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Holley Carb Tuning
Need Holley carb tuning help.
Superformance SPF890, with SVO Crate 460, 535hp version. Ford Tech recommended dual plane manifold with 750 Holley to help out midrange torque and street manners. If anyone running 750 cfm, manual choke, dual pumper, would appreciate tuning data, i.e., jets, rods, power valve, etc. Mine is out of the box stock. Seems to run rich, loads up. Any suggestions would be appreciated. Live in North Florida area. If anyone knows of a good Holley mechanic in this area, please advise. Thanks, Lynn Johnson |
Lynn,
Most carbs, out of the box, run rich. I would suggest you invest in a set of jets and start jetting it down, front and back, 2 numbers at a time. Each time you jet down go out and check your plugs. Do this by bringing the engine, under load, up to about 3 grand and just cruise there for about 30 seconds. Then cut the engine and pull over. Yank a plug or two and see how they're burning. Keep jetting down until it is too lean and then go up 2 numbers. That should set your jets. Also, on by BG (similar to Holley) I changed my linkage from progressive to one-to-one. This is done by changing the little rod on the drivers side. Available in any performance store by BG, Holley, Moroso, etc. I also put in, at the suggestion of BG tech, a 1", 4 hole spacer. Doing all these things increased my hp on the dyno by about 40-50. Roscoe |
Roscoe - thanks for your reply. Headed to the store today. Do you think NAPA will have the trottle linkage?
Will let you know results. I wanted to run the 1" spacer, but only have 3/4 inch clearance now between air cleaner and hood. Maybe I can find one in 1/2 inch size? Lynn |
Lynn,
Don't know if Napa would have it, my guess is no. 1/2" is better than none. Make sure it's a 4 hole and not just one big opening. Carburetor Service Parts Secondary Connecting Rods Part #: 20-54 http://www.holley.com/HiOctn/ProdLin...pics/20-54.jpg Roscoe |
Roscoe,
have considered going to the 1:1 linkage. can you tell me what differences you noticed in different types of driving you noticed on the street between the two linkages ?? good and bad . |
Roscoe,
Got it, the search is on. Thanks again. Lynn |
Fred,
I made all the changes at the same time so I don't know which one contributed more but there was a noticable difference in performance, especially intial power. As I said, I picked up a significant number of hp on the dyno after the modifications. Roscoe |
Roscoe, please explain the difference in the 1" 4 hole spacer vs. the one big opening?.
Lynn, also check your vacuum and install a power valve 1 1/2 to 2 points lower. |
Lynn,
750 double pumpers are race carbs. They have rich main jets, about 5 steps higher than regular street carbs. The problem is that if you dejet it 5 steps the engine will run lean at low manifold vacuum because the Pvcr ports in the power valve circuit are undersized. What you need to do is either get a new carb or reduce the size of the main jets and drill the pvcr ports in the metering block. Go to this website, it will guide you a bit. I also suggest getting a book on Holley carbs. http://www.bob2000.com/carb.htm Matt |
Lynn
Have you set the fuel level in the bowls yet. My 750 would load up then eventually stall until I set the fuel bowl level. Paul |
Roscoe, Matt, Fred,
Pulled plugs this evening and all of them are black and wet. Definitely rich, big time. By the way, getting plugs out of a 460 in a Cobra is certainly a Houdini trick. Car has been rich all along, but has been getting along as I have only driven in town, at slow speed and max temperatures. Last evening I hit the Interstate and water and oil temps came way down, and when I got off at exit and stopped at light, plugs were fouled pretty bad. This says jets to me. Certainly carb was not on idle circuit during any of this time. This engine package, M-6007-B460 came with a 850 DP and single plane manifold. Ford Tech recommended dual plane manifold and 750 DP. That's what I have. Current carb is model 4160, part no. 0-4779C. Carb has see-through sight plugs, and fuel level looks pretty good. I have not made any changes, YET. I am listening to the thought of changing carbs altogether. Any suggestions. Have more power than I need, do not plan on doing any racing, only want instant response and easy driving manners. Other than changing carb, guess best thing to do is fine the local Holley guru, and take it to him. Thanks for your help, and I am still listening for suggestions. Lynn |
Lynn,
Why don't you get some jets and start bringing it down? Roscoe (from my earlier post:) Most carbs, out of the box, run rich. I would suggest you invest in a set of jets and start jetting it down, front and back, 2 numbers at a time. Each time you jet down go out and check your plugs. Do this by bringing the engine, under load, up to about 3 grand and just cruise there for about 30 seconds. Then cut the engine and pull over. Yank a plug or two and see how they're burning. Keep jetting down until it is too lean and then go up 2 numbers. That should set your jets. |
Make sure the powervalve gasket is seated properly; if not, it will run rich. If OK, follow Roscoes advice. Good luck! Len
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