Wiesco Price increase

[Ivan]

Mr. Hodges:

How much will the gain from extra CCs be compared to a lighter piston with more compression?

I have an extra block ot two that I can get bored fairly easily, without getting into resleeving. What is the biggest piston size recommended for stock sleeves?

I am guessing the extra displacement doesnt do as much as compression ratio and dome shape etc. Maybe the more oversquare chamber would work on the torque curve, although i am not sure. I am looking at something within the grasp of a garage mechanic on an aircraft machinist budget. I would like to find the most potential for my abilities and reserves...

[The Lorax]

That, is a question for that "Dan Hodges" guy, he seems to know almost all about compression, intake and exhaust flow, porting and all that stuff. his posts both captivate and befuddle me. have a nice day and ride safe

[Dan Hodges]

Wiseco vs Ross

Great Dan.. NOW you tell me. Although I gave less than that for my Wiseco kit was less than that WITH the rings, it would have been nice to try out this other place. I would have liked to get a piston that is as high domed as the later model pistons. The Wiseco pistons are somewhere in between the 78-79 pistons and the higher domed 80-82 pistons. BUT.. even at that price, arent the rings somewhere around $40 a set? That would put this set from Ross in the same balllpark as Wiseco.

What I will say for Wiseco is that the two piston kits I have seen were machined EXACTLY the same. I took the pistons to my machinist so he could fit the bore to each piston, and all of them have been the exact same diameter.

It would have been nice to get a bump up in compression though for approximately the same price if they would have matched the late model dome profile.


Tod

Both brands of pistons are of equal quality, made of the same material and the machining on both are dead nut on however different mechanical engineers have different ideas on piston design, i.e. ring lands, anti-detonation grooves, ring gap and the finish of the skirts among other things. The Ross pistons cost $417.00 with pins for a set of 4 back in November and I bought the rings and gasket from another vendor. The dome volume on the Wiseco pistons for the XS measure 6.6 cc's and the static compression ratio with these pistons will depend on whether you use the early or late head and how much they are cut. You can cc your combustion chamber, crunch the numbers and arrive at your static compression ratio. Ross will make the dome any configeration you want for whatever compression ratio you want. A piston that is 74-74.5 mm in diameter will have a shorter dome than one measuring 71.5 mm in diameter with each having the same dome volume because the dome on the larger diameter piston doesn't have to be as tall too displace the same volume. Of course the limit on all this static compression ratio stuff depends on the camshaft you use and the phasing of same however on an air cooled street motor you don't want more than 160 psi of pumping compression if you plan on using pump gas.

[TopCatGr58]

Mr. Hodges:

How much will the gain from extra CCs be compared to a lighter piston with more compression?

I have an extra block ot two that I can get bored fairly easily, without getting into resleeving. What is the biggest piston size recommended for stock sleeves?

I am guessing the extra displacement doesnt do as much as compression ratio and dome shape etc. Maybe the more oversquare chamber would work on the torque curve, although i am not sure. I am looking at something within the grasp of a garage mechanic on an aircraft machinist budget. I would like to find the most potential for my abilities and reserves...

Hey Ivan,

From what I've read from Dan before, the 1196 Wiseco kit is about as big as you would want to go due to the thinness of the sleeves, IIRC about 2mm. IIRC the 1179 is 74mm and the 1196 is 74.5mm.

OEM is 71.5mm

Sleeve at 3.5mm thick
With the 74mm bore,
That's 1.25mm thinner or 2.25mm wall thickness,
and with the 74.5
that's 1.5mm thinner, or 2mm.
T.C.

[Dan Hodges]

Mr. Hodges:

How much will the gain from extra CCs be compared to a lighter piston with more compression?

I have an extra block ot two that I can get bored fairly easily, without getting into resleeving. What is the biggest piston size recommended for stock sleeves?

I am guessing the extra displacement doesnt do as much as compression ratio and dome shape etc. Maybe the more oversquare chamber would work on the torque curve, although i am not sure. I am looking at something within the grasp of a garage mechanic on an aircraft machinist budget. I would like to find the most potential for my abilities and reserves...

In a naturally aspirated engine you gain approximately 4% more power for each point of compression up to about 11 to 1 after which the gains diminish. The weight of the stock pistons is covered in the shop manual and even though they are smaller than the Wiseco and other aftermarket stuff they are heavier because the are cast/weaker and the others are forged/stronger and can be made lighter. On a street air cooled bike with iron sleeves like the XS you want to maintain at least an .080 wall thickness on the sleeves which limits you to a bore of 74.5-75 mm. People have taken them down thinner than that however when the sleeves get too thin and flex creating ring seal problems and last but not least, they have a tendacy to crack when hot. There are aftermarket sleeves made of exotic materials that you can run a little thinner but the material is not compatable with the rings that are commonly available. More cubic inches means more power everywhere in the RPM range however the more cubic inches you have the more breathing capacity the motor needs to make the same power per cubic inch. A bigger bore will make more power in all rpm ranges because in addition to adding cubic inches, it increases the air flow by unshrouding the valves around the bore itself. Essentially, you get as many cubic inches as you can and hope you got enough. In the XS you can resleeve the block with aftermarket sleeves and maintain a .056 wall thickness of the block itself after it's bored for the new sleeves and an .080 wall thickness of the sleeves using a 78 mm bore which will fetch 1311 cc's in an XS with the stock stroke. Your target numbers for compression for an air cooled street bike on pump gas is a pumping compression of between 150 & 160 psi and a static compression of 10 to 10.5 to 1 and like in all things there several ways to arrive at those numbers. Like the woman said, size matters

[Dan Hodges]

Long Rods

Dan,
Have you done anything with longer rods?
With custom pistons you can change the wrist pin to crown dx to accommodate a longer rod.
Get some more torque!

I have not looked at the existing geometry.

Other Dan

The rod in the XS is 5 inches long center to center and it has a stroke of 2.7 inches which gives it a rod ratio of 1.85 which is near optimum for an engine of this type and it's rpm parameters. A shorter rod and a longer stroke tends to move the power scale toward the bottom and mid range whereas a long rod short stroke configeration tends to do the opposite. This is due to piston acceleration from TDC on the intake stroke and to some degree the dwell time the piston spends at TDC on the power stroke. Rod ratios are not considered as important as they once were however a big change in rod ratio will alter the torque curve of an engine all other factors being equal. If you were going to increase the stroke of the XS by 1/4 inch or more you would probably benefit from a longer rod however the deck height would prohibit that and you would actually need a shorter rod for your stroked XS. You can move the wrist pin up on the XS piston but any appreciable amount will put it beneath the oil ring and this will require pin buttons between the pin and the ring to support the oil ring which is not kosher except in race applications. Lastly, aftermarket rods are very expensive but a lot of V-Max guys who are now building those 1500 plus cc motors are finding they need them. Have you priced a set of Crower or Carillo rods lately?

[oseaghdha]

The rod in the XS is 5 inches long center to center and it has a stroke of 2.7 inches which gives it a rod ratio of 1.85 which is near optimum for an engine of this type and it's rpm parameters. A shorter rod and a longer stroke tends to move the power scale toward the bottom and mid range whereas a long rod short stroke configeration tends to do the opposite. This is due to piston acceleration from TDC on the intake stroke and to some degree the dwell time the piston spends at TDC on the power stroke. Rod ratios are not considered as important as they once were however a big change in rod ratio will alter the torque curve of an engine all other factors being equal. If you were going to increase the stroke of the XS by 1/4 inch or more you would probably benefit from a longer rod however the deck height would prohibit that and you would actually need a shorter rod for your stroked XS. You can move the wrist pin up on the XS piston but any appreciable amount will put it beneath the oil ring and this will require pin buttons between the pin and the ring to support the oil ring which is not kosher except in race applications. Lastly, aftermarket rods are very expensive but a lot of V-Max guys who are now building those 1500 plus cc motors are finding they need them. Have you priced a set of Crower or Carillo rods lately?

Makes sense. Like I said I hadn't looked at the geometry yet, but I thought that, other than the increased dwell at TDC (which you give back on the exhaust stroke), the benefit was that you increase the time the rod pin spends at or about 90 degrees to the crank journal on the power stroke. Hence the torque shift.


Since it's at 1.85, it's already there.

Good stuff, way over my head. Thanks

[oseaghdha]

Meant to add that this is at the cost of increased side loading on the piston.

[oseaghdha]

Makes sense. Like I said I hadn't looked at the geometry yet, but I thought that, other than the increased dwell at TDC (which you give back on the exhaust stroke), the benefit was that you increase the time the rod pin spends at or about 90 degrees to the crank journal on the power stroke. Hence the torque shift.


Since it's at 1.85, it's already there.

Good stuff, way over my head. Thanks

I totally said that wrong.
There is an increase in the total time that the rod is at or about 90 dregrees to the pin journal. I actually graphed this out for several rod lengths based on milliseconds/degree. I think I was looking at 80 to 100 degrees of rod angle.

I know it's off in theoretical land, so I'll shutup now.

[Dan Hodges]

Rod Angularity

I totally said that wrong.
There is an increase in the total time that the rod is at or about 90 dregrees to the pin journal. I actually graphed this out for several rod lengths based on milliseconds/degree. I think I was looking at 80 to 100 degrees of rod angle.

I know it's off in theoretical land, so I'll shutup now.

Rod angularity is the change in angle of the connecting rod as the piston moves up and down in the bore. Connecting rod angle is greatest when the crankshaft is at 90*. A short rod engine has a higher rod angularity than a long rod engine. I have a computerized graph generated by Chevrolet engineering relating to piston depth vs. crankshaft rotation in a big block V8 engine having a 4 inch stroke wherein three different rod lengths were compared. One rod was 6.135" long, one was 6.385" long and one was 6.535" long. There are three traces on the graph, but they diverge so little at any point in the crankshaft rotation that they appear to be a single line. At 10* ATDC (the time when the most pressure is present in the cylinder on a power stroke), the difference in piston location between the longest (6.535") and the shortest (6.135") rod engine is only .0004" (four ten-thousands of an inch). Even at 45* of crank rotation, the difference is only .01". This amounts to only .43 cubic inches in a 502 CID engine. Many books and technical articles have been written concerning the importance of connecting rod length to engine performance. Of all the choices you must make when choosing lower engine components, rod length is probably the least important. When we talk about our beloved XS motor we must remember this. It is of an old design having a long and heavy rod because when it was designed the engineers had supporting data that suggested an engine of it's type needed a rod ratio somewhere between 1.8 and 2.00 however the trend now is to shorter rods because of the weight differential between the long and short rods. I could give a disertation on this subject but the bottom line is, rod length and angularity have very little real impact on engine performance.