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Here is some more detail of the 'long' intake plenum and valve covers. Note the relocated oil filler neck.

Time for some more pics today of the 'short' enlarged (75v6 type) intake and the start of runner fabrication. The two manifolds are fixed on a wooden mock-up and you can also see the chrome pipe flanges bolted on. I cut the chrome pipes off and what the exhaust man will do, is to bend 45mm OD stubs, ~100mm long so that their tops end up inline according to the carton pattern shown in the pic. OD of the plenum throats is 50mm so he will also expand the top of the pipes so I can just use straight rubber hose for the connection. More after this work is done. The plenum will be painted black but no details can be seen then, hence today's pics.
Jim K.

Nice, are you gonna test both?

As a daily, your most likely gonna do the long runners right? My bet is the shorties for peak power.

Both will see the dyno but I haven't decided which one to put on first! I like the way the short one looks though, less cumbersome.
Jim K.

75evo wrote:Nice, are you gonna test both?

As a daily, your most likely gonna do the long runners right? My bet is the shorties for peak power.

Prolly not practicle to have a dual length runner manifold on a V6 (especially 1 shoe-horned into an Alfa engine bay), but how about a dual resonance manifold like the 458 Italia/Speciale???

Hmmmm, if someone makes me one for free, I'll take it!
Jim K.

What about your ITBs? I suggest that we all chip in to pay for your dyno session, gas and a good dinner for the ITB test.

Dead serious here, 10 euros each and we get to see 1st hand report on the effects of short, long runners and ITBs. All we need is 10-15 donors. Anyone up for it? I'm in.

Hey it's not like we're giving you a million bucks but it's better than nothing

Like I've said elsewhere, I'm not after max power so a single TB is ok. Why then did I buy the ITB's? Must've been a surplus of cash splurge in the good ol' days of 3-4 years ago. Main reason I don't like them is lack of filtering and the fact that I despise sock filters! I suppose some effective arrangement and an air box like the old 6-carb V6 would help change my mind but for now, ITB's are mothballed! On the other hand, old age is catching up and I may never try them... Let's see what the motor is good for as its being built and maybe the ITB urge will surface again... Why the ITB curiosity? Kevin has said that they're worth ~20hp over a single TB setup so no mystery there!
Did a quick check today and so far, the 3.2 exceeds 8000€ -no labor. This is in line with what we figured with my Alfa mechanic, thinking that a shop must charge 10k€ for a similar engine.
Jim K.

Great write up Jim.

I'm curious as to how different the torque curves will look or feel when comparing those two plenums and the long vs short runner. designs. Assuming the deeper breathing 3.2 would have a flatter curve anyway compared to the 3.0, even without mods, would you expect the plenums to drive with significant differences in feel?

Your book (very useful btw!) indicates that low inlet port velocity could be the biggest culprit for the 24v's slight lack of low end torque compared to 12v feel. If that's the case, is the porting on this motor intended to address that specifically, or just more power/torque all around to solve the problem ?

Looking forward to next updates!

Judging from my current 24v 3liter with the short intake, I would expect significant improvement up to ~4krpm because of the extra capacity and the long intake, in agreement with simulator results. Porting was not extreme at all; shaping was the main intention. 2.5liter heads might prove to be better but this would be an expensive test. Maybe not with the same max power but definitely with better low-end performance.
Jim K.

I think I have my mind set on the short runners because mine is a track car as most tracks here require top end power. But still there will be those slow speed turns where you wish you had the extra low end grunt.

OK Jim, you enlarged the volume of the stock runners. Pretty sure that's a very very good step, but did you run it through your sim?

Runner diameter is the same, short or long. The length difference is what its all about -hence volume). The simulator shows great difference between the two, roughly ~20hp at 4krpm and then at 7.2krpm. You want that +20 for the turns but -20 high up and vise-versa? That's why I have to actually live with it until I decide which way to go. There's also the difference of increased plenum volume and I can't be sure what that does. The simulator asks for it but it gets a little hazy there.
Hopefully today the exhaust shop will deal with the runners; I'll be there part of the day.
On another note, we put a set of 10mm cams in a 147 with a 24v 3liter engine. Idles a bit rough, not to my liking. Its going in for 63.5mm exhaust, followed by dyno mapping. The cams were timed spot-on the factory marks (~109* lobe centers).
Jim K.

I know inlet makes a difference but i thought exhaust length had a greater impact on where the power was made..

what exhaust headers are you using..

would be nice to create an inlet that managed both..

been looking at some vauxhall V6 inlets as they seem to offer better solutions of the shelf than alfa but am also looking at creating something similar to yours above but for a different engine configuration in the 156

Using my own headers, 6-2-1, with 600-650mm x 42mm OD primaries. 50-80mm length change does make a difference and that's all the margin I have to play with for space constraints.
Jim K.

Time for some dyno news today: 3liter 24v engine in a 147 fwd chassis. Engine is std except for my 10mm cams, factory headers, 63.5mm OD cat exhaust and KN-type cone filter. Cams are set to factory marks. It was mapped and made 265hp (engine) and 300Nm. I don't have rpm details, will get them later. I hear idle is a bit rough for my liking but the mapper didn't spend too much time getting it right. The power figure sounds reasonable when compared to my 24v, which with inferior cams, higher CR and some porting made 272hp.
Jim K.