"T" slotted transfer ports

[Dan_Cousin]

I've been seeing that the later model engines are coming with "T" slotted transfer ports. I'm assuming it makes the engine run better but I'm having trouble visualizing why. Some "T" slots are straight up and down and some "T" and angled so the look more like a "7" than a "T".

How does the T slots work in conjunction with piston ports?

I noticed the CMB 90 small block has T slots but no piston ports.

 

[Russell Bear]

The slots are merely cosmetic. It is all a marketing scam. They are put there so that when the next manufacturer decides to "copy" it then everyone will have something to complain about.

 

[Dan_Cousin]

Yo ass!!!! :lol: :lol: :lol:

The motor modding crowd sure is quiet.

Chris/Steve Wood,

I saw pictures on your webpage of a green head with this type of slot. Whats your take on them.

I know MACs have them too but they look more like the 7 shape.

 

[Joe Warren]

Dan the T Port Mod was an ole Stan Simpson trick. They allow for the Fuel sealed inside the crankcase to blow UP thru the ports while the piston is traveling Down. Mr Stan turned some serious RPM with that mod on picco , Ops,& Mac engines.... Any Engine tweaker will tell you the shortest path to get the fuel ontop of the piston is a Sure way to Burn the fuel quicker..... if you easy the flow & raise the ex timing you going to turn more R`ssss. there are some newier mods (same intent) since that designed. the newier mods keep the mixture velocity Up higher than the T port mod.

 

[Jim Allen]

After testing both types of "T" porting on my dynamometer & torque cradle, "I can find no measurable increase in HP or RPM as a result of these modifications"; over already working standard types of porting. This is also true of the type of porting used on K motors. There may be some advantage from cooling the underside of the piston crown, but this should be done from the top side with the incomming charge.

Total crankcase volume, piston acceleration & velocity are factors which effect the velocity of the intake charge as it is pulled through the intake windows. A uniform flow in one direction is also important as well as window geometry & shape.

Engine manufacturers must come up with a new gimmick with each new model. They would better serve the public by fixing all the poorly engineered items that fail year after year. Connecting rods, wrist pins, chrome that comes off liners, incorrect metallurgy, bearings, etc. etc. are all solvable problems. Of course the solving of these problems requires through bench testing & there is no money to be made in doing this!

For example, why does the chrome continue to come off aluminum liners of some un-named manufactured engines? Are you telling me these manufacturers could not find this obivious problem when bench testing these motors before releasing them on the unsuspecting public?

Jim Allen

 

[Buckshot]

After testing both types of "T" porting on my dynamometer & torque cradle, "I can find no measurable increase in HP or RPM as a result of these modifications"; over already working standard types of porting. This is also true of the type of porting used on K motors. There may be some advantage from cooling the underside of the piston crown, but this should be done from the top side with the incomming charge.

Total crankcase volume, piston acceleration & velocity are factors which effect the velocity of the intake charge as it is pulled through the intake windows. A uniform flow in one direction is also important as well as window geometry & shape.

Engine manufacturers must come up with a new gimmick with each new model. They would better serve the public by fixing all the poorly engineered items that fail year after year. Connecting rods, wrist pins, chrome that comes off liners, incorrect metallurgy, bearings, etc. etc. are all solvable problems. Of course the solving of these problems requires through bench testing & there is no money to be made in doing this!

For example, why does the chrome continue to come off aluminum liners of some un-named manufactured engines? Are you telling me these manufacturers could not find this obivious problem when bench testing these motors before releasing them on the unsuspecting public?

Jim Allen

So true Mr. Allen!



-Buck-

 

[Dr Hydro]

There may be some advantage from cooling the underside of the piston crown, but this should be done from the top side with the incomming charge.

Hey Jim....A friend of mine, who was a top flight outboard motor mechanic until Katrina came to town, told me that pistons build up a lot of heat under the piston so it seems that you would want to cool the piston from below. While we are talking about the undersides of pistons, have you ever experimented with filling up the void under the piston head? I think the idea is to decrease the amount of area in the block which is supposed to increase the pressure in the block. I could be wrong on the theory but I heard of "stuffing the pistons" a while back. Thanks, Jim

 

[Jim Allen]

There may be some advantage from cooling the underside of the piston crown, but this should be done from the top side with the incomming charge.

Hey Jim....A friend of mine, who was a top flight outboard motor mechanic until Katrina came to town, told me that pistons build up a lot of heat under the piston so it seems that you would want to cool the piston from below. While we are talking about the undersides of pistons, have you ever experimented with filling up the void under the piston head? I think the idea is to decrease the amount of area in the block which is supposed to increase the pressure in the block. I could be wrong on the theory but I heard of "stuffing the pistons" a while back. Thanks, Jim

Pistons do build up heat on the underside, but the hottest area will always be on the combustion side. Also as the bore size becomes larger, keeping the piston crown cool in the middle becomes more difficult & the exhaust side will always be hot. The high exhaust temperature of high HP piped engines, can erode the exhaust side of a piston, making it appear as if it were sand blasted. High piston crown temperatures will produce center pockets, center holes, blued glow plugs, seized wrist pins & ovaled wrist pin holes. The upper piston walls & the piston bosses if designed properly can help carry some of this heat away, but more important is the cooling of the piston crown from the upper side, where the heat is highest. Another thing which helps piston crown cooling in the middle, is to reduce to a minimum, the dead space between the underside of the piston crown & the OD of the upper end of the connecting rod. In my motor this distance is .032 in.

I have stuffed my engine's crankcase by continuing to use a cantilevered full disk crankshaft & the bell valve induction. No, I have not tested piston stuffing because it is physically impossible in our small motors.

Jim

 

[Jim Allen]

Piston stuffers add nothing to the reciprocating weight of a piston. They are projections which come up from the crankcase & fill the piston area on its underside when the piston is at BDC. They do increase crankcase compression (primary compression). Visual examples can be found in Two Stroke High Performance Engine Design & Tuning by Cesare Bossaglia. An explanation of how a reduction in crankcase volume effects crankcase compression & engine tunning can be found in the following books; Performance Tuning in Theory & Practice by A. Graham Bell, pages 41 & 42; Tuning for speed by Phil Irving, pages 190 & 191; The Two Stroke Cycle Engine by John B. Heywood & Eran Sher, pages 198 & 199.

Jim

 

[Jim Allen]

Very technical book that has excellent information about intake & exhaust port geometry as well as tuned pipe theory.

Jim

 

[Dan_Cousin]

Very technical book that has excellent information about intake & exhaust port geometry as well as tuned pipe theory.

Jim

Jim,

How do you cool the top of the piston with the intake charge?

Also, does the dish in MAC/CMB pistons cause more problem with retaining heat. it seems like a popup dome would be better form an airflow standpoint.

 

[Joe Warren]

Jim Are these booklets on 15000 rpm 2 strokes or 30,000 Rpm 2 strokes. I have witnessed several R/C engine mods all increase intake duration so we can draw in more fuel into the case (longer duration) Then we have to have a place to put it ( case volume). Then we need to transfer this Rich air-fuel mixture to the top of the piston ASAP so we can burn it...... All of this is very important before we second stage the pipe.. then we have the 2 stroke pipe theories..... Case paking might work on a weed eater engine. But I do not see it being a Performance edge for the Nitro 2 Strokes......

 

[Jim Allen]

It is a well documented fact that peak gas temperature during combustion can reach as high as 4000 deg F & the exhaust gas temperature, despite the fact that heat is being transfered to the combustion chamber surfaces, can be as high as 1400 deg F. The heat of combustion is transfered to cylinder wall surfaces as well as the piston crown primarily by convection. During the gas exchange part of the cycle, a small amount of the heat is absorbed by the fresh intake. Any fuel which reaches the underside of the piston also absorbs some heat. With all this cooling, it is very possible for the piston crown temperature in the center to reach 700 deg F. Therefore, I use a flat top piston with a crown thickness of .120 in; an upper wall thickness of .080 in & a skirt of .048 in thickness.

My piston is effectively cooled because the main transfers are flat on the top. Even with the deflection of the incoming charge which takes place in all motors, piston cooling is adequate enough to allow very high compression ratios & very low deck clearances to be used. Also the large, short piston bosses, help draw off piston heat & stabilize piston distortion.

Pistons For Internal Combustion Engines by MAHLE GMBH gives details of temperatures & design criteria.

Jim

Jim Are these booklets on 15000 rpm 2 strokes or 30,000 Rpm 2 strokes. I have witnessed several R/C engine mods all increase intake duration so we can draw in more fuel into the case (longer duration) Then we have to have a place to put it ( case volume). Then we need to transfer this Rich air-fuel mixture to the top of the piston ASAP so we can burn it...... All of this is very important before we second stage the pipe.. then we have the 2 stroke pipe theories..... Case paking might work on a weed eater engine. But I do not see it being a Performance edge for the Nitro 2 Strokes......

I guess you will have to test these things out for yourself Joe as I have done on a good test stand.

Jim

 

[Dr Hydro]

i though he was talking about filling the piston around the pin bosses
That is what I was talking about and like I said, I forget what it was supposed to do, but it sure sounded good!

 

[F.Orlic]

While some stuff is done just to increase marketing value, piston porting and sleeve porting is not.

I have not done kind of dyno testing Jim did as I've learned long ago that what I see on dyno might not quite work as well on water, so most of my work was based on testing on water. I have read and still have many books and articles about two stroke engines but just about all of it is about 15000 RPM gas engines as Joe mentioned. Principles do apply but there is a big difference between 30 k and 35 k engines let alone 15 k and 30 k. Angles, port areas, volumes are more critical as RPMs increase and fuel control is very important.

 

[Joe Warren]

AS many of you may know Frank O (Advance racing tech) (ART) enhances the existing ports & flows the engine & installs a trick piston port, to make the fuel transaction much easier. Frank Has done several engines for myself & Others that have resulted a pile of awards & Wins...... he says what works on some engines may not work as well on another engine. But he has the mods perfected on Piccos & Novarossi. Easy to launch, Swinds a Lot of Prop...... Turns Big RPM....

 

[Dan_Cousin]

Frank,

Whats your favorite induction mod for the transfer ports and piston windows?

 

[F.Orlic]

Frank,

Whats your favorite induction mod for the transfer ports and piston windows?

I have no favorite mods, I treat every engine differently, what works on one mightnot do anything on others. I've ported P/S on all Picco and they loved it, on CMB's not so good, Novarossi works well with ported P/S and same goes for port angles, while OPS 90 will run great with flat ports Novarossi will loose all its might with the same stuff. I my opinion flow control is everything at high RPM's, missing a degree on ex or intake will not do much harm but ports that have wrong angles or badly directed fuel flow will kill the performance.