Polaris TB's

[neilca]

I have been working on a set of Polaris XL 650 throttle bodies for my new racing engine. This is what I have learned so far.

I purchased two sets of TB's off ebay for about $125 each. One thing to look for is corrosion in the throat just above the butterfly. I have lived all my life in the south and have never seen a snowmobile, so I do not know where this corrosion comes from,



I ended up buying another set to come up with 6 good throttle bodies.

I tried to find information on the stock Polaris injectors with out luck. I ended up buying some modified 30 lb injectors. See below for what needs to be machined on the injectors.




The linkage I used for the TB's required that the stock position of one side be changed to align with the linkage. See below.



Another thing about the linkage. When you snap open 6 - 46mm throats you have a massive vacuum drop in the intake. You want to slow down the the initial opening to make the engine more tunable. I used a wheel linkage to slow down the initial opening and accelerating from 1/2 thottle to wide open. The wheel changes the torque arm from very short to long as it rotates. The wheel will be turned by the throttle cable.




I made some velocity stacks that work to smooth out the air flow and double as a method to hold down the air box. The air box will also hold the TB's in place.




The intakes will hold the bottom of the TB's in place. I used silicone hose to attach the spigott mounts to the TB's.




This is looking straight down the hole. No turns in this manifold!



The final install will look like this. The scoop is from a Lola 340 and will be about 1/2 the height shown.

[parts4porsche]

That is amazing work! congrats!

I also bought two sets of polaris long ago, and wanna do the same. but I will make it on a turbo engine. let's see if I can make it work like yours.

could you share also the engine displacement you are running? and also how much HP did you make with it?

Best Regards
Tadashi

[neilca]

Thanks Tadashi,

The rest of the engine specs can be seen here

2.4 Liter racing engine

I am not sure how much HP it will make. I am hoping for 200hp at the rear wheels.

[KTL]

Neil,

That's some nice work. Well done!

You might ask Al Kosmal here on the forums for some tips, as he's done some similar work using Triumph Speed Triple ITBs.

Is the silicone coupler reinforced for vaccuum use? I'm no expert by any means. But I thought the silicone is normally used in turbo applications and therefore under pressure? Just wondering if the silicone would flex under vaccuum load?

That Lola periscope/snorkel for ram air intake is fantastico. That is a nice feature of the 914, in that its more agreeable to intake plumbing like that. The 911 rear window/body area takes a bit more work to create something similar.

Also, as an aside & sorry for the hijack, is your vertical oil pressure relief spring shimmed in any way to "compensate" for using the oil filter console? I had a filter console on my engine recently (w/out shim) and I just heard the shimming is required to use the console or lower oil pressure will occur.

[al lkosmal]

Nice work...I really like to see the different approaches DIY people are taking. very inventive. Your progressive throttle actuator is very cool. Please post how well it works, once the engine is fired up.

regards,
Al

[neilca]

Thanks guys,

I had contacted Al about a year ago and looked over his work. That is one of the things I love about this site, the free exchange of ideas.

The silicone is reinforced but I do not think it has to be. The spigot from the TB sits right on top of the intake spigot. The silicone hose is just a flexible coupling.

I had called Neil Porter, a formula car vendor, and gave him my requirements he came up with the Lola scoop. It will be perfect for my car.

I ran the filter on my 2.0 liter up until this year. I never shimmed the spring for this. I was running restrictors in the top end hoses. With the engine hot 6300 rpm in 5th gear end of the straightaway Road Atlanta I had 80 psi. I do not plan on running the restrictors in this engine nor shimming the pressure relief valve, we shall see what I get. BTW I am running a thermostat to keep fom blowing the filter apart on cold start up.

[KTL]

Ah good point about the silicone connection. I understand what you're saying, in that the silicone is just a means of joining the two pieces and not necessarily an extension/union.

Thanks for the feedback on the shimming. Just wanted to check because the shim "requirement" is the first i'd heard of. I do realize the springs & caps varied over the years but I hadn't thought of needing to shim in my case of just adding a filter.

I agree with respect to the use of the t-stat in the case. Nothing wrong with the filter being inactive until the t-stat opens. That's how a "regular" engine operates anyway with the oil cooler. I suspect the t-stat should be there in both cases- to protect the filter or the cooler from the extreme pressure of cold oil flow. My small Canton filter implosion seems to substantiate that.......

[neilca]

My first attempt at plumbing the race car I had a filter in the scavange side prior to the cooler. Blew it apart just trying to fire up the engine. I ended up plumbing in a bypass circuit using an external pressure relief valve. I like the console much better.