| Author | Message | ||
     Maddiemsu |
 Here's the Dyno showing what happens when you put XB9 Piston heads into a XB12 engine. The red line is the stock 12 heads and the blue line is the domed 9 heads. Compression went from 10:1 to 12:1, lost 3 HP at the top end and the torque stayed the same from stock but I think it is worth it for overall performance. The thing is even more of a beast now. The Firebolt has a Micron and a K&N with tuning map from American Sport Bike. | ||
| 1324 |
What kind of fuel were you running? When you say tuning map, you mean an off the shelf map or a custom tune? | ||
| Hogs |
You are trying to say, this is with using xb9 high dome pistons in place of the stock xb12 pistons in a xb12 Correct??? Also looks like you picked up power all places where I would want to be, not concern the bit ya seemed to lose on the top end... | ||
| Greg_e |
Did you adjust the ignition timing for the increased compression? If not that might be why you lost power at the higher RPMs. Overall the higher compression ratio should make the motor more efficient unless you are getting knocking at the higher RPM and that's why the power was reduced. | ||
| Maddiemsu |
It was on 91 oct pump gas. The tuning map was one that American Sport Bike has developed for the XB9 heads/micron/k&n so you could say off the shelf. Yep Hogs, 9 domed in place of the stock 12. More useable power a little sooner. | ||
| Bads1 |
You'll most likely have detonation problems sooner or later. | ||
| Crackhead |
what is your afr? and timeing? The upper end loss might be from pinging. | ||
| Hogs |
Yeah would be interested in Knowing IF your Timing was still at stock from the factory or not? OR IF you had it retarded etc...( setup when you or whoever installed the 9 pistons etc...) As well as the air/fuel Ratio that Crackhead had asked as well? | ||
| Steve_mackay |
Hals has done this to several XB12s. They get around 98HP at the wheel with a drummer & tuning with ECM SPY. BudC at Hals has this setup, and doesn't have detonation problems. | ||
| Greg_e |
Does his (BudC) machine also lose power on the top end? Everything I've ever read about building racing engines has stated that raising the compression ratio of a normally aspirated engine raises efficiency which normally raises the horsepower output. I know my old Suzuki Katana had a high compression ratio (think it was 12:1) so it can be done on air cooled motors without too much risk. Also pretty sure you could get head/cylinder kits for the air cooled VWs to raise the compression up to the 11 or 12 range without blowing them up. If that map you (Maddiemsu) mentioned was simply installed and not tuned to fit your machine I would suggest going back and doing some tuning after a decent break in run. Until then you may want to stay out of the high RPM areas. If it wasn't broken in then you might expect to get some of that back after the rings seat properly, you might have been blowing by or even sucking oil which would certainly lower the power a little. | ||
| Maddiemsu |
The dyno was done right after the mod was done so it was not broken in. When I can get some time and can find a way to get ECM Spy I want to do some tuning. Right now I'm happy with it  | ||
| Bads1 |
BudC at Hals has this setup, and doesn't have detonation problems Bud also uses this bike as track day bike and is probably running other gas I would think. Wes Orloff which is a credible Buell racer runs this set up in his drag bike. He suggest that this set up not be ran on pump gas. I'm just going off of very good person's knowledge in the field of these air cooled engines. He told me not do it unless I wanted to use race gas. | ||
| Phelan |
The reason you can run high compression in the Suzuki or Volkswagon is because they have 4-valve heads, which allows the spark plug to be located in the center of the combustion chamber, so you don't have to run any spark advance. The spark advance required in 2-valve heads that have the spark plug on the side is where detonation at higher CRs becomes an issue. If I understand correctly, the 2-valve design creates hotspots since the flame front is not evenly distributed, and, with improper timing and octane gas, will destroy pistons at higher compression ratios. | ||
| 1324 |
That is false information ^^^. The VW aircooled heads you speak of are 2V. VW didn't use a 4V head until the late 80's in select models. The spark plugs are off center. VW  The Katanas were all 4V (that I know of). It is not as simple as spark plug placement when running high compression. Aside from fine tuning fueling and timing, combustion chamber design (heads, squish pads, piston domes, etc) plays a very large role. There are multitudes of large displacement pushrod V8's running VERY high compression. Guess where their spark plugs are. | ||
| Froggy |
Yep the 7L pushrod Z06 Corvette engine runs 11:1 compression. That is the highest compression gas engine GM has off the top of my head.  | ||
| Greg_e |
I wish VW heads were 4 valves, that would make a sweet powerhouse. One of these days I'll have the money for another air cooled VW for a project car... Looks like the above heads are in the middle of a port and polish along with combustion chamber mods and probably just after a bigger valve upgrade. That chevy head has some tight clearance between the valves, do they run with much exhaust/intake overlap? | ||
| Greg_e |
As long as we are going off on tangents... How do we raise the ratio on an XB9? Is the only way to machine the heads and cylinders or does someone offer a different set of pistons that could be swapped in? If I ever build an XB9R race bike I would want a little higher ratio. | ||
| Jraice |
All dyno's are different but for a custom map/micron and 9 pistons that HP seems low. Thats the same as my stock XB12Ss with just a drummer... And you would laugh at the AF value graph, its like a curving snake up and down inbetween 13 and 17. | ||
| Jraice |
Greg... Don't know what class of racing you would be trying to fit into (liter bike twins?) but the best thing to do, however probably not the cheapest, would be to pick up a new set of pistons that will give higher compression, and pick one that is slightly oversized. Then there are shops you can send the piston to along with your heads and they will bore it out to fit, giving you a perfect super low tolerance fit. A big bore kit or just new pistons will be decent tolerances, around stock, but for real power you need someone to bore the cylinders to the exact spec of the piston. This is how my dad plans to big bore his 96 inch Hog motor to 103, and if I ever get the itch to bore the Buell up a little bit this is what I would do as well. | ||
| Fast1075 |
There is no way to compare the bathtub 2 valve Buell heads to any of the 4 valve motors...the differences in shrouding, quench, volumetric efficiency and thermal efficiency are vastly different. The main reason the (for example) Suzuki engines can run such high C.R. is the combustion chamber shape and quench design..due to the hallow included angles, the pistons need no dome...the combustion chambers have such good flame propogation they don't need a lot of ignition lead...and are far more resisitant to detonation. The Corvette head that Froggy posted has the best looking chamber for a two valve production head automobile head that I have seen...very little shrouding and excellent quench profile. |
