MYRON Posted August 26, 2000 Share Posted August 26, 2000 John, You seem to have much more experience than i do messing with carbs.. My carb is a Holley HP4150 750 mechanical unit,no choke and it has an 850 base plate. I think it is supposed to flow something like 830 CFM.. I have Dart heads with 2.05/1.60 valves, 215cc runners and i think they are 64cc chamber. I am using a Brodix HV1 pro bracket dual plane intake that is ported to match the heads and also the plenum is ported as well I am using a solid roller camshaft with .567 lift on the intake & 288 duration. I am also using crane gold 1.65 ratio rockers which brings the lift up to i think about .609... This car should have way more power than I have been able to get out of it.. The power valve that i removed has the letter "d" and a "5" across from each other it also has a "3" and "9" across from each other.. where do you think that i should start over on the jetting? BTW: It used to pull like an ox up to 6500 rpm. Now it tapers off and lolly gags from 5-6000 rpm.... Myron Quote Link to comment Share on other sites More sharing options...
John Scott Posted August 27, 2000 Share Posted August 27, 2000 Dang Myron, your engine specs are impressive! No wonder you're breaking things. I don't want to tout myself as a carb. specialist. I've read lots of articles over the years and been pretty sucessful doing rudimentary tuning on mine. I would think on a street engine I would leave the primary side powervalve in. Drag cars can get away with out PVs, when the only throttle position is wide open. Start with your vacuum reading at idle and put in a PV 2 numbers lower. The vacuum reading should be done IN GEAR for an automatic. I need to correct the way to read the #s on the PVs. Looking at the face of a PV divide the face into four quadrants with the letter in the top left. The letter is the Month code A-M with J for Sept. Directly under the letter is the Year. Across from these on the right is the pv's vacuum opening, for example 6 over a 5, meaning a 6.5 in. vacuum valve. I have 228/232 duration @ .050 on a tiny engine and manage 7 in of vacuum. I bet with a big V8 your idle vacuum is going to be higher. Start with the stock jetting. With the back plug in keep your secondary jetting about 6#s higher (some go as high as 10). Then go out and have fun with that Gtech! Quicker usually means you're going in the right direction (0-60) but for sure, a higher mph reading (1/4) is more hp. If this carb. doesn't seem to do the job, I wonder if an 850 or small Dominator is in order? Good luck. That has to be one hair raising ride when that beast is tuned. JS [ [This message has been edited by John Scott (edited August 27, 2000).] Quote Link to comment Share on other sites More sharing options...
MYRON Posted August 27, 2000 Author Share Posted August 27, 2000 Thanks for the props on the motor. If i can get it tuned properly i think it will be real scarry!.. Unfortunately I cannot draw a vaccume on it with it in gear with the axles busted! With it in park it is drawing a 10.5 vaccume. I just bought 3 different power valves and some more jets, but i will have to go find some axles before i go to tuning it!... I will be seeking more help when i get it driveable again.. Myron Quote Link to comment Share on other sites More sharing options...
Mikelly Posted August 27, 2000 Share Posted August 27, 2000 I'm in the same boat as Myron. I'm not great with Holley tuning. I've contemplated putting an Edelbrock Carb on it for the ease of setup and reliability. Anyway, Same story as Myron, when the car is right, it is scary to drive. Yesterday I swapped in 74 jets in the primary, and a 6.5 power valve was swapped in. I had a 4.5 in it and that is gone. I'm gonna stick with 79s on the secondary for now. The Secondary has no powervalve in this carb. My carb is close to the setup as Myron's, with no choke plate and flowing aroung the same number. I have annular boosters. My intake is an Edelbrock Victor Jr. Singleplane that was port matched to my Dart Conquest heads. Heads have 1.5 roller Hyrdaulic rockers and I'm running 2.05/1.6 valves in it. Cam is a 530/550 lift roller hydraulic grind with 292/284 duration. And John, you need to pat yourself on the back, 'cause you know a lot more about Holley carbs than I do, and you have given me areas to check. I already swapped the heavy springs in the MSD distributor out for lighter ones and recurved the distributor so I get more of my advance in by 3000. I haven't driven the car yet, but I'll give you an update after I drive it Tuesday. Mike ------------------ "I will not be a spectator in the sport of life!" mjk [This message has been edited by Mikelly (edited August 28, 2000).] Quote Link to comment Share on other sites More sharing options...
pparaska Posted August 28, 2000 Share Posted August 28, 2000 Guys, on the question of the Edelbrock. I like alot of the features that I read about (no spilled fuel when tuning, the metering rods are easy to change, and it is built for other than just WOT use), but has anyone used both a Holley and an Edelbrock (or the Carter AFB) and have opinions? I have a 3310 Holley (750 Vac secondary) on my motor now. A little big, but hey, it'll just just 2 barrels until the back two are needed - I have the quick change secondary spring kit in the carb. Quote Link to comment Share on other sites More sharing options...
Administrators SuperDan Posted August 28, 2000 Administrators Share Posted August 28, 2000 Pete, I have used both. Im no carb expert but what I found was for the ultimate in tuneablility and performance = Holly. For great drivablity = Edelbrock/ Carter AFB Just my .023343211 cents. ------------------ http://24.4.88.44/members/dporter/DanZ.html Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted August 28, 2000 Share Posted August 28, 2000 I HAVE TO AGREE WITH YOU. IF YOU WANT ALL OUT DRAG RACE QUALITY THEN GO WITH THE HOLLEY. IF YOU WANT TO ENJOY YOUR RIDE THEN GO WITH THE EDLEBROCK. I HAD BOTH ON MY TRUCK AND I REALLY LIKE HOW EASY IT IS TO TUNE THE EDELBROCK. THE ONLY PROBLEM I HAD WITH EDELBROCK IS THE ELECTRIC CHOKE. HOLLEY IS A GREAT CARB BUT YOU ARE CONSTANTLY TUNING TO KEEP IT RIGHT. SO, JUST MY 2 CENT, GET A EDELBROCK. I HAVE THE 750 ON MY TRUCK AND LOVE IT. I HAVE THE 850 EDELBROCK ON MY Z MOTOR BUT I HAVEN'T GOTTEN TO RUN IT YET EXCEPT ON THE ENGINE STAND. I HAVE PROBABLY RAN IT A TOTAL OF 4 OR 5 HOURS ON THE STAND SO A BRAKE IN SHOULDN'T REALLY BE NEEDED WHEN IT MEETS THE CAR. Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted August 29, 2000 Share Posted August 29, 2000 Mike - Demon now has a tuning video out for their carb that might benefit you - spotted it in my Mustang mag tonight. http://www.demoncarbs.com/index_copy.htm is their site or call (706)864-4712 to ask about it. I'll be damned if I could find the silly thing on their site (grr). P.S. folks - I know so little about carbs it's not funny. I'm learning lot's here! Wish I wasn't going to have to fool with one at all.... Quote Link to comment Share on other sites More sharing options...
John Scott Posted August 29, 2000 Share Posted August 29, 2000 Mike, please no pats unless we've solved a problem. I know too light of advance springs will cause the timing to bounce around at idle. Shooting for all of it in by 3000 is on the money. If anyone gets ahold of that carb tuning video, post the information. My tips come from 25 years of car magazines! The Holley really hasn't changed too much. I think its a great performance carburetor with the dbl. pmprs., though having more perf. potential, being much more fickle. My favorite carb. was the old Q-jets. With a few modifications they really performed well on mild street engines. Much of the fine tuning is going to be trial and error. This is a fun part of performance car ownership. I've spent lots of time on my favorite stretch of long flat blacktop trying powervalves, timing, re curving etc. Access to a wheel dyno or the 1/4 mile would do wonders. I wouldn't discount having a professional do the tuning either. With the ultra high hp some of you are running its going to be tough from the seat of the pants dyno. When I change to the smallest pulley, I know I gained a huge amount of hp. My 0-60 times were much slower due to never hooking the tires in 1st and 2nd. Fine tune the accel pump(s)/ squirters for the launch, 60 ft. then jet for max speed in the 1/4. I've heard of over 20 hp gains found in correct jetting. JS Quote Link to comment Share on other sites More sharing options...
Guest mattrp Posted August 30, 2000 Share Posted August 30, 2000 How about one of you very knowledgeable guys writes an article on all this stuff. My carb tuning experience is stick the tach on it, turn the mixtures till the rpms peak, and you are done. I have no idea where to start with jetting, power valves, etc, even though you guys are being pretty damn helpful. I was just kinda hoping for a step by step explanation of the process. Currently I have a 305 with stock heads, stronger valve springs are the only mod there, and a cam which I believe has a duration around 220, 228 comes to mind, and a lift of like 450. I don't have the numbers here, but its a torque cam all the way, no high revs. I'm running flat tops and about 9-9.5:1 compression. I have a holley 600 single pumper spread bore feeding an edelbrock performer intake. How much do you think I could gain with: Carb tuning New larger double pumper non spread bore carb New heads The motor just feels like it wants to go more, but its outta breath. My shop claims 300+ ponies at the crank, but i am doubtful. Thanks Matt 72 500Z Quote Link to comment Share on other sites More sharing options...
John Scott Posted August 31, 2000 Share Posted August 31, 2000 Matt, I'm sure there are some really good books written on the subject of Holley tuning. Most of us have experimented trial and error. I had many over carbureted hot rods 'till I figured that the biggest one on the shelf didn't always make it go faster. Double pumpers will make more power due to the instant opening of the secondaries (rapid pressure drop). This allows a denser initial fuel/air charge over a vacuum secondary carb. which needs to wait for engine vacuum to open. They're great for stick cars or higher stall autos. I've always found them a bigger pain to tune, especially if you are running one too big for the engine. Some really basic rules of thumb are 1.6 cfm/hp. And the ol' formula: Engine cid X Max RPM ______________________ 3456 Either way gives you a pretty conservative carb size. Lighter cars with steep gearing and healthy engines can go bigger. You'll see everything from 600s to 850s on smallblocks. CFM wise 600 is a pretty good selection. Out of the box jetting and PVs are usually pretty close. Its your job (And half the fun) to fine tune them. I don't know much about the 305, but fuel in and out is everything. The biggest gains I've seen in hp came from head work. The first time I spent a boatload of cash on a professional porting, polishing, cc ing, the gains were nothing short of incredible. High comp, big carbs, headers, cams, etc are all limited to what flows through the heads. I'd say $$ spent on heads for a performance project is money well spent. My 2 cents. JS [This message has been edited by John Scott (edited August 30, 2000).] Quote Link to comment Share on other sites More sharing options...
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