Carbed 2 stroke turbo guy's !!!

[TurboM700]

K will do It may be a couple weeks intill I get some time works to busy. I was just wondering if there was anything that I need to do because its a triple or anything I need to watch for.

Thanks again I'm sure I will be picking your brain here later.

Mike Fuchs

 

[Summit Guy]

Gus,

Next question, what reeds have been working on the turbo Doos. Mine is a HO not a R.



Thanks again

Paul

 

[gus bohne]

carb 600 cages with doubled up reeds are hard to beat..

yes you give up some ,, but lifes a trade off ,,,,,,,,,,,for now...


I have stainless that seems very very promising but
I won't sell them

 

[DWHalverson]

Gus, I'm haveing some custom ones built for my turbo XP kits. Not sure if there is any difference in the petal design between the R and HO engines. They have been holding up very well in my Cat. The Ski-Doo ones wont be ready till late summer/early fall though.

Dave

 

[genesmob]

Bov

Back to the BOV question. My sled is EFI. Ive tried two BOVS, Greddy and Vortech and without a BOV and I swear I cant tell the difference in throttle response or anything else. I record my boost and it doesnt spike with or without a BOV when I let off the gas. I can see where they might help with the runon problem with carbs, but, in my application I dont see them being necesary. Maybe its because the lack of vacuum that a two stroke makes compared to a four stroke. Even after an eighth mile run at 18lbs, the recorder shows the boost dropping immediately after the throttle is chopped with or without a BOV on my sled.

 

[gus bohne]

Gene,
I explained that above, EFI or any butterfly throttle valve will be unaffected by blowthrough turbocharging.

throttle blade movement is assisted by the dynamic pressure exerted on the opposite side of the throttle BLADE as its is either opened or closed..

The idea of needing a BOV is absurd ..
Glad to see some of you guys picking up on it ...:beer;

 

[markis24]

Awesome thread Gus, thanks for sharing your knowledge.

 

[Jmgsnowman]

losing power after being full throttle for 100 yards on steep pull

I have a polaris non ves 700 running about 8# boost 50/50 race fuel. Fuel pressure is about 10 psi above static around 2# boost. I seem to notice once i have been riding for awhile, i will lose power under full throttle, it almost develops a surge, comes in and out. don't seem to notice it when it hasn't been run as much. Seems to be ok on the flat. I haven't had a chance to check, but thought maybe my airfilter is collapsing, don't have a cage inside it
Any thoughts? Thanks. Great thread by the way.

 

[Zipperno]

I have a polaris non ves 700 running about 8# boost 50/50 race fuel. Fuel pressure is about 10 psi above static around 2# boost. I seem to notice once i have been riding for awhile, i will lose power under full throttle, it almost develops a surge, comes in and out. don't seem to notice it when it hasn't been run as much. Seems to be ok on the flat. I haven't had a chance to check, but thought maybe my airfilter is collapsing, don't have a cage inside it
Any thoughts? Thanks. Great thread by the way.

What is your base fuel pressure?

Base fuel pressure should be 5-6 psi at idle. You need this much fuelpressure to keep carbs with fuel on long pulls...

//Tom

 

[gus bohne]

I want to say it sounds like hot underhood air temps,, could be your air filter..???

your fiqures are confusing?
what is base fuel pressure ? 10psi ? that would put you 10 over boost, you should not be running OUT of fuel, unless of course there is an issue with your tank vent,,

You more likely would be going rich from heat soak ..

give me the answer on base fuel pressure please ..


Gus

 

[Mn Turbo]

Carb turbo question

Hey Gus, first off thanks for any help you can give.

I have a 1995 skidoo mach z 780 that I use for asphault racing. I turbocharged it using a t3/t4 stg I .82 turbine, and a 50 mm compressor from a diesel application. It ran great this way for three years, but was hard on pistons. My thinking was that the turbine was too restrictive, and had too much back pressure. I upgraded to a t3/to4e 57 trim, with a stg III .82 turbine.

Heres my problem..... shortly after building boost (7-8 psi) the motor stalls, if you stay on the throttle it will come back, and then stall again. It runs great untill it stalls. The old setup liked a lot of jet (560 main, 160-200 powerjet 2 11 psi) i'm running the same jetting, with an A/F ratio of 12.5:1 with 110 octane fuel. I've tried adjusting plug gaps, checked kill, and tether switches, minor jetting, and boost changes without any luck.

With the old setup I had tried an intercooler, and It acted the same as it does now, I assumed it was too much of a restriction, and when I removed it, all was good. So i'm thinking it may be an airflow problem.

Thanks again for any help.

 

[gus bohne]

it sounds like fuel surge, slosh or starvation..
You could have a boost side leak in the system but it would go flat rather than die.

when they run the bowls out of fuel they will tend to backfire.

Are you using a stand alone electric or an old aerocharger pulse and electric ?

its fuel handling I feel lets look at the basics.

If you are using a pulse pump that should be tossed,

you should have at least 8-10 psi over boost fuel pressure..

no more than 3-5 at idle..

could be a leak on the exhaust side that shows under load and chassis flex..
look at your tank venting system for issues to, check valves get tossed.

Is the turbo in the same mounting location as the original that "" ran strong ""
prior to this issue ?

hood changes
bellypan changes
Gus
hope it helps

 

[Mn Turbo]

Thanks for the information.

When I say it stalls, its just like when you lift after being on the throttle for a while, then try to get back in it and its loaded up and unresponsive for a few seconds.
The turbo is in the same location, but the header is new because I switched from a GN type turbine housing to a std 4 bolt... but its the same design as the old one. I'm using the same cold side as the old turbo.

I'm running a stand alone holley blue pump with a 1:1 reg.(14 psi max) Base fuel pressure is 3-4 psi, and seems to rise quickly, and accurately with boost. I'm using the oil injection tank for fuel with the stock fuel cap.... i'll double check the vent.
I'm not sure what you mean when you say "you should have at least 8-10 psi over boost fuel pressure"... a fuel pump capable of boost fuel pressure + 8-10 psi? Whats the best pump to use?

I pulled my pipes, and all the silicone was still holding on, so I believe they're sealing, but i'll add some more springs. I'm still using stock motor mounts, would some sort of torque rod be worth trying?

The hood and belly pan are the same except the exhaust now exits though the side rather than the bottom.

When I tried the intercoolers the first would stall by 660' then I switched to a larger one rated for 350hp, and then it went to about 1000' before stalling... does that make any sense?

Does my jetting seem extreme.... i'm up 160 on the mains, and 180 on the powerjets x3 (were running a Doo 700 twin @ 9-10 psi and were only up about 150 per cyl)?

Sorry for all the questions,
I really appreciate all the help

Mark

 

[DWHalverson]

8-10 psi of fuel pressure over boost with a 1:1 fuel pressure regulator means that for every 1 pound of boost that the regulator sees it raises the fuel pressure 1 pound. So if you have your baseline idle fuel pressure set at 5 psi and run 10 pounds of boost then you will see 15 pounds of fuel pressure at 10 pounds of boost.

 

[gus bohne]

The intercooler thing sounds like it should be nonexisitent without the cooler...


Am I reading you right that you ONLY have a 50mm compressor wheel ??
that in itself is suspect as I would not expect anything smaller than a 71mm wheel for a 780 triple pipe triple..

your compressor sizing should be targeted at 400-500 hp.. triple piped triples need at leaast 40% more compressor ..than say a single piped triple or a single piped twin..


Gus
you could be just too hot from over speeding the turbo..
:face-icon-small-dis

 

[Mn Turbo]

Hi, my old turbo had a 50 mm inducer. The new 57 trim has a 57 mm inducer, and a 81 mm exducer.... rated for about 450 hp, it is a peaky compressor, and likes a high pressure ratio, but I plotted it out and I think I have the extra 40%. (A 50 trim has much larger islands, and may have been a better choice)

The intercoolers are long gone, I was just wondering if that was a typical symptom of a restrictive cold side..... just trying to learn as much as I can.

I understand the 1:1 rise, but didnt understand the 3-5 psi @ idle, and 8-10psi above boost..... didnt seem to be 1:1.... unless referenced in front of slides. Mine is referenced to the air box.... 3.5psi @ idle + boost @ 1:1.

Thanks, Mark

 

[Jmgsnowman]

I want to say it sounds like hot underhood air temps,, could be your air filter..???

your fiqures are confusing?
what is base fuel pressure ? 10psi ? that would put you 10 over boost, you should not be running OUT of fuel, unless of course there is an issue with your tank vent,,

You more likely would be going rich from heat soak ..

give me the answer on base fuel pressure please ..


Gus

My base fuel pressure started out at 5 psi, i did turn it up last time out, to 7 as the base, hitting 15 at full boost. I did replace the stock vent with a larger one.
Thanks

 

[gus bohne]

Your carbs have 1.5 needle seats.. that and your low fuel pressure and poor pump choice is the problem.
Holley blue and red pumps are not even close, and they wear and surge ...


You need a std issue msd efi external pump,,, Jegs,,
YOU MUST put 2.0 needle seats in and at a minimum remove the stock screens from the 1.5's that are in there now..
If you were to just change the pump, and reference the fuel pressure regulator off the center of one of your pipes you will get the rate of gain you need and much higher volume of less airated fuel.. the dead headed holley set up you have is a nightmare...
You need a good malory type 4 port bypass boost reference regulator
sorry, dont mean to offend,, just get the correct plumbing and CURE your issues once and for all sir..

If you are unsure I can pull part numbers for you..

Gus

 

[Mn Turbo]

Thanks Gus, dont worry about a offending me.... just want to learn. I'm using an areomotive 1:1 bypass type reg now. I thought my pump might be marginal, and was thinking about upgrading it.

So by using the center of the pipe, I will get a greater rate of fuel pressure rise?

Ok,
msd pump referenced to pipe for 8-10 psi over boost.
install 2.0 needle and seats

One more quick question, can you explain fuel surge, and slosh?

Thank you very much for sharing your knowledge, its been very helpful.
Mark

 

[10001110101]

Right behind the slide would be prefered..

The bov can only react as fast as the slide falls, so use of one without the other being set up properly is moot...


If you really want to have the carbs SNAP shut, use dynamic pressure to the top of the carb fitting rather than static.

using a pitot tube in the charge tube would provide the pressure you desire for INSTANT, Snap shut throttles..

Whats really causing this is Venturi pressure UNDER the slide is higher than static airbox pressure, thus the delay in overcoming the incoming charge and dropping the slide thru it.

Using dynamic pressure would solve this for ALL carb users.
There, the proverbial CAT is out of the bag :beer;

Gus

I have an 09 rev xp that I turboed myself and just wanted to share some knowledge that I learned from it here. Run on! I could not get rid of it, I tried balance lines to the top of the slides, dynamic and static, no luck and actually the dynamic made the problem worse! I tried big and small lines to the top of the carbes, no luck. Tightened the spring on the throttle, no luck and a sore thumb! So I searched and searched until I found some information on a drag bike forum that was of interest and makes complete sense,

Run on is caused from too much air getting into the engine when the throttle is closed correct? so why are we putting air to the top of the slides? Here is what is happening:
we let off the throttle
the slides close
the turbo is still spinning and increases pressure in the airbox until the turbo stalls, and the air goes back out the compressor (without a bov)
but during the high pressure spike when the slides shut you are forcing air into the engine past the slides just like you would have a hole in the intake boot, only worse because of the pressure in the airbox. To make things worse because you are pushing air around the slide and not past the mainjet your mixture is lean which we all know makes a 2 stroke rev higher! this goes on until the the pressure bleeds down in the airbox and charge tubes or until all fuel is burned in the cases.
To solve this problem is simple, don't put pressure to the top of the slides. It IS that easy! If you look at the slides there is plenty of room for the pressure in the carb to equalize and also pressure cannot push the slide up into the carb because there is no flow there, if the pressure is equalized on top which is is without any mods the slide cannot open. If it could then this would happen to guys at sea level where atmosphere pressure is higher, just like boost does to your engine, makes it think it at a lower than sea level elevation. I now have my spring on my slides loosened up one revolution and my throttle is as light if not lighter than an efi sled, which rocks! No more sore thumb. In and out of the throttle all day long without a hint of run on, the thing runs like a stock 220hp sled!

For a blow off valve I use a Tial 50mm bov but with a soft spring so it opens at idle, the spring I used is from a automotive thermostat, i believe an eagle talon actually, but any standard thermostat will work, very soft and no leaks and very responsive action of the bov.