8 petal Polaris reed intakes

Suzukidave · Post by **Suzukidave** » Mon Jun 22, 2009 8:20 pm

And then i started with the center port and cut it down almost all the way down . It will be cut even deeper before its done right down almost to the liner .

ja-moo · Post by **ja-moo** » Mon Jun 22, 2009 11:26 pm

There are so many posts and threads, what rwhp are you looking to get?

Suzukidave · Post by **Suzukidave** » Tue Jun 23, 2009 3:59 am

ja-moo wrote:There are so many posts and threads, what rwhp are you looking to get?

Hi John , i dont really have any target HP , i am just playing around to see if can be done . I already had the block and reeds sitting in spares and i only have $39 tied up in the reed blocks .

Tom Garcia · Post by **Tom Garcia** » Tue Jun 23, 2009 5:23 am

I guess now I am going to have to do a 10-petal reed project... Dave's upped the ante!!!

tz375 · Post by **tz375** » Tue Jun 23, 2009 7:26 am

Sorry to be a party pooper Tom, but Brett in Australia has a pair of 6 petals in each intake for a 12 petal look.

So you have to come up with 14 petals to top that.

tz375 · Post by **tz375** » Tue Jun 23, 2009 7:34 am

Dave,

That's looking way cool. Boy do those look large compared to the port size.

That must make it easier to add a pair of boost ports, but will the angle be too flat or can you still point them up towards the plugs?

Did I tell you I'm playing with the idea of moving studs and going to conventional port orientation (again). I worked out the stud patterns and now I "just" need to work out how to remove everything inside the block and replace it with something completely different.

What I should do next is to work out the port area I can get by doing that and see how much better it is than stock.

If I manage it, the port count goes up to at least ten - eleven if I can work out how to machine extra exhaust ports.

Fortunately all this costs is time and masking tape at this stage. I don't think I want to cost up the real thing..

ja-moo · Post by **ja-moo** » Tue Jun 23, 2009 1:56 pm

Suzukidave wrote:
ja-moo wrote:There are so many posts and threads, what rwhp are you looking to get?
Hi John , i dont really have any target HP , i am just playing around to see if can be done . I already had the block and reeds sitting in spares and i only have $39 tied up in the reed blocks .

That's cool!

It's just seems the "bigger is better" bug has bitten. How about a 6 petal putting out 200 crank hp on a H2 motor....

Or 97 crank hp from a 500 Kawi with (comparitively) tiny reeds.......

Just don't forget the "air flow", the bigger the reed block the sharper the taper into the port.

Sometimes 44 mm carbs are just too big for a 50cc motor......lol. (comparative)

Suzukidave · Post by **Suzukidave** » Tue Jun 23, 2009 5:39 pm

Here is a view down the reed block as its milled out right now ( not finished )

Suzukidave · Post by **Suzukidave** » Tue Jun 23, 2009 5:58 pm

ja-moo wrote:
That's cool!

It's just seems the "bigger is better" bug has bitten. How about a 6 petal putting out 200 crank hp on a H2 motor.... Or 97 crank hp from a 500 Kawi with (comparitively) tiny reeds.......

Just don't forget the "air flow", the bigger the reed block the sharper the taper into the port.

Sometimes 44 mm carbs are just too big for a 50cc motor......lol. (comparative)

John , when i first picked up these 8 petal reed years ago i also thought about mounting them up to the GT750 block but changed up and went with the 6 petal Arctic Cat reeds and boxes being they were smaller as the pictures show but they were the same size Arctic Cat used on there 600~900 triple snowmobiles . It wasnt till Teaser was forging ahead with plans to use the Polaris type reeds that they also use on there range of snowmobile engines that i thought about pulling the reeds i had back out and see if there was a way to fit them up other that sideways and its looking like mounting them verticle just may work out

ja-moo · Post by **ja-moo** » Tue Jun 23, 2009 9:20 pm

tz375 wrote:
Did I tell you I'm playing with the idea of moving studs and going to conventional port orientation (again).

Just wondering how that might work better, can you give some more info? Seems you would be loosing a lot of transfer area if I am reading correctly.....

tz375 · Post by **tz375** » Tue Jun 23, 2009 10:13 pm

Let's start with the caveats. I'm still working through the issues of where each sud has to go and what changes have to be made to the bottom flange and then I'll work up the block to the head.

And of course I still have to work out how much of a transfer area increase I can achieve (if any).

Let's step back for a moment and look at stock GT750. The intakes enter at an angle so the effective area is significantly smaller than the equivalent port on a non-rotated design. the same applies to the transfers and the exhausts which are torturous at best.

In the case of the transfers, there is a lack of transfer area at the outlet and the ports can only be opened up a small amount on the outer ports before they break through into the water passages. the cores are really odd at the center line and drop off badly on the two outer ports at the rear edge. The only effective way to fix that is to cut a hole in the outside of the water jacket, weld up the transfers and then repair the outer "cover". I figure if I'm going to do all that, why stop there.

The transfer openings to the crankcase appear quite large but could benefit from an increase which is not available. I did calculate the maximum port areas and they are still shy of what I need. That should read "what I want". "need' is not relevant here is it?

Straightening the intakes and exhausts allows for significant increases in port time area and allows the boost ports to point in the right direction.

Brett de Stoop's answer is to add two huge boost ports and increase the bore and to bridge the exhaust. The 33% extra capacity must help torque but puts even more demand on the gas flow. let's face it, Brett has spent a lot more time tuning these beasts than I have and knows what works, but that still leaves other avenues to explore.

When I run a computer simulation of a GT750 in MOTA, rotating the ports back to zero degree rotation from the cylinder axis, the changes in port angles appear to create more time area and more potential power.

But at this stage this is just an interesting bench exercise. When I finish working out the design issues I fully expect it to be way out of my financial league, but it keeps my brain working.

BTW, what is that 500cc 200hp motor to which you refer?

tz375 · Post by **tz375** » Tue Jun 23, 2009 10:20 pm

JA, the thing I didn't address is how rotating a wide port into a narrow space can create more area.

The answer of course is in the length and not the width. Think H2 style crankcase mouth but with even longer ports (back to front dimensions).

An XCR800 with 72mm pistons makes around 140hp and it's not hard to get 185-205 out of that motor and it's transfers are not much bigger than an H2. I took photos of them some time ago side by side with an H2 cylinder that I borrowed to analyze Magee's reed H2 motor.

The XCR is slightly too wide to fit on top of a HT crankcase where center and left pots are siamesed. I already tried that and didn't want to modify teh crank and cases to make that work.

So I know we can't get the right port curvatures, but I can make up some of that in the size of the ports.

But it's all theoretical at this stage. just an idea to kick around.

ja-moo · Post by **ja-moo** » Tue Jun 23, 2009 11:04 pm

tz375 wrote:
BTW, what is that 500cc 200hp motor to which you refer?

Thanks for the added info!

I haven't had a chance to look at a 750 cylinder bank in person. The Kawi KR 750 went with the twisted cylinder set-up to get more transfer area and get more of a more modern "teacup handle" transfer shape.

Seems you did your homework. I can't visualize why you can't get the time/area needed, with some decent port timing, but that's just conjecture on my part.

And the 200 hp motor was a H2 750.

Suzukidave · Post by **Suzukidave** » Wed Jun 24, 2009 4:24 am

John , my avatar is the port layout for a TR GT750 just to get some idea of how the ports are layed out .

Kris Bernstein · Post by **Kris Bernstein** » Wed Jun 24, 2009 4:38 am

Dave,

Would you say the Polaris reed boxes were an easier fit than the Arctic Cat's? Have you done two of these conversions now, or did you abandon the Arctic Cat reeds in favor of the Polaris ones?
As you know, I am going to use the Vmax reeds, circa 1995 but it is never to late to try something easier and more tidy as those definitely look!
As always, Dave a nice job fro the pictures,as I can see from here...

Kris

8 petal Polaris reed intakes

Polaris Reed Boxes