XB Buell heads over 1200?

[aswracing]

Sounds like you've thought it through well, good luck!

Oh ... one minor point ... a pre-rubber 883 will have a 27T front pulley.

[rottenralph]

Why n2 cams? Seems like a wasted to me, not enough cam to make the change worthwhile.

[maru]

That much compression and that mild of a cam will give you problems on pump gas, even with a tight squish and grooves. You will have to pull so much timing out of it to keep it from knocking itself to death that you will lose more power than if you had less static compression.

What is your altitude and is 93 available?

[maru]

I also agree with Ralph, you can run a more aggressive cam without reversion problems if the rest of the package is carefully selected. I would not go to the trouble of installing a set of N2's even if they were free. Even with a 6k limit I would look in the direction of the N4's.

[tich]

I have run N2's with 10-1 SE reversed dome pistons no problems for what must be 15,000 miles.
I now have them with 9.5-1. (Diferant sporty)

I agrea with the outhers that 10.8 is pushing it to far with N2's. I would expect the N4s to still have great bottom end with that amount of compression.

[Bailey28]

I am at sea level here in Florida, and 93 octane is available at every station. Of course, it all says up to 10% ethanol as well.

By the RSR dynamic calculator, the engine with N2 cams having the intake valve close at 38* ABDC generates 211.67 psi. This is with the 10.8:1 static compression as in the combo of the 3.63cc domes and 62cc heads.

With the N2 cams, flat top pistons and a 62cc chamber for 10.2:1 static, the dynamic compression is 9.44:1, and generates 196.70 psi cranking pressure.

-----------

With N4 cams closing at 46*ABDC, and +3.63 domes, 62cc chamber, 10.8:1 static, the dynamic compression is 9.64:1, and generates 202psi cranking pressure.

With N4 cams, and flat tops, still 62cc chamber, 10.2:1 static, the dynamic compression is 9.1:1, and cranking compression is 187psi.

I need to find a balance of what will work with the 93 pump gas I can get here. I've been reading that 200-210 is the cranking pressure limit on pump gas.

I believe the correct "W" intake cam opens at 5*, and closes at 38* also, although the Andrews site has it at 8/26.... I can see why you guys are not recommending the N2 cams, they are pretty much identical to what comes stock, to within a few degrees.

I am fascinted by this kind of stuff and love to tinker. I have built several car engines using the intake valve closing points, tight quench, jetting, exhaust and distributor recurving to get great results on my street cars. My Ford 302 with Iron Windsor Jr. heads had KB forged pistons .005 above deck, 58cc chamber, .039" compressed gasket which left .034" for quench. I wound up setting the base timing to 16*BTDC, and after much testing, recurved the distributor to give only 24* total mechanical timing.

I made the most power that way. I could accelerate in overdrive from 1,000 rpm very strongly and smoothly. I also could hardly drive the car in the rain due to the tires coming unglued from the road at the lightest throttle openings. I never went over 6,000 with that car.. Short shift it and let it pull hard from down low! 93 octane pump gas, 195psi cranking pressure with iron heads. Isky 257/265 roller grind, very mild, intake closed early at 37*ABDC. 37* of overlap. I could never get this engine to knock.

This is what I wanted to achieve with the 1250 build. Efficient, high torque, strong pull from down low up to 6k. I liked the dyno sheet I saw on "Iwantmybeerback"s gallery, where he made 82hp/86tq with a mild build. But looking at his torque, almost 80 ft/lbs from 2500 rpm? That's awesome! Unless the dyno was reading unusually high that day...

I'm not a pro or an expert on this and I am very open minded to all suggestions and pointers. I am in the process of reading everything I can on this board, and elsewhere. One of the first places I looked was NRHS, and Hammer. I've got to learn how to make this model 1250 air pump work as well as or better than previous car builds. I know there is lots more than just compression and intake valve closing. I suggested the earlier build combo as a starting point, I'm sure it wil change 50 times before anything is final.

27 tooth cog, not 29. got it!

[maru]

Most everything is have heard is that 185 to 190 is the upper limit for air cooled Harleys. We have seen more than that but generally it does not work out. Sea level will help power but puts you closer to harms way as does the hot summer weather. Something to keep in mind, if you go over the top you can often get it to stop knocking with less lead but the tradeoff is less power than optimum compression and timing for a given fuel. It is clear you have put some thought into this project and I like the way you think.

[Turbo Sporty 48]

Originally Posted by maru

Most everything is have heard is that 185 to 190 is the upper limit for air cooled Harleys......
Something to keep in mind, if you go over the top you can often get it to stop knocking with less lead but the tradeoff is less power than optimum compression and timing for a given fuel........

Would you please elaborate a little more on what this means?
I like the way this thread is progressing.
Sounds like my kind of power with a long flat torque band.

[rocketmangb]

Sporty

They are refering to cranking compression

[Jimbos883]

Originally Posted by maru

Most everything is have heard is that 185 to 190 is the upper limit for air cooled Harleys. We have seen more than that but generally it does not work out. Sea level will help power but puts you closer to harms way as does the hot summer weather. Something to keep in mind, if you go over the top you can often get it to stop knocking with less lead but the tradeoff is less power than optimum compression and timing for a given fuel. It is clear you have put some thought into this project and I like the way you think.

I think at least the carbed rubber mounts run a little more cranking pressure from the factory than that 185/ 190. I know I've seen higher numbers than those a couple of times on the forum. See the referenced post from days past.


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