Largest possible aftermarket motor for FXR? : V-Twin Forum: Harley Davidson Forums

FXR2 · 02-25-2006, 09:17 PM

A friend has a 1992 FXLR with a tired Evo. Instead of rebuilding it for more power, he's decided to buy a complete aftermarket motor and we were wondering: What is the largest displacement aftermarket motor that will bolt directly in to an unmodified, HD FXR frame.

I've seen FXR's with S&S 96's and TP 107's but I wonder just how large you could go. I figure at some point the increased stroke wouldn't fit the already tight rear cylinder to frame clearance, although curiously the TP 107 is actually more compact than the stock HD 80.

We were thinking how scary/fun fast a FXR with a 124 would be but don't think that would fit. Plus, even if it would fit, would that much power require other mods like transmissions and clutches and maybe even chain final drive?

Anyway, has anybody seen a stock FXR frame with an aftermarket motor bigger than a 96 or 107? Anybody know how big you could go with this?

Thanks for any help/suggestions.

Ka-Ka · 02-25-2006, 11:37 PM

An S&S 124" will fit.

Quote:

124" Super Sidewinder™ Plus for Evolution ® Models
The S&S 124" Super Sidewinder ™ Plus is the cul-mination of years of engine building expertise. It will bolt right into a stock height Evolution frame but with 130hp on tap it is definitely not for the meek! The 124" is available with natural, black or polished finishes, and all have the ven-erable S&S Super G model carburetor and the features listed below:

freefxrs · 02-26-2006, 01:29 AM

i have a 92 FXRS and am looking to put a new motor in as well. I am leaning toward an S&S 96 but i too have toyed with the idea of a 124.

you do start to need to rethink some things with the 124. Its early days in terms of my research but i think you would need a torque arm, probably need/want a larger rear tire (i have 130 but would want to probably go to a 180) which means perhaps new wheels. Need to make room back there so you would need to go to a chain drive. It would be a sick ride however.

I am doing some research with my mechanic on this and will let you know what we come up with.

L.Linkert · 02-26-2006, 01:56 AM

The 124" should drop right in a FXR. To me this would not be the ideal engine for a motorcycle capible of good handling at high speeds such as the FXR. I would tend to look for or build a shorter stroke engine with a wider RPM range.

hdracer67 · 04-11-2006, 10:58 PM

I have seen 124" engines in fxr and flh frames, My shop put the new jims 120" in a new dyna and it runs great.

compressor#v · 04-13-2006, 10:37 AM

S&S use's a FXR as a test mule for the 124". Fits easily, and handles well also according to them.

HDWRENCH · 05-11-2006, 09:03 PM

I did a 153 for a guy with a FXR you have to do a very little bit or work on the rear of the fram but nothing that is too out of ythis world. Not having other things break due to power , well you are on your own there.

FXR2 · 05-11-2006, 11:14 PM

Quote:

Originally Posted by HDWRENCH

I did a 153 for a guy with a FXR ....

153???

smut · 08-23-2006, 04:57 PM

Have yall installed the new engines yet? What did you go with? The 124 will fit nicely but you can't stop there. You will probably need a better starter or compression releases and then you can move on to the drive line. (chain if it don't already have one.

waiting on feed back...

FXR2 · 08-23-2006, 05:31 PM

The guy that posed this question (not me) has since installed a S&S 124. He went with chain final drive instead of toothed belt. He's currently in the break-in stage of the motor but says that he can already feel a whole lot of power there.

freefxrs · 08-24-2006, 11:02 AM

Here is my '92 FXR with the S&S 124

upgraded starter, clutch and some custom machining to move the carb in a couple inches. Went with chain and a fatter tire.

its a blast to ride.

HDWRENCH · 08-24-2006, 12:13 PM

We have done 155 as well they are taller and require a evo trans but will go in a bagger with some back bone mods . Try 185 hp and 190 tq on a engine that runs so smooth has no bad manners. WIll make a 4th gear dyno pull from 2000 -6000 in 1.5 seconds. ( avg run time is inthe mid 5's for our builds a SE 103, 113 is in the mis 6's)

Rock · 08-24-2006, 12:16 PM

Quote:

Originally Posted by freefxrs

Here is my '92 FXR with the S&S 124

upgraded starter, clutch and some custom machining to move the carb in a couple inches. Went with chain and a fatter tire.

its a blast to ride.

wow and you can't tell by looking that it's any different than a stock motor with a 2:1 exhaust. just makes it tougher to race folks.

smut · 08-29-2006, 11:01 AM

Slick looking ride Freefxrs, Im thinking along those lines when mine gives up the goat. I got some over 83,000 miles and still running strong. I noticed the lower seals on the cylinders are starting to weap, won't be long now. I see its an S&S, good choice, I got a chance at an ElBruto, not sure about it, its a 100

freefxrs · 08-29-2006, 07:52 PM

Thanks smut

it is definately a rocket ship. I guess the question on the engine comes down to how you are going to use the bike. I have a Ultra Classic for touring, so my FXR is just for short hops and fun riding. Given that, i can afford to take the risks of a really large engine on a frame that probably wasn't built to handle the engine. If i hadn't bought the touring bike, i probably would have put a more reliable engine in the FXR that was likely to be more bullet proof.

i just put the new engine in and i love it so far, but i also know that i have to be prepared for some issues to possibly arise from the increased vibration and power (at least thats what some of my friends are telling me)