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It's known that 12V engines get in troubles with valve train when revving too high. 24V shouldn't have that kind of problems, but guess they got their own limits to? Sure it's somewhere, but where? Can it take 10 000rpm? The 155 DTM cars used chain drive on 24V engine to past 10k limit, but that might also be the timing accuracy issue.

What about the bottom end? How much can it tolerate with good quality performance rods and light weight pistons? How much revs have been taken out from race engines and with what kind of mods? Wikipedia says DTM engines made their highest hp's at 11 900rpm. If that's the hp peak, then the actual revving capablities must have been even higher. It's hard to find what modifications were made to make that possible.

The the breathing, how much these heads flows? Any figures? Also the power curves of race engines would be informative.

Why all these questions? Just because I'd like to build a 24V engine to rev as much as possible. To do that, it would be good to know what are the limits and what have been done. What's needed to rev it 9k?

for sure you'll need stronger rods

Forget the V6ti engine as a model!, it has nothing in common with the normal alfa24v v6. It was a FIAT designed engine, not Alfa, (the alfa 24v physically wasn't up to the job) designed specifically for the job, and revved up to 13,500rpm, at ridiculously high compression and short stroke (12:1 if I remember rightly) and a very narrow power band, you couldn't run it on pump gas by the way either. It has more in common with an F1 engine than the alfa v6.

Kimmo,
Haven't got specifics for you and know that's realy what you need. Some hard data.
Generally I think the issues would revolve around
Short strokes
Light mass for all moving components
Valve springs would be a key issue
Engine life expectancy
Very light crankshaft preferably hollow
Min. 4 valves per cylinder
Tuned induction and exhaust
A defined torque band.

..ah not really helping here. You'd know all this stuff anyhow.

don't forget the 24v has hydraulic tappets (? good word for the hydraulic variety of valve shims?) these will not work past 8000 rpm or so.

I remember the sound of the 155 DTM cars, a pure aural orgasm... I was there once in Germany as a little boy with my father and never forgot the sight of those red Alfa's leading the pack with there howling engines.

i thought the v6TI engine just had gears, not a chain?

I didn't knew that the DTM engine wasn't related to Alfa engines in any level. Thought that the rules were forcing to use some original parts. They may also be gear driven, but not belt driven for sure, I could eat that.

I red some topics about converting hydraulic tappets to solid and don't think it's too difficult. That's good point anyway, tappets are one known limiting thing which need to be dealed way or another.

At the 8k also good rods and light pistons are probably needed. Also the valve springs need to be strong enough to do their job, but what happens next?

well, to be specific, a bit like the ts 155 BTCC engine. Althout the TS engine was based on the alfa TS shell, it infact was completely reworked from FIAT/ALFA/LANCIA parts bin.
(remember, the alfa 155 was a FIAT, not an Alfa, hence the sponsorship stickers)
The same can be said for the V6Ti engine, it was a mix of bits from FIAT/alfa/lancia bins, but it had nothing in common with the original 24v alfa V6, apart from its bank angle. Corsa played with the 24 v6 alfa engine, but for one it didn't have a short enough stroke to go above 8500rpms reliably, the other limiting factor was the valve gear, which was wholy inadequate for the application and limited them to around 350hp and a 400km life span, no where near enough to beat the DTM beamers and Mercs at the time. Infact they managed to get more power out of the TS engine, having run one TS car in the first few rounds of the early DTM season. It was far simpler and probably cheaper in the long run, to design another oversquare dedicated high comp f1 style engine with gear driven cams, dry sump and custom tuned intake set up for the application, rather than having to delete the hydraulic tappeds, and re-hash the alfa V6 heads.

Kimmo, what i have heard from the guys here the belt cant go over 8500rpm reliable. (comes off). All of the race gta production car engines here had solid lifters. i think thats why the big bore conversions came in 3.3 -3.7. Still only rev these to 7000rpm max.

So at 8500rpm some bad things start happen. The belt cannot take it anymore and long stroke comes an issue. That's important information! Thanks Kevin and mjr.

What happens to belt, is it just jumping off, losing timing teeth by teeth or does it fail mechanically due to too high loading and speed? Just thinking if there's any cure for the problem. I guess racers have already though this over, but still.. Maybe kevlar reinforced belt would help some, or extra support rollers to problem areas? Or maybe two separated belts for both banks? Converting to chain drive or gears would be long route too.

I have some pics on my PC of a heavily modified timing belt setup. The engine has a one double width belt driving two toothed idler pulleys. From each of these pulleys a single width belt (shorter) drives each cylinder bank. Very neat looking and pretty much bulletproof. Unfortunately i'm stuck using this laptop for the next few days but once the pc is fixed i'll try and upload the pics or post a link to the website.

John.

The SuperTouring (ST) engine in the 155 BTCC was not an Alfa unit, it was in fact the Iron block Fiat engine used in the 155Q4. Head was reverse-flow (i.e totally redesigned) and the whole block was tilted backwards a lot. The internals was nowhere near stock.

Long stroke of the 3.2 crank? Returning to the just mentioned BTCC engine which had a Limit of 8500rpm (By rules) IIRC, it had a stroke of 90mm. The V6 has what, 78mm?
Surely there is some other issue than piston acceleration. If the belt snaps I'd look through the different parts for torsional vibrations, maybe the cams have a torsional mode around 8500? Or maybe the crank, does it have a harmonic balnacer? Is it rebalanced with the new rods and pistons in mind? Lightened flywheel? I guess it's originally designed for a big flywheel with a pressure plate and a clutch plate with a sprung center.
Can be a million things but I can't imagine the belt being the culprit because the largest load it will se is during cranking (hence Alfa original de-tensioner).

Just reinforcing the belt sounds like a band aid and not a solution

mats; what is cranking?

It means turning the crank, like during starting.

Also, compare the 3.0 24v motor to a Suzuki TL1000R or Ducati 996 motorbike engine.
Similar bore & stroke (98x66 - not quite the same). The big one is rod length - Alfas are short - you need more deck height.
Stock TL-R is good for 135hp per litre at 8500 rpm with a 9500-10000 cut out.
With the right pistons, rods, porting, intake & exhaust etc there is nothing stopping the Alfa engine having this kind of output.

Then there was the world superbike level outputs up around 200hp per litre for those big V-twins.
Anyone want to build a 3.0 24v with those numbers - I do.

I'm with Mats on the balance & harmonics - get it right or it will never hold together.

strat24v wrote:I have some pics on my PC of a heavily modified timing belt setup. The engine has a one double width belt driving two toothed idler pulleys. From each of these pulleys a single width belt (shorter) drives each cylinder bank. Very neat looking and pretty much bulletproof. Unfortunately i'm stuck using this laptop for the next few days but once the pc is fixed i'll try and upload the pics or post a link to the website.

John.

Here some nice pics for you; modified timing belt and sliding throttles for instance..





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