Zenith jetting recommendations, 2.4SS

[crater64]

My engine build is under way, being done by a very reputable builder in the region. The story thus far:

Stock 2.2T -> 2380 (2.4) via 87.5 Nickies x 66 crank. 10.5:1 JE pistons, will be shimmed down to 9.8:1 such that can stay single plug.

Case has received the necessary upgrades: squirters, oil bypass mod, shuffle pins, ARP bolts.

Heads ported to S specs.

Cams were to have been 2.2Es, but since heads ported will likely end up with Solex/mod-Solex/DC30.

Ignition is stock CDI box rebuilt by [name censored by Pelican] and a [name censored by Pelican] coil.

A sport muffler of some sort (jury still out on Dansk, Porsche Classic, Scart).

The engine builder has suggested I source a set of Weber 40IDAs to replace the Zenith 40TINs. I'd like to think the Zeniths can be appropriately jetted, that any Webers I bought would still require rejetting, and that the cost savings from rejetting the Zeniths can be reapplied elsewhere.

I've searched here and on Early S, read and reread every thread on topic. The appropriate jetting would appear to fall within a range:

Idle: 55, 57, 60
Mains: 135, 140, 145, 150, 155, 160
Air correction: 170, 180
Venturis: 32-34mm (builder recommends no larger than 32)

Have seen numerous references to the 1970s-era S t o d d a r d "sport kit" which included 34mm venturis and other jets, but the size of the jets is never mentioned.

I know this is going to take some fettling but I'd be grateful for any recommendations. Thanks for your input.

[rsscotty]

Here are some specs. for a 2.2 S engine with Weber 40 IDS, comp. ratio 8.5/1
stock S cyl. heads

Jetted on Superflow engine dyno......

Choke 32
Idle 60
Emulsion F3
Mains 125
Air Corr. 170

2.4 engine .......
Choke 32
Idle 60
Emulsion F26
Mains 140
Air 180

[targa72e]

I have a 2.4 with 9.5 JE pistons and Ecams, Ports are 36I 35E. I am using with Zeniths with the aux air system removed. Venturi are 30mm. I did my tuning using a wide banc O2 system. I had to go up two size over stock on main jets to get the correct A/F mixture, all other parts are factory specs. I should add that I live in Denver at 5280ft.

john

[Mark Henry]

I also use a wide band O2 meter, you need one. I reamed my main jets to size.
My stock weber main jets were too small, you instantly see it's lean with the meter. With my jet ream set I slowly increased the size of the jets till I was getting around 12.7:1 AFR.

I have a 3.0 performance engine, my webers went from a 125 main jet and I ended up reaming it to 155 on the main, as long as you're going up in size you don't have to buy new jets.

Engine builders advice on the webers is sound, there's just way more parts available, my weber's have bigger sized venturi's and upgraded emulsion tubes, etc. I just rebuilt a set of Weber IDS ('67S) carbs and I had all the parts I needed, including new shafts, in two days.

[crater64]

Originally Posted by Mark Henry

Engine builders advice on the webers is sound, there's just way more parts available, my weber's have bigger sized venturi's and upgraded emulsion tubes, etc. I just rebuilt a set of Weber IDS ('67S) carbs and I had all the parts I needed, including new shafts, in two days.

Subject of the post is moot, as I agreed with the builder's suggestion to swap in Webers. I also agreed to not shim the CR down and to go down the slippery slope of twin plugging. Probably not going with E cams, either, rather mod-Solex or mod-S.

The builder described his goal for the end product as "a streetable ST motor," which actually sounds pretty appealing. Now that I've sprung for the added cost of the Webers and twin plug conversion, I'm going to have to contain costs elsewhere.

[crater64]

Thought it'd be worthwhile to post some pics on the work in progress, if only as evidence that I wasn't spitballing.

[Trackrash]

I will tell you what my jetting was on my SS2,5. But if you want to get yours right install an AFM. Otherwise you are shooting in the dark. AHIK.

SS2,5. 66 x 90mm w/ 8.5-1 CR. 36mm ports, E cams, sport muffler, 40mm webers.

I know some guys have used zeniths, but I never could get them to work on my 2,5, so webers are the carb to use. Nowdays ITBs and EFI is looking like a good way to go.

On my motor I ran.

32mm vents
110 idle air
62 idles
135 main jet
170 airs
F3 emulsions

Yes, 9.8-1 is a good number, above that should require twin plugs. Either a mod solex or mod S cam will work for you, it just depends what RPM range you want your power. Personally I would go with the mod S, keeping in mind that you won't have much umph below 4k rpm.

[crater64]

Yep, going Webers, mod-S and twin plugs. Will be using an AFM. Thought about going 90x66 but 87.5 the largest slip-fit cylinder to fit the mag 2.2T case.

[crater64]

Since I guess this is what amounts to a build thread, I'm adding a few more photos of the work in progress.

[crater64]

Well, the motor is in the car, but the gearbox is in need of fettling. Please excuse the horrible condition of the rear latch panel, the grime, and the quality of the paint overall. Hard to believe that's Irish Green in the photo. Whoever painted the car for the PO should have been raked over the coals or worse for the poor prep.

[crater64]

The build and the gearbox work is done and the car is home again. A couple of things changed between my mid-2022 post and now. I'll summarize them here but will likely start a separate post.

87.5 Nickies x 70.4 crank. 10.5:1 JE pistons. No shims. Displacement 2540 cc.
Twin plugged. 2x6-pin CDI boxes.
Mod-S cams (DC40).
Weber 40s.
SSI heat exchangers.
Scart Sport muffler.

I'm waiting on the jetting and the dyno numbers with the final build sheet, but an initial run gave numbers in the ballpark of 215-220 hp at the crank.