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Jetting for 45DCOE


Guest Anonymous
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Guest Anonymous

I was wondering if anyone could make any suggestions on jetting for a set or 45DCOE. The webbers are on a 75 2002 with 10:1 pistons, 292 cam, and a set of headers. I'm trying to get it in the ball park. This car is a project and another set of carbs (smaller) isn't a choice. I need to make these work. Any help would be appreciated.

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Guest Anonymous

I looked this up in the Braden book for you. there are

no listing in the tables for 45's on a 2 liter motor,

just the 40's so I'll give you several and you can go from there. hope it helps.

2 40DCOE's 2000cc

Etube-F16

Main-120

air corr-190

idle jet 50-F8

Standard 45DCOE jetting

main-145

Etube F16

air corr-155

idle jet 55F8

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Guest Anonymous

after posting that I thought it was. basicly it works

like this. Increase your main jet size to riched, more fuel. smaller to go lean. the air correctors are opposite. smaller to richen, less air. larger to go lean. You realy should buy a book if your going to run

carbs. The Pat Braden book has a lot of info and shows

you how to calculate all of this stuff. To much to post

though.

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Guest Anonymous

I have 40 DCOEs - and run 65F8 idles for non-airbox, and 60 F8 for when the filters are on....MUCH smoother "off idle" transition than the 45 or 50 idle jets everyone (incl. Braden's book) recommended to me, and what was installed at the factory.I have 120 mains in now...but will be installing 115 jets to see if it's any better with the air box on at upper rpms.

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Guest Anonymous

Paul's right. Most people run the idle circuits on these things ridiculously lean. However, don't forget that transitional throttle mixture issues are dealt with almost 50-50 by the idle circuit AND the accelerator pump - you can play around with both to change the ratio, which then changes throttle response as it relates to rpm and butterfly position. To boot, you can also fiddle a small amount with main jetting to smooth out the full throttle grunt AND transition, though it's essentially the "elephant gun" approach.

Try running medium-rich idle jetting (55s, and play around with emulsion jetting on the idles - the "F" setting after the initial number) and fatter accelerator pump jetting (45 pump jets), with larger pump discharge/exhaust valves (no one ever touches these, to their loss - they effectively let you fine -tune pump jetting beyond the relatively broad 35-40-45 range; larger exhausts is leaner pump shot, essentially - although they're actually fooling around with shot duration AND quantity). It'll give you a smooth off-idle transition and still give decent rip in the upper rpm ranges (pump jetting is effective up until 1/2 to 3/4 throttle butterfly travel).

Personally, I've found that 60s or 65s tend to be too rich of a transition mixture (not to mention you end up closing down the mixture screws a bit much) with the proper pump and exhaust jetting.

Remember, it's all based on vacuum conditions and throttle position, NOT rpm. You can get these things perfectly smooth and ridiculously powerful compared to a downdraft, but it takes some time and a significant amount of jetting and venturi trial and error (in case you were wondering, Paul, Sybil is only about 85% right).

Hopefully, the by-now-far-too-long article I'm in the midst of putting together for the FAQ on DCOEs will be done some time soon.

HTH.

Sam

O==00==O

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Guest Anonymous

Pump jetting also acts, to a small extent, as a top-end enrichment circuit - but it's upper top end, where the air correctors have been in for a while.

Sam

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Guest Anonymous

....and she felt very very nice. (Tim and I did a little side by side comparo) Smooth, even power. I think you done pretty good on the DCOEs there. Now...all she needs is a 3.91 rear end - THAT will wake her up a bit with that 5 speed!

I hadn't seen the car in a while - and I was marveling at how nice everything is - and how cleanly all the small mods, etc were perfromed.

she sweet Sam...and she has a good home still!

Paul

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Guest Anonymous

Paul-

Thanks for the compliments. Just tried to build the car right...and I know she's in a good home ;)

As for the jetting, she always seemed to lack a little low-end grunt, even taking into account the diff ratio not being optimum. I never really finished the jetting process - if I had more time, I'd probably richen up the idle air circuits a bit (transitional throttle stumble), go to a step larger main venturis (I think 34 is about all that cam/compression/head flow/exhuast could take and still be as flexible, but 32s seemed to be choking it a tiny bit)...

and add the air horns. The few times they were on the car, they made a significant difference in torque all across the range (no real surprise there, it's what they do), and booted throttle response/torque down low to where I expected it to be. Since I had no airbox or filter setup at the time to go with 'em, though, I left them off and jetted for the setup as is (which is, obviously, leaner than running with the horns on).

Looking forward to seeing you guys again in a month!

Sam

O==00==O

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