Couldn't resist!

[daz]

Do you think the 4mm spacer is not neccessary then

[alfaspence]

Quote:

Originally Posted by daz Do you think the 4mm spacer is not neccessary then

[alfaspence]

After thinking about it loads, ive decided to go for the twin plenum arangment as per the australian car (siamese 2 into 1 runners) but my plenums will have a different design (not the 90 deg pipes out the sides holding the T/b's)

So iam now on the hunt for another 24v plenum (preferably 164) and 2 sets of qv/ gta/ 166 3ltr runners (mine are damaged)

[Duk]

Quote:

Originally Posted by alfaspence After thinking about it loads, ive decided to go for the twin plenum arangment as per the australian car (siamese 2 into 1 runners) but my plenums will have a different design (not the 90 deg pipes out the sides holding the T/b's) So iam now on the hunt for another 24v plenum (preferably 164) and 2 sets of qv/ gta/ 166 3ltr runners (mine are damaged)

[Rookie ROX]

For the same reason he went with the IMSA kit I imagine - It looks awesome!

ROCK ON
R~R

[giuliettaevo]

another idea for the intake... uses the original 24v manifold with a piece of a gtv6 manifold welded on and the original place for the throttleplate closed off. you can use your 24v throttle on the gtv6 mounting.

[alfaspence]

Quote:

Originally Posted by Duk Why?

[alfaspence]

Quote:

Originally Posted by giuliettaevo another idea for the intake... uses the original 24v manifold with a piece of a gtv6 manifold welded on and the original place for the throttleplate closed off. you can use your 24v throttle on the gtv6 mounting.

[nizam]

Naw, just keep it in this one thread, we already know it's "Spence's 24v build thread"

[alfaspence]

Quote:

Originally Posted by nizam "Spence's 24v build thread"

[Duk]

A good road car engine has a good spread of torque.

For that reason (when I get off my own ***) I plan to build a manifold that has inlet runner that start at 1 3/4" and taper down to 1 5/8". Each runner will have a length of approximately 400/450mm from the valve.

From Autospeed.com http://www.autospeed.com/A_107771/cms/article.html:
"A starting point for working out the length and diameter of intake runners can be gained from the following equations. In a Helmholtz Resonance system (one with runners connected to a common plenum), US-based engineering guru David Vizard suggests that a runner length of 17.8cm at 10,000 rpm makes a good starting point. (In this context, "runner length" refers to the distance from the inlet valve to the plenum chamber.) Add to this length 4.3cm for each 1000 rpm less that the system is being tuned for. Tuning for peak torque (not peak power) is the norm, and so if the engine were being tuned for 4000 rpm, a runner length of 43.6cm would be required. You can see that for an averagely-sized engine bay, the longer the runner that can be fitted in, the better"

I prefer to look at engines that, while in more general purpose cars, have a good reputation for having a nice broad torque curve, and are of similar engine specs. They all tend to have long runner manifolds.

You have the advantage of better head and larger port area than a 12 valver. I would be looking at a runner diameter of atleast 45mm. Some people may try and tell you to use a smaller diameter runner to give better low rpm torque. This isn't applicable to EFI engines (Alfa got it wrong IMO). Use runner length to give good low/mid range torque rather than strangle top end breathing.
Try and keep plenum chamber around the same voluum as the engine if you can.

My 2 cents

[alfaspence]

nice one Duk! at last, some science to this stuff! i had been told that the original plenum didn't contain enough volumn....
I knew that i couldn't (and iam too fussy anyway) just cobble any old rubbish on there... I want it right, same as all the top race teams do (but theirs is for track work, mine for the road) i want to optimise what ive got and what i can do.....