ALFAGTV6.COM

[Jim K]

Zamani, let me elaborate some on power production and revs.
Power, rpm, displacement and airflow are all related. It has been found, that maximum power capability can be predicted, when airflow is known, as well as the rpm where this power will be made, with a very good degree of accuracy. This prediction applies to an intended racing engine with optimized parameters like cams, exhaust, CR etc.
Suppose that on a 12v 3liter, with std heads and std runners, we want to use the wildest cams, highest CR and big headers...the max power possible would be about 236hp at 6700rpm. Before you rejoice, consider that the CR used for this will be around 12 and the cams+headers would probably make the beast useless in the low range.
Now, if you somehow had looong intake pipes, it doesn't mean max torque would move lower in the scale, just that the shape of the curve would 'rock' around the max, increasing a bit lower and decreasing higher in the range. The same effect you would have with long/short headers.
Too much head flow, means you move your expected max power higher in the range. I will (again) remind you of the excellent 1990 M3 evo head...178cfm, indicating max power to be around 310hp at 9400rpm, which happen to be almost the exact actual numbers for the particular engines (the best examples of which in the old ETCC made even more power, 350@9500!)
You now start fiddling with our 3liter heads and while power capability may go up, so will rpm! For the 24v, things are worse! Sure it can make power, lots of it, but the revs can go over 9K !! Remember, this is the maximum capability! Lower cams etc will lower power and revs, suit yourself (and your pocket!). Therefore, anyone contemplating V6 racing power must be definitely prepared to buy suitable rods and (I would suggest) pistons.
I hope this helped put things into perspective.
Still, I prefer interviewing Playmates!(....Here we go again!)
Jim K.

[Zamani]

Jim,

Given an engine spec, say the spec you just mentioned for the 12V, what effect will ITBs have on the power curve? I know it will help make idle a little smoother on my car but besides that? Throttle response?

I'm curious, because Honda's F20C (S2000) flows better than the S14 head (a comparison was done by one of the head shop down in Southern California using a super flow machine I believe, and the guy who linked the article is an M3 2.5L owner www.30performance.com ).

Yet, Honda didn't even bother with ITBs on ANY of their high powered little beasts.

So what kind of gains do you expect to get on your current 12V?

In one of my recent emails to Beninca he mentioned that he built a 3.0 12V, 12:1 ross pistons, autronic, ported gtv6 plenum, bigbore headers, with QV cams. Will beat a stock 24V for sure.

[Jim K]

Last things first, sounds like a hell of a motor Beninca built!

When we talk flow, we mean the entire intake tract! While the 12v head alone is pretty good flow-wise, you bolt on the stock runners and you got yourself a dud! ITB's will let the thing breathe throughout the rev range and give you the potential for 270hp@7400rpm with everything else equal. Now this engine version will be much better in low revs with a hot cam, because there is almost no cyl to cyl communication. Using ITB's should not have any disadvantages anywhere in the range. The main drawback for this solution has always been the costs involved (ITB's+ECU+mapping etc). AHM in the UK have an excellent kit, but goes for more than $4K !!
As far as expected power from the one I'm building, since I don't have special rods and pistons, I must limit revs to 6500 for safety. This would give potential for about 245hp with everything working for that rpm (cams,headers,CR). Realistically, with a fast road/rally cam and the CSC headers, I think that 220-230 is on the cards, with very good everyday street manners. It remains to be seen, slowly but surely.
Jim K.

[Micke]

Jim,

what's the part giving in making you stick to 6k5? I mean the piston speed is still rediculous!

As I see it a "single" throttle has one advantage. It doesn't have to be that big as only one cylinder sucks at the time.

How about a rig with one Helmholz resonator fed from a 70 mm TB for each bank of 3 cyls? Might have some disadvantages in the low range yes, but should be a monster at high rpm. Runners, plenums, etc must be optimised of course. Should be pretty cheap to make from TS scrap

[Zamani]

Micke,

Isn't that what schrick did for the VW VR6's inlet manifold? At certain RPMs a certain valve closes or open.. whatever..... but I think what it does is it seperates the flow between one group of 3 cyls and the group of 3. I think it's called the VSR manifold. I suspect the firing order also needs to be taken into account for this to work effectively.

[Micke]

Z,
my suggestion is a simple intake manifold without any fancy flaps. Just two Helmholz resonators.

What you mention is used in (almost) every modern peformance car. Flaps change the effective runner lengths and plenum volumes. This yields a better torque over the entire rpm range.
Making something this fancy is out of my range. For racing it's not really needed as I don't care about <5000 rpm.

[Mats]

Yet, Honda didn't even bother with ITBs on ANY of their high powered little beasts.

Why bother, they have V-Tech, they actually switch between cam profiles, not altering timing. This means that they can use a common plenum at low revs and idle without the problem you get with wild cams i.e. EGR.

Micke, the way I remember it the v6 has pretty short rods right? short rods means higher acceleration forces and if the rods are kinda on the limit at stock redline you will amplify the problem exponentially (as you most likely know). Mean piston speed is worth absolutely nada unless you keep an eye on the stroke/rod-length ratio which in turn will give you the maximum acceleration.
Please don't ask me for a formula.

[Zamani]

Mats,

Damnit it's VTEC. Hehe. BTW you are correct, 3 lobes per cylinder. So BMW only has VVT on the E36 and newer M3s and that's an adjustable cam advance only. I guess it makes practical sense not to have ITBs on VTEC cars for anything but super serious racing.

[Zamani]

For those interested in rod length vs. piston acceleration:

Here's a graph showing some relations:

http://www.e30m3performance.com/tech_ar ... ccel-1.gif

I've been reading his website for a few years now, it's really a good site (despite the fact that he uses a modified S14 2.5 )

OK now back to ITBs.

[Jim K]

Good morning guys (last morning before the Ring!! )
Micke, I'm not afraid the engine will explode after 6k5, but what I want to aim at, is a motor optimized for this rpm. Remember, I'm not out to build a race engine, but one which can be duplicated without too much trouble by a lot of people and be mainly an every day tool, doubling as a trackday toy. If I believed that everyone is waiting for the book to go race, I would act accordingly and limit my options to full race stuff, but I think that it would not be realistic. The average enthusiast is interested in some performance increase for daily use and this is what my feeling is from reading the various Internet sites. Believe it or not, the largest Italian site (umpteen thousand members) proves their performance aspirations go as far as changing air filters, brake pads, wheels and rear mufflers. Shocks is a major change and cams...non-existent! (And this has nothing to do with engine size taxation). You should see how many days they can debate on one type of wheel design! They are perfectly happy doing this and it keeps the very busy site alive. Obviously, if they buy any car book, they would do so out of curiosity, not as a possible source of how to do things. It may come as a surprise to many, but in Italy car conversions as we interpret them, are dead and have been for a long time now. GB, Au, NL, US, Japan, Ge, are the main conversion markets. Look for the countries where the most perf-oriented mags exist. As far as sites go, this one and BB are leading the performance-junky drives.
So you see, I must aim for the broadest reader base, not for the sake of sales but to cover as best I can what the majority expects. Suppose we passed out a questionaire, how many readers would be inclined to buy Carillos, forged pistons, ITB's and large valves (among other things) to build a race motor? What would they do with this motor once built? I think you know the answer.
Back to tech, I agree piston speed is low at 6k5 and going by the old 4000fpm figure the 3liter is good for ~8k3. Piston speed? For which piston-stock? It does sound uncomfortably high, especially when you think of the 7krpm limiter of the 164 Q4. I have no way of testing the actual capability before meltdown, but I believe in playing safe. A dynamically well balanced assembly with proper lubrication and clearances can comfortably do 7-7k2 all day, but the target must be overall performance, not just top end potential (IMO). I would love to be able to afford all the good stuff myself, but think of it another way: Someone with the financial resourses to buy the best, usually knows where to go to get a race engine built-very rarely do people like that build things themselves as they can't be bothered. They are not exactly DIY fanatics and that is no insult, they pay for what they want get it and enjoy it as well as the next guy. And surely the builder they go to, sure as hell won't need my book to tell them how to do their job!
Wow, another long-winded speech has ended, please visit the concession bar!
Micke, you still got time to come see Maurizio and me tomorrow!
Jim K.

[Maurizio]

As far as sites go, this one and BB are leading the performance-junky drives.

that is why I stick to this site, no blabla, but realy good stuff.

@Z the E30 site is really good! once every half year I look at it and am always amazed about the good setup and the explaining the guy does, you almost could get a weak spot for a E30 M3

[Zamani]

Well let's see we've covered the intake runner length and size. I guess the thing we haven't covered about ITBs are:

Should the throttles be close to the heads or should it be further out? I.e if the length from the tip of the trumpet/stack to the valve face is X, will the position of the throttle make a significant difference? I'm thinking the position is more an issue of what is more practical.

Good luck to you all at the Ring!

[Micke]

Jim,

long post. I guess you're right.

Matz,

Dunno anything about the VR6 except really crappy fuel economy.
IMHO the rod ratio is not as critical as generally assumed. I did calculation like the chart Z referred to. Remember the acceleration is a function of rmp^2 so this is much more critical anyway.

Of course if we speculate again, we could use the 2.0V6 crank with big bore and get the compression up by longer rods. This gets difficult and expensive though.

[Jim K]

Long/short rods, eh? You guys are asking for it! One thing I remember very well, was a long article by the great Smokey Yunick about the pros and cons of rod lenght in restrictor engines (which is a good approximation of ours!). I assume you are all keeping the same bore, just changing rod/piston combos, right?
Mats, how come you only detonate when I mention M3's? Its your duty to rack both Z and Maurizio for secretly consulting obscene sites! (And learning how proper engines work)
On the other hand, I suspect Z is secretly building a killer motor, as witnessed by his clever questions and general activity, heheh!
Jim K.

[Micke]

I have a book from Smokey and it gives things to lose sleep about.

If I remember correctly the Alfa con rod ratio is about 1.8 for 4-bangers and the sixes too. This should be acceptable for "Jim's customers"

For an ultimate engine it might make sense to fiddle around with shorter stroke, BIG bore and valves to suit plus long con rods but then you don't have ANY std parts when something needs replacing.