jt1 Posted December 14, 2006 Share Posted December 14, 2006 355 NA 1st gen SBC, 10.5:1, pump 93 Carb is a Holley HP4150 830 annular, 86 square, 2.5/2.5PV, 32 high speed bleeds. Does it need: More jet F&R? More jet rear? Less high speed bleed? Check fuel pressure? Ebay the carb and go EFI? All help would be appreciated. John Quote Link to comment Share on other sites More sharing options...
getZ Posted December 14, 2006 Share Posted December 14, 2006 what's the spike at around 3200? A stab at the throttle usualy makes the accelator pump move and the reading go rich not lean. Also what are the two different colors representing? I assume you are tuning for power and not economy or emissions. 14:1 is chemicaly ideal, but rich is where you'll find more power at 13:1. Some people even favor a bit richer at 12:1 for carbs. I believe there is a graph from the edelbrock website that tells you how to jet, unfortunately it is for a carter or edelbrock. It doesn't look you are running that bad aside from the spike. Of course fuel injection will give you greater adjustability, but it is an expensive upgrade. That of course is just my opinion. I put an edelbrock pro-flo and it doesn't really make any more power (at least not that I notice), but I do enjoy cold startups. Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted December 15, 2006 Share Posted December 15, 2006 Looks like you need more pump shot and smaller high speed air bleeds IMO. Quote Link to comment Share on other sites More sharing options...
rytherwr Posted December 15, 2006 Share Posted December 15, 2006 IMO, go with EFI. I just changed a Bill Mitchell 600 hp 454 special edition sbc from a 1050 Dominator/World Products single plane to a Mass Air Flow system pretty much out of a 93 Mustang. Uses modified Edelbrock Victor Jr, Ford sensors, Chevy MAF and Ford EEC computer. Works absolutely great! After installation, I turned the key on a few times to build fuel pressure and it didn't turn over more than 3 times before it started. Almost always, if tuned properly, you will get around the same HP with EFI as you do with a properly tuned carb. It is tuned a little rich from the vendor, but I took it to the dyno and thrashed it for a few hours and had another chip burned. Plugs are nice and light brown no matter how I run it now. Where the EFI really shines is start-up (hot and cold), low end torque and especially driveablilty. Pls note I am using a MAF system vice MAP. MAF system does a LOT of the tuning for you as long as your MAF is set up for the injectors you are using. Had it down to the track last Sunday and ran consistent 6.71-6.73's in the eighth mile. Did I mention it is a great system??? ) Wayne Quote Link to comment Share on other sites More sharing options...
Turbo Meister Posted December 15, 2006 Share Posted December 15, 2006 I don't know what type or delivery capability fuel pump you are using but at WOT the AFR should remain constant and not lean out. It appears your engine is not getting enough fuel at higher RPM's. Quote Link to comment Share on other sites More sharing options...
Guest timmy72240 Posted December 15, 2006 Share Posted December 15, 2006 bro your fuel curve needs a heavier foot maybee two i shift my 355 chevy sbc roller every thing at 7500 havent blown one yet still trying...... Quote Link to comment Share on other sites More sharing options...
Paz8 Posted December 15, 2006 Share Posted December 15, 2006 You failed to mention the ignition system specs, spark timing plays a part in setting up the mixture on the carb. Just thinking out loud here. Quote Link to comment Share on other sites More sharing options...
jt1 Posted December 15, 2006 Author Share Posted December 15, 2006 GetZ: The lean spike surprised me, because the motor has no stumble or bog to it at all. I'm going to play with the cams and squirters a little. The two lines are two separate pulls, the first one blue, the second red with the idle mixture richened up a little. Economy isn't an issue, I want to make good power and not get into detonation. Doc: Will the smaller HS air bleeds flatten out the top of the curve, or the entire curve. This is the first carb I've messed with that has replacable bleeds. Wayne: Right now I'm going to stick with the carb. Two many other projects going on to make an EFI switch right now. Maybe one of these days I will get into the twentieth century. Hans: I wondered about the fuel pressure too, since this seems to me like a ton of carb and jet for a 7K 355. I don't have a guage, I need to put one on and check that possibility. Pump is a 6psi Carter. Timmy: You might be right. Several other people have suggested I just don't run this thing hard enough. I'm working on it. Dyno guy suggested one size smaller jet in front, one size smaller HS bleed in front, and two sizes smaller HS bleed in rear. We didn't have the right bleeds on hand, so I'm going to round some up and go back. Edit: Paz: Ignition is a MSD 6AL w/MSD dist. Timing is 18/36, black bushing, with two blue springs, getting full advance at 27-2800 rpm. John Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted December 15, 2006 Share Posted December 15, 2006 GetZ: The lean spike surprised me, because the motor has no stumble or bog to it at all. I'm going to play with the cams and squirters a little. The two lines are two separate pulls, the first one blue, the second red with the idle mixture richened up a little. Economy isn't an issue, I want to make good power and not get into detonation. Interesting Doc: Will the smaller HS air bleeds flatten out the top of the curve, or the entire curve. This is the first carb I've messed with that has replacable bleeds. There are three fuel circuits there, idle, low speed and high speed. You need to work on the high speed. Hans: I wondered about the fuel pressure too, since this seems to me like a ton of carb and jet for a 7K 355. I don't have a guage, I need to put one on and check that possibility. Pump is a 6psi Carter. Absolutely imperative that you make sure you have adequate fuel pressure at WOT, you'll need/want 7 to 8 psi at WOT IMO. Make sure the fuel bowls are set correctly, it may be just that your fuel bowl level is dropping and leaning it out!!!! Fuel delivery depends on signal, a 355 on an 830 carb isn't going to have alot of signal. Contrary to popular belief a large carb on a small motor tends to run lean due to low signal, requiring larger jets not smaller. Dyno guy suggested one size smaller jet in front, one size smaller HS bleed in front, and two sizes smaller HS bleed in rear. We didn't have the right bleeds on hand, so I'm going to round some up and go back. Edit: Paz: Ignition is a MSD 6AL w/MSD dist. Timing is 18/36, black bushing, with two blue springs, getting full advance at 27-2800 rpm. John IMO I'd work on the fuel pressure issue FIRST! Making sure you have adequate fuel delivery is easier than messing with air bleeds and jets, when in the end, if it's a fuel delivery problem, you'll be starting from zero again!!! Well, not zero but you may find changing all those air bleeds and jets has no effect. First you need to size the pump to the HP output of the engine, I don't know what the carter puts out, but your probably pretty close if line sizes are correct for that flow. Then you need to measure the fuel pressure under running (dynamic) conditions, so you can see if there is a problem with fuel pressure. IMO, if everything is OK, then start messing with the carb! People take note that on a pretty mild motor it's running pretty good with an 830 carb. Just when you thought it'd drown it. And for the people saying your not running it hard enough, you run it where it makes power! I shift at 6000 and trap at 6500... Quote Link to comment Share on other sites More sharing options...
dustin280zx Posted December 15, 2006 Share Posted December 15, 2006 for it leaning out at the higher rpms, i agree with dr. hunt. check the fuel pressure. Quote Link to comment Share on other sites More sharing options...
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