Ducati Monster Forum

Recently needed to adjust the ignition again on a 944 hi comp 1992 SL/SS.

 Some years go I had set an ignition map on the Ignitech for this bike after a full rebuild by a mate and mentor of mine. The bike has FCR39s on long manifolds, it also had stock cams advanced/dialled in by Brad Black and someone in the past skimmed the heads giving a very high comp with the JE 94mm pistons. The map worked well and the bike ran very strong pulling 3rd gear wheelies. It was a hard starter with very high cranking cylinder pressure and we rebuilt the starter and replaced the sprag bearing. With advanced stock cams, skimmed heads and 94mm JEs it was a beast to turn over. It ran premium fuel of course.
We decided it had such high comp that it could take more cam and I got some 900ie cams off speeddog and a local bloke fitted them to stock specs. I added an enlarged airbox. We hoped the hotter cams would bleed off some cranking compression and give the side effect of starting easier and give some more top end too. It worked well and the bike turned over much easier, because the cranking compression was reduced. There was also a stronger midrange surge which felt good when overtaking.
Some upper mid range pinging appeared so I knocked off a degree or two from 5000 rpm. This raises the issue of cranking compression Vs potential compression at higher rpm. Someone suggested that the enlarged airbox also contributed to this as it increased the sub filter airbox volume and working with the hotter cams added to the potential compression at higher revs.
I have only dealt with half a dozen or so hi comp desmodue motors and would invite comment and discussion from those who know these motors well.

Was hoping for an around the campfire with a few drinks type discussion. Its winter here and shed time for projects. Theres not many people available to discuss this stuff.

Well, it'll be up to 100 degF here soon, so I'll pass on the campfire.  [laugh]

I think the main change that helped the cranking would be later intake closing.

More later......

100 :D
I knew the timing numbers would help starting. The thing had so much comp we wouldn't lose anything down low with hotter cams either, that and it is a very light bike. The owner was questioning how a "hotter" cam would lower cranking compression and got a second opinion which of course backed me up on the cam's numbers with later intake closing.

But the comp went up elsewhere in the rev range due to the increase in effective compression.

Another reason for variable cam timing.  My bike with 10.1:1 compression ratio and stock cams is about all the battery can handle. 

I'm of the impression the starter/starter circuit is barely up to the task of a "normal" compression. The "blower" bike single was a hard starter with a lightened flywheel, but when I switched to a "stock" weight flywheel it started much easier (it ate the sprag, so needed apart).

Not a big surprise there, as the starting equipment is not far beyond that found on a Pantah.
It has been upgraded a few times, there are different gearsets.
Those cams are very small overlap and the intake closes early, so they're going to make high cranking pressure.
Brad played with cam timing on a 1000SS and found that the OEM spec was good.

Quite a few of his cam fiddling sessions seem to find that the intake closing at 65 deg ABDC is a pretty good setting.

I fitted some adjustable pullies to my 750 a while back, and advanced my cams from ~118 intake centerline to 114 (which puts closing at 65 deg ABDC).
It felt like it gained a little power, and also ran a little smoother at low rpm donking around town.

I think it builds low rpm cylinder pressure giving a bit more pep through to the mid range at least. On a very hi comp motor its too much of a good thing. Must help a stock motor substantially.

Does the DVT retard the cams at start up, advance them through the low and midrange rpms and retard them again for top end rpm?

Hopefully, that's not Celsius.... although here in Texas it's feeling like 100C.   [thumbsdown]

As a lower cost alternative to the longer cams, retarding the ones it had would help the starting, as the later inlet closing is the big factor.
May have been about a wash as far as power.

AFAIK, the Ducati DVT is controlled hydraulically by a servo-valve, powered by oil pressure.
I don't recall seeing any detailed explanation of the strategy.

Kickstart mod!

wasn't there a bike that had a valve on the cylinders that stayed open until the starter revs got up to a certain speed?

http://www.dansmc.com/comp_release2.htm (http://www.dansmc.com/comp_release2.htm)

also
http://shop.pitsterpro.com/frdez-d-compressionsystem.aspx (http://shop.pitsterpro.com/frdez-d-compressionsystem.aspx)
(http://shop.pitsterpro.com/images/products/detail/FRDUniversalDecomp4inwatermark.jpg)

For some reason, this just showed up in my unread posts notice . . .

Now, if you take care of food and drinks, I can join you sitting by the campfire to discuss these issues . . .

I think nearly all of the new Harleys have 'em.

XT660 Grizzly ATV has one.

My XT600 has one that works off of a cam system on the kickstart.
Had no idea how effective it was until the cable broke.

240cc?  whoa.  so i can use it on my chainsaw... but not my bike...

Interesting discussion as I've just installed 12:1 forged pistons in my 748s...  But, I'm at 5000+ feet elevation, so we have less air up here.

forged?  couldn't get real ones eh?  that's the breaks..

cracking yourself up today...eh counselor? ;D

Interesting to see how it runs up there. You staying with stock cams and intake?


The very high cranking and mechanical compression on that 944 was corrected with a cam change adjusting corrected compression and increasing effective compression around peak torque output (which moved higher up the rev range).
It got me thinking about the relationship between those components including porting and airbox/intake mods. It raises the question of what kind of compression people are talking about.
 I suspected the enlarged airbox may have contributed to the increase in effective compression in conjunction with the 900ie cams. Would like to see this motor ported. Gotta get the bike back on the dyno.



I remember decompression levers btw. ;D

He's on a roll. ;D

Those 12:1's will get you down to the top of Mulholland or thereabouts...

Gotta admit, I enjoyed that.

Craslo, got any info on that DVT?

you mean Ducati Variable Timing? It does have a "decompression" setting built into it . . . Different to 1199/899/959 Panigale . . .

Yes, maybe some factory stuff.

DVT has a "built in" code that depresses one exhaust valve enough to release preasure so that the engine starts easier while the Panigale, has "a lever" that pushes exhaust valve open to release preasure . . .

Sadly, now, all my privileges have been eliminated and no longer have access to tech writings [official]

Probably a dumb question. :D

We lost our "inside man", The Mole! ;)

ah, that's what it was.  i knew it was something like that

Stock cams, valves & intake system.  Being of smaller displacement should help w/starting amperage draw.  Should have all the bits to complete it by this weekend so I'll keep everyone posted.

Interesting side note for the 4V folks:  Ferracci 12:1 forged 748 pistons will close the gap of the NGK DCPR9E plugs.  So, I had to swap over to the NGK R2525-9's.

Had the same issue with an 944 Vee Two hi comp Pistal kit and the Denso iridium equivalent of NGK DPR8EIX-9.
Sure enough holding the plugs side by side showed about 2mm difference in the projected reach.

The Pistal 853 pistons tolerate the DCP plug.

FBF use Wiseco ay?

I think they've also used JE.

I think that's the norm for FBF.

Regarding the crowns of the pistons....

I'm only working from a really small sample size, but I've found that the Pistal and Mahle products are better than the JE and Wiseco product.

Actually, the rest of the parts of those pistons are nicer as well.  :P

In what way,  machining, finish or shape?

These are JE's and they've been discontinued for a while now.  FBF recommended me to use the Champion RA59GC plug, but I had already bought the R2525-9's.  I should be able to fire it off tonight and see how it sounds/runs.

Wonder what the dyno will say. Sigma site says the best bike Ducati didnt make or something like that.

Recently dealt with FBF 750 pistons that had knife edge sharp valve reliefs I had to smooth. Protrusion hot spots. Beautifully polished however.

Pretty much everything.

This is as close to an apples-to-apples as I can get:

(https://c7.staticflickr.com/8/7658/27583566030_fe3614f152_c.jpg) (https://flic.kr/p/J2sZbE)

(https://c4.staticflickr.com/8/7327/27785391091_35c70ce339_c.jpg) (https://flic.kr/p/JkioK6)

A FBF 88mm hi-comp, pretty sure it's a Wiseco on the left, vs. a Mahle 91mm on the right.
Mahle is 3mm larger, yet only 12g heavier with the pin.
FBF is naked aluminum, but Mahle piston is coated everywhere, and has some sort of other coating on the skirt.
FBF is pretty chunky, while the Mahle is pocketed above and outboard of the pin, and the pin bosses are contoured.
Mahle has a shorter pin, with a tapered bore.
Mahle crown and dome fit the combustion chamber better, so end up with a more efficient squish.

Neither piston fits the chamber all that well, which annoys me greatly.
The cost of doing it properly is minimal.
As an example, the squish area of the FBF is totally flat.
The mating chamber area is domed slightly.
So the squish is limited by the very edge of the piston, and gets wider as you go toward centerline.
So it's squandering compression.
Not a deal-breaker, but fixing it is troublesome.

It's not a totally fair comparison, as the Mahle are likely 2X the price of the FBF.
And in a street motor application, likely not much benefit.

It's just annoying that they both could have done the crown properly for maybe $10 more in machining and design per piston.
And it'll cost far more than 10X that to fix it even halfway.

Sigma is likely referring to the 853 kit.  Although I wanted an 853, due to budgeting reasons, I had to settle for a 12:1 748.

I figure at the elevation I'm at (5000 feet), the only thing the 12:1's will net me is a return to sea-level horsepower & torque values.  :-\

Meh...  It'll do ok.  Better than it was.  (that comment much mirrors Speeddog's post above...)

I thought I had some pics of the 853 Pistals I put inn a customer's 748.

Can't find 'em at the moment.

But they're absolute hard-core bike porn.  [drool]

I can only say that the 853 motor I got from Dragsterhund with Pistals and 748R cams makes within a couple of horses and a couple of pounds of a typical 996 BiP that's stock on the vet's dyno

It just spins up faster and farther.

I do kind of miss the 996 though. It made the kind of power that felt like it was going to pull your arms off.

Yep thats right. I remember now.
You going to run a dual map switch, sea level and mountain maps?

I wonder which one laps quicker.

Whichever one has the faster rider. ;)

That FBF piston a JE?
Off the shelf pistons that fit bang for buck rather than done for the specific bike ay? So a safety margin on the squish rather than max efficiency . I've been using JEs for cost and "drop in " fit. I note the domed Vs plateau crowns I've seen. I remember seeing Pistals with a "nipple" crown.

;D

Pretty sure the FBF's are Wiseco.

I've got some slightly tatty 900 JE's, and they've got the JE logo under the crown.

Yeah thats right. I forgot that. Its the Pistals with the nipple crown ay?

Haven't had my hands on a 2V Pistal, and don't remember from pics.

(http://motowheels.com/images/M85757092.jpg)

No need.  I never get out of the mountains these days...

That looks like a good thing to do.

Update:  12:1 pistons installed w/the aforementioned R2525-9 plugs.  Wow.  These upgraded the non-existent mid-range to somewhat existent!  Bike has a noticeably more punchy exhaust sound.

I also filled it up with the Engine-Ice brand coolant.  Bike has yet to crest 180'F and that's high-compression and in New Mexico...

Feelin' good about all this!  [thumbsup]

I might try that coolant in the Gixxer.

Does the 748 have a custom map for the elevation?

I run Kool_Aide from Maxima. I don't even have a fan and when running in the heat on the track I never see over 180. It will heat up if sitting in the hot pit idling.

Wow, commuting in warm (~90) temps and slowly splitting traffic, I've been seeing 200-215...

I'm not sure if the additional airflow from speed is more effective at cooling than running 11 K is at heating. I suspect it is.

No, just running an FBF "Stage 1" chip for the 748.  Got a high flow air filter and some 50mm carbon cans (which I'd like to trade for some 45's eventually...)