Hi there from New Zealand!

My bikes a '98 fatboy, which up until recently was mildy modified - SE aircleaner, SE ignition module, Vance & Hines twin slash 3" slipons with quiet baffles, Andrews EV3 cam, & jetted carby (48 slow jet, 190 main, circlip set at middle on needle, & 2 1/2 turns on idle screw).

It ran real sweet - never any coughs, farts, pings etc.

Anyway... in the never ending pursuit for more horsepower I decided to bump the compression up. So I fitted SE 10:1 cast pistons (for stock heads), a SE4 cam, SE hydraulic lifters, 5 angle valve job, and SE adjustable rods. The reason I went with this setup was because I wanted a straight bolt on kit where I didn't have to calculate/guess/measure anything, and Harley had this exact same setup in one of their SE catalogs. I thought by doing this I would avoid all the usual problems. Plus I actually like stuff that Harley makes, it's normally good quality stuff (although I see that things like the SE4 cam are actually made by other manufacturers - but good stuff nonetheless). And another reason is that we just don't get the selection of aftermarket Harley stuff down here that you guys in the States get.

The cylinders were bored out 0.010" from stock. The only issue I had was that the gasket surface on top of the cylinders and bottom of the heads was reasonably pitted (where the head gasket sits between). The pitting seemed to take the shape of the pattern in the head gasket, which looked original. The engine shop ended up machining both the head and the cylinder to clean them up. He reckons he took about 3-5 thou off each (so maybe 10 thou in total).

The bike's back together, it starts and runs like a dream, but I've now got a problem with detonation. In NZ we have a choice of 3 octane ratings for our gas - 91, 95, & 98. You can buy 91 & 95 everywhere, but 98 is not as readily available. When I run 95 I get bad pinging, but only when I put the motor under load (like twisting the throttle when I'm doing 15 mph in 5th). When I run 98 the problem is virtually gone, but once or twice I may hear it on a trip, but even then it's only one or two light pings - but it's still enough to annoy me (and I sorta wonder if it's hurting the motor)

I'd like to be able to run 95 gas, but I'm guessing that the compression is too high (yeah, like you need to be a rocket scientist to figure that out!!). Static compression is 200lbs. I'm wondering how much difference maching the head and cylinder made, and whether sticking in a thicker head gasket would solve my problem (which I don't really want to do)? I'm also wondering if I can solve my problem by sticking in a cam which has a later closing intake valve which would drop the corrected compression ratio (I read this on the interweb thingy. I get the general concept, but I don't quite know how you apply it).

On this note the SE-4 (which is virtually identical to the EV27) has an intake valve that closes at 36 degress ABDC. The intake valve on a SE-11 cam closes at 47 degrees ABDC. Would the SE-11 cam drop my compression ratio and possibly solve my detonation problem, or have I totally misunderstood how things work.

Anyway... It would be great if someone could give me their thoughts on this setup

Cheers from the South Pacific!

 

You are correct, detonation is very bad for your engine.
Different cam would help, with current cams you need to work on your ignition curve. Maybe retarding the whole range by a few degrees will solve it, otherwise individual parts of curve have to be modified.

 

I am not tech savvy enough to address your question directly, but I did notice that you said "I get bad pinging, but only when I put the motor under load (like twisting the throttle when I'm doing 15 mph in 5th)". I don't think any cam change or any octane gasoline will prevent this. In 5th gear at 15 MPH, you are seriously lugging that engine and it will ping severely.

 

I have singh grooves machined into my combustion chambers and I have no detonation issues at all. I am @ 10.2 CR

 

I too have an 98 Fatboy. Great bike. You are correct in looking at the intake valve closing point to bleed off cylinder pressure. Right now 200 psi cranking pressure is too high. You need to be below 185 psi for the gas you want to run. The SE-11 would be a better choice than the SE-4 camshaft you now have. There are some dynamic compression calculators on the internet that will help you find the best intake valve closing point. You need to be less than a 9.5:1 dynamic compression ratio. This will give you good power and still run on the gas you want. You will also need to dial in your ignition timing.

 

I agree that 15 mph in 5th gear is not what you want to do.
It is also tough on the rods, rod rollers and crank pin
I also agree that the #4 cam set @ 200 psi ccp is a bit much.
Question;
Does that bike have a 65T rear belt pulley?
Scott

 

I missed the 15 MPH on fifth part. My bike wants at least 20 MPH on first gear, I'm grabbing for clutch below that.

 

Is the bike equipped with a 65T rear belt pulley??
Scott

 

Hi there - 15MPH in fifth is not something I would normally do. This was just to illustrate how badly I have to load the engine in order to get it to ping.
Cheers
STU

 

Hi there - 15MPH in fifth is not something I would normally do. This was just to illustrate how badly I have to load the engine in order to get it to ping.

Yep, the rear pulley is 65T

Cheers
STU