Oddball cams in a 748/853 - Ducati.ms - The Ultimate Ducati Forum
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post #1 of 26 (permalink) Old Jan 11th, 2017, 11:07 am Thread Starter
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Oddball cams in a 748/853

Hi guys. I recently picked up a 748 in boxes that someone had given up on a long time ago as a project for the year.

Previous owner had spent a good chunk of cash on some nice parts that I'm still going through/working out.
I found pistal 853 pistons new in boxes along with some 94mm 916 barrels.

I have the bottom end of the motor all buttoned up now looking great so am moving onto reassembling the heads. This is where it gets a bit strange.
I have a set of T1 SPS intake cams and a set of OF 748R exhaust cams.

The heads look like bone stock 748 heads with 29/33 valves. Doesn't look like either have had any porting work and the combustion chambers look totally standard. Question is will I be able to run this oddball cam setup without having to have any major work done on the heads with decent results?
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post #2 of 26 (permalink) Old Jan 11th, 2017, 1:42 pm
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We all know the T1 SPS cams work great on both sides. The 748R exhaust is higher lift than the T1, but not as nearly as extreme as the 748R intake. Duration is also 20 degrees longer than the T1 exhaust, but substantially shorter than some other desmoquattro options. I am not a tuner and can't give you absolutes, but I think with the right timing these should work quite well. Not sure how the significantly smaller 748 valves (compared to 996) will affect flow, but somebody will be able to advise you on that, as well as timing.

'01 996R, 851 Adamo/Leoni racebike, '97 900 SS CR, '91 ZX-7R K1 homologation, '93 CBR 900 RR, '89 NSR250 MC18r5k, '01 Derbi GPR50/75,
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post #3 of 26 (permalink) Old Jan 12th, 2017, 12:22 pm Thread Starter
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Thanks for chiming in mate. Nice to know it may work out to be a nice combo. Guess there is only one way for sure to find out!
Luckily the bike was cheap enough that a little breathing on the heads could be on the cards if it would benefit hugely.

Just cant find any info of anyone ever running this cam combo which makes me a little nervous.
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post #4 of 26 (permalink) Old Jan 12th, 2017, 12:49 pm
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It probably isn't worth all the hassle and money to upgrade to 30/34 valves. I suspect if you get good cam timing recommendations and set those properly it will all work quite well for a street bike.

'01 996R, 851 Adamo/Leoni racebike, '97 900 SS CR, '91 ZX-7R K1 homologation, '93 CBR 900 RR, '89 NSR250 MC18r5k, '01 Derbi GPR50/75,
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post #5 of 26 (permalink) Old Jan 12th, 2017, 1:31 pm Thread Starter
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Yeah we will see. Now I could just do with someone with a little more knowledge than me to suggest some base cam timing figures I can start with.
Going to try get the squish close to 1mm if I can and maybe clay the valve pockets in the pistons just to make sure I'm not going to run into grief with the extra lift, that is if I ever finish the horrible task of getting shimmed up from scratch.
I actually priced up some offset woodruff keys at a dealer the other day and JESUS H CHRIST!! their about a million% more expensive than the non stepped ones. 19 a key to be exact.
Would work out a lot cheaper to get some slotted pulleys.
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post #6 of 26 (permalink) Old Jan 12th, 2017, 3:26 pm
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Be sure to check alignment of the lobes on the 748r cams are not going to be in the wrong spots. Lobe spacing is different on those IIRC. That said I think I have a customer running 748r cams just fine.

If you find the piston pockets are not deep enough then consider modifying (thinning) the intake cams to use them as exhaust cams. They are close to sps spec so they would match your intakes just fine. I have done this a number of times and have a high mile 996 running them for at least 20,000 miles with no added wear to the rockers.

Yes offset keys are pricey but what are the options? You could pick up 4 oem adjustables from the 620,800 motors but unless you are planning on dyno time and playing with different cam timing there is little to no benefit and they are heavy.
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post #7 of 26 (permalink) Old Jan 12th, 2017, 3:48 pm Thread Starter
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Already checked on the lobe spacing on both pairs of cams. They seem to sit just fine, everything looks like its in the right place. Have both the intakes shimmed up now. Gotta love those half rings!!Its an amazingly tedious job doing the closers when the heads are bare and you've no idea what size shim to start with. At least all the rockers are good so a bonus there.

Don't have any standard cams for this one mate, only these two pairs that came with the bike in the boxes of head bits.
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post #8 of 26 (permalink) Old Jan 12th, 2017, 4:11 pm
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it's only the 748r inlet that have different spacing.

you won't find anyone using this combo due to cost of them, (jocke may have) it's what stops anyone changing cams. if you're pissing and moaning about a 19 quid offset key you'd fit well into the demographic of those who won't buy cams due to the cost.

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post #9 of 26 (permalink) Old Jan 12th, 2017, 4:44 pm Thread Starter
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Quote:
Originally Posted by bradblack View Post
if you're pissing and moaning about a 19 quid offset key you'd fit well into the demographic of those who won't buy cams due to the cost.
Thank for the input there mate. Just thought it may be more advantageous getting some used slotted pulleys to adjust and dial these in. Nothing wrong with offset keys but hey a bit saved here and there all helps. Yes I am tight just ask the wife
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post #10 of 26 (permalink) Old Jan 12th, 2017, 6:06 pm
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Lol..........

Brad have you seen this combination used R exhaust and sps intakes? I assume it is due to the inlet spacing they did not use the R intakes but maybe it is what they found. If It does not work oen inlets to turn into sps exhausts are cheap and plentiful used.

Some times it is not the cost of the offset keys it is the problem of finding them. Brook Henry must still have some adjustable aluminum ones available but then they will be much more money and an unknown benefit?
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