Does size matter...?

[keith1562]

Yesterday my wife took me to an appt. On the way there her car developed a trans. fluid leak (bad line). So I had a 45 minute ride with my wife & my mechanic after he hooked up her car to his wrecker. It didn't take long for the subject to turn to my 72 Q-code. After all he rebuilt the engine after I bought it 5 yrs. ago. I mentioned that it was running great, but seemed a bit flat at high r.p.m. (5000+) I told him that the carb. (Carter comp. 625cfm) seemed a bit small. I went on to explain that I had 2 other carbs. on hand, a Holley 750 vac. sec. (& an extra metering block for the secondaries) and a Street Demon 650 vac. sec. along with a "track" kit for the current carb., with a variety of metering rods and springs. I also told him I have a rebuild kit that will work on either the Holley or Demon. His opinion was that if I went with the big Holley it may be that it wouldn't perform well with the modest size runners of my current intake (Edelbrock Performer). He did think that the huge ports of the 351c would benifit from a more dense charge of air/fuel. What I'm looking for is more high end but not at the expense of low rpm torque. I had always thought that the increased air/fuel velocity offered by modest runners was best for all around performance, rather than the shear plenum volume allowed by larger runners. Then again it is a 351c, & we all know that the rules that apply to small port heads don't always hold true for Clevelands. Does anyone have any idea which combo would perform best? Please keep in mind the 3 carbs. I mentioned & my current intake vs a large runner, possibly single plane intake. By the way I'm running a single profile cam with .524 lift & 216 degrees duration along with a 3.73 trac-lock & the stock toploader 4 spd. I am going to have the rear-end rebuilt next spring & I may step up to a 3.91. Obviously gas mileage will be poor, though with the small carb. I'm getting 16 to 19 mpg combined in town & interstate (75-80 mph). Also does anyone know what the Boss 351's came with from the factory in terms of carb., & intake?
I look forward to any and all input! Go ahead and throw in your 2 cents!!
Thank you,
your friend
Keith

[ylwhrse]

The Holley style carbs always seem to make better torque and horsepower over the carter/edelbrock style.To my knowledge most clevelands that did not have the ford carb or quadrajet style Holley all came with the Holley 4 bbl carb in a 735 CFM. I have run clevelands for years both in various stock/semi stock and full on race form and most of the time they like carberation. But it depends on what you really want the car to do. At a minimum I would say the 650, but really in my gut really says to go with the 750 and possibly have to jet it down a bit to get the final jetting correct. If all carbs are functional and not in needing a rebuild I would buy some mounting gaskets and give them all a try. You didn't say but I am assuming your engine does have the 4 bbl heads (hopefully the closed chamber variety) as they assist in the burn process and give more compression and unlike the open chamber heads actually help with detonation. Another area to check is timing. Not sure where you live but the clevelands really do like more timing than ford recommended. your cam is a fairly mild performance cam but I bet it could benefit from more timing. I wouldn't hesitate to try somewhere around 26-32 total with 12-16 initial but that depends on your altitude and what fuel you run. I have run into several motors over the years with upgraded cams and folks still running stock timing that were totally disappointed in even swapping the cam. I would also check to be sure the vacuum advance is working in your distributor. This is an easy check but you need a hand vacuum pump. Pull the dist cap off and pull the factory vacuum line off, hook up the vacuum pump and initiate a vacuum. The arm attached to the plate inside the distributor should move (pull into the vac advance) effectively moving ( advancing the timing) by moving the plate. If the advance is working properly you should also after you stop pumping the pump not lose any vacuum or have the plate move back to its starting point. If that all checks good then secondly make sure you vacuum line for the vacuum advance is hooked up to the ported side of the carb. Most carbs have 2 vacuum ports, 1 which has vacuum all the time even at idle and the other port only has vacuum when the throttle is moved when you start to drive. The side that doesn't have vacuum at idle and only vacuum when the throttle is opened is the one you want to hook the distributor to. I would also then check for vacuum leaks but I would suspect you would have other driveability/idle issues if you had some of those going on. Hope this helps. If I can help any further don't hesitate to ask on here or even message me.
YLWHRSE

[Steven Harris]

Thanks Ylwhrse.

That is the consensus when dealing with carburation for a Cleveland.

Keith, let us know what you end up finding works best for you set up. It will help us help the next guy.

[keith1562]

The Holley style carbs always seem to make better torque and horsepower over the carter/edelbrock style.To my knowledge most clevelands that did not have the ford carb or quadrajet style Holley all came with the Holley 4 bbl carb in a 735 CFM. I have run clevelands for years both in various stock/semi stock and full on race form and most of the time they like carberation. But it depends on what you really want the car to do. At a minimum I would say the 650, but really in my gut really says to go with the 750 and possibly have to jet it down a bit to get the final jetting correct. If all carbs are functional and not in needing a rebuild I would buy some mounting gaskets and give them all a try. You didn't say but I am assuming your engine does have the 4 bbl heads (hopefully the closed chamber variety) as they assist in the burn process and give more compression and unlike the open chamber heads actually help with detonation. Another area to check is timing. Not sure where you live but the clevelands really do like more timing than ford recommended. your cam is a fairly mild performance cam but I bet it could benefit from more timing. I wouldn't hesitate to try somewhere around 26-32 total with 12-16 initial but that depends on your altitude and what fuel you run. I have run into several motors over the years with upgraded cams and folks still running stock timing that were totally disappointed in even swapping the cam. I would also check to be sure the vacuum advance is working in your distributor. This is an easy check but you need a hand vacuum pump. Pull the dist cap off and pull the factory vacuum line off, hook up the vacuum pump and initiate a vacuum. The arm attached to the plate inside the distributor should move (pull into the vac advance) effectively moving ( advancing the timing) by moving the plate. If the advance is working properly you should also after you stop pumping the pump not lose any vacuum or have the plate move back to its starting point. If that all checks good then secondly make sure you vacuum line for the vacuum advance is hooked up to the ported side of the carb. Most carbs have 2 vacuum ports, 1 which has vacuum all the time even at idle and the other port only has vacuum when the throttle is moved when you start to drive. The side that doesn't have vacuum at idle and only vacuum when the throttle is opened is the one you want to hook the distributor to. I would also then check for vacuum leaks but I would suspect you would have other driveability/idle issues if you had some of those going on. Hope this helps. If I can help any further don't hesitate to ask on here or even message me.
YLWHRSE

Thanks for the info. it is very helpful. I do have 4v heads that I thought were open chamber but have since come to question the originality of the engine. I found a casting date on the block that, although incomplete led me to believe the block is from 1970. That's good news if the block & heads are '70 vintage (but it would only have 2 bolt mains.) The engine was completely rebuilt 5 years ago. Stupid me I didn't even look at the heads and block while they were out of the car. As I recall I was suffering with a nasty case of flared up back pain. My car is a "Q" code and I was told by the previous 2 owners that it was original. So who knows.
Thnaks a million for your input,
Your friend Keith
P.S. Do you know what it means if there is a "dot" next to the big "4" on 4v heads?

[ylwhrse]

The Holley style carbs always seem to make better torque and horsepower over the carter/edelbrock style.To my knowledge most clevelands that did not have the ford carb or quadrajet style Holley all came with the Holley 4 bbl carb in a 735 CFM. I have run clevelands for years both in various stock/semi stock and full on race form and most of the time they like carberation. But it depends on what you really want the car to do. At a minimum I would say the 650, but really in my gut really says to go with the 750 and possibly have to jet it down a bit to get the final jetting correct. If all carbs are functional and not in needing a rebuild I would buy some mounting gaskets and give them all a try. You didn't say but I am assuming your engine does have the 4 bbl heads (hopefully the closed chamber variety) as they assist in the burn process and give more compression and unlike the open chamber heads actually help with detonation. Another area to check is timing. Not sure where you live but the clevelands really do like more timing than ford recommended. your cam is a fairly mild performance cam but I bet it could benefit from more timing. I wouldn't hesitate to try somewhere around 26-32 total with 12-16 initial but that depends on your altitude and what fuel you run. I have run into several motors over the years with upgraded cams and folks still running stock timing that were totally disappointed in even swapping the cam. I would also check to be sure the vacuum advance is working in your distributor. This is an easy check but you need a hand vacuum pump. Pull the dist cap off and pull the factory vacuum line off, hook up the vacuum pump and initiate a vacuum. The arm attached to the plate inside the distributor should move (pull into the vac advance) effectively moving ( advancing the timing) by moving the plate. If the advance is working properly you should also after you stop pumping the pump not lose any vacuum or have the plate move back to its starting point. If that all checks good then secondly make sure you vacuum line for the vacuum advance is hooked up to the ported side of the carb. Most carbs have 2 vacuum ports, 1 which has vacuum all the time even at idle and the other port only has vacuum when the throttle is moved when you start to drive. The side that doesn't have vacuum at idle and only vacuum when the throttle is opened is the one you want to hook the distributor to. I would also then check for vacuum leaks but I would suspect you would have other driveability/idle issues if you had some of those going on. Hope this helps. If I can help any further don't hesitate to ask on here or even message me.
YLWHRSE

Thanks for the info. it is very helpful. I do have 4v heads that I thought were open chamber but have since come to question the originality of the engine. I found a casting date on the block that, although incomplete led me to believe the block is from 1970. That's good news if the block & heads are '70 vintage (but it would only have 2 bolt mains.) The engine was completely rebuilt 5 years ago. Stupid me I didn't even look at the heads and block while they were out of the car. As I recall I was suffering with a nasty case of flared up back pain. My car is a "Q" code and I was told by the previous 2 owners that it was original. So who knows.
Thnaks a million for your input,
Your friend Keith
P.S. Do you know what it means if there is a "dot" next to the big "4" on 4v heads?

Yes Keith as far as I know it really doesn't mean anything. It was just part of the mold. Some were very visible and some not as much. I wouldn't worry about 2 bolt mains really unless you are concerned with originality. I personally have turned 2 bolt main engines to 7000 rpm, s with main bolts and 8000 with studs. Remember Bob Glidden back in the day turned his protocol cleveland to 9000 and higher, granted he did a fair amount of machine work and oiling mods. But the cleveland really is a strong engine if good machine work and careful assembly takes place. With no modifications at all except replacing rod bolts with good ones and use a good high volume oil pump and good assembly all but really questionable blocks in the first place will/should live to 6500 with no worries.YLWHRSE