any advantage to switching 351c-4v heads

[Animal Lawyer]

Newbie question - stock 1973 Q code (351c4v) mustang convertible. I have read much about the 1970 closed chamber heads over the open chamber heads I presently have. Is there any advantage and can I swap heads to the cc without changing pistons? Assuming I can do it (I am not sure if the 1973 pistons are compatible (clearance wise) with the 1970 heads) is it worth the effort? What will I gain and what will I lose? Stock 351c 4 speed with 3.25 9" ls rear.
 

 

[machattack]

Im not the one to answer this question however......... several folks on here that can with GREAT enthusiasm.  Where you guys at?  Spike? Don C ? Hemikiller?

These guys can flood you with knowledge.  As Im sure many others can as well.  I have an interest as well and will follow the answers.

 

[Tnfastbk]

Here is an article discussing one vs the other.

https://pantera.infopop.cc/topic/351c-cylinder-heads-open-chamber-vs-closed-chamber

 

[Hemikiller]

You can bolt on a set of closed chamber heads to your factory 73 351-4V engine. The '73 was the first year with dished pistons, which reduced the compression further than the open chamber head alone, to about 8:1. 

You'll gain about a point of compression with the 71 D1AE-GA heads, 1.25 points with the 1970 D0AE heads. Another "quick" fix is to replace the timing set with one that allows you to advance the cam 4° to compensate for the retarded timing ground into the factory CJ cam. 

 

[c9zx]

What Hemikiller said and nothing to be lost, gains from idle through max RPM. Consider a .030 MLS head gasket for more gain in compression. If you are concerned about deck and head surface being too rough for MLS gaskets spray the gaskets with copper coat. I know that Cometic and others say not to do so but, I've done it twice with no problems. Chuck

 

[Animal Lawyer]

Any idea about how much a set of D0AE heads should cost? I will definitely be looking to make the swap. 

How big a job is the timing swap and are the results worth the effort/cost?

 

[Don C]

It's not a real big job, the radiator, water pump, harmonic balancer/crankshaft pullies, and timing cover have to be removed. 

Yes, to really get the potential benefits from the head swap you should correct the cam timing. The camshafts in the CJs have a little better grind than the M codes, when the cam timing is set right.

When you find the heads I would have them machined for adjustable rocker arms and have hardened valve seats installed and install new valve springs and one-piece valves. Have the valve guides checked also. 

 

[Animal Lawyer]

Any idea what I should expect to pay for a set of D0AE-6090-N heads?

 

[TommyK]

A set of used properly prepared ready to run closed chamber 4V heads are probably going to cost $1000-$1500 depending on how they are set up and the parts used.

 

[Carolina_Mountain_Mustangs]

I realize everyone has their own opinion. Depending on how many miles on your engine might need to consider pulling the engine and building the whole thing. 
On the heads. Search around I got a set of 70 CC for $125 complete. I ran ads on Craigslist to find them. He also had lots of other parts I got for great prices. He had a 31 spline traction loc I looked at and did not take for $150 and couple weeks later called him to get it and he had sold. He had bought up the parts to build a 71 M code then he crashed and totaled it and never got to use them.  I tore them down and took and had tanked and magnafluxed and are good. Me I would never put hard seats in just adds more areas for failure. I have cars that ran on nothing but unleaded gas for 100,000 miles and had a Y block so not modern, never an issue. As long as you are not running timing so high you are not slamming them closed you will never have a problem. Especially if you use Lucas gas additive that replaces the lead. Most will never drive enough miles to notice. 
If you got to our local drag strip all the Cleveland guys here are running 2-V heads. Better low end torque without having to wind so many rpm's. Of course you can also get the Australian 302 heads that have the 2-V runners and 4-V size valves. 
I have eight Cleveland cars and a couple extra engines. The one I drive is a 73 with 2-V heads, flat top pistons bored .050" over with cam and MSD, headers and dual exhaust. Runs decent and no issues so far. Has AC and just stock radiator keeps it cool. 
BTW if your car is an original 1973 convertible with 351 4-V Q code with 4 speed it is one of 293 that were built so pretty rare pony. They made 3,610 Fastback / Mach 1 and 325 coupes. So if original keep all the original parts if you ever sell can add value.
If you do change the heads be sure your baffle is still in the block under the thermostat and get the correct Cleveland 295 deg. thermostat. Also you can put the head gaskets on backwards so be sure you look for the FRONT on the gasket and install that way. Most have a logo printed on one side and if you put the logo up one will be backwards. I use just good grade Fel Pro gaskets with no sealer just wash surfaces with brake cleaner. Always run a tap in all your threaded holes and clean before you go together. 

 

[Don C]

I had a Y block I had taken out of a '64 F100 and transplanted into a '55 Willys 4x4 wagon and ran it for 30+ years on unleaded with no problem. However, the '70 390FE I put in the '64 F100 only went about 15 years before the valves recessed enough to cause the engine to idle rough. Pulled the heads off it and some were recessed more than the thickness of the valve heads. The Willys wagon was my daily driver and our family weekend trips into the mountains, so it was driven a lot. The F100 was only used occasionally, so the 390 probably had 1/4 the miles of the Y block in the Willys.

Since then I have installed hardened seats in everything pre-1974, and haven't had any seats come loose, but I use only good machinists.

 

[machattack]

I had a Y block I had taken out of a '64 F100 and transplanted into a '55 Willys 4x4 wagon and ran it for 30+ years on unleaded with no problem. However, the '70 390FE I put in the '64 F100 only went about 15 years before the valves recessed enough to cause the engine to idle rough. Pulled the heads off it and some were recessed more than the thickness of the valve heads. The Willys wagon was my daily driver and our family weekend trips into the mountains, so it was driven a lot. The F100 was only used occasionally, so the 390 probably had 1/4 the miles of the Y block in the Willys.

Since then I have installed hardened seats in everything pre-1974, and haven't had any seats come loose, but I use only good machinists.

Off the main subject line but speaking of jeeps .

Here's a picture of the Wifeee, Son, Me and the 1964 jeep Gladiator pick-up. We used this pickup hard running a 100 mile trap line 40 years ago.

 

[Animal Lawyer]

Of course you can also get the Australian 302 heads that have the 2-V runners and 4-V size valves. 

I just started looking at the aussie heads, I just added a 1970 4v cast iron intake manifold and hooker 6915 (4v) headers. Would I have to swap those to 2v, too to use the aussie heads?

btw i am saving all original parts to be able to return to stock

 

[droptop73]

What do you plan to do with the car? Select parts that will help you get to that goal. Will the existing 2v heads provide what you intend to do? There are some real strong running 2v engines out there. 

 

[Hemikiller]

By the time you buy the Aussie heads, have them machined and the valves/springs/retainers replaced, you could spring for a set of aluminum. 

FWIW, there's nothing wrong with the 73 4V heads. The open chambers supposedly flow more due to less valve shrouding. If you wanted a stout street motor, you could swap in a set of forged flat top pistons to get the compression up to @ 9:1, swap to a larger cam and with a few tricks, have a nice 400+ hp street cruiser. The build below was poste don the 351C Facebook page. Look at how flat the torque curve is.....

 

[Animal Lawyer]

I bought the car for a fun street driver. Wanted the q code (but a bit more power & compression would be nice (Ok a lot more would be even better)). 
My mechanic wasn’t able to adequately rebuild the 4300d leading to a swap to 1970 square bore manifold, 670 afm SA carb and dura spark II and hookers.

I’m adding working ram air and subframe connectors (Tinman). suspension and brakes redone by P.O., may swap in close ratio ps box.

Not sure yet if I want to pull engine and rebuild, so, looking at most cost effective bolt ons for now. Trying to stay with pump gas, too

 

[Don C]

Imagine a torque curve like that on an engine that isn't supposed to have any low end.  :goodpost:

 

[Animal Lawyer]

Would I need to bore it .30 over or could I simply change pistons and cam, and achieve most of the benefit? I'd prefer not to have to pull the engine (It's not the actual pulling that bothers me, it's the 4 most expensive words in the english language "while I'm at it...")

 

[droptop73]

What's the end game you're looking for? How does the car perform as is? Will you enjoy it more with a bit more compression? 

Not trying to spoil the fun but if you gain 50hp will you really notice it on the fun meter? I'd like to see you enjoy the car and keep it fun to drive.