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MG MGB GT V8 Factory Originals Technical - 500 CFM vs 400 CFM Carburetor
|Has anyone with a 3.5L engine switched from a 500 CFM to a 400 CFM carburetor. Were the performance and other improvements worth it.|
|Jim...You might check with Dan Lagrou of D&D...he has a good handln intakes, carbs, and proper jetting.|
|Both are overkill for this engine. Rick is right about D&D. I told Dan what I was building and he downjetted a 500 Edelbrock for me. I can dig up the numbers if anyone is interested on what he suggested for a stock 4bbl 215.|
|Scott: If you have the jetting information that would be great.|
I called D & D and described the mods to my Rover 3.5 with an Edelbrock 500CFM carb. He sent me #1441 metering rods and #1421 jets. My engine is bored 20 over, 10.0:1 pistons, fairly agressive cam, porting and polishing of heads, ceramic coating on pistons/combustion chambers, ceramic coated block hugger headers.
I haven't run the engine yet as I'm just doing final assembly.
Not sure that a 400cfm carb will offer any advantage over a properly rodded/metered 500cfm.
I ran a 500cfm Carter on my Olds 215 engine for a couple of years - performance was very smooth and with no bogging off idle. The only issue that I had was that the carb ran rich in the cruise mode with the standard (out of the box) rods and jets.
|Here is my setup and recommendations for the 500cfm Edelbrock, per Dan:|
Stock '63 Buick 215, 10.75:1, stock heads and cam but less restricted exhaust planned, stock timing.
Same carb set up as Phil O above. 1441 (0.062x0.052 rods) and 1421 (0.80 jets).
|I tried the 1441 rods and 1421 jets and drive ability was terrible (too lean). Havenít had time to experiment with a slightly richer but leaner then what I have now setup. Others have had success?|
|I would think that the .083 main jets would be lean enough.|
|Jim, What engine setup are you running? |
Carl, do the jets and rods need to be switched as a matched set? What goes with 0.083?
|My engine (rover 3.5) runs a very rare 1961 edelbrock twin two barrel manifold,I have adapted Ford V6 carbs that flow 300cfm each (David Vizard book)the car runs sweet with good mpg and plenty of power on a otherwise standard engine.|
Sort of, but not exactly. :)
There is a range of rods that can be used with each step of jets. The rods are more easily changed to fine tune you application.
Someone posted this excellent link not long ago:
More Edelbrock specs & tuning guide:
Right now I am using .083 main jets with .068X.052 metering rods and .092 secondary jets.
|I swapped the jets and needles on my Edelbrock to .083" (#1422) and .067" x .047" (#1443) respectively.|
Car runs great and got the air/fuel mixture set to 13.7:1 (I've got access to a gas analyzer).
|I have a 3.5 SD 1 Engine (cr 9.35) fitted to my GT and installed a Holly 390 on a JWR dual plane inlet.|
Primaries are jetted .51, secondaries .53.
Exhaust and headers are comparable to the RV8 style.
I have done this conversion and setup nearly 20 years ago and have not found any reason for further mods.
My only problem is that I feel uncomfortable at speeds of more than 210 kilomertern/hour on the Autobahn.
Calculating flow rate, the 390 is more than adequate as far as the engine is still in stock condition.
Power at the fly is @ +190 HP (DIN).
Gearbox is SD 1 5-speed, Rearaxle is 3.3:1
on 175-14-HR tieres on 5.5 inch rims from a Relian Scimitar GTE.
|I think I'd feel a little uncomfortable at 130mph in a 'B. The only thing I could suggest is a 3.09 rear end which might make things a bit more relaxed at speed, at a cost of worse acceleration.|
|I wish we had somewhere around here to attempt speeds like Ralph has tried. May have to ship the car to Germany.....|
Dave: "The only thing I could suggest is..."
For comfort, I'd suggest more toe-in and a different ratio steering rack. If I sneeze my car makes a nice neat lane change, God love it! IMHO MGBs are better suited for twisty mountain roads vs. the Autobahn. I'd leave that high speed nonsense to boring cars (like BMW, Mercedes, Corvette...) and trains.
Let's see now. What was this thread about?
Oh. I did in fact switch from the 500cfm to the 400cfm - but then I switched back. My 500 was nice and new, whereas I picked-up the 400 used. With 20-20 hindsight I can advise that used carburetors are "pigs in a poke". The 400 SHOULD be better, but the one I had was apparently worn out (beyond what a rebuild kit would fix.) The 500 works fine. Probably its progressive secondaries are the reason we can get by with it so nicely. I wonder if we ever really get them open? Mine sits on a stock Buick manifold. I had to re-jet when I moved to Colorado, of course. (I don't recall jet numbers.) One day I'll upgrade to F.I.
This thread was discussed between 11/05/2005 and 25/05/2005
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