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ndmp40
22nd September 2006, 05:38
What is a good rule of thumb for hp and tq increases when going from a 15* piston/head to a 30*? (All else equal)

Liam
22nd September 2006, 06:09
I don't understand what the "*" in "15*" and "30*" means!
Let me know!

toe
22nd September 2006, 06:18
15 degree domed piston vs 30 degree domed piston.

I'd also assume that the head is at the same angle, and there's a good match between the two....

gwcrim
22nd September 2006, 15:18
There's far more to this question than you're asking. Too many variables. You really can't go from a 15* set up to a 30* w/out doing more work. And it all boils down to cylinder pressure and squish characteristics. What about your fuel selection?

ndmp40
22nd September 2006, 23:24
NHRS knows my build, they set it up. I just want to know what they think I will gain by going 30*. It was an option I declined when I bought it.

NRHS Sales
22nd September 2006, 23:30
It probably will end up giving you about an extra 2-5 hp if all else remains equal. But normally with a 30 degree build we also bump up the compression and install bigger valves(stage 3) so it is tough to know for sure since all else really does not remain equal.

I have just finished my t-storm heads in thsi same configuration. Went from a stage 2 with 15 degree pistons to a stage 3 with 30 degree pistons. Should get it all back together in a week or so and hope to get it on the dyno next month after break in. Should be very interesting to see how much extra power it will make. It made 101hp at the rear wheel with the stage 2 set-up.

ndmp40
23rd September 2006, 15:50
Dan-
Sound like what I want to do. Mine is at 100hp/103tq on Metty's dyno.
1. So you can take my Stage 2 XB 15* and make them 30*, and go Stage 3 with the 1.90 valve?
2. Does this use a common piston, or do we have to have one custom made to make the quench work right?
3. How much more compression can we go with pump gas? Do you gain the compression by cutting the heads? If not, how?
4. What cams are you using in your build? I have the 536's now.
Thanks for helping out!
Neil

aswracing
23rd September 2006, 17:46
Yours is an 88incher, right?

The problem with going 30 degrees is that it gives up squish area, which tends to aggravate detonation.

To compensate for that, you have to make the dome taller. But that of course makes the compression higher.

When you're dealing with an OEM head that starts life at 62cc (XB) or even 67cc, it's hard to get enough volume into the chamber to keep the compression streetable and with adequate squish area.

Therefore 30 degree dome angles are mostly used on race motors.

Now, at smaller motor sizes, it's not so bad. For example, what Dan is doing is a .200 dome height and that works at 70cc on the chamber. We did a bunch of unshrouding and sunk his valves some to get that volume. He'll be about 10.8:1 or so, which will work on pump gas so long as he runs enough cam, which he will.

But when you go to 88", and try to do a .200 dome (which really isn't enough because as a percentage of the total area, the squish area is still too small), you have to get the chamber quite a bit bigger to make it work. More displacement naturally raises compression unless the chamber is made bigger to match, and you're dealing with a head that's truly made for a much smaller motor.

Also, as you cut the chamber larger diameter, even staying at 15 degrees the valves naturally get uunshrouded more, just because the cut will end up deeper when it reaches the valve area. So by going bigger, a 15 degree cut starts working better.

Bottom line, on an 88 incher I would not go to a 30 degree unless you're building a race motor.

I designed what I think is the ultimate piston for an 88 inch street motor, here's a picture:

http://www.nrhsperformance.com/images/claytrimmed.jpg

This is a 15 degree dome that goes all the way to the edge of the piston with enough height to give good squish area, and then it's dished in the middle to keep the CR streetable. This piston gives 10.5:1 at 72cc with .030 of squish clearance. It works really, really well.

It does require that the chamber be machined to accept it, there are no stock heads it'll work under. But we almost always have the customer's heads come through the shop when we do an 88 incher.

We also have other 88" pistons that work under stock chambers, and we have them for every stock head except 883 heads. We have those for folks who just want to put them under the factory head with no changes. But this is the better way to do it.

If you really want to do a 30 degree on an 88 incher and have streetable compression, you really need to go to an aftermarket head. They're designed with a chamber that's big enough. We've used them all and the STD's are the best product we've found. We do quite a few of them, albeit most of them for race motors.

We do quite a few S&S heads as well, and they may be a touch cheaper, but the STD is the better product.

ndmp40
24th September 2006, 15:24
Thanks for taking the time to provide a detailed reply. Yes, I have one of your 88 inch kits.
My XB's are stage 2 with 15*, I asked for 10.5 to 1. What piston did you provide? Is it like the one you reference above? I cant remember what it looked like!
I will not go with the 30*, as I wish to keep it very streetable. But getting the heads run through the CNC machine for the stage 3 ports and having the larger intake valve is still worth it, correct?
What about a 90' kit, can you get a 15* dome like the one you have for the 88 kits?
Thanks for all the help!

aswracing
24th September 2006, 16:01
I'd need to look up your invoice to see what pistons you got. But we came out with that piston in mid to late '05. Call the shop tomorrow and Dan can look it up for you.

We haven't yet done that piston in the 90ci size but we certainly can, with a lead time of about 6 weeks. So far we've just done flat tops in the 90" kit. But it makes sense. It's our most popular piston on 88 inchers right now.

Yes, on a big motor, doing the Stage 3 over the Stage 2 on an XB head makes a bigger difference. We'll do the chamber work all included, and unshroud the valves heavily too. But keep in mind that much of the Stage 3 advantage will come in at higher lifts. The .536 is an awfully mild grind for this size motor. Stage 3 will work better, but the cams will quickly hold you back.

ndmp40
25th September 2006, 01:56
I have my eye on the S+S .600 cams, good?

cadiero
25th September 2006, 02:29
Those .600 cams are great! My brother runs those in his Buell we havn't got a chance to dyno it yet, but it really runs great! You really got to watch the geometry and clearance the rocker boxes.

NRHS Sales
25th September 2006, 20:02
S&S 600 cams are a very good choice for an 88" motor with stage 3 heads.

sporty58
29th September 2006, 14:43
S&S 600 cams are a very good choice for an 88" motor with stage 3 heads.

They are also a pretty sweet choice in a 1212 build. I replaced a set of .551s in this build with the .600s and love them. I gave up a little bit on the bottom but gained a lot up top. In previous builds I have also used the 630/585s and the .536s and i would have to say this is my favorite set. It would be interesting to see a comparison between the .536 and these.

NRHS Sales
29th September 2006, 16:56
The 536 and 600 comparison will be coming soon! I currently have the 536s in my bike and once it is re-broken in I plan to install a set of the 600s and see how much difference there is between the 2.

cadiero
29th September 2006, 17:10
Cool! Looking forward to that! Been kinda thinking about the .600 lift cams.

klown
29th September 2006, 17:33
looks like an easy enough device to use, but I've gotten so used to doing it by the book, I'd consider that a complication. You still have to move that oil from the green hootus into some other container for proper disposal, and you've still got to pull the filter, which is where most folks tend to get dirty, unless you use the 2liter coke bottle method...:smoke

NRHS Sales
29th September 2006, 19:26
Klown,

???????

ndmp40
28th October 2006, 13:03
Yours is an 88incher, right?

The problem with going 30 degrees is that it gives up squish area, which tends to aggravate detonation.

To compensate for that, you have to make the dome taller. But that of course makes the compression higher.

When you're dealing with an OEM head that starts life at 62cc (XB) or even 67cc, it's hard to get enough volume into the chamber to keep the compression streetable and with adequate squish area.

Therefore 30 degree dome angles are mostly used on race motors.

Now, at smaller motor sizes, it's not so bad. For example, what Dan is doing is a .200 dome height and that works at 70cc on the chamber. We did a bunch of unshrouding and sunk his valves some to get that volume. He'll be about 10.8:1 or so, which will work on pump gas so long as he runs enough cam, which he will.

But when you go to 88", and try to do a .200 dome (which really isn't enough because as a percentage of the total area, the squish area is still too small), you have to get the chamber quite a bit bigger to make it work. More displacement naturally raises compression unless the chamber is made bigger to match, and you're dealing with a head that's truly made for a much smaller motor.

Also, as you cut the chamber larger diameter, even staying at 15 degrees the valves naturally get uunshrouded more, just because the cut will end up deeper when it reaches the valve area. So by going bigger, a 15 degree cut starts working better.

Bottom line, on an 88 incher I would not go to a 30 degree unless you're building a race motor.

I designed what I think is the ultimate piston for an 88 inch street motor, here's a picture:

http://www.nrhsperformance.com/images/claytrimmed.jpg

This is a 15 degree dome that goes all the way to the edge of the piston with enough height to give good squish area, and then it's dished in the middle to keep the CR streetable. This piston gives 10.5:1 at 72cc with .030 of squish clearance. It works really, really well.

It does require that the chamber be machined to accept it, there are no stock heads it'll work under. But we almost always have the customer's heads come through the shop when we do an 88 incher.

We also have other 88" pistons that work under stock chambers, and we have them for every stock head except 883 heads. We have those for folks who just want to put them under the factory head with no changes. But this is the better way to do it.

If you really want to do a 30 degree on an 88 incher and have streetable compression, you really need to go to an aftermarket head. They're designed with a chamber that's big enough. We've used them all and the STD's are the best product we've found. We do quite a few of them, albeit most of them for race motors.

We do quite a few S&S heads as well, and they may be a touch cheaper, but the STD is the better product.


Well,I have decieded to go with the 90" kit with a custom piston like shown above, and have my stage 2 XB 15* heads upgraded to stage 3 with the bigger valve, etc.
Do you need to have my heads to build a piston, or can we get the process moving now and send the heads in later? I will be using the S&S 600 cams, so we need to talk about what compression ratio to build.
Let me know on the pistons, I can send you the money in advance.

NRHS Sales
28th October 2006, 16:12
I already have that style piston in stock for a 90". But we will need to do combustion chamber work on your heads for it to work properly. You will not be able to use the cylinder kit with your current heads. You must have the heads cut before you can use it. call me on Monday

ndmp40
2nd November 2006, 05:42
Thanks for the reply- I have been busy moving my business into a new location and remodeling/renovating and have not had time to call. It might be another week the way things are going, but i will get to it!
And I planned to have the heads upgraded to stage 3 (mentioned above), so that should not be a problem. Thanks again for the patience!