Race Engine Forum UK

Any chance of a comparison pic 'original <-> new ones' Chris?

This is the only pic of the original air intake I have here at the moment. Back/side view only. But as you see, 90 degree bend and no wide lip or nice taper.

Those are exactly the same trumpets that I have in my engine

Urbancamo; Do you have Dellorto carbs with the long emulsion tubes?

I'm a bit concerned that the wide lip of these trumpets will not fit in because of the e tubes obstructing them.

A small lip may need to be cut into the trumpets to fit against the tubes.
Have to see this weekend.

I have DHLA's = horizontal ones. So no protruding e-tube holders for me.

Same thing applies to Weber IDF's too with long emulsion tube holders. Looking at the DRLA pictures, those trumpets might pass them just barely. My guess and estimation is that they will fit.
Some DRLA's are equpped with long e-tube holders and some of them have the short ones.

Brit01 wrote: This is the only pic of the original air intake I have here at the moment. Back/side view only. But as you see, 90 degree bend and no wide lip or nice taper.

I think you are leaving out a very important part of the original inlet here. The boxer engine on the Alfa cars (just like on the original VW beetle engine and Porsche cars) is factory equipped with a resonance mechanism that involves all four cylinders, both banks. This gives pulse filling using Helmholz resonances between the two banks. By eliminating the original setup, you may gain high RPM power, but you lose all possible plenum resonance benefits, including opposite cylinder pulse pressure for the rest of the range. Helmholz resonance is a large part of the efficiency of modern engines and can easily give you fill rates that are over 30% better in the normal working range of a street car, compared to using individual velocity stacks. You may want a different characteristic for your engine, but it's primary design is for street use and they didn't just slam this whole 90 degree setup with central air box thing on because it was cheap and easy. It is well thought over and I'm certain that they did a lot of calculations and trials to get it working properly for the designed purpose.

That, the fact that the inlet tracts will indeed be shorter with just the trumpets and the matter of air filtering. Will these trumpets go in a K&N-style square box? If so, you will be sucking in a lot of hot underbonnet air. Maybe not a good idea where you live (hot summers, lots of slow traffic).

regards
Tom

Homme, with respect - don't get into Helmholz.

It's not Helmholz.

GC

Homme, with respect - don't get into Helmholz.

It's not Helmholz.

Now you're confusing me gentlemen. I have been told about the dynamics that occurs within the airbox but never knew it would make too much of a difference eliminating the airbox.

Yes I was intending to use K&N style oval box filters.

Well once I get the flat spot eliminated, new coil tested etc I can test the engine with the new trumpets without investing in new oval filters yet. Just a few spins around the block on a clean fresh day.
It's winter now and averaging about 5-10 degrees during the day.

Compare with the original set up and with the trumpets alone.
If I notice a big drop in low end torque then I will sell the trumpets and keep the original design. But they do excel at higher rpm and make a beautiful sound.

I've spoken to other boxer owners with trumpets and they haven't noticed much difference, even in hot areas like Cyprus and Malta. Maybe when stuck in traffic they lose a little performance but once on the move again it soon picks up as there is plenty of air flow around the boxer.

We'll see. Trial and error.

My new book tells you much of what you would wish to know about pressure waves.*

Removing the airbox:

1. If it currently receives ducted air from ambient - not the underhood - you will lose power from changing to filters taking air from, well, the hot underhood region.
2. If the airbox is too small - which I doubt - it creates a pressure drop which reduces power over one running at an atmospheric pressure state.
3. If the open end of the rampipes are closer than about 1" to the airbox that will generate a power loss.
4. Highly unlikely that K&N will give more power than the OE filter. It will just sound more powerful.

Hope that helps.

G

* PS would some kind owner of same kindly confirm that is true?

yep. I spent (or mis-spent) 15 years with an Alfasud and its boxer engine. Over that period, I (with a friend who also owned an alfasud) did quite a lot of 'development' work on the chassis, brakes, suspension and engine. On the latter, the conclusions that we came to were
(1) on the valve front, bigger is not necessarily better. We tried enlarged ports and larger valves. It helped with top end power and ruined lower end torque.
(2) Cams. The green cloverleaf cams seemed to work well in road trim. Higer lift, longer duration cams from BLS again gave more top end power but with loss of tractibilty
(3) airbox vs KN filters. Tried both on the same car on a rolling road in York. Stay with the airbox but put a KN air filter in it
(4) Jettings The idle jet is 52 as standard. This is for emissions at MOT time. As soon as the MOT was over, back went in the 55's to remove the dreadful flat spot on initial acceleration. WE experimented with different emulsion tubes, main jets etc and came back to OE for the tubes and never bigger than 140 for the mains.
All the above was done on my hybrid 1600 engine which had 87mm pistons and a 1500 crank in a 1500 block. My friend Stefan had a 1.7 with hydraulic cams (mine were solid lifters).
All the above is based on trial and error and lots of road testing (plus a bit of rolling road) but is not scientifically proven. Just my thoughts.
Andy

3. If the open end of the rampipes are closer than about 1" to the airbox that will generate a power loss.
4. Highly unlikely that K&N will give more power than the OE filter. It will just sound more powerful.

Yes I will make sure the filters are high enough if I decide to go that route.

Not too much of a concern if I don't get more power. Just don't want to lose it.

(4) Jettings The idle jet is 52 as standard. This is for emissions at MOT time. As soon as the MOT was over, back went in the 55's to remove the dreadful flat spot on initial acceleration

Interesting Andy thanks. I have 52's now. Were you working with DRLA's 40's with 32mm chokes?

(3) airbox vs KN filters. Tried both on the same car on a rolling road in York. Stay with the airbox but put a KN air filter in it

Under normal driving conditions did you notice much difference between the 2?

MODEL POST!

Thanks for passing on that important info Andy!

GC

New coil ready for installation tomorrow and some nice new Castrol TWS.

Just removed the old one.

Ballasted! It has 2 numbers on the bottom. I will do some research on these.

0 221 600 002
1 227 020 010

Well it measures 1.5 ohms on the primary same as new.

BUT when I installed the new one and turned the key wow what a difference.
It started up so easily:)

Haven't tested it on the road yet.

Guy, until your new book is ready, would you (or other members?) have good web links about the pressure waves and Helmholz in inlet systems? I'd love to learn more.

Primary coils almost never burn or break. IF they do, you're usually completely without spark. Measure the secondary. In fact, measure your new one and write down what you measured now. You'll have some reference in the future of the actual value, not just manufacturing standards.

Primary coils almost never burn or break. IF they do, you're usually completely without spark. Measure the secondary. In fact, measure your new one and write down what you measured now. You'll have some reference in the future of the actual value, not just manufacturing standards.

Well still got the stubborn flat spot. At least I know I have a nice new coil! Not sure how long they last but the original was 24 years old.

I'll increase the idle jets from 52-55 tomorrow to see if this makes a change.
Easier that getting the floats out for now.
(too flippin cold to be messing with them for now).

I'll make a note of the measurements whizzman.