38 DGAS carb

[baltobernie]

Hey Pope,

I suspect that every chassis dyno is a little different, but each shop calibrates theirs to a known engine. In my case, the shop is a Miata specialist, and Ed has dyno'd probably a hundred cars in our horsepower range. He also has an extensive body of lap time info from the nearby road race circuit in Miatas and a BMW 2002 that he has successfully campaigned over the years. He says that my 102 RWHP equates to 125 SAE on his dyno. I've heard elsewhere that a manual transmission RWD car typically loses 25% throughout the system.

DC Fiats is trying to book Ed's shop for our 2010 Tech Day. I too am curious to see some Real World numbers on well-running, yet stock Spider motors.

[magi111]

I have enjoyed reading your articles. It is well written. It looks like you spend a large amount of time and effort in writing the post. I am appreciating your effort. . .

Custom Exhaust Pipes

[Daniel]

drive train loss is closer 15-20 % on rear wheel drive vehicles

[wmausbach]

Hey that's great info. What is the lift on your cams? By the way your conversion from rear wheel hp is a little optimistic. Most give a 115% to 120% conversion factor, however you have very good results for a 1800. I do agree that RWHP is the only way to measure and is more accurate for real world performance.
ciao
Wayne

[baltobernie]

That's pretty much what I thought regarding starting off the line and gradually easing into it. I think I even have a way(s) to make it progressive.

Hey Matt, I'll send you a 38DGS to experiment on, and you can keep the carb if you'll provide a progressive linkage for my new one. I've eliminated the chokes on these, which makes swapping jets and adjusting mixture on that side so much easier. Would make a great Lemons carb as-is, but I'd like better street performance.

[manoa matt]

Bernie, I started this thread a long time ago( almost 2 years to the day) when I saw a 38DGAS carb on the Honolulu craigslist. I went to look at it and it was junk. Missing jets and jet holders, drilled holes in the throttle plates, drilled holes through the side of the venturis, misaligned synchronous linkage etc. I passed on it, then later picked up a set of dual Weber 40DCNF carbs for $20. One is good and the other is for parts. I made an adapter plate and offset manifold studs to mount it to the stock dual plane manifold. I haven't gotten a rebuild kit, or bought the appropriate jets yet.

I just went home to Cincinnati for Thanksgiving and saw a 38 DGES on the local craigslist there. It was a good deal as it came with an extra jet kit and an electric fuel pump and the carb had only been run for about 6 months. Guy was asking $200. I never had time to go look and figured I have enough carbs to play with at the moment( 5 sets of duals), so I passed on it. Now I'm thinking I should at least went for a look and offered $175. http://cincinnati.craigslist.org/pts/2683898489.html

I can't remember how I was planning on making it progressive unless I took the linkage off a spare 32ADFA carb, but a simpler method would be to grind the teeth of the secondary throttle cam, so the primary throttle cam can rotate about 3/4" before the teeth engage the secondary throttle cam. One or both cams would need to be re-indexed on the throttle shafts and some adjustability built in .

That only takes into account the linkage. There may be other issues with progression holes, and jetting that could make the idea of turning a synchronous carb into a progressive an exercise in futility. (I can see John Passini shaking his head) I'd still be interested in tinkering with it, but can't promise anything.

My friend Boogiedude has a 38ADL that is progressive and would bolt right up, I can ask if he is interested in selling it.

[So Cal Mark]

grinding the teeth off one gear won't allow the throttle plate to fully open

[baltobernie]

Bernie, I started this thread a long time ago( almost 2 years to the day) when I saw a 38DGAS carb on the Honolulu craigslist.

Time flies when you're having fun!

I can't remember how I was planning on making it progressive unless I took the linkage off a spare 32ADFA carb, but a simpler method would be to grind the teeth of the secondary throttle cam, so the primary throttle cam can rotate about 3/4" before the teeth engage the secondary throttle cam. One or both cams would need to be re-indexed on the throttle shafts and some adjustability built in .

Interesting. But if you ground off a couple of teeth on the "secondary" (indicated), wouldn't it never engage the primary? If you removed "primary" teeth, how would you "catch up" so that the secondary would fully open? I would think that the secondary would be shy of fully open by the number of teeth that were removed?



If you could get this to work, it would be great, as I could use different jetting in primary & secondary. I've finally got my carb working OK, so I'll pass on the 38ADL. But give this some thought, and my offer still stands. BTW, I have a nearly-complete set of all three jets for this carb, and you could use what you needed for your particular engine. This thing is a monster compared to the OE fitted to the engine.

[manoa matt]

The teeth grinding was just a quick brainstorm, but yes grind them off the primary, and it will eventually catch the secondary. But as stated the secondary would not fully open unless you come up with a separate linkage piece that throws the secondary open at a faster rate as the primary is coming to the end of it's rotation.

The good part is that on both, the progressive and synchronous the throttle shafts rotate in the same directions. If the throttle shafts are the same distance apart you might be able to transfer over the progressive linkage from the 32 to the 38. You would need set screws to position the primary and secondary throttle stops. The one stop seen in the pencil picture could serve as one of the stops.

[baltobernie]

deleted

[manoa matt]

"Hey, wait a minute. Can I remove the gear from the secondary shaft? It looks swaged on pretty well. If I could get it off, I could rotate (index?) it clockwise until it just misses the modified primary gear (with a couple of teeth removed). Then tooth #4 of the primary would engage tooth #4 of the secondary. Hmmm, you may be on to something here ..."

It still won't allow the secondary barrel to open fully. Think about it this way. You grind off 3/4 of the teeth on the primary gear and re-index the secondary gear. The primary will rotate 3/4 of the way before engaging the secondary gear. As the primary rotates the last 1/4, it will also rotate the secondary 1/4. The secondary will only open 1/4 of the way. There needs to be a compound cam or lever that translates 1/4 rotation of the primary to full 90 deg of rotation for the secondary.

I think swapping the linkage from the progressive to the syncro is going to be the least head scratching and will allow you to return the 38 back to syncro if it dosen't work. I would advise against cutting the gears or un-doable modifications unless I was 110% sure it will work as intended. Trying to find spare gears will be a real pain. See if there is a little pin that that can be punched out to remove the gear.

[124JOE]

i guess im a hands on guy. i see things and try to figure the best i can,
so ive seen this post and didnt realy read it as i cant get a 38 dgas carb
however i worked rc cars"ran fixed and sold"for a few years
and those gears look fimillior
heres my thought theres traxxas,hpi,duratrax,team losi,team associated and a few more
but AFTERMARKET parts "gears are meatal and better plastics"

that said cut and match,a bigger gear on the primary and a smaller gear on the secondary
should give you that 1/4 turn prime to 90 degree sec set up
so you can cut those grears at the bottom and still get to FULL THROTTLE

KO im guessing
so tell me your thoughts on that please

ho ya i forgot robbinsonracing for steel gears
others can be AL

[wmausbach]

It would be easier to find a 36 DCD that already has the progressive linkage. They were stock on the earlier Fiats. The maximum chock size on the 38 DGAS is 27mm the same as the 36 DCD (They are replaceable like the IDF). THe DCD style is a lot more common and it has a wide range of parts available. The DCD is one that Ferrari favored on a lot of the V12's such as the Tessa Rossa.
Just my opinion, Ciao
Wayne