351M headers, carb?
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Elder User
Joined: Oct 2010
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From: Maryland
351M headers, carb?
Ok, so after christmas i plan on installing a set of headers, flowmaster exhaust, and maybe a intake manifold and a carb. The engine is stock, after installing a set of headers, k&n filter and exhaust, what size carb would be good? I was thinking a holly truck avenger 670cfm??
Senior User
Joined: Mar 2008
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best bet for the headers are the dynomax ($100 or so from jegs) an as for intake if you use the edlebrock performer intake you could use the 670 cfm carb, but imho its still a bit big for a stock 351. the lil 500 cfm 2 barrel holley should be plenty. i run the 650 edlebrock on my bronco with a built 400 an its waaaay overcarbed for the high elevations i run it at. bein as you're on the east coast, you could prolly get away with the 670. depends on what you use the truck for. if its a 4x4, an sees lots of time in the dirt an off camber, i would recommend the edlebrock because of the center float bowl. but for street use on a 2wd, nothin beats the holley. (i still think the 670 is a bit overcarbed for the 351) maybe the smaller 390 street avenger would be a better deal?? its all a big expirement really. the 670 can be rejetted an with the proper tuning, it could work. just my $.03.
cam carb an intake kits for them are fairly cheep, around 500-700 an the cam makes a world of difference. the 351m an 400 are sevearly retarded in cam timing
cam carb an intake kits for them are fairly cheep, around 500-700 an the cam makes a world of difference. the 351m an 400 are sevearly retarded in cam timing
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Joined: Nov 2008
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mdr,
depending on the intended use of your truck you may want to do more research on the exhaust. I stuck with single, 2.5" pipe and a turbo muffler to maintain the most low end torque.
The 351M is not a racer and isn't going to beat anything in terms of speed. But it is a puller. I've known a few to put headers on and revert to stock manifolds. You may want to consider just the intake/carb changeout.
The Autolite 2100 series is a great carb and is well suited to the 351M. It's a great, easy carb to learn on and they are out there in number. A good rebuild and some tuning and you'll save some serious $$ that your engine probably won't appreciate anyway.
The following I.D. Nos. (found on the side of the float bowl behind the accelerator pump rod) will give you the individual CFM ratings.
Stamped No + CFM
.98=190
1.01=240
1.02=245
1.08=287
1.14=300
1.21=351 (this is mine)
1.23=356
1.33=424
Keep us posted as to what you decide. There are and infinite array of combinations that folks are already running and they can help you out.
depending on the intended use of your truck you may want to do more research on the exhaust. I stuck with single, 2.5" pipe and a turbo muffler to maintain the most low end torque.
The 351M is not a racer and isn't going to beat anything in terms of speed. But it is a puller. I've known a few to put headers on and revert to stock manifolds. You may want to consider just the intake/carb changeout.
The Autolite 2100 series is a great carb and is well suited to the 351M. It's a great, easy carb to learn on and they are out there in number. A good rebuild and some tuning and you'll save some serious $$ that your engine probably won't appreciate anyway.
The following I.D. Nos. (found on the side of the float bowl behind the accelerator pump rod) will give you the individual CFM ratings.
Stamped No + CFM
.98=190
1.01=240
1.02=245
1.08=287
1.14=300
1.21=351 (this is mine)
1.23=356
1.33=424
Keep us posted as to what you decide. There are and infinite array of combinations that folks are already running and they can help you out.
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Elder User
Joined: Oct 2010
Posts: 602
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From: Maryland
Thanks for all the info. As for the exhaust right now, i have the stock manifolds, y pipe, and a dynomax ultraflow welded muffler and no pipes, just dumps right under the cab. I also just added a k&n extreame flow air filter and an accel coil. But, i think i am also going to add a set of accel wires because the stock distributer to coil wire dont fit the coil right.
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Elder User
Joined: Oct 2010
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From: Maryland
Yeah, i just liked the sound of the flowmasters. But the dynomax sounds good too. Do i need pipes? How does my exhaust sound in terms of tq? Also, is the autolite 2100 the stock carb? I was just considering swapping it out because like i said, the truck and engine are compleatly stock, and I checked for vacume leaks, tightened everything, and it still "boggs down" instead of accelerating. I dont want burnouts, just to go when i floor it. I would have no problem rebuilding the stock carb, but how do they work when working right? Like i said, i just want the truck to run right, idle right, and run smooth
Posting Guru
Joined: Nov 2007
Posts: 1,305
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From: Montgomery, IL
The biggest problem with the 351m/400 engines is that the factory cam is retarded 4 degrees. This was done for emissions reason back then and it killed the performance of these fine engines. If you want to wake this engine up put in a cam with 0 degree retard and you will see a huge difference. You don't need a big fancy cam, just a nice stock replacement grind cam will make a huge difference.
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Elder User
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From: Maryland
Is there any cam that you would recommend that works good for the 351M? Will a cam work with a stock engine?
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From: Montgomery, IL
So, if you check this link out you will find some good information and a decent starting point for what you are trying to do.
232-206-3 - Dual Energy Buy the KIT and you get everything you need, cam, lifter, and timing chain. About $400.00 online from Comp, maybe cheaper from Jegs or Summit or your local speed shop.
It is not going to require a new carb or anything and you can still run the stock exhaust. EVERYBODY tends to over-carb their engines because they think it is cool to run a 750 double-pumper and then they complain about poor performance and mileage and blame it on the damn carb being screwed up when in reality the engine does not need that much carb. Your stock 2 barrel should work just fine.
Mark
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Joined: Nov 2008
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Mark is right. Depending on the year of the truck the cam is retarded. I think by Model Year 1977 the cam was normal again.
Yes the Autolite 2100 is stock on the Fords and some AMC vehicles too. It is the "go to" carb for off-roading.
Read here for some good info on the 351M .......Bubba's M-Block Ford V8 Workshop
Yes the Autolite 2100 is stock on the Fords and some AMC vehicles too. It is the "go to" carb for off-roading.
Read here for some good info on the 351M .......Bubba's M-Block Ford V8 Workshop
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Joined: May 2006
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From: North Dakota
I think the most of the time people put too small of carbs on..... I originally had a 750 cfm on mine, but I have a bracket master cam in it... rated to valve float at 6800 rpm, I useto run a 750 on it, now I have a Predator on it(variable 390-930cfm) so far I love it.
If you are not changing the cam a 600cfm is fine and dandy.
If you are not changing the cam a 600cfm is fine and dandy.
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What size are the primaries on your headers? Over on the Corvette forum there are a lot of people who swear up and down that 1 3/4" headers are too big and give up too much low end torque on a 350. Nevermind that it has been dyno proven time and time again that there are absolutely no losses at wide open throttle and the horsepower gains are substantial. These people claim that the part throttle losses in low end torque are extremely noticeable and that you would do better with a set of 1 5/8" primary headers.
Now personally I've done 1 3/4" headers on my 350 and didn't notice any loss of torque whatsoever, in fact quite the opposite. Any loss of torque I experienced came from the cam that I put in, which is tailored to really run in the 3500-6500 RPM range. For a truck though, that would probably never see 6000 RPM, I might would consider that there probably is some merit to what people say, you might actually gain something in your power band by going with 1 5/8" over 1 3/4"
I know on my 302 I'll probably look into 1 5/8"
Now personally I've done 1 3/4" headers on my 350 and didn't notice any loss of torque whatsoever, in fact quite the opposite. Any loss of torque I experienced came from the cam that I put in, which is tailored to really run in the 3500-6500 RPM range. For a truck though, that would probably never see 6000 RPM, I might would consider that there probably is some merit to what people say, you might actually gain something in your power band by going with 1 5/8" over 1 3/4"
I know on my 302 I'll probably look into 1 5/8"
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