Upgrading a stock 103

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Jun 22, 2020 | 08:13 PM

#11

twincam10353

Thread Starter

Road Master

Joined: Mar 2020

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From: New England

Here is the thing with the cams, you really need to make a decision on where your build will end. I guess I need to decide if I will ever approach top end work in order to decide on the cams...

Jun 22, 2020 | 09:02 PM

#12

Max Headflow

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Joined: Dec 2005

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From: poway

Quote:

Originally Posted by 60Gunner

S&S 570s make a nice bolt in cam on a stock 103. They're in that exhaust shootout.

I ran a set in a 96 and 103 with ported heads and they sucked. The WOT number may look good but throttle response down low was real poor. Kinda like 510s in a 95 ci motor.

Jun 23, 2020 | 01:21 AM

#13

rhuff

Elite HDF Member

Joined: Jul 2007

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From: 48.067222,12.863611

Comes down to money and return on bang for the buck.

A bolt in like Woods 222, Andrews 48, CR 570-2, or MR103 will yield you some decent results. Prob a 10/10 increase.

A 107 kit is significantly more, but not ridiculous. You can use your stock TB and your exhaust, etc. Mild head work would be necessary if bothering 107.

After those 2 options, the only ones I ever see as reasonable are a crate 124 or a 124 built from your cases. Some would argue a 117 with your crank prepped, but for that money, the 4 5/8" arm from S&S is the way to go.

Least hassle and most reliable (generally).... bolt in cam.

Jun 23, 2020 | 01:41 AM

#14

eriksweden

Cruiser

Joined: Aug 2019

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From: karlstad

Quote:

Originally Posted by Max Headflow

I ran a set in a 96 and 103 with ported heads and they sucked. The WOT number may look good but throttle response down low was real poor. Kinda like 510s in a 95 ci motor.

How much compression did you have on these ? I am happy whith mine 103/ss 570 at 10,4

Jun 23, 2020 | 05:03 AM

#15

60Gunner

Grand HDF Member

Joined: Sep 2017

Posts: 4,359

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From: Dubuque, IA

Quote:

Originally Posted by Max Headflow

I ran a set in a 96 and 103 with ported heads and they sucked. The WOT number may look good but throttle response down low was real poor. Kinda like 510s in a 95 ci motor.

There's plenty of good results with them so don't blame the cams. Must've been your tune or maybe your exhaust. An exhaust will make or break it with cams like this. Seen it plenty of times with cams with overlap. Run a crap exhaust and expectations fall short. Hog boring your heads and killing velocity will kill low end too.
Run great in mine. 90+ft.lbs from 2200rpm on with Rush slip ons. Anything lower is lugging it anyway. That's on in a stock 103 at 9.6:1. CC of 191/189.
I'm throwing in a .030 head gasket and calling it good to get my cc up around 205.

Last edited by 60Gunner; Jun 23, 2020 at 05:35 AM.

Jun 23, 2020 | 06:37 AM

#16

Notgrownup

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Joined: Mar 2009

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From: Snow Hill, NC

Do it once, do it right. Don’t half *** it.

Jun 23, 2020 | 09:12 AM

#17

twincam10353

Thread Starter

Road Master

Joined: Mar 2020

Posts: 1,078

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From: New England

How do I figure out which cams with be a good fit for my exhaust? Bassani RR3 2-1 full-length.

Jun 23, 2020 | 09:23 AM

#18

Max Headflow

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Joined: Dec 2005

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From: poway

Quote:

Originally Posted by eriksweden

How much compression did you have on these ? I am happy whith mine 103/ss 570 at 10,4

They were low. about 9.2 and 9.9. 10.4 helps for sure.

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Jun 23, 2020 | 10:04 AM

#19

Max Headflow

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Joined: Dec 2005

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From: poway

Quote:

Originally Posted by 60Gunner

While i do think part of it may have been running good heads. The exhaust was a fatcat with quiet baffle that should have given good low end.. The cam came out and put in a woods 5 and the bike ran a bunch better on the low end and really didn't lose any up top. Heads has 1.7 ports, 1.9 intake valves, 1.61 exhausts. Flow 260 in 220 ex. at 28. They weren't hogged out too much but I'm sure using a stock set of heads or a set with a big reversion step would have helped. Bumping the CR up to 10.5 would have helped for sure. Bike, IMO, ran best with the woods 777 as a 103. The big difference was exhaust duration between the 2 cams. The SnS570 with 260 degrees would over-exhaust and kill the low end throttle response. WOT dyno runs didn't look to bad, but the bike felt sluggish down low. I later went to a W777 which is close to the 570 in intake duration but much less exhaust. Ran that for 30000 miles. It's now a 107 at 10.4 with 777 at 20000 miles. Runs even better.

The fact that you think you need a little more compression shows that it's a sluggish. I'd shoot for something higher than just a head gasket. Rush slipons through a CAT will have more back pressure and help.