Potential of going with larger valves. Questions

[70_Fastback]

Current heads are '68 302 'J' Code 4V heads heavily ported, but still have stock 1.78 / 1.45 valves.  Spring pockets have already been machined & 7/16" screw-in studs w/ plates are installed.  1.6 roller rockers.

Assuming that I may have valves damaged & could potentially be yanking the heads off, I would want to upsize the valves since that was the only thing that I didn't do the fist time.  Is it a simple upsize to a (standard ?) che\/y valve size - 1.94 / 1.60 over the stock 1.78 / 1.45 ?

Isn't this a typical Ford upgrade over the stock size?


I will farm out the head work to have the seats enlarged.  But, what else is required on my end?  Do I just buy stock che\/y valves - or it is a "special - enlarged" Ford valve that I'm looking for - for stem length, diameter, etc?  Is it a 351 valve? 

I want to be able to reuse my new springs, retainers, locks, etc that are already installed on my heads.

Thanks

[70_Fastback]

   None of you opinionated SOBs have chimed in yet?

Where's the love?

[Sluggo]

  None of you opinionated SOBs have chimed in yet?

Where's the love?

Did it not run well enough?

[silverblueBP]

Hey douchebag, why don't you call Dean and talk to him about the heads? He could probably give you any info you want / need.

[AzPete]

Talk to your head guy for what he says you need. I have heard that they are just stock Chevy valves but I have never worked with them....

[70_Fastback]

Hey douchebag, why don't you call Dean and talk to him about the heads? He could probably give you any info you want / need.

Gimme Deans digits - but make sure with him if it's ok that I dumb him down on the phone...  :wstup

[70_Fastback]

Did it not run well enough?

I'm tearing it down.  So I'm not putting it back as it was.  What fun is that?   :nice

[Sluggo]

Gimme Deans digits - but make sure with him if it's ok that I dumb him down on the phone...  :wstup

Now there is an understatement :dumas

[70_Fastback]

Damn, I'm pretty much speechless for dat one...

 :bird

[silverblueBP]

Gimme Deans digits - but make sure with him if it's ok that I dumb him down on the phone...  :wstup

Sorry, I've already taken care of that!

[monkeystash]

There are plenty of variables in changing valves.  Are the lengths exactly the same?  When they grind the seat, will the valve sit further into the head?  These factors will change your spring pressures, installed height, retainer to seal clearance, coil bind, etc.  Don't just assume the machine shop will check all this.  Give them your cam card and valvetrain specs so they can set up the heads correctly.

[tarafied1]

I did the Chevy valve thing a few years ago. The stem size is the same but they are shorter so you need custom pushrods (longer). Also you want to make sure the valves arn't shrouded by the combustion chamber. I used 66 289 castings which had small chambers and had to do a lot of grinding to unshroud the larger valves. I'm not sure if you will have the same issue on your heads. It would be a good time to cut the seats out and put hardened (unleaded) seats in however. As I recall the 289 heads needed a LOT of porting on the exhaust side to benifit from the larger valves. There is a boss for the smog fittings (mine didn't have smog fitting but the casting was the same) which really restricted the flow. Plus they are small anyway so hog out the exhaust side pretty good. Finally, you will need to check piston to valve clearance depending on the cam (lift), the larger valves could contact the pistons.
Larger valves are only a benifit at higher RPM's and may cause a small and unoticable drop in peak torque. You would have to track test or dyno to measure the difference IMO.

[70_Fastback]

The heads already have hardened seats installed along with all new bronze valve guides too.

So you think it may not be a big benefit for me to upgrade?

And here is my cam specs:
http://www.compcams.com/Cam_Specs/CamSpecPrinterFriendly.aspx?csid=795

[tarafied1]

The benifit will be at high RPM's. That cam is a good high RPM cam so as long as your valve springs can shut the valves and not "float" them you could wind that motor to 7K still making HP. That's where you will see a gain, it should continue to "pull" at a higher RPM range than before (although hard to tell by the seat-of-the-pants). On the street, the low end will not improve and might suffer slightly. I was running a similar cam with my Chevy Valve heads and she would breath easy at 7K (I was afriad to go higher with stock cast crank). If you have the suggested 4.10:1 gears and high stall converter you may get the RPM's up there a lot. What I have found is that torque is king on the street. My 429 is outta breath at 6K but it will get there in a hurry. My high revving small block was a PIA, fussy, hard to start, not real practical street engine. I had 10.5:1 CR, 750 CFM Holley, double rollor chain, windage tray, high volume oil pump, rollor rockers, screw-in studs, etc, etc. My mild 429 is more fun to drive on the street than my wild small block was.

[70_Fastback]

Interesting.  The engine does not see a lot of high rpms.  I'm typically 2k to 3600 most of the time.

I'm going to have to give this one some more thought.

[Starfury]

My question is...why are you wasting time with OE heads?  Even ported, stock head castings suck.  Unless you're building an MCA show car (which you're obviously not), I don't see any reason to throw money at stock heads.  If you're trying to save money, go search a few junkyards for '95-96 Exploder 5.0's and pull the GT40 heads for yourself.  If you're not trying to save money, pick up some aftermarket heads.

FWIW, I'm running exhaust port-matched '68 J code heads with 1.90/1.54 valves that almost touch.  Any larger and they would touch.  The only reason I'm running them is because I got them for cheap from a coworker fresh from the machine shop, with cam-matching Comp Cams hardware installed.  I was running out of $ towards the end of the engine build, and I got them for the price of the hardware alone, so I couldn't pass it up.

[70_Fastback]

Like wise, I got mine cheap and did all of the work on them.  I don't have the extra cash to drop on new heads either.  So I want to make the best of what I've got basically - with minimal costs.

[tarafied1]

Interesting.  The engine does not see a lot of high rpms.  I'm typically 2k to 3600 most of the time.

I'm going to have to give this one some more thought.

the 268H or 280H is a much better street cam with gobs of torque if you're not winding it out. They still rev to 6K when you want to.

[daveSanborn]

Assuming that I may have valves damaged & could potentially be yanking the heads off.....

I wouldn't assume that the valves are damaged.  Why would they be?  Your 351 is not a Honda 4 cylinder with an interference fit valvetrain.

[Starfury]

the 268H or 280H is a much better street cam with gobs of torque if you're not winding it out. They still rev to 6K when you want to.

Having run both, I'm much happier with the 280H (w/Rhoads lifters).  It's more happy to wind up to 6k, and I take it there fairly often.

70fastback, if you need to do head work, I'd suggest looking for some GT40's before you put time/money into those J code heads.

[70_Fastback]

70fastback, if you need to do head work, I'd suggest looking for some GT40's before you put time/money into those J code heads.

Just curious - Why?  What's the large difference between the 2 ?

[70_Fastback]

I wouldn't assume that the valves are damaged.  Why would they be?  Your 351 is not a Honda 4 cylinder with an interference fit valvetrain.

Hey Dave,

I am anxious to find out if there is any or not.  The concensus Is basically a 50/50 split on opinions on this one - if I sustained valve damage or not.... 

I honestly don't know for sure, as never having experienced this yet - but logistically it seems possible, to me, that if a valve was fully open with the cam stopped that a piston could possible ting it a little though...  I just don't know.  I would rather be sure than sorry though.

[daveSanborn]

I still can't fathom that you've not torn into the engine yet.

I spun a bearing on my 347 last Summer/Fall.  The crank and rods were in the trunk of my DD within 24 hours driving around looking for a machine shop.  I can't stand it when something is broken.

[tarafied1]

I honestly don't know for sure, as never having experienced this yet - but logistically it seems possible, to me, that if a valve was fully open with the cam stopped that a piston could possible ting it a little though... 

That's all I'd be worried about, been there and done that... twice, bent at least one valve each time.

I still can't fathom that you've not torn into the engine yet.

me either, drives me nuts to at least figure out what all I need to do to fix it even if I have to wait for funds, I want to KNOW what I'm dealing with right away, but to each his own...

[tarafied1]

Having run both, I'm much happier with the 280H (w/Rhoads lifters).  It's more happy to wind up to 6k, and I take it there fairly often.

70fastback, if you need to do head work, I'd suggest looking for some GT40's before you put time/money into those J code heads.

I've used those lifters before, I felt like they sucked the life outta my engine compared to when I took them out.

and to answer your question, the GT40 casting is a better design in terms of the ports and the combustion chamber... better flow and more even burning cumbustion (less detonation or hot spots for high compression engines)