looking for advice on a carb

[mustangmike6996]

the cam is .541 intake and .544 ex im not sure what im going to do yet for rocker ratio but id assume 1.5:1 or 1.6:1 rollers its looking like 700 CFM or so with vacuum secondaries will be the most versatile carb for the money. ill probably go with a holley double pumper or QFT if i wanna spend a little more money.

 

[clement]

^That carb is like a more expensive QFT. For the the price of that AED, you can get a (Jeg's 793-SS-680-VSK) 650-680 cfm QF with a braided feed line, filter, and pressure gauge. Your 351w probably only needed larger squirters not another carb. I don't see how you could've gained 3 tenths by tuning your idle mix. Power is gained by adding or taking away fuel or timing or a combination of both. For the cash you guys spent on the carbs you tried, you could've tossed those Cleveland heads for some nice AFRs or ???
Do your homework mustangmike- if you go too small on cfm, you'll be leaving HP on the table. If your cam is anywhere in the .600+ lift range or your engine is built for 5500+ rpm, 750 cfm will fit the bill and can be tuned properly without stumble and instant response.

A. the 3 carbs were what we had between the two of us and another friend from previous projects. so they were bought and paid for a long time ago. so, the $600 spent on the AED wouldnt not have bought a set of AFRs. and if we wanted to do that we just would have put my TEA 225 high ports on his motor. not to mention these cleveland 4 barrel closed chamber heads flow over 300 cfm, so do really think just because a head says 'AFR' on it the car would be faster? its a 10.5:1 flat tappet, pump gas motor that runs 6.90s in the 1/8 on motor. its a high 10 second combination with a bunch of old garbage we had lying around. the 830 was leftover from my 347 that went 6.40s 103 on the motor. but back to topic, the AED picked up a tenth and a half in the 60'. im sure a set of AFR stock valve center windsor heads that flow the same or less with the valve way to close to the cylinder wall would have picked up the 60' up too, or not.

B. you think we didnt change squirters, jets, and air bleeds on all of them? we did. we spent 6 months tuning this thing and hadnt picked up anything and all the holleys had a stumble. and the holley tech line had no idea why. the 650 had the least stumble but was down 3 mph to the 830 and had to be short shifted due to running out of breath.

C. we havent even tuned on the AED yet, we set the idle mixture.

D. we spents hours on the phone with holley trying to make their carbs work. appearantly there is something different about the AEDs and the holleys. maybe they atomize the fuel and emulsify better. get what you like. i just report what worked.

 

[mustangmike6996]

A. the 3 carbs were what we had between the two of us and another friend from previous projects. so they were bought and paid for a long time ago. so, the $600 spent on the AED wouldnt not have bought a set of AFRs. and if we wanted to do that we just would have put my TEA 225 high ports on his motor. not to mention these cleveland 4 barrel closed chamber heads flow over 300 cfm, so do really think just because a head says 'AFR' on it the car would be faster? its a 10.5:1 flat tappet, pump gas motor that runs 6.90s in the 1/8 on motor. its a high 10 second combination with a bunch of old garbage we had lying around. the 830 was leftover from my 347 that went 6.40s 103 on the motor. but back to topic, the AED picked up a tenth and a half in the 60'. im sure a set of AFR stock valve center windsor heads that flow the same or less with the valve way to close to the cylinder wall would have picked up the 60' up too, or not.

B. you think we didnt change squirters, jets, and air bleeds on all of them? we did. we spent 6 months tuning this thing and hadnt picked up anything and all the holleys had a stumble. and the holley tech line had no idea why. the 650 had the least stumble but was down 3 mph to the 830 and had to be short shifted due to running out of breath.

C. we havent even tuned on the AED yet, we set the idle mixture.

D. we spents hours on the phone with holley trying to make their carbs work. appearantly there is something different about the AEDs and the holleys. maybe they atomize the fuel and emulsify better. get what you like. i just report what worked.

there is a lot of good info in this. i just dont think i can spend 600 bucks on a carb at this point in time. 300-400 wouldnt be too bad tho.

 

[mtaqua]

again, I'd look at someone who builds carbs if you are going with anything other than a stock holley. the cost is the same as the upgraded carbs and you can have one built for your motor by someone who you can call and talk to on the other end of the phone. rather than calling a tech rep at summit or jegs to help trouble shoot/tune.

 

[mustangmike6996]

again, I'd look at someone who builds carbs if you are going with anything other than a stock holley. the cost is the same as the upgraded carbs and you can have one built for your motor by someone who you can call and talk to on the other end of the phone. rather than calling a tech rep at summit or jegs to help trouble shoot/tune.

im not worried about tuning the carb, im an ASE master tech. I just want the right CFM and setup to start. i can tweak it where it needs to be.

 

[WTFO]

the cam is .541 intake and .544 ex im not sure what im going to do yet for rocker ratio but id assume 1.5:1 or 1.6:1 rollers its looking like 700 CFM or so with vacuum secondaries will be the most versatile carb for the money. ill probably go with a holley double pumper or QFT if i wanna spend a little more money.

What pistons, rods and stroke are you running with this cam? Unless you have a massive dome piston- 1.6 would be safe given that you're also using stock length push rods.

 

[clement]

free drop, deck height, how sunk the valves are in the seat, how much the deck of the heads have been cut, HG thickness, rocker ratio, ramp rates, the intake opening event and the exhaust closing event determine PTV clearance. you can have the same lobe and depending on the centerline its ground on can clear by a mile or not even be close to clearing. just because a pushrod is stock length doesnt mean its the correct length.

 

[WTFO]

A. the 3 carbs were what we had between the two of us and another friend from previous projects. so they were bought and paid for a long time ago. so, the $600 spent on the AED wouldnt not have bought a set of AFRs. and if we wanted to do that we just would have put my TEA 225 high ports on his motor. not to mention these cleveland 4 barrel closed chamber heads flow over 300 cfm, so do really think just because a head says 'AFR' on it the car would be faster? its a 10.5:1 flat tappet, pump gas motor that runs 6.90s in the 1/8 on motor. its a high 10 second combination with a bunch of old garbage we had lying around. the 830 was leftover from my 347 that went 6.40s 103 on the motor. but back to topic, the AED picked up a tenth and a half in the 60'. im sure a set of AFR stock valve center windsor heads that flow the same or less with the valve way to close to the cylinder wall would have picked up the 60' up too, or not.

B. you think we didnt change squirters, jets, and air bleeds on all of them? we did. we spent 6 months tuning this thing and hadnt picked up anything and all the holleys had a stumble. and the holley tech line had no idea why. the 650 had the least stumble but was down 3 mph to the 830 and had to be short shifted due to running out of breath.

C. we havent even tuned on the AED yet, we set the idle mixture.

D. we spents hours on the phone with holley trying to make their carbs work. appearantly there is something different about the AEDs and the holleys. maybe they atomize the fuel and emulsify better. get what you like. i just report what worked.

So how was it that changing the idle mix gained the 3 tenths? I guess everything else on the car was exactly the same as the previous pass you made. You guys had three "garbage" carbs sitting around and all three freakishly had a stumble? Sounds like you guys kept putting too small of a carb on the engine to begin with until the 850 was bought. Do you think if you were the Holley Tech guy you'd be able to fix your stumble over the phone? Not possible. Your drinking team couldn't figure it out with the car in front of you. The 830 was out of breath because of the ring and pinion you guys are probably running too. I'd imagine that a Dominator would more like it on your set up. Also, do you think just because your heads have Trick Flow on them, that makes your car faster than a car with AFR? Did Ford make some aluminum Cleveland heads? Lighter means faster. I'm sure that's a large part of the equation to your car's 6.90 ET.

 

[WTFO]

free drop, deck height, how sunk the valves are in the seat, how much the deck of the heads have been cut, HG thickness, rocker ratio, ramp rates, the intake opening event and the exhaust closing event determine PTV clearance. you can have the same lobe and depending on the centerline its ground on can clear by a mile or not even be close to clearing. just because a pushrod is stock length doesnt mean its the correct length.

Yes agreed- all in the name of finding out piston to valve clearance with that cam, heads, block etc. 1.6 is still a conservative ratio taking all that into consideration. Also, what the hell is "free drop"? Sounds like some made up BS.

 

[clement]

So how was it that changing the idle mix gained the 3 tenths? I guess everything else on the car was exactly the same as the previous pass you made. You guys had three "garbage" carbs sitting around and all three freakishly had a stumble? Sounds like you guys kept putting too small of a carb on the engine to begin with until the 850 was bought. Do you think if you were the Holley Tech guy you'd be able to fix your stumble over the phone? Not possible. Your drinking team couldn't figure it out with the car in front of you. The 830 was out of breath because of the ring and pinion you guys are probably running too. I'd imagine that a Dominator would more like it on your set up. Also, do you think just because your heads have Trick Flow on them, that makes your car faster than a car with AFR? Did Ford make some aluminum Cleveland heads? Lighter means faster. I'm sure that's a large part of the equation to your car's 6.90 ET.

we started with my 830. then went to the 750 HP, then borrowed the 650 HP. since the 830 worked on my 347 (which had smaller heads) we tried it. the 830 wasnt out of breath, the 650 was. slow down and read. the holley tech people make suggestions of changes, which we had already made. as said before, all we did was pull the AED carb out of the box, set the idle mixture and ran it. i feel i have been pretty clear about this point. generally, when you put a new carb on an engine the first thing you do is set the idle mixture. perhaps you should call John Dickey from AED and ask him the differences between their stuff and the holleys. Since he is the one that suggested the 750 HO modified for the clevor.

free drop is the amount of space from the piston at TDC to the valve when the valve is on the seat. any more questions? do you have any more assumptions about the combination that you'd like me to clear up for you? or maybe you would like some other technical terms explained to you?

maybe you could elaborate on how you alluded to pushrod length effecting PTV clearance? please.

while you are at it could you please tell me about all the sub $3000 pump gas stock crank, rod, block 351 windsor longblocks you have put together that have run 6s in the 1/8 mile naturally aspirated? since you seem to want to question my technical knowledge and experience, why dont you tell us about some of your experience in this area?

 

[WTFO]

Now you are making sense about your carb swaps. Also consider me schooled on 'valve free drop'. Although, I don't believe it would typically be an issue with a street engine (low compression). And unless I'm way off the pushrod is directly related to piston to valve clearance. Raising your rocker ratio is just like putting a longer pushrod in your valvetrain. I've never built any sub $3000 engine. Not even when I was putting together Chevrolets.

 

[clement]

putting too long a pushrod in will actually hold the valve open when the cam is on the base circle and the valve is supposed to be closed. if the pushrod is too short you are going to have some valve lash, which with a solid roller you need a specified amount but with a hydraulic could be disasterous. even on a pedestal mount you not only have to have the right length because you only want to go a specified amount past zero lash, but also a specified torque setting for the rocker fasteners. and while to can use shims under the pedestals, you can only take that so far. so if the heads, deck, valve stem length or any other variable has changed you really need to use a checker PR before ordering new PRs. but you are right on about the higher ratio not only increasing the lift at every given point, but also increasing the rate of accelleration of the valve and what may have barely cleared with a 1.6 ratio may hit with a 1.7. i was just curious what you meant by the pushrod length effecting the PTV. if the PR is too long and it holds the valve open when the lifter is on the base circle, hitting would be a definate possibility.

 

[mustangmike6996]

putting too long a pushrod in will actually hold the valve open when the cam is on the base circle and the valve is supposed to be closed. if the pushrod is too short you are going to have some valve lash, which with a solid roller you need a specified amount but with a hydraulic could be disasterous. even on a pedestal mount you not only have to have the right length because you only want to go a specified amount past zero lash, but also a specified torque setting for the rocker fasteners. and while to can use shims under the pedestals, you can only take that so far. so if the heads, deck, valve stem length or any other variable has changed you really need to use a checker PR before ordering new PRs. but you are right on about the higher ratio not only increasing the lift at every given point, but also increasing the rate of accelleration of the valve and what may have barely cleared with a 1.6 ratio may hit with a 1.7. i was just curious what you meant by the pushrod length effecting the PTV. if the PR is too long and it holds the valve open when the lifter is on the base circle, hitting would be a definate possibility.

so what is the best way to determine the correct length push rod?

 

[clement]

pattern on the valve tip

 

[woodsnake]

"so what is the best way to determine the correct length push rod? "
You have to measure. Use a light weight spring and an adjustable push rod. You want to get the narrowest sweep as close to the center of the valvestem as possible.