Don Terrill’s Speed-Talk

I can say this because it has happened with a pair of CNC heads I bought. It was a "hedge" type chamber and the intake charge would wash the spark plug tip costing about 50 horsepower and a lot of throttle response, in a 650 horsepower small block. After many other attempted fixes in the ...

I happened to notice an unusual photo on the Franz and Grubb website: a twin plugged Bonneville 650 cylinder head with the second plug positioned directly between the intake and exhaust valves for each combustion chamber. Obviously the whole point of dual plugging a two valve hemi chamber is to spee...

The finger follower actually changes rocker ratio throughout the cam lobe travel because of that center-line change on the opening and closing sides ... actually, you can visually see the different flanks on the cam lobes; it is that obvious. "Finger followers" are used with roller or fla...

Can Roller Tappets and Finger Followers Use the Same Cam Profiles? No. Not only no, but you could destroy your valvetrain if you grind a profile designed for a roller lifter on a finger follower cam. With a roller lifter that rides in a lifter bore, the centerline of the lifter and roller wheel int...

I was looking at some photos of cam lobes used with finger follower DOHC 4 valve engines and others used with pushrod roller tappet 4 valve engines. Lo and behold, to me the lobe profiles looked so similar as to be nearly the same! Granted, a DOHC 4 valve mill has a lighter weight valvetrain, and so...

nonetheless shimless buckets are extremely lightweight compared to shim-over and shim-under buckets. Admittedly, my hand's-on shim-under bucket tappet experience is limited to a few old-school designs. I do see a number of late 4-valve Japanese designs come across the bench. Are those using shims r...

So the obvious question here seems to me: if all else was exactly equal, just how close could a shimless bucket engine get to a finger follower engine in terms of idle-to-redline performance? That depends on the application. A flat follower(bucket) can give you the same exact valve lift curve as a ...

Quoting sensei Cameron from a 2019 Cycle World article ( https://www.cycleworld.com/about-those-finger-followers-on-sportbike-engines/ ): "When Kawasaki recently switched its ZX10R literbike from inverted bucket tappets to finger followers, the project leader on that model, Seiji Azuma, had thi...

Some years ago an A class (single engine 510 "limit) boat was a consistent last place finisher. heavy boat with 3 onboard, ran like hell in the straightaway but dogged down in the corners. could not make it around a corner worth a crap, bogged down, had to lift the drive to try to keep the rev...

Lately I've been testing the KTM Duke 390 as a temporary city ride and track day ride alike. The 390 is a liquid cooled single cylinder of 373cc, with bore and stroke of 89x60, and a four valve DOHC head. From the factory wheel hp is 41 to 43, and wheel torque is 24 to 26. When properly fettled with...

Modern DOHC 4 valve engines are much narrower than they use to be. A Ford Modular motor is a poor example at packaging and if you ever look at something like a Ducati with similar or larger bore sizes, they take up way less space. That said, you’re comparing a boutique (even if mass produced) produ...

The only advantage of the "Finger Follower" setup, is the package size of the valve train. You can get the same exact valve lift curve with other valve trains, but it would be bigger and heavier. Going to a radius bucket follower, would require a much larger cam lobe and base circle, and ...

After reading the three links below, I think I finally understand the DOHC and finger follower obsession within the engine building world. Those of you with more experience than myself please confirm or deny the following, since I have been a dedicated pushrod enthusiast for many years, and have onl...

JC565Ford wrote: ↑Mon Apr 10, 2023 4:14 pm
Is this a road race bike ?

Would be, yes.

Your question is one of broad generalities and little specifics beyond a change in stroke. Using your provided B&S and making up some reasonable "other" inputs. This is what I would guess for change, all other things remaining static. It is based solely on percentage of change. Regard...