Alfa 1600 Twin Cam

[mc-racing]

Hi,

I want to build an engine for my 73 GT Junior which i am restoring since a year.
Compared to other Cars the drive ratio is very short, in 5th gear 60mph (100km/h) @ 3500rpm, 100mph(160km/h) @ 5500rpm, so the engine should rev at least 7000 before the Power drops. It should be used on road, but it should be fun too on our historic hill climbs here (this is not a racing class, it only free driving on a closed mountain road )

Here are some facts of the engine:
The stock engine has 78mm bore and 82mm stroke and has wet liners, i want to get the liners drilled to 78.8mm or 80.0mm and custom pistons from CPS or JE with a more modern dome shape to create some squish.
The stock head has 41mm intake valves and 37mm exhast valves, both with 30° seats.
On the Intake it is possible to fit an 42.5mm valve an recut the stock seat to 45° or up to 45mm valve but only when the spark plug hole gets a reducing insert to get a bit more space for a bigger valve seat.
The stock inlet runners are tapered from 40mm to 32mm and 202mm long, the inlet port tapers to 30mm and is 65mm short, the exhaust port has 31mm diameter an is also 65mm long. The head has 80° Valve angle, the ports are horizontally and straight.
The crank and the rods are forged an reliable to about 8000rpm, so they will stay.

I tried to build a model in a professional engine simulator, but to try some cam profiles i have to know more exact flow bench results of this heads, maybe with some bigger valves.
I built a diy flowbench, but it's not calibrated and i have not enough heads to try different valve setups.

I would be happy if somebody has some flowdata, hints or other experiences with this engine .

kind regards from austria
markus

[Guy Croft]

Re your observations Markus:

1. The stock engine has 78mm bore and 82mm stroke and has wet liners, I want to get the liners drilled to 78.8mm or 80.0mm and custom pistons from CPS or JE with a more modern dome shape to create some squish.

I would not mess with the liners. Get new and keep the standard size and Flexhone them to the appropriate finish for the race rings (likely 240 grade silicon carbide). More squish? Well if it's a pure hemi like the 2 liter this is pretty-well impossible. I'd need an idea of the cc volume and a photo of the chamber to comment accurately, but I've done piston design for the 2 liter which - after valve/seat work - has about 90cc chamber volume. To achieve a high CR (I managed 10/1) is very difficult indeed and I think that many who boast higher may well be, er 'kidding'themselves. And your engine has a much smaller swept volume than the 2 liter.
I've discussed this problem with CP Pistons (who you did not mention you might like to know but I am a long-established agent for them) and the reason is a big dome - on most forging blanks - means shifting the ring pack up the piston and using quite thin lands especially the top one. You have to have a generous clearance betw dome and head too and adequate valve-piston clearances as well and that all 'eats' into the intruder volume. And I used offset valve reliefs on the 2 liter as well to reduce the impact of the cutouts on CR. It is a mistake to imagine that having a gigantic dome (for highest possible CR) is a great thing because it reduces the burn rate very significantly - the flame development is impeded by the mass in its way. Low burn rate really robs power and increases the specific fuel consumption dramatically (ie: your gasoline is wasted).


2. The stock head has 41mm intake valves and 37mm exhaust valves, both with 30° seats. On the Intake it is possible to fit an 42.5mm valve and recut the stock seat to 45° or up to 45mm valve but only when the spark plug hole gets a reducing insert to get a bit more space for a bigger valve seat.

A 42/37mm valve combo is plenty big enough. You could go 44 inlet with the 37 ex but no way bigger. Yes, 45 deg angles are a 'must-have'.

3. The stock inlet runners are tapered from 40mm to 32mm and 202mm long, the inlet port tapers to 30mm and is 65mm short, the exhaust port has 31mm diameter an is also 65mm long. The head has 80° Valve angle, the ports are horizontally and straight. The crank and the rods are forged an reliable to about 8000rpm, so they will stay.

I would open up the controlling section of the inlet ports to 34mm. How well the ex ports flow is critical. The 2 liter version has terrible ex flow in standard form whereas even the standard inlet ports are plenty big (and good) enough to attain 200bhp at 2 liter capacity. When you do your flowtesting first test bare-port flow inlet and ex (no valves in) and see what the E/I BPF flow ratio actually is. You need to get it it 72% or better, so if it is lower than that start opening up the ex port to raise the ratio before you do any mods at all on the inlet. Ideally the relative flow should be the same as the ratio of valve areas, eg: for a 42/37 combo the ratio of areas is 78%. Increasing valve size will only affect that ratio IF the valve throat diameter is increased too. (That is a totally separate thing from the influence of the bigger valve on valve-in response per-se).

I hope this helps some to begin with, if you post some good photos I will do the same.

G

[mc-racing]

Hi Guy,

Thank you very much for your answer.

Yes the 1600 is a true hemi, but a bit different to the 2L.
The Alfa-Nord was engineered as 1300 and 1600, the 1750 and the 2000 were made at least 15 years later and especially the 2000 is a bit strang with its offset valves.
The combustion cambers in the 1600 are symmetric and my head has the port floors located higher than the 2000 heads.

IMHO there are 3 different 1600 heads out there, the oldest one is with big Ports and single spark like in the early Giulias, the second one is the GTA twin-spark head also with very big ports and the last one is the one like mine form the mid 70s with the port sizes i wrote in the first post.

Are you sure that the ports should be bigger?
I fear a bit making the ports bigger, because there is a story out there that Autodelta concluded after looking into the Lotus Cortina head and the Coventry Climax engines in the late 60s, that the ports of the old heads are to big and homologated reducing pipes for the Gr.2 GTA, the should be fitted with epoxy in the inlet ports. The homologted diameter was 29mm, some years later Alfa changed their castings oft the stock heads to 30mm.
In this days some german engine builders doing the same with every Nord-engine size, they drill the ports a bit bigger and fit venturi shaped reducing tubes in the ports.


The squish.....

The 1600 combustion camber has 72ccm and 80mm diameter as the head gasket ( yes, 80mm they used the same casting on the 80mm bore engines 1750 and giulietta 1350), the 80mm came from a 1mm margin which is about 45° angled, the real hemisphere has 78mm diameter
Alfa romeo produced pistons which should create a squish for the Motronic-Alfetta and the last RWD Spider series.
About the same shape is used by tuners like paul spruell, for the smaller engines.
here is the link to paul's je-pistons...
CP Pistons manufactures about the same shapes for company in munic.


This Pistons should create some squish at the round areas between the valve pockets and according to the engine builders, there should be no problem with detonation up to cr=10.5-11:1 when the distributor is modified to do less advance (max 28°) or with a programmable ignition.


i will do some flowtesting soon then i will post some results and pictures.

with kind regards
markus

[Guy Croft]

OK - Markus - I do need some high def photos of the head - the ports from both ends, chamber etc. Not much interested in what non members do, we can figure this out together here better.

Never seen one, I'm 'driving blind' without any photos and so is every other reader interested in this!

G

[fingers99]

I'm almost certain that for the GTAs Autodelta twin-plugged those engines to overcome (or at least, ameliorate) the slow burn/hemi issues.

Whether this is feasible on the stock casting, I have no idea -- Autodelta (much like Abarth back in the day) would have had pretty much full access to everything the factory had to offer.

It would be very interesting to see how this went against the "increase the squish" approach.

Back then they were tremendously effective race cars.

[mc-racing]

Hello everybody,

Sorry for the long delay.
I had to stop the 1600 engine project, because the head has damaged cam bearings, a crack in one combustion camber and the crank is worn.
This is much to expensive to repair compared to what that engines are worth. So i tried to find another head, and a crank, but finding usable 1600 parts turned out not to be easy, i found only parts in as bad condition as mine.
But i found somebody who has a stock on some 2L Alfetta engines. I'm going to get there in 1 or 2 weeks to buy some engines, then the project will restart.

best regards
Markus

[corriedw]

Hi Guy, would you kindly direct me to the thread where you developed the Alfa 2000 cylinder head. My search skills seem to be lacking. Thank you.

[Guy Croft]

I may have deleted it, if the paid membership is encouraging (a mere 35 so far) I intend to rebuild some of the old posts.

Sincerely,

G