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Holley carb and performance, what do you advise me to do ?
#1
Hello guys, I just mounted the 4V Holley 1850-3 carb in my 72 Mustang Grandé.

The car has a 351C engine and there was a 2V Motorcraft carb in it.
So I bought a Weiand 4V intake and that used Holley 600 CFM carb. Now everything is set OK and the car runs great, a bit less HP at lower engine RPM, but when I go over 3000 RPM it opens nicely and the engine delivers a lot more power. Big Grin
I'd like to try something (in the future) that can deliver more power at lower RPM, what do you advise me to do ? New carb, more CFM ?
The engine in the car isn't the original one, it's a 1971 351C 2V (now turned into a 4V).
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#2
You don't want to go bigger cfm to get better low end power.

Check the power valve to see what vacuum it is set at. (You will have to take off the front bowl to check). A good rule of thumb is 1/2 of whatever your idle/cruise manifold vacuum is. It's possible it isn't opening soon enough (or too soon). Do you see any black smoke from the exaust at the lower RPM's?

You can also play with the spring settings on the vacuum secondaries. Believe it or not, they could be opening 'too fast'. Often people will say they can 'feel the secondaries' opening but what they really feel is the engine catching up to the added available air flow. There is a spring kit you can buy with several different springs. Do not try to modify the spring, do not remove the check ball.

You might look at the timing and how fast you are getting to about 34 degrees advance. Clevelands like a lot of initial timing and they like to get it in before 3000 rpm (general rule). Do you have a vacuum advanced distributor? Is it hooked up to manifold or ported vacuum?

Only change one thing at a time. Wink


'Mike'
73 Convertible - 351C/4V CC heads/4bolt/forged flat tops/comp 270/rhodes/mallory unilite/tri-power/hookers/glasspacks/c6/3.50 limited slip/Gear Vendors/Global West sub frames, strut rods and shelby style traction bars/ Rear sway bar/tilt steering (not original)

Pics of modifications included in:
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#3
Thanks, that's what I thought, so maybe it's that spring thing that has to be adjusted. Which spring kits do you advise me to get ?


will e;37373 Wrote:You don't want to go bigger cfm to get better low end power.

Check the power valve to see what vacuum it is set at. (You will have to take off the front bowl to check). A good rule of thumb is 1/2 of whatever your idle/cruise manifold vacuum is. It's possible it isn't opening soon enough (or too soon). Do you see any black smoke from the exaust at the lower RPM's?

You can also play with the spring settings on the vacuum secondaries. Believe it or not, they could be opening 'too fast'. Often people will say they can 'feel the secondaries' opening but what they really feel is the engine catching up to the added available air flow. There is a spring kit you can buy with several different springs. Do not try to modify the spring, do not remove the check ball.

You might look at the timing and how fast you are getting to about 34 degrees advance. Clevelands like a lot of initial timing and they like to get it in before 3000 rpm (general rule). Do you have a vacuum advanced distributor? Is it hooked up to manifold or ported vacuum?

Only change one thing at a time. Wink

  Reply
#4
http://www.holley.com/20-13.asp

They are available from a lot of on line places. Here in the states they are at some local auto parts stores as well.

Did you adjust the timing at all when you put the new carb on?

'Mike'
73 Convertible - 351C/4V CC heads/4bolt/forged flat tops/comp 270/rhodes/mallory unilite/tri-power/hookers/glasspacks/c6/3.50 limited slip/Gear Vendors/Global West sub frames, strut rods and shelby style traction bars/ Rear sway bar/tilt steering (not original)

Pics of modifications included in:
  Reply
#5
Is this the intake? http://www.summitracing.com/parts/WND-7516/?rtype=10
If it is, the torque loss at lower RPMs is due to the intake manifold being a single plane design. A larger carb would just make the low RPM torque worse.

Chuck
  Reply
#6
Yes timing is adjusted and yes this is the IM I have, anyway I don't really understand how a dual plane IM would do better ?
Thanks.
  Reply
#7
Sly_drums;37460 Wrote:Yes timing is adjusted and yes this is the IM I have, anyway I don't really understand how a dual plane IM would do better ?
Thanks.
This is not the most technical explanation but, I think it will explain why the dual plane would work better for your application. Chuck http://www.popularhotrodding.com/enginem...ewall.html

  Reply
#8
Fantastic article!!!

[Image: 2rr7aiv.png]

Just cruising along minding our own business when BAM!!! The LAWS show up.
  Reply
#9
Thanks ! That's great input !
  Reply
#10
That is a really good article. I loved the last line:

"While logic dictates that a single four can meet any street engine's requirements, emotions ensure that multi-carbs are here to stay."


Guilty as charged...


'Mike'
73 Convertible - 351C/4V CC heads/4bolt/forged flat tops/comp 270/rhodes/mallory unilite/tri-power/hookers/glasspacks/c6/3.50 limited slip/Gear Vendors/Global West sub frames, strut rods and shelby style traction bars/ Rear sway bar/tilt steering (not original)

Pics of modifications included in:
  Reply
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