Port height - too tall for freestyle?

[ATS_Aaron]

This thread is really for ATS_Scott, but he is trapped with his wife at Ikea right now so he can't ask.

We ride 99% flat water. Over the winter he Sport Ported a 650 6m6 motor and then at the last minute decided to bore it to a 701. It ran well, but he yearned for more power.

I recently bought a pair of old race skis, one was a limited ski and the other was a Super Stock/Modified ski. Scott wanted more power so we dropped the Super Stock/Modified motor in his ski. Here are the mods (that we know of):

MSD total loss ignition
Protec billet head with 3 bolt girdle
61X cylinder bored to 84mm
WPS (we think) pistons
very, very ported
62T cases also very ported to match the cylinder/sleeves
R&D intake manifold
C/F reeds with stuffers
reed spacer
Big 48mm carbs

In the race ski it was using a type 4 dry pipe with water injection, but Scott installed it with his B-pipe using the old 650 (small) chamber.

So we rode it last weekend. It seems like the carbs are set up really well, but the ski has no bottom end. You pin it and it goes, goes, then HITS and I mean arm yanking HIT. The delay in the HIT has totally screwed up Scott's timing for jumps or tricks.

So in search of some better bottom end Scott pulled the cylinder yesterday to look at the porting. He measured from the top of the deck down to the top of the exhaust port and came up with 33mm. Are the exhaust ports too high for freestyle?

Is the carb size a problem for freestyle?

He took pics and will post them when he breaks free of Ikea.

Thanks in advance,

Aaron

 

[robertg]

I tried a Pro Tec cylinder last year, I think the exhaust port was 36mm from the top of the cylinder. It had the same power band that you have. I would say the exhaust port is too high. I believe stock is 39.75mm.

 

[#ZERO]

Yep… the stock Yamaha 701 61x cylinder has a below-deck exhaust port height of 39.6mm and the stock 760 cylinder is 37.6mm.

You're almost 7mm above the stock exhaust port height.

What size domes are you running and what are your compression readings?

 

[ATS_Scott]

Ok escape from IKEA was successful... well if you consider having to return a table and then buying another after hours of deliberation a success... uggg. I HATE shopping... :banghead::banghead:

Actually after telling Aaron 33mm I think it was actually 37mm from top of port to deck. Here are some pics. The other cylinder is a big bore 61x shown for reference. It's exaust port height was identical to the SS cyl.

http://webpages.charter.net/whiteturbomr2/62T superstock/cylinder 6.JPG

So what do ya'll think of the porting? Did somebody actually know what they were doing?

Those points on the back of the sleeve at the edges of the boost port, line up perfectly with the ring gap. Makes installation a little difficult. But after an hour of frustration I found the key... Pull the motor and the carbs and it's a breeze....

 

[turbohatch3]

looks like a hack job

 

[#ZERO]

With that porting and epoxy work I almost didn't recognize this was a yamaha engine. :bigeyes:

Who ever did that job was definitely experimenting around with some new ideas. :scratchchin:

 

[waxhead]

They knew what they were doing
some of its a bit radical in the sleeve cutting down
they cut alot further than i would have cut

 

[#ZERO]

It looks like more of a racer experimenting porting job then a freestyle job.

Most freestyle port jobs are usually 66% of the bore size and racing port jobs are about 68% with 70% being the maximum.

The exhaust ports are extremely wide and tall; I'm really surprised that you didn't snag a ring or worse.

:bigeyes: The piston skirts are trim away up to the wrist pins; you couldn't even check for the proper clearance if you had too.

 

[waxhead]

if you saw my cylinder you would see alot of stuff like that in it

Mine more radical in some areas and less in others

ie i have a whole lot more support on my port

i liek the way he has tried to give more transfer port volume but i think its lost a bit to much piston support

 

[waxhead]

can we see down the intake on the cases please

 

[ATS_Scott]

can we see down the intake on the cases please

Like the last pic? looking @ the reeds? or from the intake manifold side? The engine is back together and in my ski right now... I didn't pull the intake, just the carbs, so no pics other than what you see for now.

http://webpages.charter.net/whiteturbomr2/62T superstock/

pic # 6 is hopefully what your after?

 

[Matt_E]

That's an all out port job, damn.

There are a few good reasons evident in those pictures as to why you're lacking bottom end. the boost ports appear to be useless, that kills bottom.

If you want bottom end back, you'll need another cyl.

 

[ATS_Scott]

Should I keep the cases or should I get something more stock?

 

[Matt_E]

I would start over on the cases, too. I would be the last person to say this, but geez.

 

[WaveDemon]

I can sell you a running 650 for cheap

 

[waxhead]

there is a large chunk missing fromthe cases and its not helping support the cylinder

how did this thing go on the top end
as in like what rpm does it pull

 

[ATS_Scott]

It's VERY similiar to my 785 Pro power output. Very soft on the bottom, my ported 6m6 was way stronger, then around maybe 3500-4500 it flips the power switch and it's GO time. It's really a great running engine, just hits too late for my taste.

 

[waxhead]

is this with the total loss in it ?

and what base timing are you using on the ski

 

[#ZERO]

That's an all out port job, damn.

There are a few good reasons evident in those pictures as to why you're lacking bottom end. the boost ports appear to be useless, that kills bottom.

If you want bottom end back, you'll need another cyl.

Hey Matt… I'm just curious as to why you think the boost port has been compromised by the porting and epoxy work.

It appears to me that someone was trying to enhance the flow to the boost port and auxiliary transfer ports.

This was probably not a good idea on this engine because it would push some of that main transfer ports charge right out that wide exhaust port.

 

[ATS_Aaron]

is this with the total loss in it ?

and what base timing are you using on the ski

Yes with total loss, and it's an older pro II unit, 4270. Base timing... I haven't checked. When we got it, it had a 5000 rpm module for initial retard and a 3 degree per thousand retard rate, and nothing in the revlimiter socket. I added an 8000 rpm module, and the retard rate module has had a resistor soldered in place, 4.07k ohms resistance across the module pins.

Can I use the starter with the flywheel cover off? and I don't see a TDC mark. I may have to find TDC too. yippee.....:banghead:

WTF... This is Scott, and I THOUGHT I logged Aaron off......