>Tony wrote:
>>Hello all, I've got a '77 Spitfire 1500 with Weber DGV carb and headers on
>Then Randy replied
>> You already have more carb than the 1500 can use. Indeed, enough that
>getting
>>the car to accept full throttle at low rpm is a problem. I am not saying the
>>DGV conversion is a *good* thing. The jetting as supplied and the manifold
>
>> That said, you're not going to make any significant performance gains by
>> changing to a different carb set up. Changing to the twin SU/Stromberg or
>> a single sidedraft Weber/Mikuni/Dellorto may gain you something in
>drivability
>> but not much in terms sof raw power. 70's cars were seriously detuned to
>meet
>Sorry Randy but I would have to seriously disagree with here :
Sorry, Gerry, but I would have to disagree with that. The places where your
reply relates to the original post and my reply, you agreed with what was
said.
>...
>I fitted a Weber 45 (?) DCOE carb, a 4-branch manifold, Lucas comp. dizzy,
>and removed the fan (I have an electric fan). Initially the carb was way
Okay, Tony has a 1500 with a 32/36 DGV on it. This carb presents a throttle
bore area of 18.22 cm^2 to the cylinder. You reply using a reference of a
Weber DCOE 45 (or maybe 40). The 45 presents an area of 15.90 cm^2, while a
40 gives 12.57. I realize it is better to compare choke sizes to
determine flow potential, but I do not have that data on either carb.
Comparing thottle bores is close enough for this. I stand by my statement that
the DGV is more carb than a stock 1500 needs.
>....
>The car felt great ! throttle response was instantaneous, power above
>2500 rpm was strong, the engine would rev beyond 6500 rpm (although somewhat
>noisy !)and fuel consumption was about 26mpg.
Throttle response and fuel milage... two parts of drivability. I did say that
the DCOE/clone or twin stromberg/su setup would beat out the DGV here.
>...
>I don't remember the 1/4 mile times but the fastest 0-60 time was
>12.1 seconds (I think the standard Midget was around 15-16 seconds), which
>showed that I had boosted the power of the engine quite considerably by making
>the 4 changes I have described earlier.
Oh, btw, stcok 1500 valve springs give up long before 6500. Sure this thing is
stock? Twasn't unusual for a 1500 to need a rebuild before reaching 50K.
>Okay so the Weber DGV is not as good a performance carb as the DCOE, but I
>think
I didnt say that. I said that due to the poor jetting as supplied, and the
cheap, badly designed manifolds included, the DGV conversion kits are not all
that hot. There is nothing wrong with the basic DGV, just as there is nothing
wrong with a SU or Stromberg (except that auto-choke). See Scott's excellent
post about SU's. Unforch, Scott's article did not go into the scope of flow
control. Assuming the carbs being considered at not vastly over or under sized,
there is a whole lot more to be gained or lost in the manifold than in
changing from one carb type to another. The DGV manifold is bad. The stock
1500 is worse. The MGB (75->) is the ultimate in absurd. And, due to
the nature of the carb design, most DCOE manifolds are quite good.
David Vizard's book "Tuning BL's A Series Engine" goes into great detail,
in plain understandable English, on the subjects of SU's, Strombergs, Webers,
and manifolds. Very worthwhile reading for anyone with a 4 cylinder that
has one of the above.
>ANYTHING is better than the stock ZS. I have a DGV carb for the Midget which
>I may swap and see what the difference is, But I remember when I first fitted
>the DGV and threw away the ZS, the performance increase was substantial.
If you do this, I would love to hear the results. I have never had the chance
to do back-to-back tests using the same engine/etc. I have tuned and driven
many different British cars (literally hundreds) with DGVs, DCOE's, ...just
about everything. My observations, which I have stated here several times, is
the DGVs are finicky cold, bog, and, with the poorest manifolds, flood when
turning. And it could all be cured with a little jetting, and a properly
designed manifold.
>To the original poster :
>If you are thinking of getting a Weber, and want power - get the DCOE. You
Uh, Gerry, he *already* has a Weber, a DGV. You even quoted that part of his
original post. Tony originally asked (effectively) if yet another carb swap
would improve performance. I replied that given where he currently is, the
next step ought to be more compression, then cam/ports. Do you disagree with
this, and if so, why?
Randy
randy@taylor.wyvern.com
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