851 needs help!

Jammin851

During a track day I broke a belt on my '91 851 Strada. Damage was minimal (bent intake valves on the horizontal cylinder). Easily fixed with a new set of valves, but the exhaust valves are getting a little burnt and all the valves should be replaced so I'd like to do something else. My Aprilia Futura has so much more power than my 851 and I'd like to sharpen the performance of my favorite ride. Ebay has many engines for auction and I could pick up a nice Testastretta for under $2K so that's the direction I'd like to go. With the engine swap, I've seen a few ideas for the engine management mainly using the 998 ECU grafted into the venerable 851's old harness. However, I'd like to run the stock throttle bodies and the stock ECU if it can supply the motor correctly. Any ideas or roadblocks in my plan?
Dirk

griff851

Hi Dirk, I can't help you much with the grafting of engines etc, but I do have a word of caution which may be stating the obvious,but. You need to be able to stop as well as go.
I myself had the same problem with my 1990 851.Vapid, is a way to describe it. I was always wondering where the zoom was. 12 years later, bit by bit, I have found most of it. The addition of the 748 heads will finish it off. Then I'll turn it into an 888!
The Testastretta, is a beautiful smooth engine, of that, there is no doubt. One might even say they are very "Fluid" compared to the rawness of a desmoquattro. Unfortunately, part of it I believe is the throttle bodies and its ecu, ie its advanced engine management system. And I'm not exactly sure, but I think the cases are a bit wide for the 851/888 frames.
I suggest a quick look (Ha ha) at Moto one diaries and FIM FAQ's. Very very informative.

http://www.moto-one.com.au/performance/
http://www.fuelinmoto.com.au/

Hope this is of some help.

Jammin851

Thanks, I'm thinking of other options which I found on these pages including a 996 conversion. My goal isn't necessarily to have the baddest fastest 851, I just don't want it to be embarrassed by my Futura.
Dirk

Mr.R

Hi Dirk,
The ST4S motor is fairly easy to transplant, if you also use the wiring loom and ecu from the ST4S, whack in some 996sps cams and a suitable chip....FIM UM222??
It should run OK with your 851 injection set up, but you may need to sustitute the Red injectors if you have them for Greens (Higher flow/bigger holes), you'd get a usefull power hike.
It should make over 120rwbhp.
You might want to upgrade your brakes though!

Steve

griff851

Just to add on to Steve's comments. The ST4s don't have the Testastretta eng. Its a 996 Desmoquattro. They began with the 998's an continued after that in 749's 999's 1098's and 848's Ain't nought wrong with a 996 eng. They're a wee powerful beasty for sure.

marvin

As stated above the St4S engine is the easiest swap, has been done numerous times. I am putting a S4RS engine in my 92' 851 (testa engine). check out the "projects" section of this forum for a few pics (not very far along yet).
The biggest problem with the testa engine is the throttle body spacing being different. You could use your TB's but would have to either mount them individually and actuate with a dual cable set-up, or construct bracing between the TB's.

P.S. Other issues with the testa:
Have to fabricate an airbox, fabricate or modify exhaust, possibly clearance issues with the deep sump/lower fairings.

Jammin851

Would you say that the 996 st4 motor would be the easier choice?
Dirk

marvin

Jammin851 wroteWould you say that the 996 st4 motor would be the easier choice? Dirk

Yes! Although a ST4 is a 916 (will also work). The 996 is the ST4S.
If you just want to pep your engine up a bit find some 888 or 916 cylinders, 888 pistons and 748 heads (unshrouded) and it will be quite a bit faster. I used 916 cylinders, bored and replated by Millennium to 95mm, Pistal pistons and had a high compression 907cc engine that was really quite nice. I hope I'm as happy with the Testa engine, may miss the rawness even though it has quite a bit more power. I should probably have put my St4S engine in it and had both power and rawness!!😏

Jammin851

I'm now definitely in the market for a 996 motor from the st4s. Should I repair my old engine and keep it for originality?