Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties Horsepower


Post Sat Dec 15, 2007 9:36 am

Posts: 21
Location: Murphy, North Carolina
How much horsepower does a stock 45 produce, year is 1947? How much can I get out of it with modifications such as head work, valve work, porting and polishing, performance cams and pop-up pistons? I don't wind it out much nor do I want to. I want to produce the most torque between 2500 and 3000 RPM. I am not really interested in lightning up the flywheels, my experience in doing this results in being harder to kick start and doesn't idle very well. What does polishing the rods do? Is it worth the work required to do it? I ordered Panic's book on "45 Performance", but it has gotten here yet, so I thought I would get some opinions first, I am sure it will help me digest the material when it gets here.


Post Sat Dec 15, 2007 10:28 am

Posts: 1654
depends on the motor, a WL makes 23 or 24 bhp depending on which source you read.

I've been doing a fair amount of research on this and the conclusions I have come to are as follows;

1- #6 heads are a bolt-on upgrade which produce a noticeable increase.
2- WLDR cams or regrinds from KNS produce a noticeable benefit
3- ditch the Linkert and get a Mikuni or Amal, not more than 34mm. If you've got the small G-type manifold, ditch that as well and get the WL type
4- 12 volt electrics improve the starting
5- a free-flowing exhaust ( there's a good suggestion in panic';s book ) produces a little bit.
6- bigger inlet valve - KNS again
7- auto advance timer from J&P produces easier starting and smoother mid-range running, not that starting is really an issue with 45s anyway
8 - make sure your oil pump is in good order
9- accurate squish clearance - 0.035" to 0.040" and the SAME on both cylinders
10- modified breather is usually mentioned.

if you are stripping the motor anyway, T&O flywheels up to 4 1/2" have a high reputation. Don't waste time polishing the rods on a motor like that. Any time you spend balancing your flywheels and making sure the bottom end is as free and accurate as it can be, is well spent.

some folks speak of boring out the crankcase baffles and fitting piston skirt oilers. I tend to suspect that this is best suited to hot motors mainly used on track, although some people report using them successfully in the road. The maths suggest that the gains are quite small, although they certainly exist.

pop-up pistons are highly controversial, which has lead me to the conclusion that they are probably best avoided for a street motor.

porting and relieving is a complex subject and you will need to do some research. The benefits are real if you get it right. Get it wrong and you can end up using a lot of fuel to no purpose
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Sat Dec 15, 2007 11:43 am

Posts: 2688
Location: Los Angeles, CA
5- a free-flowing exhaust ( there's a good suggestion in panic';s book ) produces a little bit.

What is Panic's book titled? Where can it be had?

Post Sat Dec 15, 2007 9:20 pm

Posts: 783
Location: Victoria, Australia
I've almost forgotton how to post on this board. I agree with most of the former comments with a few exceptions. Do not fit the pistons tight. Allow a bit more clearance, around .003" is fine (there's more distortion in side valve cyls by virtue of the exhaust valve placement and the motors run hotter up top as they don't run oil through the heads like an OHV. If you run the clearance I suggest, remove the baffles you'll find the oil runs considerably cooler as there's less pumping going on within the cyls pushing air & oil mix through the slots. You'll also free up some power. Anders (who?) used to do this with his flathead builds. Modern oils do a better job of lubrication. You'll probably change it more often than required anyway because you're an enthusiast. You don't need pistion oilers (mines been together like this for the last 8 years) Don't bother running the worlds most efficient oil control ring if a bit gets past the piston there's a margin of insurance if your nervous. Try and maintain torque whilst improving top end with a bigger inlet valve if using on the'll be more user friendly. Don't overcam it other wise it will be a pig (or is that hog) on the street. Use long exhausts, do not increase the ex pipe diameter and adjust the backpressure on each pipe with a simply made "large adjustable rotating washer" fitted at the end of each pipe to optimise power across the RPM range. Automatic advance is a waste of time especially if you get the squish right and keep this to the minimum figure. I run mine (magneto) fully advanced. 45s are not like big twins to kick over...and it won't ping or knock if you pay attention to detail.

Post Sat Dec 15, 2007 9:24 pm

Posts: 202
Location: Middle England UK
Chris Haynes wrote:
5- a free-flowing exhaust ( there's a good suggestion in panic';s book ) produces a little bit.

What is Panic's book titled? Where can it be had?

45 Performance Book.

Go to one of Panics posts,click on link for stroker flywheels.
Scroll down and see Victory Library Books.

Post Sun Dec 16, 2007 6:46 am

Posts: 1654

thanks for that. I've seen some of your previous posts, they came up while I was researching.

comments about baffles and skirt oilers are interesting. I hadn't thought of the oil temperature angle. I've never used skirt oilers on British bikes with open crankcase mouths and never had any problems

agree about the oil control ring. I never worry if my BSA leaks a bit, if it leaking out it must be getting there first. Leaky rocker boxes on Royal Enfields excepted!!!

KNS do a series of cams with various comments about porting, relieveing and stroking, in line with your comments. If you have any particular comments on cams for a 4.5" stroke 45, I'd be interested to hear them. I know someone who is running a ported and relieved 45" with #6 heads and WLDR cams and reckons it is pretty good.

I've always used the longest exhausts I could fit on any sidevalve, agreed. Personally I prefer a 2 into 1 for twin cylinder engines, gives more torque for a small trade-off in top end.

I need a timer anyway so that's why I thought of the auto advance. I had one on a panhead once and it made a big diference to starting and riding around town.
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Sun Dec 16, 2007 9:00 am

Posts: 21
Location: Murphy, North Carolina
thanks for the input. If I were to install a larger intake valve wouldn't that require alot of machine work? or is there enough meat on the existing valve seat to just grind it to the larger size? I am not sure why the motor company installed crankcase baffles in the first place. Was it done to minimize bottom end pressure? If the baffles were removed will I need to re-slot the scavenger pump timing hole? I run synthetic oil in my 07 twin cam 96 and in my supercharged 5.4L 06 F-250 (602 HP!!!), what do you think of running this oil in the 45?


Post Sun Dec 16, 2007 9:57 am

Posts: 1654
the crank-case baffles were fitted originally to minimise over-oiling of the oil control rings. Modern rings render them superfluous in that respect, and they definitely act as a baffle and increase pumping loads on the pistons. Whether they are required for piston skirt oiling, and exactly what the options are, is a matter of a certain amount of debate but if someone says ( as they have ) that they run happily without them, fine.

there is a modification to the breather valve described in panic's book, several threads here refer to it as well. Seems useful.

speaking of lubrication there are verious threads here regarding upgradede oil pump and pump work generally. Some people fit Sporster pumps.

port and valve sizes are a complex subject BUT, it is possible to fit the KNS oversize valve with very little work other recutting the seat 'according'. This is generally reckoned to be a useful upgrade. You can do a lot more with ports and manifolds, get panic's book and start reading the threads here. You'll soon get the sense of it.

personally I've always used a straight 50 mineral oil in 45s. Old engines with fairly large clearances and roller bearings ( little or no oil pressure ) don't get the full benefit of modern oils and anyway they tend to leak with light oils, more than usual that is
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Sun Dec 16, 2007 10:07 am

Posts: 591
Location: Crewe, Great Britain

Hi 45Brit,

""personally I've always used a straight 50 mineral oil in 45s. Old engines with fairly large clearances and roller bearings""

I agree with you there, but i'm pretty sure the old engines would be quite happy to run on more fluid oils, but generally, it's the oil pumps that are not designed to pump stuff that thin, hence the engines will tend to wet sump a lot more...

As you also intend to go racing on your 45, a straight 20 will give you a few more ponnies due to much less drag!!!


Post Sun Dec 16, 2007 10:58 am

Posts: 1654
yes... no.... sort of....

I use Castrol R40 for my 250 BSA on methanol. I use R30 for older wet-sump engines on dope ( I once had a 1934 Blue Star BSA grass bike, which ended as a catastrophic gearbox failure and I sold the engine to someone who used it in a road bike )

I was going to try it on petrol with a 20/50 mineral oil and if succesful, use methanol and R40 on the 45 for hillclimbing. Its a lot of nuisance but it's only twice a year... unless it ends up being successful enough to try events like the Saltburn Sprint, in which case I will build a bike for the purpose from parts to hand
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Sun Dec 16, 2007 3:08 pm

Posts: 32
Location: Oklahoma City OK USA
I was glad to see enigma's post. This is not 45" related, but hp & torque just the same. In 1975-76 I had a '74 XLCH Sporty
all stock except 38MM Mikuni & either 1-7/8" or 2" drag pipes. WFO it was great, but in town/traffic stumbled & farted alot. I was working at a H-D dealer, and one of the "old school" wrenches said he could fix it without spending any money.
We pulled the pipes, and about 6"-8" in, drilled a 3/8" hole on the inside (frame) side. He took 2) 3/8" x 1" bolts & slotted
both the hex-head, and threaded end (paralleled), then took ( I believe cam washers, or tranny shims) that had the OD of the pipe ID, and brazed them in the slotted heads. He fished them up the pipes and thru the holes, and nutted them. We
started test runs with the "washer" straight inline with the pipes, each run we would turn the bolt a few degrees, ending
somewhere around 30 degrees off straight thru. It made the whole package rideable, very little power loss @ WFO or (what I thought was important then) noise. The pipes did blue near the washers, but "Blue-Away" helped.
I've told this story to modern racers that kinda squint one eye & think "sure ya did"
OH, and when we had found the best adjustment, we center punched the pipe in line with the slot, when something changed, the washer alignment was the first & easiest thing to check!
old harley parts are MY 401K!

Post Sun Dec 16, 2007 3:51 pm

Posts: 1654
I know some people who stumble and fart a lot.... must try that. Drink less beer and eat less curry usually does the trick for me.

I've often seen that 'rotating washer' trick referred to. It wasn't usual over here, probably because Amals have wider ranges and more adjustable parts than Linkerts or Tillotsons . But I have more than once improved a supposedly tuned bike by putting the old silencer back on, which is really only the same thing by another name - varying the back pressure to alter the gas velocity and hence, cylinder filling, especially at medium speeds
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Sun Dec 16, 2007 11:51 pm

Posts: 783
Location: Victoria, Australia
Don't use a fully synthetic oil as this type of oil apparently causes the roller bearings in the crank to skate and slide rather than roll. Synthetics were designed for modern engines with very tight clearances running shell type bearings.

Post Mon Dec 17, 2007 1:54 am

Posts: 1654
I usually use Morrison or something similar, sold here in UK for Classic and vintage engines. For running on dope I use Catrol R
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Mon Dec 17, 2007 8:32 am

Posts: 21
Location: Murphy, North Carolina
So what I am getting here is that running 2 into 1 long pipes on the "45" creates a simular back pressure as the rotating washer (just not ajustable). Which would increase the torque were I want it, at mid range probably due to increased scavenging in the cylinders. Is there enough intake/exhaust valve lay-over ground into the cams for this? Or should I consider a regrind to extend the timing to take advantage of it?

And dont run thin super lubricating oil in an old loose roller bearing engine.


Post Mon Dec 17, 2007 9:42 am

Posts: 1654
1) 2 into 1 pipes were commonly fitted to British twins such as the Triumph Trophy to provide better silencing and smoother mid-range power, often in conjunction with a single carb but fairly fierce cams. There is a small trade-off at the top end, but not much.

I've always reckoned that any sidevalve engine goes best with the longest pipes you can fit, for maximum scavenge effect. Don't increase the pipe diameter for the same reason. Playing with different silencers and end sections has the same effect as the washer trick.

2) stock 45 cams are as soft as a soft thing, with extra soft bits. Any regrind will buck them up. Go to the KNS site and look under cams, there is a fair bit of info there.

3) extra compression is a good thing, good head/barrel sealing surfaces are a must. Get new #6 or WLDR heads from Kurt at 45 Depot and kill both birds with one stone. Kurt can also supply WLDR cams, contact slowrider ( he's on here somewhere ) for his view of this, he has got them in his engine.

4) I didn't know about the rollers skidding, but I'll believe it. Plus, old roller-bearing engines have very little oil pressure anyway. For sure an over-thin oil will make your engine leak like a good 'un.
Shoot, a man could have a good weekend in Dallas with all that stuff...

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