lowering 61x port timing

[teton]

I just got a 61x head that i need to replace the sleeves in, i had good success compression wise decking my last head 8 thousands, and squish was right on the money, I know decking the bottom of the cylinder has been done on 62T jugs to lower the port timing. so its got me curious......what if i where to deck the bottom of my 61x cylinder instead of the top, would the lower port timing be beneficial in this application? I'm thinking the same 8 thousands......

 

[WaveDemon]

let us know how it goes. I'm thinking you'll get a real short powerband.

 

[teton]

could porting fix this?......i need to research into this, just wondering if anyone had done it?

 

[#ZERO]

You're only going to change the port timing 1/2 degree by milling the cylinder bottom .008 thousands.

The exhaust ports already open at 90.5 degrees and going to 91 degrees won't be that beneficial IMO because the mechanical advantage of the crankshaft is already on the downside.

If you're going to trouble of removing the sleeves, I would at least do some porting to improve performance.

 

[teton]

ill be doing porting eather way just wondering which side would be better to deck, top or bottom, i do see your point though. i thought it was more around 87....but i dont know where i got that number in my head from.....if the port was lower couldnt i increase exhuast port height more without loosing low end, seems like it would be safer then increasing the port width over the 70% mark

im trying to experiment with this cylinder instead of just widening my exhaust port/cleaning up the transfers as usual. #0 do you know much about the boost port duration, ive seen a lot of porting with the boost port lengthened significantly.....anything i could try with that?

Can you tell the machine shop i work at FSU engineering school is not very busy! ha

 

[#ZERO]

Why do you even want to even change the cylinder height, you'll just be causing yourself trouble in the future? :shrug:

If you have access to a machine shop, you should install some big bore sleeves in that 61X cylinder if you have the time. :scratchchin:

Anyway while the sleeves are still in the cylinder you should use a right angle scratch awl and scribe some lines in the aluminum casting around the boost & transfer port windows. Then when the sleeves are removed you'll see where the porting needs to be done. Porting while the sleeves are out makes it a real piece of cake.

While the sleeves are out you should make the boost port tract wider by a few millimeters on either side in the aluminum casting and thin bridge between the main & auxiliary transfer ports. You can also extend the main transfer ports a few millimeters toward the exhaust ports to improve performance.

Also I wouldn't go over 68% on the exhaust port width for freestyle use and keep it straight on the sides. Anything above 70% is usually for racing and the ports are more oval shaped.

Here are the specifications for the 61x 701 cylinder.

90.5° Exhaust Port Opens
121° Transfer Port Opens
179° Exhaust Duration
118° Transfer Duration
30.5° Blowdown Time

Here are the specifications for the 62T 760 cylinder.

87.5° Exhaust Port Opens
120.5° Transfer Port Opens
185° Exhaust Duration
119° Transfer Duration
33° Blowdown Time

The boost port duration is the same as the transfer port duration because they're at the same height for both cylinders.

Hope this helps, good luck with the new project.

 

[DCRocks]

Here are the specifications for the 62T 760 cylinder.

Ok, quick question, is there a 64x 760 cyl as well as a 62t?

Are there any major differences?

 

[kevbo]

Good question, I never measured the OD of 760 liners but I think they are too thin even at 84mm. Aftermarket liners are the best option if you must have a bore.

 

[teton]

Why do you even want to even change the cylinder height, you'll just be causing yourself trouble in the future? :shrug:

If you have access to a machine shop, you should install some big bore sleeves in that 61X cylinder if you have the time. :scratchchin:

Anyway while the sleeves are still in the cylinder you should use a right angle scratch awl and scribe some lines in the aluminum casting around the boost & transfer port windows. Then when the sleeves are removed you'll see where the porting needs to be done. Porting while the sleeves are out makes it a real piece of cake.

While the sleeves are out you should make the boost port tract wider by a few millimeters on either side in the aluminum casting and thin bridge between the main & auxiliary transfer ports. You can also extend the main transfer ports a few millimeters toward the exhaust ports to improve performance.

Also I wouldn't go over 68% on the exhaust port width for freestyle use and keep it straight on the sides. Anything above 70% is usually for racing and the ports are more oval shaped.

Here are the specifications for the 61x 701 cylinder.

90.5° Exhaust Port Opens
121° Transfer Port Opens
179° Exhaust Duration
118° Transfer Duration
30.5° Blowdown Time

Here are the specifications for the 62T 760 cylinder.

87.5° Exhaust Port Opens
120.5° Transfer Port Opens
185° Exhaust Duration
119° Transfer Duration
33° Blowdown Time

The boost port duration is the same as the transfer port duration because they're at the same height for both cylinders.

Hope this helps, good luck with the new project.

why would this cause trouble in the future?

 

[Big Kahuna]

Ok, quick question, is there a 64x 760 cyl as well as a 62t?

Are there any major differences?

The 62T cylinder is a 701 not a 760

 

[#ZERO]

Ok, quick question, is there a 64x 760 cyl as well as a 62t?

Are there any major differences?

I should have probably left the 62T part out of the 760 cylinder, it can be called a 64X cylinder too. The port timing on the 62T 701 and 760 cylinders are about the same. The only difference is that the transfer ports are angled upward on the 760 sleeves and the 62T 701 are completely flat.

Good question, I never measured the OD of 760 liners but I think they are too thin even at 84mm. Aftermarket liners are the best option if you must have a bore.

The outside diameter of 62T 701 sleeves measures 87.35mm and 760 sleeves are 88.80mm at the very bottom where the sleeves get thinner. The big bore sleeves range from 90.08mm to 91.09mm and are the same diameter all the way down to the very bottom. So if you bore a 760 sleeve to 86.5mm the sleeve thickness at the very bottom will only be 1.15mm and the big bore sleeves will range from 1.8mm to 2.3mm at the same bore size.

why would this cause trouble in the future?

You might want to sell that cylinder someday or install a stroker crank in that engine and milling it down may cause some problems.

 

[waxhead]

I think if you lower the port timing you will lose power every where

 

[kevbo]

You could get the .008 you want from the base gasket.

 

[teton]

so if i go big bore, do i need to taper the bore on the cylinder so the sleeves fit right?, or is it the same bore from the bottom to the top, also what are the best sleeves for going big bore? where would i get them..... and what would be my press fit clearence for new sleeves....

 

[#ZERO]

With big bore sleeves the bore and counterbore has to be increased along with the depth depending on where you want to set your port timing.

Your sleeve choice depends on what type of engine you are building, stroker, rod length, piston compression height, domes etc.

The LA sleeves have been the easiest to install without having to modify the port heights. They can be installed flush with the top deck height to give a port timing one degree lower then the 62T specs. Also the Northwest, R&D, Riva, Watcon sleeves are great if you're going to build a flat top or stroker engine. They can also be used with stock stroke, dome pistons but the transfer ports need to be altered slightly.

All the sleeves need to be installed in a preheated cylinder with an interference fit of .004" then as the cylinder cools off the sleeves need to be held down with a clamping fixture to make sure they stay seated properly.

 

[D-Roc]

could you bolt on the head to help keep the sleeves seated while cooling or do you need to use something a little more complex?

 

[#ZERO]

Some flat top engines require the sleeves to be installed lower then the deck surface before machining and cylinder heads are only flush with the top deck.

I use an old Riva head plate with some domes bolted to the cylinder, to hold the sleeves in place while cooling off.

 

[D-Roc]

and are you cooling the cylinder slowly in an oven over a certain amount of time or just let it cool on its own? it looks like you have it in a hotbox of some sort.

 

[#ZERO]

It's an oven specifically made for powder coating that has an internal fan system to circulate the hot air evenly.

It works great for heating the cylinders up to 450 degrees for 30 ~ 45 minutes, to install the sleeves.

They just drop right in with there own weight because the aluminum casting has expanded from the heat.

When the cylinders are bored out with a .004" interference fit, it gives a few minutes of work time to get the ports line up perfectly before putting it back in the oven with the clamping fixture above. I'll let it stay in the oven for another 15 minutes before applying more torque to the plate. Then I'll put it back in the oven with just the circulating fan on till it cools down completely.

 

[waxhead]

When you use kawi flatops the pin is 4mm higher in the piston so the sleeves need to be lowere as tge piston is sitting 4mm lower as well