F54 L28 bottom end rev limit?

[thehelix112]

Phred,

Awesome. I appreciate the posts/time. There is no way I would contemplate building my planned engine myself. I think I could rebuild an L (I never have), but I don't have the experience/tools to do it to this level. I have no questions (thank god I hear you say?) about your post, all makes perfect sense to me. Looking forward to more of your posts.

Dave

[Phred]

Dave,

I have a fair amount of experience with boring and honing performance L-engines, so I'll pass along my thoughts. They may be diffrerent than other peoples ideas, but that's what makes the world go round.

With respect to L-28's, the F-54 is the only one to start with if you have a lot of cyl. pressure in mind. Before the F-54, about .060 was all the block could handle. I remember trying to go further, sometimes you could. But block/core shift causes the cly. wall thickness to to be inconsistant. You might end up with a nice thick wall on one side, and a very thin wall on the other side. No good. Finally, technical advances caught up with the need. Now, small portable ultra sonic testers have taken the guess work out of block/core shift. These testers have a small probe that you slide around the inside of the bore, and it reads the exact wall thickness on a digital readout. If you find a good block, yes you can bore well past .040. Lots of people have bored to over 3 liters with sucsess. Most of these are street racers. But, the more you bore the less strength the cyl. has to fight the pressure in a highly stressed engine. An engine which is designed to produce the max HP possible, must have a stabile bore. Even if a smaller bore is needed to assure this. The main reason you must have a ridged, straight bore, is ring seal. If the bore distorts in service, The rings will not be able seal all that mixture and compress it into that wonderfull explosion. So #1 is a straight, round, ridged bore. For optimum ring seal, I strive for a finished bore that is .0003 tighter at the top of the bore. Which with the extra heat produced at the top, expands more than the lower part of the bore, and ends up straight when hot. Also it must be within .0003 (three ten thousanths) of being round. A round ring can't seal against an out of round bore. Also a Torque plate, or deck plate is required when honing. It is torqued to the same value, and ideally with the same fasteners as will be used on the completed engine. This will distort the bore right where it counts, at the top of the ring travel. Also the main caps must be torqued similarly. Then final honed. For years, I even honed Coswoth formula atlantic, formula ford and Sports 2000 with the block pre-heated, with hot water circulating within the block, to simulate the exact distorsion conditions the bore would be under. It makes a difference if you're looking for that last little bit of power.

More later.

Phred

[Gav240z]

Phred do you have much experience with lightening rockers? I ask because we are looking to save some weight by drilling out some weight in the rocker arms and then getting them all balanced. I was just curious if you had any thoughts or comments on this process?

[EricB]

Phred

I've got to admit I am pretty impressed with the level of detail you're going into.

I forget did you say you were retired from the SCCA scene or do you still build these motors on a regular basis?

-e

[MikeW]

Thats why F-1 engines rev so high. They are regulated to a certain displacement, and the only way to make more HP is to up the revs.

Speaking for F1 engines and high RPMs, here's a really cool video. Note how responsive the engine is:

http://www.smele.com/video/

[240ZX]

Gavin, I'm no expert but drilling the rockers to loose valve train mass sounds like premature failure to me! I understand that some engine builders will smooth, polish and balance the rockers....but drilling holes in a high stressed member seem questionable. Phred will likely add to this, based on his experience.

P.S. If you paint the rockers RED, it will improve your HP 50%!!!

[gramercyjam]

Dave,

You can't do what you don't dream of first. Your questions are valid, but you must understand that high rpm is NOT the goal, but the results of trying to build the most HP out of a regulated size of engine. Thats why F-1 engines rev so high.

I'll just jump in here with a counterpoint. Although I have never read or heard this view, from my own experience, I suspect that high RPM's may actually be part of the car control puzzle.

Have you ever notice that it is much easier to drive at the limit in corners in a lower gear at high RPM's than a higher gear at low RPM's? I have.

[Murph]

gramercyjam: Wouldn't that simply be because you have more power 'on tap' so to speak, in the higher gear, than in the lower gear? If you had an engine with double the capacity, making the same power at half the revs (everything else being equal) it'd behave much the same around the corner at that lower rev point.

[e_racer1999]

^^that sounds right

[gramercyjam]

gramercyjam: Wouldn't that simply be because you have more power 'on tap' so to speak, in the higher gear, than in the lower gear? If you had an engine with double the capacity, making the same power at half the revs (everything else being equal) it'd behave much the same around the corner at that lower rev point.

Thats not what I'm talking about. I'm talking about control of power. This is due to gear ratios. input RPM/output RPM. fine thread VS coarse thread. 100:1 VS 1:1.

[Murph]

?

Wouldn't it be the same thing really? At higher revs you have more power at WOT and more engine braking off the throttle = better control over the cars attitude with the right foot? Also, a smaller change in throttle position will have a larger change in power output than at lower revs = better responsivness. Is that what you mean?

[gramercyjam]

Exactly the opposite. Larger change in throttle is a smaller change at the rear tires. Less responsive. It's real easy to mash down the pedal. Resonsivleness is something amatuers worry about. That is _easy_ to achieve. The key is control. How closely can you walk the line between a crash and a win?