2 bbl to 4 bbl conversion

[Omie01]

Ok, this will be a little long winded, but here's my situation. I have a 2bbl 351 cleveland that was rebuilt 1000 miles ago. I took the valve covers off and the inside of the motor is spotless, and has many signs of just being rebuilt. Heres my questions:I have a set of 73 4bbl OC heads that have been rebuilt. I would like to convert my motor to a 4bbl. I know I need different headers and Intake/Carb setup, but can I keep the flat top pistons? I would like to avoid taking the short block apart. Can I put a new cam in with the fresh cam bearings if I don't damage them? Which cam should I run to get "BOSS" like power? (330-375hp). I plan to upgrade the rocker assembly to screw in studs, and roller rockers with guide plates. Do I need a multi notch timing chain to retard timing? The new heads have been shaved 20 thousandths. The valves have been replaced with one piece valves, but they have the multi-groove keepers, will this be ok if I stay just under 400hp? The current motor has a new harmonic balancer, and has great oil pressure. The block is a 2 bolt bottom end. I would like to stick with a hydraulic roller cam. Are there any other considerations I have to make? I have tried to supply as much info as I could, If you have any further questions please ask. I would like to convert to 4bbl motor using my fresh 2 bbl cleveland short block and my rebuilt 4 bbl OC heads. Oh, and I already have an electronic ignition in it too. Any help would be greatly appreciated!! PS. I dont want to run aluminum heads because I want to build a "BOSS" clone. And right now I can't afford CC heads.

 

[will e]

My personal opinion is there isn't much point going with 4v heads that are open chamber if you have a fresh engine rebuild on the 2bbl heads.

What are your 'driving' plans for the car? Daily driver with nice manners? Weekend fun car? Occasional trips to a local drag?

We also need to know the other details since it is all a package. Transmission, stall speed on the converter and rear end gears. What exhaust do you have now? Headers and duals or stock?

You mention you want to stick with the hydraulic roller cam, is that what is in there now?

Your post is a little confusing as I am not sure what you currently have, what the 4bbl heads have and what you want to do.

And don't get too into building a 'boss' clone. Build what works with what is now available. You can make it look old school but, for example, a 'boss clone' would not have a hydraulic roller cam... (or headers)....

See my sig for what I run.

 

[TommyK]

It has been done many times before.

http://www.7173mustangs.com/thread-green-72-fastback-former-429-460?highlight=chamber

Flat tops and open chamber heads will be fine.

The camshaft spec is critical. Hydraulic roller is great choice if you can afford it.

I would contact an engine builder who is a cleveland specialist like Lykins Motorsports to get a custom ground cam based on what your goals are and how you intend to use the vehicle. He can also help you with the induction component selection which needs to be matched to the cam and the rest of the drivetrain.

http://www.lykinsmotorsports.com/

Lots of cleveland help here:

http://www.the351cforum.com/index.php

 

[Omie01]

My favorite driving style is track driving, I imagine myself doing 70-80 mph on a curvy back road somewhere. I was thinking 2800 stall, I am having the rear diff converted to 3:50.1 as we speak, I know the "BOSS" was 3:91.1, but thats a little too steep for me. I want my power curve to start around 3000 rpm, so I think the 4 bbls are a better choice. I am building a very tight suspension system, and have upgraded to wider magnum 500's for road handling. Like I said, a "close" boss clone, as I dont have a 4 speed either.

 

[Kit Sullivan]

The 2-V Cleveland engine retrofitted with an aftermarket 4-bbl manifold and 4-bbl carburetor usually gives much more impressive street performance than a Cleveland with the 4-V heads on it (OEM style).

While the 4-V Cleveland heads make for some serious drag-strip performance, they suffer from a small bit of slowed low-RPM airflow velocity due to the cavernous high-flow capability of the heads...limiting its off-the-line performance somewhat.

The 2-V heads with a 4-bbl manifold/ carb combo flow very well at low RPM, giving phenomonal off-the-line snap. Only at the upper ends of the RPM range do the 2-V heads show any limitation.

For a car used in typical street duty, with an occasional "stop light" drag race, I feel the 2-V heads with the aftermarrket 4bbl manifold/carb is the better choice.

Let the arguments begin...

 

[mjlan]

I'll add my $0.02 here as the 2V vs. 4V debate has raged since 1970...

I'm with Kit on this one, it honestly sounds like you might be better off optimizing your 2V combination. If you are looking for spirited driving with an automatic and 3.50 gears, the 2V heads with an upgraded cam (spec'd or custom ground by someone who is familiar with the Cleveland) and an intake and carb upgrade to a four barrel would probably be much more enjoyable and driveable in the off-idle to 4500 RPM range where you will be on the street.

If you would have said I'm changing to a late model manual transmission with an OD and changing to 3.50 gears, then I would say 4V heads FTW. My reasoning here is that the modern OD manual transmissions have different gearing to take advantage of the overdrive: if you compare a TKO 600 with 3.50 final drive, the overall ratios are very similar to those of a close-ratio toploader with 3.91 final drive. This steeper overall gearing lets you take advantage of the PRO's of the 4V head (upper-RPM power) while minimizing the CON's (weaker low- to mid-range torque).

I'll finish up by saying that this is my opinion, and you have to be honest with yourself about how you are going to use your car. While 400hp at 6500RPM is cool, are you going to be beating the crap out of your motor every time you take the car out? Or, would you rather have 300ft/lb at 3000RPM, planting you back in the seat as soon as you get on the gas, at an RPM that you will see pulling away from every stoplight or accelerating out of every corner...

 

[mach71351c]

If you plan on going with a roller cam and already changed to 3.50 gears The 2v 4v no bottom end debate is over.

 

[jbojo]

You mention 73 OC 4v heads which has a intake valve size of 2.05 and exhaust size of 1.65 which is exactly the same as a 2v head. Only difference would be the port sizes. I can't see any benefit gain by swapping out the heads that you have and since the motor was rebuilt 1000 miles ago. I would use the time and cash for other things. Just my 2 cents.

 

[will e]

My favorite driving style is track driving, I imagine myself doing 70-80 mph on a curvy back road somewhere. I was thinking 2800 stall, I am having the rear diff converted to 3:50.1 as we speak, I know the "BOSS" was 3:91.1, but thats a little too steep for me. I want my power curve to start around 3000 rpm, so I think the 4 bbls are a better choice. I am building a very tight suspension system, and have upgraded to wider magnum 500's for road handling. Like I said, a "close" boss clone, as I dont have a 4 speed either.

I think your logic is pretty sound based on what you said is your favorite driving.

The argument on 'low end torque' doesn't apply for what you are looking to do.

To answer your other questions. You should be able to put another cam in without changing out the bearings. Verify what is in there now.

My understanding of the multi-groove keepers is they are a little looser than single groove. I think it isn't the HP of the engine but the RPM's you that get them. For what your are looking at doing I would spend the money and go single groove.

Bottom end the 2 bolt main is a good block and you should be fine.

 

[c9zx]

The 4V port is higher and therefor straighter, the cross sectional area is also larger. Even with the "small" valves, there is an advantage. As TommyK said, cam selection is critical. The 2V vs 4V debate got started, and continues until today, because people use in-line valve and Chevy experience to select the camshaft for the 4V. Most cams, off the shelf, have too much duration and too tight Lobe Separation Angle which causes way too much overlap resulting in a soggy bottom end terrible street manners. At the same time most don't have enough lift to fully utilize the 4V heads. The stock 4V reach full flow at .600 lift or more. The stock 2V heads reach full flow just above .400 lift.

If the cam bearings were changed at rebuild there is no need to change them again, assuming they were properly install the first time (especially the front one).

You will need to know several things before you talk to cam grinders. You must know the real static compression ratio and fuel octane. Here is a good calculator. http://www.diamondracing.net/tools/. You will need to know a lot of specific data to use the calculator. There are others that require less data and are less accurate. Confirm that they really are flat tops not flat tops with a dish.

The multi-groove, rotating valves would worry me at high rams (not a HP issue). Spend the money for the right springs and very good pushrods and get the valve train geometry right.

If you stay with the 2V heads and want to upgrade the cam you won't need as much, if any, split duration (more on the exhaust) as the 4V.

Let us know what you decide. Chuck

 

[Omie01]

I think for now I may stick with the 2bbls, and get a 4bbl intake/carb. I know I want to run the 4 bbls eventually for the RPM's. Like I said, I like track driving. I have been doing a lot of research on this, I think when I swap to the 4bbls, I want everything to be fresh and new. Thanks for all the input everybody. As soon as I get everything together I will post some pics. Again, Thanks everybody!!!

 

[barnett468]

ok heres what i would do.

DISTRIBUTOR GEAR

Roller cams require special gears some aftermarket distributors have them, I just use comp composite gears because they work with everything

Install hardened pin in your distributor gear if the distributor is original.

QUENCH/SQUISH CLEARANCE

Getting your quench/squish distance to .042 - .035 on any head where a portion on the combustion chamber is closed off will reduce potential for detonation and increase compression and in my experience is vitally important to getting the most out of any engine. The process below is less helpful on open chamber heads necause there is no "pad" in the cylinder head for the piston to squish/compress ait against so often a simple milling of the head ito get the drsired compression is the best that can be done.

Put each end cylinder on tdc:

Place a flat metal bar or ruler over the edge of the cylinder

Stick a feeler gauge between the bar and the piston and write down the number

Buy head gaskets that will make the distance from the highest piston to the cylinder head surface as close to .035 as possible . . also buy the gasket with the bore size you have . . ok, don’t choke but these gaskets are around $85.00 each but it might cost you a lot more if you don’t do this if your engine detonates itself to death . . the factory milled the block surface on the boss 351 engine for this exact purpose.

http://www.shopengineparts.com/productdetails.aspx?emid=16&cid=40&pid=2665&vtype=Domestic+Auto&make=Ford&model=289%2c+302%2c+351+%26+351C&type=engine

heres the .030 thick one.

http://www.jegs.com/i/Cometic+Gaskets/245/C5871-030/10002/-1?CAWELAID=1710620159&CAGPSPN=pla&catargetid=230006180000849621&cadevice=c&gclid=CL_p8PuowsICFdNj7AoddwwAcA

COMPRESSION

Now, use an online compression calculator to see how many cc’s your heads need to be to get your compression to 9.3 – 9.5 if you are less than 1000 feet above sea level.

Now…for every .010” your heads are lowered from stock beyond .032” you should mill the intake surface on each heads .005” . . This will prevent any intake fitment problems . . this means that you need to add the amount removed from original fron both the block and head and add these numbers together . . if you use a thinner gasket than the standard fel-fro ,.040” thick one, you need to add that number to your calculation also.

COMPRESSION CALCULATOR

http://www.wallaceracing.com/cr_test2.php

CAM

If you want an off the shelf cam I would run the one below for your app.

CRANE HR-216

278°/286° advertised duration

216°/224° duration at 0.050"

0.562"/0.586" valve lift

58° overlap

112° lobe separation angle

LIFTERS

Crane nor Morel with .700 diameter wheel.

TIMING CHAIN

One of these first two are fine . . if you have a wad of money, buy a rollmaster for $135.00

http://www.summitracing.com/search/part-type/timing-chain-and-gear-sets/brand/cloyes-gear/make/ford/engine-size/5-8l-351/engine-family/ford-cleveland?N=4294899544%2B400043

OIL PUMP

I would not spin the engine up over 5500 without a high pressure spring in the pump especially if you have not done any oil restriction mods.

PUSH RODS

They must be chromoly . . If your lifters have a hole larger than .040” I would buy push rods with a .040” hole . . this will help improve oiling of the crank and rods.

VALVE SPRINGS

You need high pressure springs for a roller cam . . get the ones the cam mfg recommends.

INTAKE MANIFOLD

Eddy RPM if you have clearance

CONNECTING ROD BOLTS

If they are stock I would not rev this over 5500 . . If they have been replaced with high perf bolts like arp’s then you are fine.

EXHAUST

If your pipes are smaller than 2 3/8”.

CARBURETOR

If you are on a budget a 750 slayer vac secondary . . If you have some money then a 750 annular booster SS750-VS-AN.

SPARK PLUGS

Run Autolite AR24’s . . gap them to .038”

COIL

MSD epoxy coil

IGNITION BOX

MSD 6

PERTRONIX III

This will substitute for the MSD box.

THERMOSTAT

Run a stant premium 180 with the bypass block off plate below.

http://www2.cougarpartscatalog.com/waterrestrictplate.html

PLUG WIRES

Any decent wires but you might consider ceramic boots so the headers won’t cause premature boot melting . . summit racing sells them.

IGNITION TIMING

I would do the following to start with,

set the initial to 10

set the total advance so it ois around 32 degrees at around 2800 - 3000 rpm.

set the distributor vacuum advance so it adds a total of 6 - 8 degrees and connect it to ported vacuum, not manifold vac.

.

.