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Sportster Motorcycle Engine Conversions Advice, questions, and tips for 1200, 1250, 1340, 1450 etc... for Sportster and Buell motorcycle engine conversions

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  #1  
Old 22nd October 2019
Turbo Sporty 48 Turbo Sporty 48 is offline
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Default 570's or 536, 560's @10:1 Compression

Thinking of giving up on turbo and going all naturally aspirated.
Would likely go 1275, flat top pistons and either 570, 536 or 560 cams.
Got a set of turbo toasted heads that need rehab so there is an opportunity to make some package choices. Is 7500 rpm's too much to ask?
The goal is to simplify. Pump gas only, 10:1 compression ratio please.
Would you consider 30 degree reverse dome pistons but not sold on them.
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Old 22nd October 2019
Tomcatt Tomcatt is offline
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Quote:
Originally Posted by Turbo Sporty 48 View Post
Would likely go 1275, flat top pistons and either 570, 536 or 560 cams.
Pump gas only, 10:1 compression ratio please.
Would you consider 30 degree reverse dome pistons but not sold on them.
I'm not sold on 30 degree squish bands either, I don't like the idea of more material (and surface area and a convoluted shape) added to the piston crown. Everything is a compromise.

I think with all your listed cams, other than the 570's, you'll want 10.5:1 pistons. They have minimal "domes". You need to get back the cranking pressure the later intake closings will lose.

I'd add SE .575's to your cam list for consideration.
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  #3  
Old 22nd October 2019
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Start doing your calc's
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  #4  
Old 22nd October 2019
Tomcatt Tomcatt is offline
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Using Hammers' Compression Calculator:

Hammer 570's with an actual static 10:1 cr: 205 psi

Hammer 560's with an actual static 10.5:1 cr: 198 psi
SE .536's with an actual static 10.5:1 cr: 196 psi
SE .575's with an actual static 10.5:1 cr: 193 psi

With stock pistons/cylinders/heads and "dropped in" SE .551 cams I get 185 psi on my gauge. Going to a Hammer 1275 10.5:1 kit should bump that to 204 psi. My "in the spring when my garage warms up" project.

Last edited by Tomcatt; 24th October 2019 at 00:56.. Reason: sp
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Old 22nd October 2019
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Hammer said the 560 needs 10.5 to work.
I've got 88" with flat tops & late model heads with the 560 cam's love how the combination works. I've ridden 15k now, going for a ride today. but I don't need to rev it , it goes hard every time I open the gas.
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Quote:
Originally Posted by jkinkade View Post
...I don't need to rev it , it goes hard every time I open the gas.
More displacement has that effect...
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Old 23rd October 2019
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You had written, "is 7,500 rpm too much to ask?" It is for 570 cams. There is not much more left in the 570s after about 5,500 rpm
Seems like the 560 cams with better compression may be more appropriate.
Ride safe.
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  #8  
Old 23rd October 2019
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1275 with 62cc heads and flat tops is right around 10:1

I'd think you'd need a lot more compression and much bigger cams to make good power up to 7500 RPM. And serious head work to go with the combo.

I'd almost always preffer to have a small efficient chamber and flat top pistons, but that's not happening with these engines. 30 degree (squish band) pistons work well if you have a big hemi type valve layout and chamber...
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Old 23rd October 2019
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Referring to Hammer
https://www.1250kits.com/tthoppingup1200.shtml
halfway down the page
"Cams and 1275 Kit Together - When you combine cams with a 1275 kit, you can get some impressive gains, even without porting your heads."
Observe 2 charts, 1275 and 570 cams and 1275 and 560, both look really good.
Wonder what the 536 and 575 cams would look like powerwise.
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  #10  
Old 26th October 2019
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Hi, jumping into this thread if you don't mind. Got a project coming up this winter with my '99 engine, allredy got a pair of XB heads sitting on my shelf and a 45 Mik with Hammer manifold.
Now torn between 570 and 560 cams, I am going to keep the heads stock, exept for opening the innlet to match the Hammer manifold and maybe a 5 angle valve seat job.
My brain says 570 but there's something about that red-line rush from a hotter cam...
Toughts?
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