TS MAX REVS ?

[MD]

I am interested in hearing from anyone using a standard spec twin spark  8valve engine in a racing application as to what peak revs the engine will tolerate reliably.

Cheers.

[Neil Choi]

MD

My recollection and record keeping might not be so accurate but for what it is worth.

I had a standard TS in a pretend race car which I ran reasonably well for a few years.  Short story is:  ran for awhile at a good number of sprints, consistently rev-ed to 6000-6500 rpm comfortably, bounced off limiter (is there one?, forgotten).  Then at a Winton round, went really aggressive, did over rev-ed to 7000-7500 rpm a few times, then the last time it didn't like it too much, engine went bang and stopped.  Head off, hole in piston, cracked liner, broken valves in that particular cylinder, destroyed head, so either spring and/or valve or a combination of things went bad.  I thought it was an electrical problem, initially!!!! (only kidding).

Not sure if this is what you wanted know or help.

Neil

[hammer]

MD,

As you know, I know stuff all about engine building and have only been on the track for 5 seasons, but here's what I learnt about twinnies:

I ran a 75 Twinspark on the track for two years, with the engine and gearbox in bog stock form (stock intake, headers, ecu etc). I had it dyno'd at 117hp at the wheels, with peak power at 5800 rpm and peak torque somewhere around the 4/4.5k mark. Rev limiter kicked in at 6250. That car weighed 1060kg with the cage in it and the fastest time around the QR sprint circuit was 64.89.

There was a further 80-100kg that could have come out of that car, which would have significantly improved the lap times.

If you have a standard twinnie I don't believe you should rev the shit out of it. They have great torque and reasonable power and if you change gears at 6000rpm you'll have a blast, lap in decent times and the engine will last for years.

Great to see you on the weekend (although only briefly).

Cheers,

Brent

[MD]

Thanks Neil & Hammer. Definitely the sort of info I am looking for. As you know, you lose around 1500 rpm per shift. So that you start the next gear close to peak torque which I agree is around 4.5K, a shift point at 6000rpm seems ideal which is what I have with a hard cut at 6250.

Problem arises due to ratios when the revs are too high for say 2nd but road speed is too low for 3rd. Extending the rev range up even though there is no added power up there would help overcome some ratio issues (perhaps) and so I was wondering how far up the range I should take the shift point (occasionally) on standard valve springs before the head throws in the towel.

I think  I will play it relatively safe and limit shifting to 6500, what do you think?

[hammer]

MD,

Gear selection won't be an issue at Lakeside where you only use 3/4/5 anyway.

At QR (sprint circuit) some transaxle pilots take snake gully, the crossover and turn 6 in second and others take it in 3rd. With a standard 4.1 final drive 2nd is preferable. I used to find the twinnie bogged down below peak torque if I used 3rd. You have to give it a good dose of heel toe going from 4th to 2nd into turn 3. You'll also be on the limiter as you exit six, shifting from second to 3rd and probably not making 4th until the start-finish line (at which point you should be doing 140/145 kph).

Not sure how the engine will fare running up to 6500rpm, but I do know you'll have a pretty competitive package even running to 6250, given the cab's light weight, good brakes and rigid structure.

Cheers,

Brent

[MD]

Hi Paul,

No worries about the mixtures cause  I got it mapped out to 8000 rpm so that side is of no concern. I am more concerned about the mechanicals. I am assured that the rods are good for 8800 which amazes me. So what remains
is the valves springs and valve bounce. That's what concerns me most but some one out there may be using OE springs for big revs, I don't know.

Hammer,

You are right in the pocket of what I am talking about. All turns after turn 2 at QR seem preferable to take in 2nd for my 4.1 and `16" rims and 50 aspect ratio tyres. However to stay on the pace and not drop speed, I am doing around 6ooo rpm but the handling can take much more pace but if I stick in 3rd, it's too tall so another 1000 RPM should see some arse hauling through there in 2nd making use of all the handling advantage. Anyhow, that's my humble take on it for now. No doubt will change with more experimentation.

Going to take it to Lakeside on December the 1st and do some more testing and that will give me a chance to compare notes with you regarding the gears you mentioned on that track.

[Duk]

So what remains
is the valves springs and valve bounce. That's what concerns me most but some one out there may be using OE springs for big revs, I don't know.

What about the valves? Aren't they a little bit prone to loosing their heads when revved to the moon or is that just the V6's?

[MD]

OOh that's stretching my experience a tad ! Obviously the valve break up is rpm related but it is also a factor of other things such as head mass,spring return rate and stem size to name some. That's one of the benefits of 4 valves per cylinder, the valves being smaller mass to start with. However when you get valve bounce, you get oscillations and resonances that the cam cannot control and disaster follows.

If you get a chance, track down a You tube doco on valve and spring behaviour at high revs. You will find it amazing.The springs not only compress and decompress but they carry on like a ballerina doing swan lake !

When race engines are built to high rev specs, each spring should be tested through the rpm range it is to work in together with the exact cam profile intend to be used. Even though skilled engine builders know from experience what spring rates to install for a given application, there is no guarantee that the nominated spring rates that are supplied will be the exact (or close tolerance) cousin of its mates . After testing a well known brand batch, I have seen 45% of the spring set returned to supplier for failing to be within spec.

So springs ain't just springs..

Being aware of these problems, Ducati doesn't use any :http://www.youtube.com/watch?v=ocfIYUc5bpU

[Duk]

http://www.youtube.com/watch?v=_REQ1PUM0rY&feature=related

[MD]

Stawun..

[vin sharp]

Yes to everything said so far, but take particular note of Neils reply. This tells you pretty much how far you can venture very occassionally.
Risk of valve bounce/float is the main problem where you can bend a valve slightly and then it eventually fatigues in the neck and breaks from constantly being flexed when it gets pulled back onto the seat....this usually happens by surprise some time later when you're not over-revving it. The other common thing with momentary valve bounce/float is that a tappet shim can escape from between the stem and bucket and invariably gets smashed up and can lead to dropped valve into engine.
Rods should be ok for some time.....however, down here we have seen several long-used track t/sparks break rods 1/3 down from the top, just fatigue, no bearing issues, so I am sceptical about the material. On the other hand I have NEVER seen a 2.0 single plug rod just break and would prefer to use these where possible, but requires special piston.
Cheers,
Vin

[MD]

Thanks Vin. Always great to get factual advice.I have a street engine installed in the Cab which is a used one but in very good condition. I know Alfa engines are tough but I dont want to over stress it simply out of ignorance so thanks all for chimming in.

This is not strickly in keeping with the revs side of the topic but is TS related and I just want to pass on this caution to all TS engine user and builders. It doesn't warrant a topic of its own. See photo.

The hand over sprocket set are not the same as the 116 or the 105 series even though they appear to be. There is no keyway locking the large to the small sprocket. They are simply pressed onto the shaft. In some circumstances, these sprockets can rotate on the shaft and the rest is engine history.

The solution is to use a set from the 116 or the 105 series that has a keyway interlocking the two.

Experience can be a good teacher and can cause a medical condition to the hip pocket nerve..

[Duk]

Ouch!
It really is sad to see engines going backwards in terms of durability.
Obviously producing cars is a business first and reducing production costs gets profits up (or helps to offset increasing expenses), but from the petrol heads perspective, its a little disheartening.
It's not just Alfa Romeo, though. Legendary engines from other makers were replaced with lesser examples.

Excellent info from MD and Vin.

[MD]

I should clarify the circumstance.
It is likely to be when you are using high lift cams and heavier valve springs that requires more strain via the cam chains. Otherwise, it's probably adequate but to be sure, I would still change it.

[vin sharp]

MD, regards using a 105/116 sprocket assy, beware the dimensions are NOT the same as a T/S. From memory (and it's been a while) I think the T/s has closer centre distance an the pairs of chains. 105/116 sprockets need to be pressed apart and a face machined to correct alignment, otherwise the top chain will run back at an angle to the cams.
Cheers,
Vin