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Old 12-18-2006, 11:17 PM   #1
Shmeddie
 
Join Date: Dec 2006
Posts: 46
Default 351 cobra jet?

okok so i located a guy who said he has a 351 cleveland.... i got the numbers and when i check up on them it said the 351 was a cobra jet not a cleveland...

so i was wondering whats so special about a 351 cobra jet?
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Old 12-19-2006, 10:06 PM   #2
Indy
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Default RE: 351 cobra jet?

Hi Shmeddie,

Plenty of differences between the Cleveland motors. There is the CJ(like yours), 4V, Boss, H.O...

Theysome arelike this...

Brake HP:
CJ = 280 @ 5800rpm
4V = 285 (1971), 300 (1970)
Boss = 330
HO = 275

Torque:
CJ = 345 @ 3800rpm (1971)
4V =380 (1970), 301 (1972)
Boss = 370
HO = 286

Mains:
CJ = 4 bolt (1971), 2 bolt (1972+)
4V = 2 bolt
Boss = 4 bolt
HO = 4 bolt

Crank:
Boss has larger Main Journals and Connecting Rod Journals.

Piston:
CJ = Cast Aluminum, Flat-Top 9.0:1 Compression
4V = " " " "10.7:1 Compression
Boss = Forged Aluminum, Pop-up 11.1:1 Compression

Camshaft:
Different between the 4 Clevelands. You want the Boss unit IMO.
CJ and 4V = Hydraulic Flat Tappet
Boss and HO = Mechanical Flat Tappet

Heads:
Different volumes between part numbers.
Valve diameters are all the same.
CJ and 4V rocker bolt = 5/16"
Boss and HO rocker stud = 7/16"

Intake Manifold:
CJ and 4V = Iron
Boss and HO = Aluminum

And many more... However, the important things are that the Cobra Jet block has 4-bolt mains,camshaft can be upgraded and heads can be machined to BOSS specs (should be minimal, as the valve diameters are the same), pistons can be upgrade for higher compression etc...

Interested to know what the plan is! Good luck
Indy
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'69 357W in '79 Fox Mustang .030" Flat-Tops, 11:1 Compression.
'86 T5, 8.8" Posi w/ 3.73 FRPP gears.

Holley 750HP/DP and Fuel Pump, RPM Intake, RPM Heads (2.02"/1.60"), Comp Magnum Rockers, Comp Pushrods, Lunati Voodo Cam, BBK Long Tubes
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Old 12-19-2006, 10:29 PM   #3
Shmeddie
 
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Default RE: 351 cobra jet?

well a guy is selling me the heads block and intake for $100. i had him get the numbers off of the block for me and it turned out it was a cobra jet not a cleveland when i ran the numbers on the net... i dont know what im gonna do with it yet.. all i know is my main goal is to have it built before i buy another stang (for a project car). so if you have any good setups you think i should run with it im open for suggestions. (main goal is to be pushing over 400hp. all throttle no bottle. also street/strip setup. daily driver if my other vehicles break ) thanks for all your help Indy
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Old 12-20-2006, 05:56 AM   #4
atomsk680
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Default RE: 351 cobra jet?

Quote:
ORIGINAL: Shmeddie

well a guy is selling me the heads block and intake for $100. i had him get the numbers off of the block for me and it turned out it was a cobra jet not a cleveland when i ran the numbers on the net... i dont know what im gonna do with it yet.. all i know is my main goal is to have it built before i buy another stang (for a project car). so if you have any good setups you think i should run with it im open for suggestions. (main goal is to be pushing over 400hp. all throttle no bottle. also street/strip setup. daily driver if my other vehicles break ) thanks for all your help Indy
what year is the block? 72?

so if your doing a block up build, get good crank and pistons,do not bore it out past .030, any more and the block is useless, get a good cam, i highly suggest roller cams, maybe some new heads, AFR's, matching intake, around 700cfm-750cfm carb, longtube headers, do not exceed 11 CR in the cylinders cause race gas be very expensive. get a good tranny for it too and whatever rear you have, trac-loc and some god gears, should be over 400HP then
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Old 12-20-2006, 12:39 PM   #5
Shmeddie
 
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Default RE: 351 cobra jet?

i was gonna try taking the heads and getting them ported and polished... but idk i still have to go pick everything up and go through it... I am hoping these heads are like the cleveland heads.. but will see


also.... i was talking to a guy at the strip and he said he knows a shop that can get those old cleveland heads to flow as near if not better then most aftermarket heads. anyone ever hear of them flowing that good?
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Old 12-20-2006, 12:43 PM   #6
Shmeddie
 
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Default RE: 351 cobra jet?

o sorry... yes it is a 72.. the heads look like they are 71. the intake is a 72 also
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Old 12-20-2006, 09:31 PM   #7
Indy
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Default RE: 351 cobra jet?

The 351CJ is part of the Cleveland family of motors. So, yes the heads are the "famous" high flowing canted valve type. IMO, you don't really need to do much work to the already awsome cylinder heads. I would probably polish, maybe not port to maintain port velocity. IMO again, those heads already flow well enough for 351cubes. The only other thing I would consider doing on the cheap would be to mill the heads down to combustion chamber volume of the Boss heads. This will raise the effective compression ratio. http://www.csgnetwork.com/compcalc.htmltry link to calculate approximate compression and other handy specs when modifying your motor.

That's more of my penny's for ya!
Indy
__________________
'69 357W in '79 Fox Mustang .030" Flat-Tops, 11:1 Compression.
'86 T5, 8.8" Posi w/ 3.73 FRPP gears.

Holley 750HP/DP and Fuel Pump, RPM Intake, RPM Heads (2.02"/1.60"), Comp Magnum Rockers, Comp Pushrods, Lunati Voodo Cam, BBK Long Tubes
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Old 12-20-2006, 10:32 PM   #8
Shmeddie
 
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Default RE: 351 cobra jet?

thats a handy lil link you posted thanks man
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Old 12-21-2006, 09:54 AM   #9
Indy
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Default RE: 351 cobra jet?

No probs... This is a super helpful forum, so just trying to do my part!

Good luck!
Indy
__________________
'69 357W in '79 Fox Mustang .030" Flat-Tops, 11:1 Compression.
'86 T5, 8.8" Posi w/ 3.73 FRPP gears.

Holley 750HP/DP and Fuel Pump, RPM Intake, RPM Heads (2.02"/1.60"), Comp Magnum Rockers, Comp Pushrods, Lunati Voodo Cam, BBK Long Tubes
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Old 12-22-2006, 01:12 PM   #10
Shmeddie
 
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Default RE: 351 cobra jet?

wow.... so no one respects a verbal agreement any more.. i called the guy on the day we set up to make the exchange and his wife answers and says he already sold it....[:@][:@][:@]


back to the drawing bored...i guess im just gonna look for a set of cleveland heads[>:]
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Old 12-22-2006, 01:12 PM
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1972, 1990, 351, 351c, bolt, bolts, cleveland, cobra, engine, heads, jet, motors, mustang, pistons, rocker

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