Did I over Carb?
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Posting Guru
Joined: Apr 2011
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From: Orlando area
Did I over Carb?
Is my carb too big? Truck seems more sluggish than prior to cam/carb swap. Maybe it justs needs some fine tuning.
460 (30 over)
9.5:1 compression
Trick Flow Specialty heads (72cc cambers), 2.20 Intake and 1.76" Exhaust valves.
Cam: Crane PowerMax, lift .556 Intake, .580 Exhaust (at valve)
duration @ .50; 216 Intake, 224 Exhaust
lobe seperation; 112 deg.
rpm range: 2500-6000 rpm
C6 tranny with 2800 stall convertor
37" Tires, and 4.56 gearing
Carb: Holley Street Avenger 870cfm
Truck weighs in at 5700 Lbs
460 (30 over)
9.5:1 compression
Trick Flow Specialty heads (72cc cambers), 2.20 Intake and 1.76" Exhaust valves.
Cam: Crane PowerMax, lift .556 Intake, .580 Exhaust (at valve)
duration @ .50; 216 Intake, 224 Exhaust
lobe seperation; 112 deg.
rpm range: 2500-6000 rpm
C6 tranny with 2800 stall convertor
37" Tires, and 4.56 gearing
Carb: Holley Street Avenger 870cfm
Truck weighs in at 5700 Lbs
Laughing Gas
Joined: Oct 2010
Posts: 997
Likes: 2
From: Rock Valley, IA
For an engine that beefy, I wouldn't think so. What is your timing at since you swapped the cam? I know that in my hobby stock car that has comparable lift/duration our timing is at 36 advanced. That's idling at around 1100 rpms and the throttle response is excellent. You have to advance the timing quite a bit for a cam that radical..
EDIT: I'm assuming you're going for speed and not a tow truck. Also, I wouldn't advance the timing as much as my hobby stock. I only said that as an example that you might want to advance the timing a bit more than stock to get a little more pep out of her. I have mine at 12* BTDC. My cam isn't as radical as your so you may want to go to 14*.
EDIT: I'm assuming you're going for speed and not a tow truck. Also, I wouldn't advance the timing as much as my hobby stock. I only said that as an example that you might want to advance the timing a bit more than stock to get a little more pep out of her. I have mine at 12* BTDC. My cam isn't as radical as your so you may want to go to 14*.
More Turbo
Joined: Oct 2009
Posts: 731
Likes: 6
From: Jonesborough, TN
Hey Country,
I doubt if its the carb. That motor is going to gulp gas and the 870 should not be to big for it, of course much depends on all of the other components present.
In this case, I would suspect the cam. The powerband is from 2500-6000, so you need to spool that beast up to 2500 rpm before the torque kicks in, and that is what gets that truck moving (especially with those 37 in tires). A cam with a lower rpm range may provide better take off for you.
What kind of intake do you have? Headers or stock manifold? All of those things can affect the torque curve and thus, takeoff, or lack thereof. I hope that helps in some small way. I am not an expert, by any means, but I did a lot of research when I built the 408 stroker for my project.
Ron
I doubt if its the carb. That motor is going to gulp gas and the 870 should not be to big for it, of course much depends on all of the other components present.
In this case, I would suspect the cam. The powerband is from 2500-6000, so you need to spool that beast up to 2500 rpm before the torque kicks in, and that is what gets that truck moving (especially with those 37 in tires). A cam with a lower rpm range may provide better take off for you.
What kind of intake do you have? Headers or stock manifold? All of those things can affect the torque curve and thus, takeoff, or lack thereof. I hope that helps in some small way. I am not an expert, by any means, but I did a lot of research when I built the 408 stroker for my project.
Ron
Fleet Mechanic
Joined: Jul 2011
Posts: 1,916
Likes: 4
I think you'll see much better results with a 750 CFM carburetor.
Smaller primaries and secondaries equals greater air velocity and fuel atomization.
http://www.holley.com/data/types/pic...A_IntoZOOM.jpg
Holley's neat little chart says at 6000 RPM you would do just fine with a 750 or a 770.
If it were me, I would personally go a step down on cam size and down to a 750 or 650 CFM carburetor. It's way more street friendly.
Smaller primaries and secondaries equals greater air velocity and fuel atomization.
http://www.holley.com/data/types/pic...A_IntoZOOM.jpg
Holley's neat little chart says at 6000 RPM you would do just fine with a 750 or a 770.
If it were me, I would personally go a step down on cam size and down to a 750 or 650 CFM carburetor. It's way more street friendly.
Senior User
Joined: May 2010
Posts: 369
Likes: 2
From: BC Cana'duh
I agree with the smaller carb idea.Try a 750 vac.sec. or try a heavier spring in the 870 sec vac. housing.That cam isn't too much.224 @.050 for a 466 is great.My flat tappet 554" 574" comp cams has 234@ .050 and my truck will fry the tires("32 w/3:50 ears) from a dig.Also I run a 3310 vac.sec 750 cfm.Had a 670 Street Avenger on an aluminum headed 357 sbf and always had fine tuning issues with it.I ve read neg. reviews from some top engine builders/tuners on 460ford.com,and can relate to some of the issues they have with them.Mainly the primary metering block is of poor design and causes problems.I've since replaced mine(Street Avenger) with a 1850 Holley and the truck runs much better.
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Joined: Jan 2001
Posts: 56,984
Likes: 2,738
From: Virginia
This is a classic case of changing the personality of a engine that used to be a low revving low compression truck engine, into a higher rpm racing engine. Stick that thing it a mustang now, and it would fly. In a heavy truck, it has problems.
Your 4.56 gears are good, but the 37 inch tires are taking their advantage away. If you have more near stock size tires on it, it would make a big difference.
Hopefully the carb is vacuum secondary, and hopefully your intake is dual plane. If both are true, then the cam may be the only thing you can do to bring the power back down into the lower rpms so you can use it.
Your 4.56 gears are good, but the 37 inch tires are taking their advantage away. If you have more near stock size tires on it, it would make a big difference.
Hopefully the carb is vacuum secondary, and hopefully your intake is dual plane. If both are true, then the cam may be the only thing you can do to bring the power back down into the lower rpms so you can use it.
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Thread Starter
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Posting Guru
Joined: Apr 2011
Posts: 1,636
Likes: 5
From: Orlando area
Hey Country,
What kind of intake do you have? Headers or stock manifold? All of those things can affect the torque curve and thus, takeoff, or lack thereof. I hope that helps in some small way. I am not an expert, by any means, but I did a lot of research when I built the 408 stroker for my project.
Ron
What kind of intake do you have? Headers or stock manifold? All of those things can affect the torque curve and thus, takeoff, or lack thereof. I hope that helps in some small way. I am not an expert, by any means, but I did a lot of research when I built the 408 stroker for my project.
Ron
I corrected my profile. I do not have the Edelbrock manifold (that was several years ago).
Thread Starter
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Posting Guru
Joined: Apr 2011
Posts: 1,636
Likes: 5
From: Orlando area
You can never have enough power - you just run out of money at some point.
Thread Starter
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Posting Guru
Joined: Apr 2011
Posts: 1,636
Likes: 5
From: Orlando area
This is a classic case of changing the personality of a engine that used to be a low revving low compression truck engine, into a higher rpm racing engine. Stick that thing it a mustang now, and it would fly. In a heavy truck, it has problems.
Your 4.56 gears are good, but the 37 inch tires are taking their advantage away. If you have more near stock size tires on it, it would make a big difference.
Hopefully the carb is vacuum secondary, and hopefully your intake is dual plane. If both are true, then the cam may be the only thing you can do to bring the power back down into the lower rpms so you can use it.
Your 4.56 gears are good, but the 37 inch tires are taking their advantage away. If you have more near stock size tires on it, it would make a big difference.
Hopefully the carb is vacuum secondary, and hopefully your intake is dual plane. If both are true, then the cam may be the only thing you can do to bring the power back down into the lower rpms so you can use it.
Yeah - it is dual plane intake with vacuum secondaries on the Holley. Also vacuum advance on the distributor.
Thank for your reply.
Thread Starter
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Posting Guru
Joined: Apr 2011
Posts: 1,636
Likes: 5
From: Orlando area
For an engine that beefy, I wouldn't think so. What is your timing at since you swapped the cam? I know that in my hobby stock car that has comparable lift/duration our timing is at 36 advanced. That's idling at around 1100 rpms and the throttle response is excellent. You have to advance the timing quite a bit for a cam that radical..
EDIT: I'm assuming you're going for speed and not a tow truck. Also, I wouldn't advance the timing as much as my hobby stock. I only said that as an example that you might want to advance the timing a bit more than stock to get a little more pep out of her. I have mine at 12* BTDC. My cam isn't as radical as your so you may want to go to 14*.
EDIT: I'm assuming you're going for speed and not a tow truck. Also, I wouldn't advance the timing as much as my hobby stock. I only said that as an example that you might want to advance the timing a bit more than stock to get a little more pep out of her. I have mine at 12* BTDC. My cam isn't as radical as your so you may want to go to 14*.
I need to go back out and check the timing. I think it is around 8 BTDC with full advance at 28 degrees. I haven't looked in a while and I forget where it ended up.
My vacuum at idle is around 10-12.
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Joined: Jan 2001
Posts: 56,984
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From: Virginia
You have to set your timing by ear, since you have changed everything around. After all this, you might need to then get an adjustable vacuum advance. If it pings and runs terrible when the vacuum line is hooked back up, you have too much advance with the vacuum , and I would leave it unhooked rather than back the timing down even more.
Laughing Gas
Joined: Oct 2010
Posts: 997
Likes: 2
From: Rock Valley, IA
All kinds of this ^^^^^^^^
You should see your vacuum go up as well when you increase the timing.
How much have you messed with the idle mixture screws on the carb? The best thing I ever did on my truck was have the vacuum gauge hooked up, slowly turn the mixture screws out until you get the highest possible vacuum, then turn them back in until the vacuum drops a half a mark. Then do the other side the same way.
You'll notice a big difference after you do that.
You should see your vacuum go up as well when you increase the timing.
How much have you messed with the idle mixture screws on the carb? The best thing I ever did on my truck was have the vacuum gauge hooked up, slowly turn the mixture screws out until you get the highest possible vacuum, then turn them back in until the vacuum drops a half a mark. Then do the other side the same way.
You'll notice a big difference after you do that.