for the info. Just ordered it. If you dont mind me asking, what kind of a turbo setup are you using turboxp?

 

[triple7]

Oh thats right my bad!! I talked to him, really good dude.

 

[DWHalverson]

Is that who turboxp was Jake?

Dave

Oh thats right my bad!! I talked to him, really good dude.

 

[triple7]

Nope, I thought it was. I checked, turns out Boostit is Dave Bell the turbo kit dude. I don't know turboxp. Dave Bell was a good dude when I talked to him though.

 

[turboxp]

Who is turboxp

My name is Glenn and i am from the flat lands of Sask Canada but never ride here we ride in BC alot.Sorry never replyed was off line for few days.I used an areo 53 on mine just because of the simplicity of it less pluming.And no i didn't use it because it spools alot faster but it does spool fast.We ride with garret guts and they work really well also.
Good luck
GLENN

 

[DWHalverson]

Glad you got that worked out. Now that you mention it---I remember. Funny how that works.

Dave

Nope, I thought it was. I checked, turns out Boostit is Dave Bell the turbo kit dude. I don't know turboxp. Dave Bell was a good dude when I talked to him though.