Engine swap possibility - Harley Davidson Street Forum - Street 500 and 750
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post #1 of 27 Old 02-16-2019, 11:26 PM Thread Starter
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Engine swap possibility

Ive been shopping the idea around for awhile now to try and figure out how to get more power out of my 500 and the 2 ideas that are leading the way are either attempting to swap in a 750 motor which i would need to find out what i would need parts wise to do the conversion or finding out from the vendor who makes the big bore kits what all would need to be done to make the 800 kit fit my motor. From what i understand, from the case down the motors are the same but i haven't called anyone to try and hunt further info yet i figured id check with you guys first and see if anyone else has looked into either option before who could possibly help with a little guidance. My biggest question on the engine swap is would my current ecm work for the new motor with just a Vance and hines fp3 or would i need a power commander to reflash it instead? Or are they a different ecm altogether. Are there any other major parts that dont directly swap over? I think someone had said before that the 750 has a larger throttle body but thats as far as i got into researching the idea before. Also before telling me to just trade it in for a 750 instead, i think i can manage the engine swap for less than 2 grand, i highly doubt i can get into a 750 for less than 2 grand haha
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post #2 of 27 Old 02-17-2019, 03:46 AM
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Revolution Performance are the only big bore kit providers as far as I know. Using one of their kits will get you another 50cc, and that is for both the 500cc and the 750cc. The limiting factor is the thickness of the crankcase 'mouths' where the barrels attach to them. There just isn't the required thickness to safely increase the bore by more than 2mm.

As the stroke of the two engines is identical at 2.60" - 66mm I think it is safe to assume there must be differences in the upper crankcase castings of the two models, otherwise you would be able to drop the 750cc top end onto a 500cc bottom end. However even given that fact, I find it unlikely that you couldn't swap engines as a whole and put the 750 mill into the 500 cycle, purely because of the increased production costs for HD in having to produce two separate frames. Mind, that's what I think, that's not a given.

Would the ECM work? Not with the standard 500 fuel map. The FP3 could certainly flash a 750 a/f map to it.

Then there are the 'not knowns' to consider. Off the top of my head;

Are the exhaust ports the same size or will you need a 750 exhaust?

Are there other implications of swapping two different ECM's should you need to?

Are the final drive pulley ratios the same for 500 and 750?

Are the swing arm length's the same? - drive belt?

Can the 500 fuel pump cope with the 750's demands?

All nitty gritty things that you will need to sort out and made more difficult by Harley's reluctance to make technical specifications available or easily accessible.

No doubt it can be done, with a bit of hassle. You'd have to make sure you have a good sense of humour to take it on.

I notice what you say about trading in for a 750, but the fact remains it is the simplest and most cost effective option if more power is your goal.

Your 500 must have some value to offset against buying the 750.

And when time comes to sell your 500/750 conversion, you'd expect people to be a little bit wary of buying it, which translate as rock bottom resale. Why take a risk on an unknown when the potential buyer can go to HD and buy a 'proper' 750?
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post #3 of 27 Old 02-17-2019, 11:38 PM
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I was entertaining the thought of putting a 750A Street rod motor on my xg750. No need to have a bore kit for the stock 750. Here are the differences....

Basically, both bikes are using the same 749 cc, liquid cooled V-Twin motor (named Revolution X). Street 750 comes with a standard tune for this motor while Street Rod gets high output setup for more power. Compression ratio on Street 750 is 11.0:1 while fuel supply is managed by a single port, 38mm Mikuni injector, producing an output of 59 Nm at 3750 rpm.

When it comes to Street Rod, the compression ratio is increased to 12.0:1 and dual port, 42mm Mikuni injectors are used for fuel supply. This results in 62 Nm of maximum torque at 4000 rpm. Gearing remains exactly same on both the bikes.
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post #4 of 27 Old 02-19-2019, 01:53 PM
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Originally Posted by Solo750owner View Post
I was entertaining the thought of putting a 750A Street rod motor on my xg750. No need to have a bore kit for the stock 750. Here are the differences....

Basically, both bikes are using the same 749 cc, liquid cooled V-Twin motor (named Revolution X). Street 750 comes with a standard tune for this motor while Street Rod gets high output setup for more power. Compression ratio on Street 750 is 11.0:1 while fuel supply is managed by a single port, 38mm Mikuni injector, producing an output of 59 Nm at 3750 rpm.

When it comes to Street Rod, the compression ratio is increased to 12.0:1 and dual port, 42mm Mikuni injectors are used for fuel supply. This results in 62 Nm of maximum torque at 4000 rpm. Gearing remains exactly same on both the bikes.

They also increase the RPM range on the Street Rod version.
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post #5 of 27 Old 02-19-2019, 04:53 PM
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Originally Posted by Solo750owner View Post
Gearing remains exactly same on both the bikes.
In fact the gearing isn't the same on both; the Street Rod has effectively taller gearing because it has a much bigger rear tire. It's true that the transmission is the same, and the quoted final drive ratio is the same, but the 15" rear tire on the Street 750 delivers lower effective gearing than the 17" rear tire on the Street Rod.


That's one reason why the 1/4 mile times between the two bikes are the same, even though the Street Rod has more power. It has the power, but it isn't as effective at putting it to the ground as the smaller-wheeled Street 750 is.
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post #6 of 27 Old 02-19-2019, 07:26 PM
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It you want a 750 and you have a 500. Think about this. Spent the money to make your 500 at 750 , resale it is still a 500 and will not bring one dime more than a 500 unless you find a fool. If you want more power and a Street is the type bike you want . Take the hit sell yours buy what you want a 750 Street of a 750 Street Rod.

You purchased a 500 great, you have out grown it even better move on.
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post #7 of 27 Old 02-20-2019, 12:12 AM
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Yup! Thatís exactly what I did. I traded in my used 500 and bought a new 750. In the long run it was easier, plus the 750 has some added trim and better quality parts. Just bite that bullet.


Evan


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post #8 of 27 Old 02-20-2019, 06:01 PM
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Originally Posted by Solo750owner View Post
I was entertaining the thought of putting a 750A Street rod motor on my xg750.
Didn't you discuss that in another thread and eventually gave up on the idea because it was going to get WAAAY too expensive and difficult to be viable?


Some of the other posters are probably correct that trading in the running xg500 on another bike would be the best way to go. Making a Franken bike out of a pile of broken Streets is understandable if you wanted a project and possibly a bike on the cheap, but not as a way to get more power out of a already working motorcycle.

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post #9 of 27 Old 02-20-2019, 07:33 PM
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I’m also curious about dropping in a 750. If it’s as simple as swapping in an engine assembly, throttle body, fuel injector, and flashing a map it is worth doing.

The main problem is nobody has gambled the $2,000 on trying it yet.

I’m getting happier with my 500. With V&H pipes (baffle removed), air intake, and after autotune it’s fun as a commuter bike. Usable until the Streetfighter 975 comes out, with a year or two delay for them to fix any bugs.

If I could drop in a 750 I’d do it. But I’m not going to spend how much you really would have to spend to swap bikes.

My conclusion is the question is valid. The answer is nobody has had the guts to try it yet 🙂
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post #10 of 27 Old 02-21-2019, 11:49 AM
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I shouldn't guess about such things but will. I'm guessing you would just need to swap out the engines and ECM, or maybe just flash that. I don't know that it's a matter of nobody having the guts to try it so much as the dollars don't work out. Unless you have a really inexpensive parts bike lined up it's easier, faster, and cheaper to just trade bikes.
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