installing 1800 35/75 head on 2000 block

[blufun]

Hi guys,

I'm pretty sure I've researched this before I made the decision, but now that I'm getting ready to do the job, I thought I would check with the forum experts to cover anything I've missed. It's pretty straightforward, I'm simply replacing my stock 2L head with the 1800 35/75 head(freshly machined) on the 2L block, from what I've been reading this is all I need to do. I will use my same 36/36 euro carb, 1800 intake man., and 4/2/1 headers, are there any other changes I need to make before I begin? Thanks so much in advance guys, much appreciated.

[18Fiatsandcounting]

I'm not aware of anything in particular that needs to be addressed. I'd check the oil and coolant passages between the block and head to make sure everything lines up, but I believe they all do (or are very close). The head gasket for the 1800 and 2L engines are the same, so that's not an issue.

Just curious though: What is a "35/75 head"? I've heard of 35/75 camshafts, but I haven't heard this in reference to a cylinder head.

Also curious as to what 36/36 euro carb you will be using? A 36ADL?

-Bryan

[blufun]

Hey Bryan,
Thanks a bunch for your reply, sorry I didn’t specify the 35/75’s are the cams. I’m just getting educated on this stuff from reading info on this forum. What’s so funny is that I started a few months ago to rebuild the tranny and front suspension only, but decided to do more upgrades as I went along. I’d installed the carb/headers/intake man 20 yrs ago and removed all of the emission stuff. The carb is a Weber made in France 36/36 w/manual choke, that’s all I know about it but it made a significant improvement over the 28/32 stock carb in terms of performance and quick starts. I was pleased with everything as it was, but reading the posts on this forum influenced me to do a little more. It is what it is, thanks again good buddy,

[18Fiatsandcounting]

Sounds like a cool project, so let us know how it works out.

Back in the late 1980s, I put a 2L block in my '69 spider but kept the original cylinder head. This worked until this past summer when I decided to pull it out and reinstall the 1438cc engine just for old times sake. But, that's a 1438 head and your 1800 head will work much better on a 2L block as they're both set up for 84mm bores.

My limited understanding is that the combustion chambers on the 1800 head are better, and the intake ports are pretty good. The only downside is that many of the 1800 heads have the air injection lines into the exhaust ports, but these can simply be closed off. By the time the 2L engine came around, it wasn't long after that it became fuel injected and so the air injection ports weren't needed.

Once you get the engine running, you'll probably need to do some jetting on that 36 Weber carb, and there are various approaches to this. Lacking a dyno, my approach has always been a flat and lonely stretch of road where I can do timed acceleration runs in a single gear (3rd or 4th) from 2500 to 5500 rpm or so. Change the jets, keep testing and changing until you get the best performance.

Anyway, keep us posted.

-Bryan

[Nut124]

Where did you get the 35/75 cam timing(?) numbers from?

I did not think any stock US cam had that much duration.

[blufun]

Hey nut124, I have a 1979 2L and swapping out the 2L head with an 1800 head with 35/75 cams, they are definitely not the stock cams. What exactly does it mean when you guys mention 40/80, 42/82 cams and etc? Obviously the higher the numbers the higher the cr’s right? Can I still use my stock cam pulleys, does the same static timing marks line up the same? Please explain to a novice like me if you don’t mind good buddy. Thanks much for your reply, much appreciated.

[blufun]

Bryan any particular reason why you went back to the 1400 eng? I guess I’m a little confused about the air injection ports, I have them on the 2L head, for some reason I didn’t think they were on the 1800 heads, at least I was hoping they weren’t. Thanks.

[Nut124]

Hey nut124, I have a 1979 2L and swapping out the 2L head with an 1800 head with 35/75 cams, they are definitely not the stock cams. What exactly does it mean when you guys mention 40/80, 42/82 cams and etc? Obviously the higher the numbers the higher the cr’s right? Can I still use my stock cam pulleys, does the same static timing marks line up the same? Please explain to a novice like me if you don’t mind good buddy. Thanks much for your reply, much appreciated.

Here's a pretty good and quick read on cam timing:

https://www.tildentechnologies.com/Cams/CamBasics.html

Note that it is written presuming a V8 single, in block cam. The LSA does not really apply to DOHC.

The job of the cam is to control the valves to fill the cylinder with as much air as possible for combustion and then exhaust the burnt gases. Cams are characterized by mainly by lift and duration.

At higher engine speeds the time that the intake valve is open is very brief and a cam with longer duration is needed to fill the cylinder. Longer duration hurts low speed torque as the intake valve opens while the piston is still moving up. This causes reversal of the intake flow at low engine speeds. Similarly, the intake valve closes when the engine is way past BDC, piston almost half the way up. This causes reversal of intake flow as well at low speeds. At higher speeds, the momentum of the air in the intake runners counters the reversal and aids cylinder fill.

[18Fiatsandcounting]

Bryan any particular reason why you went back to the 1400 eng?

Nostalgia. While I miss the increased torque of the 2L engine, I also missed the free revving aspects of the early engines. 7000 rpm and above with no issues, and while you can do this with a modified 2L engine, the early engines just had a feel to them that seemed to match what I remember as a kid growing up with Fiat spiders.

You're right, some 2L heads have the air injection ports as well as some 1800 heads. It's not an issue if your head has them as it won't affect performance if you don't have the rest of the air injection system. If the head has air injection, you will see four plumbing "cavities" in the head, one by each of the spark plug wells on the exhaust side. You'll likely need to plug them, though.

As for cams, Nut124 is the resident expert here. I'll just add that any given cam is optimal over only a narrow engine rpm range, and engine designers picked cams that offered the best match of horsepower, torque, fuel economy, driveability, smooth idle, emissions, longevity, etc. If you want cams that offer more performance, those are available but some of the other aspects may decrease. As an example, you could get a cam that had great performance at 7000+ rpm but wouldn't perform worth squat when driving around town.

The numbers for a cam specify the points at which the cam opens and closes relative to the crankshaft rotation. So, a 35/75 intake cam would start to open when the crankshaft is at 35 degrees Before Top Dead Center (BTDC), remain open all the way to Bottom Dead Center (BDC), and then close at 75 degrees After Bottom Dead Center (ABDC). In reality, it's vastly more complex than that.

If none of the paragraph above makes any sense, there are books or blogs or YouTube forums or the like on cam timing. Might be helpful. Or just ask here on this forum.

-Bryan

[Nut124]

Here's another cam site with nice explanation:

https://www.iskycams.com/cam-degreeing. ... 20strokes.

[blufun]

Hey Bryan and nut124,
THANK YOU for taking the time to “school” me on this stuff, I’ll be busy doing the necessary research to get this right, I have to because I own it now:). I’ll keep you guys posted on my progress because I’m sure I’ll be asking you more questions as I proceed. Thanks again and Happy Halloween:)
Cheers.

[Nut124]

Hi guys,

I'm pretty sure I've researched this before I made the decision, but now that I'm getting ready to do the job, I thought I would check with the forum experts to cover anything I've missed. It's pretty straightforward, I'm simply replacing my stock 2L head with the 1800 35/75 head(freshly machined) on the 2L block, from what I've been reading this is all I need to do. I will use my same 36/36 euro carb, 1800 intake man., and 4/2/1 headers, are there any other changes I need to make before I begin? Thanks so much in advance guys, much appreciated.

You might want to check the casting numbers on your heads to find out exactly what heads they are. The casting number is located on top, behind the coolant outlet.

[blufun]

Nut124
What would the casting number tell me? Any examples? Thanks much.
Cheers.

[Nut124]

It would tell you what head you have and what the new head is.

Many of these engines have been worked on. No guarantee your 2L has a 2L head on it.

How do you know the new head is from an 1800?

[18Fiatsandcounting]

One way to tell spider cylinder heads apart is by the outer diameter of the valve guides. All engines up through mid 1978 used 15mm OD guides, while late 1978 onward used 14mm guides. If no guides are installed, you can just measure the diameter of the hole for them.

So, late 1978 heads for 1800cc, and 2L heads, would be 14mm while 1438, 1608, 1592 and 1800 up to mid 1978 would be 15mm OD.

-Bryan