Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties whats an decent number?

whats an decent number?

Moderators: Curt!, Pa

Post Sun Oct 21, 2012 3:16 pm

Posts: 15
I've an heavily modified 45( actually 56cu) which i am pretty pleased with.
So i made the mistake and dyno'ed it.
I was so sure that i've had an 40+ish hp number.
But the dyno took me down to earth with an 31rwp number. So what's an decent number for these engines?
What would an bone stock 45 put out on the dyno`?
I have done almost every mod i know of, accept Pop up pistons and really wild camgears. I have the wldr replica gears.
And what could be expected out of those modifications?

Thankful for answers. Elffors

Post Mon Oct 22, 2012 10:17 am

Posts: 1608
depends - are you talking about at the crankshaft or at the back wheel?

HD quote 23bhp for the 45 in stock trim and that sounds about right. BSA quoted 13bhp for the 500cc M20 and The Indian Scout is quoted as 22bhp ... 01934.html

Same article quotes 35 bhp from a professionally tuned racing Scout.

Allan Girdler's "Harley Buyer's Guide" states that the K model produced about 30 bhp in road trim and the KH, a claimed 38 but no actual measured figures are quoted to prove it. There are some fairly wild numbers quoted in various sources for the various KR variants but I don't think they are relevant here.

I would have thought that a back-wheel figure in the low 30s was about right for a roadgoing, stroked WL. For comparison a stock Triumph Tiger 100 was listed as 27bhp and the Thunderbird as 34 bhp.
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Mon Oct 22, 2012 1:03 pm

Posts: 15
It's rwp or rear wheel power. Well, then the figure isn't that bad after all.
Has anyone else put their 45's on the dyno?

Since im pleased with the bike i should just leave it as it is, but.....

Winters here in sweden are long and gruelling so... I've bought an eaton m45 blower for it.

The set up i'm thinking about is as simpel as simpel can get. Draw trough carb non intercooled.
i can think of a zillion reason why i should not do this, but i'm happy to hear more.
is it going to work at all, or is it just going to overheat badly and seize?

Post Mon Oct 22, 2012 6:14 pm

Posts: 303
Location: wooster oh usa
31 rwhp is very respectable for a street motor. you are greatly limited by your cam choice.the wldr cam profile is very mild.

Post Mon Oct 22, 2012 8:23 pm

Posts: 386
If you have 31 at the rear wheel you are doing good! The best W series race engines made no more than mid 40s at the crank, anything over high 20s at the rear wheel is quite good. And unless you are particularly anal about numbers it really means nothing!

Post Tue Oct 23, 2012 5:00 am

Posts: 15
It's my first vintage bike, previously i worked with turbocharged japanese fourbangers, And anything under 300bhp would put you in the hall of shame.
So i have no referense base or friends who has vintage bikes and the ones who do have older bikes never strap them to a dyno.
I just love to tune engines but i have no clue if its a good runner or a lemon.

I stumbled over this bike dirt cheap and i found out it was much more rewarding to work on, and im not afraid to die anymore then i ride.
The adrenaline rush is gone but riding this old bike is much more enjoyable in so many ways.

The reason for the wldr cams was that it the only ones i could get my hands on here in europe. but im thinking of
Buying lobes from enfield racing or machine them my self.

Post Fri Oct 26, 2012 7:50 pm

Posts: 367
Location: Bergen, Norway

I had one claiming to have dynoed several WRs They were all in the 32-34 range on the back wheel.

I always wanted to Dyno my wl stroker, but then i never got the time.

The difference after the mods feels like at least triple power :D , maybe the Dyno will only dissapoint..

Anyhow if I ever test it i will post the figure here..


Post Sun Oct 28, 2012 10:24 am

Posts: 15
Hello gus!

Since i started this thread i realized my number is an decent number.
It would be very intresting if you could put your stroker on the dyno.
Bergen is not far from here, if it would ever stop raining there, maybe i go check it out :mrgreen:

Tuning an engine an not put it on a dyno, is like taking a very strict diet an not reward your self by stepping on the scale afterwards. I want to know!

Post Sun Oct 28, 2012 11:25 am

Posts: 367
Location: Bergen, Norway
Rains a lot in Bergen???

It only rains 200 days a year, half of that statistically falls during the night when your asleep, the other half fall while you either are inside eating or doing other stuff or while at work. So the rain In Bergen is just a myth :) :)


Post Mon Oct 29, 2012 11:39 am

Posts: 693
Location: somerset, oh usa
I vote for KHK cam lobes as they would take much better advantage of the improvements already made. Set up will need checked as they have about .030" more lift than what you have.

Post Mon Oct 29, 2012 3:27 pm

Posts: 15
Is'nt KHK lobes the brutale ones?

i like those :D

but i would need even stiffer valvesprings and a pair of new heads and k-model pistons

Because, i milled down my current heads to bump compression up. But i lost alot of clearance and flow over the intake valve.
So if i opened up the engine again i would like to start with new heads with more flow over the intake and do the pop up piston mod and keep compression in check by a mix of milling and welding.

I dont know if i do this, this winter. im Short in both money and time

Post Mon Oct 29, 2012 5:08 pm

Posts: 693
Location: somerset, oh usa
They are somewhat hourglass shaped but still provide easy starting and good idle and even better....more streetable HP.
Not necessarily. Since you milled the heads, I'm assuming you used #5's, so long as you didn't take more than an 1/8" off the gasket surface, you should be okay.
Making a cutter for establishing the valve pockets is easy (if not already deep enough) and then blend them into the chamber.
Pop ups would not be required nor radical relieving of the flow paths to realize a benefit.
Perhaps not KR quality HP but you'll get more "bang" out of the effort already put forth.

Post Tue Oct 30, 2012 5:29 am

Posts: 15
Well, i could do with more streetable hp. Now it kicks butt at idle revs followed by a mellow midrange and then nothing.... The dyno said the same thing. The hp curve climbed vertical and then took a 90 degree turn and flattened out. i had 52nm at 2000rpm it peaked at 54nm at 2900rpm and 42nm at 5000rpm.
Your'e right i started out with number 5 heads and i think i bumped up the compression to 6,25.
I don't remember, but i think it was about 3mm that i milled of the heads.
Maybe if there is enough material at the head"roof" two carve out a decent valvepocket, then i should give this a go after all.

Post Tue Oct 30, 2012 8:29 pm

Posts: 745
Location: Pa. , USA
If you want power on top you may have to loose some on the bottom, WLDR cams are pussys, you will at least need KHK grinds and you need breathing space around and over the intake valve, my higher rpm motor runs low comp. heads , K pistons, KR grind cams ect. ect. ect., but it's only good for racing . mho , Tim
Vintage roadracing, Class C, AHRMA # 335

Post Wed Oct 31, 2012 1:14 pm

Posts: 15
I don't mind a little pussy once in a while.
Hell, my favorite way too spend an friday night is in my garage with a case of beer tinkering with the old harley. Now i know why.
The old " it's me or the harley" ultimateum just got a little toothless :D

loose at the bottom if you gonna gain on top is obvious.
What can your'e full tilt engine do in terms of power or speed?

Post Wed Oct 31, 2012 2:14 pm

Posts: 303
Location: wooster oh usa
my old wr would pull mid 30's hp with f grind kr cams wr cyls. etc. power came in around 3000rpm. it wasn't a super tuned engine as i was not that good of a rider. LOL the khk cams are close to the f grind but fully streetable. you need bruce(argetsinger) roller tappet wr tappet guides and steve (37ulh) valve springs.if you are running chevy six intake valves you have already opened up the intake valve pocket in the head..but if not it's easy to cut the pocket with an old valve with a lathe cutting tool layed flat across the top and brazed into place. silly putty or dap window glazing caulk works good to check clearance.steve is much more knowledgable than i am on these mods. barry

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