the new motor has je pistons(88 inch 3 13/16) custom built for the t storm heads. these heads have a 20 degree angle. I have a chance to buy some wiseco pistons for back up. they are the k1733.
http://www.wiseco.com/PDFcatalogs/hd04-evol.pdf
I cant determine what angle thier dome uses . I think the stock cut for t strom heads is eihter 10 or 15 degrees. so maybe the wisecos are 10 or 15 degree. but the heads have a 20 degree angle cut. (apparently thats what je uses.)Does this difference make the pistons
a) tottally incompatable.
b) compatable with no huge issues. (explain)
c)compatable and will lower cr.
d) compatable but with squish issues and probable pinging
e)any/all of the above.

need help to decide if these pistons should be purchased and used in the future to lower the engines compression in order to run nitrous.

I wouldn't mix & match dome shapes. I asked Aaron about it once and he was dead against it. Probably D is your answer if compression is over 10:1. But you'll never know for sure unless you try. I'd like to run 20 degree domes with my 30 degree heads. At 13:1+ compression, pump gas isn't even an option.

G'day Narley


If ya gonna run nitrous then I'd be lookin at some pistons with some crown matrial in 'em.

The Hurricanes I've got for my 88" are THIN...way too thin for nitrous, I'd end up with holes in the tops.

I thought the angle on the T'storms was 10* which would give 20* included.

I machined my heads a degree or two more than the pistons to clear the gasses easier

I'll measure some pistons if I remember.

I wouldn't mix & match dome shapes. I asked Aaron about it once and he was dead against it. Probably D is your answer if compression is over 10:1. But you'll never know for sure unless you try. I'd like to run 20 degree domes with my 30 degree heads. At 13:1+ compression, pump gas isn't even an option.
hey crim...talk to me. this bike is gonna come with 20 dergreed tstorms and custom 20 degree domed je pistons...at 15-1 ! I want that changed.
add base gaskets ...where there are none.
add head gasket where ther are noe! (its o-ringed.)
how much will that drop it. I have two needs...one is to drop it enough to keep it streetable. i will carry concentrated race gas in the tool bag. enough for emergencies to bring a tank up to 107.
the other thought is to lower it and then add nitrous. ...the goal is 150 hp.
so i will start with the gaskets , but should I just do the new pistons or will the 45 base gasket and a head gasket do the trick. the cams are redshift 643 so the intake closing is really late @61 degrees.

Stevo,
I thought the angle on the T'storms was 10* which would give 20* included.

clear that up for me...I dont get it.

A dome on a piston is normal calculated at the angle from horizontal or flat.

SO a 10* dome is machined at 10* from flat

BUT if you were to measure the INCLUDED angle of the dome it is 160* Which is 180* (flat ) minus 10* plus 10* = 20*

Not common. it's just that I've seen some manufacturers use this for dome measurements ...it's bullsh*t as far as I'm concerned as I measure from the flat on ONE side of the piston.


Is that any clearer or have I just made it worse????????

I'll draw a picture and scan it if ya want.

you mean since each side of the dome has a 10 degree angle they call it 20. looking at its profile ...10 up the left and 10 up on the right....means 20 ?unbelievable... because 10 up angle from one side BUT only one side would leave no dome ,but rather an slanted design...oh well.

That would be a 10* SLANT or WEDGE then. common on V8 stuff.

To me and most guys in the industry a 10* DOME is a DOME with a 10* side. Which means it also has a 10* side on the other side,and the other side and the other side..... all the way around. ;)


IS that clearer.......???????????????????

alrighty. so the pistons are 10 degree and the heads are 20...I am seeing that this will leave a few ccs of extar comustion chamber...thus lowering cr. This is what i want..so will the angle diff be a problem.

yeah ya loose some of the effect of the quench band.

I run my heads about a degree or so extra. just to help clear the gasses while still acting as an effective quench.

Another thing to look at with tight quench on domed pistons is to allow for radial piston expansion in your quench clearance calculations.....

Fortunately with a Harley the stretch in the cylinders under operating temps helps a lot BUT it's still something to keep an eye on and it can be a BIG problem in the car stuff or jappas that don't have as much barrell expansion during runnning

hey crim...talk to me.

OK, my engine would have been about 16:1 with the pistons as bought. I had a machinist cut the domes down as far as safe and that brought the compression to 13:1. Flat tops would lower it to 10:1.

With 13:1 and the HQ adjustable ignition, I can't stop the pinging on pump gas. I've tried every trick in the book and some that weren't in the book. Different jets, carbs, ignition settings, oil cooler, and coating the piston tops. Fortunately, a nearby gas station keeps 110 on hand. But if I keep the bike, flat top pistons are the real fix.

Problem with adding base or head gasket thickness is that you mess up the quench (squish) clearance. It needs to be in the 0.032 area to control ping.

You can also try different cams. In my case, I was limited to only two different sets as valve clearance became an issue. So again, I was screwed. Look for cams that have a very late closing intake. Red Shifts are known for that.

red shift 643 with a very late 61 degrees. My best calcs show a corrected cr of under 12-1.
a local gas station keeps 110!!!what the hell...this small town stuff amplifies the problems...91 tops here.
I need to know wheter to change to the 12-1 or if a base gasket 9where there is NONEnow) will be a better move?

the squish area is the band around the rim of the combustion chamber right. so changing to the wiseco shouldnt affest that rim...just the center of the combustion chamber where the lower dome isnt reaching as high into the chamber....

Anything over 11:1 can be a handfull to run on pump gas. It depends a lot on the individual engine and how well the combustion chamber parts all match. As long as the wisecos have the same angle on the dome, I'd choose the ones that would produce the lowest compression. If you're under 12:1 you stand a decent chance at running pump gas.

But make sure you check the clearance of the squish band. It needs to be near 0.032. Anymore can result in pinging.

Oh, and the 110 gas station is in a little redneck town on the Ohio River. The owner of the small chain is a bike/car/boat nut and he keeps it on hand for his collection as well as other bike/car/boat nuts.

Did the cranking compression test (cold) got 240 front and 245 rear. the calcs i did for corrected compression ratio had come out to 11.7 corrected but stated that the cylinder pressure would then be about 260 lbs.
So i did some more figuring and this cylinder pressure worked out to about 11.2-1 corrected...any thoughts guys?

Cranking pressure is no indicator of the static compression ratio. Cam timing has too great an impact on cranking pressure. The same engine with different cams would have two very different cranking pressure readings.

Did your calculations take all that into account?

Used the rsr calculator
http://www.rbracing-rsr.com/comprAdvHD.htm
15-1 static...this what i was told
3.812 stock stroke, 3.812 bore
6.926 stock rod length
inlet closing 61 degrees
boost zero and finally altitude of 3000 feet.
that gives 11.5 -1 at about 253 psi. So I am thinking the 15-1 was off.
leaving all other knowns the same. i entered 14.5 -1 static and it give about 240 psi and ccr at 11.1-1....
So thats is less scary to add a small shot of nitrous to...what do ya think.

wow this is some serious technical stuff

wow this is some serious technical stuff

yeah...but its better than blowin shit up.....I enjoy math, but as a gearhead i am a newbie...

yeah...but its better than blowin shit up.....I enjoy math, but as a gearhead i am a newbie...


Maths is great but somnetimes ya gotta just go with the feel


"it's in the fingers, it's in the blood" a quote from a OZ drag racin film made years ago called "Running on Empty"



We are still not at a stage where we can predict everything that's gonna happen for any given change in variables.... we're closer but still no where near there yet....


Measure the crown thickess before ya go stickin nitrous on and make sure ya have a retard switch on ya ignition if ya gonna ram a heap in at those compression

the dyna 2000i ignition has a handy retard mode that kicked in when I hit the nitrous. The screaming eagle /crane hi4 doesnt have that...but it does have a programmble feature which I could set up with a curve for when i want to do nitrous runs. HMM, I could set a curve with some retard at the same rpm as I set the new edelbrock kit to kick in the nitrous.
a dyna 2000i would be way easier...

Now here's an idea ........ an inline (between pickup and module) delay unit....

Programmable delay and operating as an override when activated..... not sure on the electronics but if i can think of it someone has probably made one or at least could make one...

stevo...just readin bout some programmable ignitons....seems you can ground their voes wire and it will retard timing...had muccch experience with the SE programmable ignition ( methinks its a crane hi4 powerlink.)

If it's a HI 4 Powerlink then it's no prob ... I can send you a copy of the software to play with if ya want BUT you'll have to buy your own one to get the cables...

I'll get back to you when I'm back in town

the se ign...looks identical to the powerlink