Need a little porting help with a Hyway 272 cylinder.

[Ronie]

Little background. I have an older white top 61 that I put a Hyway 272 cylinder on. The squish is .0195 and I opened the exhaust up 3-4 milameters and lowered the intake to 79. Compression is a little over 150psi cold. It just doesn't run like I feel it should, lacks torque, so I'm going to cut a .040 pop up and shorten the blow down to maybe 18, it's at 20 now. Any suggestions would be appreciated. As it stands the timing numbers are,
EX 100
IN 79
TR 120

I've went through around a tank and a half trying different tunes and this is the best I could get.

 

[srcarr52]

In my opinion you have too much exhaust duration to make decent torque on that platform. I'd say get the squish band cut and lengthen the exhaust duration but you already have too much intake duration as well. Ditch that jug and start over or commit to filling the intake floor with epoxy.

 

[Ronie]

In my opinion you have too much exhaust duration to make decent torque on that platform. I'd say get the squish band cut and lengthen the exhaust duration but you already have too much intake duration as well. Ditch that jug and start over or commit to filling the intake floor with epoxy.

Thanks for the input. I don't mind using a little JB Weld on the intake. Do you think a shorter blow down would help it out any?

 

[srcarr52]

Thanks for the input. I don't mind using a little JB Weld on the intake. Do you think a shorter blow down would help it out any?

A little, looking back at my notes it seems I favored around 18deg blow down, exhaust around 102 and intake around 77.

 

[cuinrearview]

@Stump Shot @Canadian farm boy

 

[Ronie]

A little, looking back at my notes it seems I favored around 18deg blow down, exhaust around 102 and intake around 77.

Thanks, If I drop the jug .040 it should be around 102 for the exhaust and I'll use some epoxy to get the intake right.

 

[huskihl]

The 670 Jred I did a couple months ago was 102 120 78 and seems to run really well

 

[Stump Shot]

If you didn't do any area work on the intake you can get away with more duration, both just won't do, so it's hard to answer the question directly if that makes any sense. If this is the case I would run it first without adding epoxy if in the low low eighty's.
I think the the guys have got you on the right track here. 103-104 exhaust is a great work saw target. This said you should have a screamer on your hands(play type saw) now, the compression is low in my experience with stock cylinders. I would recommend going over your cylinder with a fine tooth comb and check for it being out of round etc., if you find anything suspect, it's really not worth your time investment. If this ends up being the case(which I suspect it is) I would highly recommend finding a OEM cylinder to work with, used with a Meteor piston is a good money saving option, or a new kit which is not much more than the AM now days.

 

[PogoInTheWoods]

Or try a different carb depnding on what's already there. Opening up the intake block itself (with the right carb) will provide significant additional gains regarding flow. If it has a larger venturi carb with the original older intake block it'll be pretty choked up to begin with regardless of what you do to the intake (porting-wise).

May want to put a different ring in it, too. 150# is kinda low for a fresh top end on one o' those..., especially given the squish you have.

Don't know much about porting numbers, myself. Just considering other possibilities before the epoxy and re-grinding if you haven't already covered those bases.

 

[Ronie]

Thanks everyone for your help. I'm going to do like srcarr52 suggested and go with an OEM cylinder. I've got a couple of 670 cylinders and couple of new Meteor pistons so I'll use the numbers that huskihl posted with one of them. I also have a NOS 670 carb I can use on it.

 

[Ronie]

If you didn't do any area work on the intake you can get away with more duration, both just won't do, so it's hard to answer the question directly if that makes any sense. If this is the case I would run it first without adding epoxy if in the low low eighty's.
I think the the guys have got you on the right track here. 103-104 exhaust is a great work saw target. This said you should have a screamer on your hands(play type saw) now, the compression is low in my experience with stock cylinders. I would recommend going over your cylinder with a fine tooth comb and check for it being out of round etc., if you find anything suspect, it's really not worth your time investment. If this ends up being the case(which I suspect it is) I would highly recommend finding a OEM cylinder to work with, used with a Meteor piston is a good money saving option, or a new kit which is not much more than the AM now days.

You're probable right about that cylinder, somethings not right and I'm better off going OEM.

 

[David Young]

The 670 wont work easily because the 670 has a different intake arrangement with a rubber boot

 

[David Young]

even a oem 266/268 jug would be better in my opinion. but it will also have a different intake than the 272

 

[Ronie]

The 670 wont work easily because the 670 has a different intake arrangement with a rubber boot

I have a boot and flange I can use on it.

 

[David Young]

it sounds like the carb isn't just right have you given it a fresh rebuild?

 

[Ronie]

even a oem 266/268 jug would be better in my opinion. but it will also have a different intake than the 272

I have a 266 cylinder I could use but it looks like someone lost a clip and it cut a couple of gouges below the upper transfer on one side. I'm saving it for a backup.

 

[Ronie]

it sounds like the carb isn't just right have you given it a fresh rebuild?

New straight out of the box 260A

 

[huskyboy]

New straight out of the box 260A

Check metering lever height

 

[srcarr52]

Before you mess with any of the porting... have you tried advancing the ignition timing a bit?

It seems a little lazy upon spool up which is normally be an indicator of too much intake duration... but it can also be lack of timing.

 

[Ronie]

Check metering lever height

Before I put it on another saw make sure it's right.