valve sizes..

[427Fastback]

Hey guys...I bought a set of the edelbrock 427 Heads for the 427 in the Mustang with the plans of putting the stock size 427 MR valves in it..I have converted them to the 16 bolt exhaust flanges and done some port and bowl work..(clean up).Recent reading is making me think I dont need valves that big and it may actually hurt me.

Engine is a 9.8 to one 4.25 bore 427.Comp 270S cam.I have roller rockers,headers etc etc.Intake will hopefully be one of Jays 2pc ones otherwise it will be a Perf rpm...

Car will be around 3000lbs and 100% street driven.It would easily pull 6400rpm with the CJ valves in C8-H heads and CJ manifolds..

Looking for opinions on valve sizes...The cam is staying in..I dont want solid rollers on the street and Hyd is not a option.(C5AE C/O block)

Share your opinions please on the valve sizes..

Cory

[jayb]

What is your horsepower target?  My guess is with that cam, you don't need the bigger valves.  The CJ sized valves should be fine...

[hotrodfeguy]

Not to hi-jack but would the MR valves hurt him on the 4.25 bore at all? I am not shooting holes or anything just wondering if it would hurt at all. Sometimes it may be a case of lets do it now with the option of going with a larger cam later option. this way he would be set up for it and not have to do a full teardown.

[jayb]

Well, that's a good point, and no, I don't think going to, for example, 2.19 and 1.71 valve sizes would hurt.  I just don't think they'll help the engine any, because that is a pretty mild cam.  If the engine is slated for an upgrade later, then maybe it would make sense to go with the bigger valves now.

[427Fastback]

I have had the 270 in there for over 20 years..I know there are better cams available now but i really dont want to go through the flat tappet break in horror..My HP target is obviously limited by my cam.The short block(20,000 miles on it) is still assembled so i really dont want to strip it and have the block drilled for juice lifters.It is what it is and I am ok with it..Its a good eng (bottom end is still std,std) and its always been a "happy" engine...

The new heads,headers and intake should add some noticeable power to it..
I just dont want to defeat the purpose by installing too big a valve.
MR valves would be the absolute largest I would go..

Cory

[DEANs427]

Cory,
you can make that cam "bigger" by advancing it and tightening up the lash. also getting your quench to about .40 is a big factor. I have built a few street 427's with compartively small cams and made good power with street manners. JMO

[ScotiaFE]

So the the C8 heads had Compression of 9.8?
The ED 427 chamber is bigger like 5 or 6 cc's bigger.
You may even see a net loss of power with the new heads because of the the lower compression.

[My427stang]

OK, lots of assumptions here, but if you can keep open up the valve bowl and still keep a consistent taper from intake surface to valve seat, I'd go 2.19

Not that it's a huge amount, but assuming a valve size of 2.19 vs 2.09 and a lift of .530, you are going to get about 5% more curtain area at any given lift.

Seeing you have a big bore, and assuming you port the bowls, I'd go big, it sure wont hurt anything and you have a LONG way to go on a 427 bore before there are any intake issues.. 

[427Fastback]

I had around 10-1 with the C8-H heads...I have CC'd everything and will need to mill the edelbrock heads .030 to get it back up to around 9.8 to one.The edelbrock 427 heads CC'd @ 76CC which is what they are advertised as...

I have long been running my valve lash between .015 and .018 cold...
Most of my porting effort is on the bowls and exhaust..The intake port size on the heads appears to be fine.Certainly larger than the unported RPM manifold..

Cory

[hotrodfeguy]

Another cam option would be a solid roller, they make some really nice street grinds now. But I would go with the larger valves even with the small cam you have now. As said you have more area to move more air with, at any given lift. What do you have to loose.  And if it were me I would port back into that RPM intake a few inches, again whats to loose, and its free power to gain all you put in is your time there. 

[427Fastback]

I have no objection going to a solid roller but how long is it going to last sitting at a traffic light running at 800rpm.....Cory

[hotrodfeguy]

A roller is going to live longer than a flat tappet all things the same, here are some cams that are close, some are a bit wicked but dont get hung up on the lift numbers. The crower has 10 degrees more duration and would be real close to what you have now as far as duration and character. The roller will come "on" harder and hang on longer. I would not be surprised to see you hit another 40 hp with that cam. The MR valves the crower roller cam would certainly work very well together with that RPM intake and ED heads. You would have a steller package working together. 

http://www.summitracing.com/search/Department/Engines-Components/Section/Camshafts-Valvetrain/Part-Type/Camshafts/Make/FORD/Cam-Style/Mechanical-roller-tappet/Engine-Size/7-0L-427/Camshaft-Usage/Street/?Ns=Rank%7cAsc

http://www.network54.com/Forum/76346/message/1351037238/Some+unshrouding+pics

[jayb]

Not sure I'd agree that a roller will live longer than a flat tappet in an FE.  Most rollers have much more aggressive valve action than a flat tappet, including higher lift as you mentioned.  That's tough on the lifters, and there are plenty of people who've lost roller lifters on the street, but never had problems with flat tappets.  Durability is probably not the reason to go with roller lifters.

[427Fastback]

The lack of oil to the roller lifters at a idle is my main concern..The resulting carnage is not worth the risk to me..I chose the 270S in 1988.Cam selection was very limited,Also aftermarket blocks and heads were not available so I built the engine for torque and to last...I chose to be conservitive as 427's were expensive then and good blocks were hard to come by...

Cory

[ScotiaFE]

Yes, they are so much cheaper and easier too find these days.