748R Airbox

[CrimsonCloak]

Has anyone built or adapted something similar to the 748R airbox to a standard desmoquattro? I've seen some folks adapting the shower system to non-r, but would there be any benefit to having the larger airbox capacity? While we're at it, is there any benefit to grafting a shower system from a 748R or 749/999 on there?

Just about to be snowy for a loooong time, and I need a good project for the winter. Preferably something that takes quite a bit of time, and not too much money

[Ben710]

I have a 748R airbox and shower on my 955. The airbox hmmm yeah and no, don´t have any before and after because it was a full rebuild going from 748 to 955. The shower gave more punch up the rev range. Airbox should do the same, but can´t say 100%. The tuner said "it´s all the small things you do".

[TomTom]

Big or not? noone has ever evaluated it as far I know.

Since Ihave a friend in building stuff in cf I had one made as large as possible, down all the way to the engine, fun build, good or not.
Now I'm going to have a bit of use from that since a new motor is going in that needs the extra space.

[CrimsonCloak]

May have to locate some 748R bits. Hey TomTom, is your airbox setup for showers or the standard style throttle bodies?

[DukeDesmo]

Not sure if the 748R airbox will fit, or if it is just just for 'Kyalami' frames?

Anyway you can get a larger airbox from EVR EVR Edo Vigna Racing it's claimed to be double the volume and the bike will breath better with it.

I have one on my 916 and it works very well.

I don't know about shower injectors but wouldn't think they'd be worth much without extensive tuning?

Here's a pic of EVR airbox next to a stock airbox;

[CrimsonCloak]

Yeah I forget about the R frame crossbrace...would make it a bit more interesting. That airbox is always tempting, but they're pretty pricey. Plus I'd want one with the bulge in the front where the radiator surge tank sits. Maybe I can fashion one out of fiberglass and paint it black?

I had assumed tuning would be involved, but then anything worth doing requires some tuning.

I don't even really need to be messing with it, but I'm running out of motor mods that don't require a swiss bank account. I have cams (degreed to spec), big valves, porting, high comp 853 pistals, squish is set, balanced crank, aluminum pulleys and tensioners, bored TB and inlets, matched injectors, etc...

I just like fiddling with it I guess.

[DukeDesmo]

Originally Posted by CrimsonCloak

Plus I'd want one with the bulge in the front where the radiator surge tank sits.

I originally bought a 996RS airbox with the 'bulge' but; it was still smaller than the EVR and to fit it required not only removing the coolant tank and ignition switch/steering lock but also cutting off the frame support that holds the ignition switch/lock to the bike, plus junking the oil breather box and fitting the underseat breather, fitting larger air intakes, larger TBs, a new fuel tank plus the corsa header tank - which won't fit if you have a temp gauge etc - it would get very costly, very quickly so I ebayed the airbox and bought the EVR, which worked out cheaper in the long run...

[CrimsonCloak]

Yeah the RS tank is kind of a deal breaker, I thought for sure there was an earlier style unit that looked like a stock airbox, but with a bulge. Hrmm, maybe I should just ebay some more stuff and go EVR.

[TomTom]

Originally Posted by CrimsonCloak

Yeah the RS tank is kind of a deal breaker, I thought for sure there was an earlier style unit that looked like a stock airbox, but with a bulge. Hrmm, maybe I should just ebay some more stuff and go EVR.

Ok, here goes nothing

You are thinking of the 916 RS box, it had the bulge but was above the tb's.
I did a ton of testing with stacks and stuff on the 996 and noting at all makes a big improvement when it goes to space to things, for example box wall, sorry to say.

The only thing that acctually worked was wide stacks with the length to tune to 9,5k around 2-3 hp improvement, basically moved the ve around but the top end ve was so much better I figured it payed off, at the track at least, which is the place I use it.
No stacks at all gave the same topend, so I'd try that before doing anything.(based upon my tuned version yadayada)

As I wrote in another thread I took them to an injector specialist and had the spray pattern figured out, and it was NO spray at all, just a squirt even at 6 bar. Same goes for 999 shower injectors which was tested also at the same time, NO spray at all.

And no the injectors on the 996 was the original item, I have a 748r rack laying in garage but I never got to it, testing this rack with a good spraying injector(obviously not stock 748r injector as it is identical to 999) would have been nice, but options are limited within a reasonable budget.

I just got a set of 1198 injectors to try, hopefully they have some sort of spray.

[chris steedman]

I have tested 2 identical tuned (by me) 916 bikes . Both are the same spec but one has a large airbox and i can confirm there is nothing worth while in it . They look great but your wasting your money as a power bolt on.

However as with a 916 or 996 the power band is all over by 9.500rpm . On a bike built with a powerband of max power being produced at 11k-11.500 rpm we will see gains from a larger box

As with the much shorter and wider shower injection system the gains will be higher up the rev range from the different tuning frequencys the short intake stacks provide us with . Again fitting these to sometihing like a 916 bp or 996sps with its 9500 rpm powerband it will be likely to loose power all over the range. To make use of them the engine will need headflow and cams that can move the powerband into the tuning range of the shorter shower injection system. This means a cam combo with 748r or G exhaust cam.

[CrimsonCloak]

I would think that even my relatively shorter stroked big bore 748 would be done making power by 10~10.5k. Maybe when Doug tunes it this winter I will find out if that is true. I do recall Doug saying he fitted a large box to a 996 with no real improvement either. So far we've seen two experienced tuners with a methodical scientific approach come up with little improvement, I'd say that makes it an open and shut case. It looks like if you don't run RS rpms, you don't want an RS airbox...

[CrimsonCloak]

Do you think shower injectors would show a gain if we spaced out the velocity stacks to retune them for a slightly lower rpm range?

[DukeDesmo]

Originally Posted by chris steedman

I have tested 2 identical tuned (by me) 916 bikes . Both are the same spec but one has a large airbox and i can confirm there is nothing worth while in it . They look great but your wasting your money as a power bolt on.

Hi Chris, as you willl recall mine was the big airbox bike but, IIRC the other bike had a complete bottom end rebuild/blueprint, whereas mine was just heads/squish/valve timing, all things being equal (as were the power outputs) it would seem to me that the big airbox gave as much as the blueprint in terms of power? - if bottom end blueprint gives any increase?

Either way the bigger airbox gives a much better 'growl' particularly when shifting at 9k+.

[chris steedman]

[quote=DukeDesmo;582031]Hi Chris, as you willl recall mine was the big airbox bike but, IIRC the other bike had a complete bottom end rebuild/blueprint, whereas mine was just heads/squish/valve timing, all things being equal (as were the power outputs) it would seem to me that the big airbox gave as much as the blueprint in terms of power? - if bottom end blueprint gives any increase?

The bottom end blueprint doesnt give a sausuage up to around 9500 anyway. It does guarentee a smoother engine from the finely balanced crank and flywheel assembly and a more positive shift from the G box. Tom Tom also built one - top end only with the same powernumbers and laying all three graphs on top of each other in WinPep all show the same curves exept yours with a +1.5 hp gain at 2 specific rpm points from memory . Maybe ill double check that and put them up. its been a while since i looked through them

[DukeDesmo]

Originally Posted by chris steedman

The bottom end blueprint doesnt give a sausuage up to around 9500 anyway. It does guarentee a smoother engine from the finely balanced crank and flywheel assembly and a more positive shift from the G box. Tom Tom also built one - top end only with the same powernumbers and laying all three graphs on top of each other in WinPep all show the same curves exept yours with a +1.5 hp gain at 2 specific rpm points from memory . Maybe ill double check that and put them up. its been a while since i looked through them

Would be interesting to see them all on top of each other if you can post it.

[TomTom]

Slightly off topic, I did run a 998 in the dyno that was balanced by chris and it was SMOOTH, well done c.

I have had the sps to try things with and the conclusion is that the stock parts are very good, if someone asked for recommendations it would be:
modified heads by someone who actually understands what it's about, good pistons (construction, fitment, comp), camtiming and a serious tune. No fancy bits required.

A perfectly good example is the 916 that chris did the heads for and I took care of cam timing and tuning, a few notes here 916 CJS-racing headwork, refining stock parts. Compared to a stock 916 with slipons its a bit better http://www.hypertrick.net/reports/gr...S_vs_Stock.jpg
Both bikes fully warm and heat sinked, so no tempering with the graphs.

[CrimsonCloak]

No question, a good tune is the most important to performance, followed by changing the various tolerances to spec. After that I would say massaging the stock items or moving them to an improved spec. And then in last place is putting tons of expensive (and impressive looking) parts into the bike, carefully selecting them to make sure they suit your goals.

[chris steedman]

Originally Posted by DukeDesmo

Would be interesting to see them all on top of each other if you can post it.

Duke desmo e mail me and ill send you the overlapped charts to post

[DukeDesmo]

916 dyno runs overlapped;

[Ben710]

Blue and green, 1 pixel wide, you guys are clever... lol. I can´t see shit on the diagram when it comes to which is which.

But(!): you need more POWER!