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Lets talk DCOE 45 on a MGB

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mgracer38 Avatar
mgracer38 James Darby
Rugby, uk, UK   GBR
Bob,
Agree its not ideally. There is a drop around 4000 where is rich. Initially it had F7's and the wave was more pronounced.
Hopefully will get it flatter next time.

James

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larrym Avatar
larrym Larry M
near Sacramento, California, USA   USA
1968 Volkswagen 1600 "Manx"
Hap - et al

long time ago (well sort-of long ago) - we had several dcoe jet/etc discussions here - i will look for my old notes & Butch Gilbert's advice, & post/threads

i ran/run a dcoe45 on an 18v with Butch's datsun-J billet cam & Butch's advise on carb-manifold mods

i never had a rpm flat-lining problem like you describe, nor did any of my race buddies who ran the Butch setup since mid-1990's

- able to hit 7500 with little problem

fwiw - no other mods - when i switched to a milder D9 cam on an MG billet - it chewed up the gears in 2 weekends at 7000 rpm+ - a well known MG cam gear problem posted here many times - (that's not relevant to your question - but is relevant to other racers who want cams that can survive high rpm)

for those who care - i found a source for datsun_J billets, and had 2 of 'em ground to my spec by Delta in the last 2 yrs - Basil used to supply, but no longer does so\
.



**************

If they say it on the Internet, it must be true.

Speedracer Avatar
Speedracer Platinum Member Hap Waldrop
Greenville, SC, USA   USA
1967 MG MGB Racecar "The Biscuit"
In reply to # 3514389 by larrym for those who care - i found a source for datsun_J billets, and had 2 of 'em ground to my spec by Delta in the last 2 yrs - Basil used to supply, but no longer does so\
.


I just rebuilt a engine for a guy who had a Datsun cam in his MGB, and the cam was relatively new to the engine, like 3 weekend from new, it broke and chunked out a large section of the drive gear on the cam. While the Datsun cam may have a better gear count and angle, it's made out of cheap cast iron, an option I would never consider. Now if one made new Datsun cams out of steel, then OK.

On the Weber, I think he still looking at the right combo of jets, and air correctors. He could not get to good dyno with AFR software before the weekend, which is the Jefferson 500, so the track will be his dyno, and he as all the stuff necessary toake the changes.

I will say this, because it needs to be said to new racers. Gong to dyno only serves one purpose, to nail your fuel mixture, some would say ignition timing as well, but we've already figured that one out enough to not mess with it on the dyno. So if your local chassis dyno does not have a good AFR hook up that interacts with their dyno software, then it is not worth going to the dyno, until you find one that does. Get your car running pretty good before you go, or you waste alot of time, and once that has all occured, then dial in AFR, and you are done.

I am pretty convinced there is nothing you can do with single DCOE 45 that will make it better than two good HS6s. I know, I know I just threw Webers racer's world into tail spin, and many will tell me I am full of shit, my challenge to them is to see for yourself. Smaller, but more efficient does not equal more power. So there ya go, haters can hate now smiling smiley



Hap Waldrop
Acme Speed Shop
864-370-3000
Website: www.acmespeedshop.com
hapwaldrop@acmespeedshop.com


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fast-MG.com Avatar
fast-MG.com Gold Member Dave Headley
Cortez, 4 corners, Colorado, USA   USA
Hap, as you and I have discussed, the advantage 1 3/4" SUs have over a 45DCOE is manifolding. The SUs get a straight shot into the port while the DCOE has compound curves in the manifold to port runner. Now, using the best DCOE manifold is helpful(IMO the straight runner Cannon is not one of those), also opening up the DCOE to larger chokes(38 or 40) or a bigger 48DCO will get the performance closer to the SUs. The best setup is two 48s using only one choke per port runner which gives the advantage of DCOE fuel control and a straight runner. This of course depends on if you have an engine built that can use the better carb flow. BTW, my preferredSU carbs for these is the HIF6.


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larrym Avatar
larrym Larry M
near Sacramento, California, USA   USA
1968 Volkswagen 1600 "Manx"
In reply to # 3514672 by fast-MG.com .... manifolding. The SUs get a straight shot into the port while the DCOE has compound curves in the manifold to port runner.

- dunno about the curved flow in those dcoe manifold versions from APT, like the Maniflow or the SU Parts Vendors 45dcoe version - have one of Mike Pierce's TWM (Warnerford copies)

the 801 canon is not curved, but "flow irregularities" do tend to create coanda effect

- which in effect starves one of the 2 cyls on each port - i.e. only running on cyls 2 & 3 at idle, where it is most noticeable

the Butch Gilbert "fix" for that on the Canon 801 is effective - at least it was it was for me & several others; - it worked on the curved TWM too
(Butch was not fond of those curved versions)

you can find the "fix" discussion here
me too - http://www.mgexp.com/phorum/read.php?1,1946177

i found a longer text version of the ananlysis & fix from an e-mail conversation with a racer guy in Australia - but what is in the post is enuf for any handy fellow to duplicate

turns out i actually did the "fix" on the TWM too - it is out in storage somewhere



Edited 2 time(s). Last edit at 2017-05-20 02:32 PM by larrym.

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bills Avatar
bills Bill Spohn
W. Vancouver, , BC, Canada   CAN
I've played around a fair bit with Weber sidedraft carbs (and Dellortos and Solex), and finally came to a couple of conclusions.

1 - the Webers and that ilk probably can produce bit more full throttle power, but getting them set up just right can be a real swine, while SUs (usually in the 1 3/4" size - I've played with 2" and am definitely not a fan) are easier to tune and seem more forgiving.

2 - on engines with one carb throat per cylinder, I love Webers. I've run 40s on my vintage HRG crossflow engine and on my Lamborghini (which would pull smoothly from 1,000 rpm in 4th gear from about 10 mph to well over 100 mph without a burp) and 45s on my large capacity MG Twin Cam and on a hot street 87 mm bore Triumph engine, with similar results.

Horses for courses I suppose.



Bill Spohn www.rhodo.citymax.com/carstuff.html
Current: 1958 MGA Twincam (race car (170 bhp)),1962 MGA Deluxe Coupe (98 bhp)
1957 Jamaican MGA (200 bhp)1965 1971 Jensen Interceptor (350 bhp)
2009 Pontiac Solstice GXP Coupe (350 bhp)
2007 BMW Z4M coupe (340 bhp)
Recent: 1969 MGC roadster (175 bhp),Jensen CV8 (375 bhp),
1969 Lamborghini Islero S (350 bhp), 1988 Fiero GT turbo (300 bhp)
North Vancouver BC

B-racer Avatar
B-racer Jeff Schlemmer
Shakopee, Minnesota, USA   USA
1950 Willys Jeep Pickup "Ratrod"
1971 MG MGB
2014 Dodge Charger
After re-reading your posts beginning to end, my suspicion is your AFR gauge may have a skew. I have 3 LM-1 meters now and they all read a little different. I check baseline on my wife's EFI car (Charger). One meter reads 14.9, one at 14.7, one at 13.9 all when using the same O2 sensor. As long as I know which one I'm using, I just calculate in the skew. Innovate says they all work perfectly. ??? The 13.9 one has been retired.

If you go significantly rich at 6500 it would indicate an ignition misfire. Make sure you have 12+V at the coil at that time by wiring a voltage gauge direct from the coil. 13+V would be better. Hopefully nothing else is stealing power from the coil, like an MSD.



jeff@advanceddistributors.com



Edited 1 time(s). Last edit at 2017-05-25 08:01 AM by B-racer.

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