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Jetting
:confused: I have a 351 W with a Holley 650 and a Edelbrock Aircap intake manifold. The problem is it runs real rich with 68s. I am at 6500 feet in elevation. I was wondering what jets other people have and at what elevation?
Brad |
Are you using a PCV valve? Carb sometimes needs to be jetted richer to adjust for extra air from PCV.
Are you using a hydraulic roller cam? These things really pull vacuum, and carb may need leaning out because cam works so well. I have similar setup. 351W, 650 Holley DP, hyd roller, Ede Perf RPM. Holleys come from the factory with worst case jetting. For a more optimum street motor, they need leaning out. I jetted primaries down to 64 - 65. |
Jack21
Yes I am running with a hydraulic roller cam. Thanks for the info. Guess I'll change the jets soon. Thanks |
Jack 21
What are your secondaries jetted at? My barry grant 650 dp came with 70primary and 78 secondary. Im getting a new jet kit this week and am going to do a little experimenting. I think most of the carbs are delivered rich. later guys |
Really need a cam, head and intake profile to suggest proper jetting for your setup. In my case I'm running a 342ci, 750 custom dp with 78 primary and 84 secondary and a 3.5 power valve. I don't have much vacuum. And I am running a hydraulic cam, it just happens to be 245-256 duration with 595 lift. Also running Victor intake and heads with 210cc intake runners.
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BG 650dp, AFR 165heads, rpm air gap, Crane 2030 216d at .050 intake and 220d at .050 exhaust. .533 intake lift, .544 exhaust lift.
thanks |
351W motor has TFS TW heads, Perf RPM, CompCams retrofit hydraulic roller 224I/224E w/.533 lift. Using CompCams pro magnum steel roller rockers, 7/16" studs, 1.6 ratio. Motor idles rock solid at 850 RPM, and pulls 15" - 16" vacuum at idle.
Initial setup with Holley. Switched to a BG Demon 650 DP. Wow! What a difference. Honestly, if you're using a cam with over 222 deg intake duration, these B.G. Demons are well worth the extra $100 over the cost of a Holley. But also too rich with out-of-the-box jetting. Switched power valve from 6.5 to 8.5. Jetted 70P/78S down to 67P/75S, and could still go leaner. I can understand why factory jetting is so rich with some of the cams guys use. Hardly any vacuum. But I wish Holley & BG would advise us about this. |
I also forgot about your elevation. You will need around two jet sizes lower to have the same mixture as someone at sea level. What octane fuel you run actually will have a little to do with it also. But mainly if you're going from premium to 110+ octane. Smaller jets the higher the octane. What jets and powervalve you use is based mostly on vacuum. i.e on my stage 3 650 double pumper I ran 72 primary and 75 secondary. I've done nothing but switch to a custom 750 double pumper and now I'm using 78 and 84. All because the differential pressure across the carb is lower. I need bigger jets so this carb will suck in the same amount of fuel my 650 did for any given air flow.
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