[redhawk44]

Hey guys, looking for the experts to chime in. I have a 1974 400ci, TH350, headers with dual exhaust. I am looking to do some improvements in the power area. Right now I have 17 heads they are off of a '68 350ci with 1.96/1.66 valves with 80 cc. The cam is a Erson TQ20H with 214/214 duration. That's about all I know about the internals, I haven't torn anything down. My question is this, is the heads I have all that bad? How big of an improvement would 6X heads give me? I know the valve are a limiting factor, I'm just trying to justify the costs. Would a cam swap do anything for these heads? Jeff

[Will]

Just sticking to comparing heads - the 6X will flow better, especially at low lifts (below .400") but the chambers are large enough that you will lose significant compression.

There are two types - 6X-4 and 6X-8. The -4 variants had chambers with approximately 91-95cc volumes. The -8s are quite a bit bigger. I don't remember exactly but in the neighborhood of 110 CC, IIRC. If you want to go to 6X heads, make sure you get the -4 version as the -8s are useless on a 400 unless you're going forced induction.

if you change nothing else but the heads I don't think the increase in flow will make up for the loss in compression.

Any specific recommendations about how to get more performance from your current setup require more information - What rear gears? What vehicle/weight? Stock converter or aftermarket?

[pontibeast]

My 6X-8 heads cc'd at 98 and I was able to mill them to 90cc which brought compression on my 455 to 9.78. Had them ported and they came out to 250/220 @ .550 lift. Not sure if they are differing cc's for different years but this is what mine came out to .

[rexs73gto]

Are you stuck on 6X heads or are you also looking at any different # heads to ??. Because there are a lot more heads out there depending on what your going to do to the engine , & what you plan on having when you get done. ??

[72blackbird]

No.17s give you a 9.3:1 SCR on a 400- you'd have to mill over .050" off the deck of a set of 6x -4s to take the 94- 91cc down to the same 80cc. It's better to have the bowl opened up and 2.11s installed, screw in studs added to your no.17s, instead of trying to take all that metal off the deck of a set of 6x-4s.

A street port will take flow into the 230-240 cfm range, and the 9.3:1 SCR will make good power on 91.

Geno

[panhead59]

My 6x-8 heads cc'd at 99. Was told they were milled .040 but I think that is stock on those heads. I don't think they were ever milled. Could be wrong. ooops, sorry, you were looking for "experts".

[Cliff R]

I've used and cc's a boat-load of 6X heads. In almost all cases the 6X-8's come it at 101cc.

The 6X-4's usually around 92cc, but I see them range as high as 96cc.

Neither one is a good choice for a 400 build if you are trying to get a decent compression ratio for optimum power on pump gas. Cutting them really hard to get there quickly causes issues in other areas that need to be addressed, like the intake bolts not lining up......Cliff

[pontibeast]

Cliff, I will definitely defer to your level of experience. Mine came off a locked up 400 I got for 100 bucks as an add on to a 428 I got and they very well could have been milled before I got them. I did have to have my intake milled as well due to taking them down so much.

[redhawk44]

Answers to the questions:
-I am not stuck on 6X heads I should have asked if " is there a better head out there for my application?"
-3700ib weight, stock converter and the gears are something else I am currently looking at, right now I have 2.78 gears but am in the process of a different rear end with 3.07 gears. I am also planning to go with a 200r4 or a700r4 tranny.

My plan for this car ( 1965 LeMans convertible ) is a street machine. Enough power to have a little fun but still be able to drive it for little trips ( 300 - 400 miles ).

I saw from 72Blackbird something about installing bigger valves, I was not aware that this was possible. Does this take a specialty shop or can any place that does heads do this?

[Cliff R]

For all practical purposes the 68 an later "D" port castings have similar flow characteristics, large or small valve.

Since the heads you have are 80cc chambers, I'd have them opened up for the 2.11/1.77 valves and set up for screw in studs. We do this here, and much prefer using similar castings, like the 1969 #46 heads for 400 builds, rather than search in vane for the big valve castings and pay too much for them.

Besides, working with "virgin" material, the machine shop can put the valves all at the same height in the chambers, which isn't going to happen if you starting out with big valve heads, and many of those will have sunken exhaust seats, and really need seats installed to come up with a good end result.......Cliff

[redhawk44]

What does this cost at your shop Cliff? To have bigger valves and threaded studs installed.

[Cliff R]

I have mine done elsewhere, my equipment hasn't been used much in the last 10 years, aside from a few tractor engines and a couple of Kohler and Onan engine for my John Deere 212 and 318's.

Modern equipment is much faster, and more accurate when it comes to opening up small valve heads for the larger valves, so I send them out and pay for this sort of service.......Cliff

[pontibeast]

Originally Posted by redhawk44

What does this cost at your shop Cliff? To have bigger valves and threaded studs installed.

I just had mine done and these are the prices I paid

clean heads which were filthy 40
Install 8 guides 50
Install 8 hardened exhaust seats 80
cutting seats(valve job 60
milling .045 60
cut for spring cups 40
port and polish with flow sheet and fill crossover 500

Not sure what other shop charge for these, but this is from my receipt.

[redhawk44]

Thanks Beast, That was to put 2.11s and 1.77s in? what size of valves did you start with? What heads did you have worked on?

[74Grandville]

Originally Posted by pontibeast

I just had mine done and these are the prices I paid

clean heads which were filthy 40
Install 8 guides 50
Install 8 hardened exhaust seats 80
cutting seats(valve job 60
milling .045 60
cut for spring cups 40
port and polish with flow sheet and fill crossover 500

Not sure what other shop charge for these, but this is from my receipt.

this sounds like a good deal, especially the milling.

[Squidward]

Paul Carter at Koerner Racing in Tucson did my small valve heads for big valves. I have 47's, which are about the same thing as 17's. After guides, springs, hardened seats, and big valve conversion with ferrea valves, I think I was out the door for around a grand. Of course, every job can have variations. Well worth it imho.

I'd do the 17's even if you didn't go with big valves. Your cam is radical, so I think small valves would breathe just fine for your described combo. But if you have to get all the work done to them anyways, you might as well give yourself room to grow.

[redhawk44]

My cam is radical? I thought it was on the mild side. Very easy going on the idle, no lope to it. I guess I'm still learning though.

[pontibeast]

Started out with 2.11 and 1.66 for 6X-8. Plan on having engine in and running in about 2-3 weeks and over to get dyno tested by a member here a week or two after that. I will post updates once I get it running.

[Will]

I'd guess that's a typo. Never heard anyone call a 214@.050" cam radical ....

Converting to big valves is probably your best bet. Any machine shop that can rebuild heads can do this job, but finding a shop that takes the time to do things right and turn out quality workmanship can be a challenge.

The cost at any particular shop should be the same to do this for any small valve head you give them. All '67 and later small valve heads had 1.96" intake valves. Most had 1.66" exhaust valves.

A couple thoughts on your gearing - Be sure to match your final drive ratio (rearend gear ratio x OD ratio in trans) to the engine or you can end up with a final drive ratio that is too tall to be useful. if you stick with a mild cam then you can go pretty tall but if you go bigger on the cam you'll want to go a little deeper on the gears.

[redhawk44]

Thanks Beast, looking forward to see your numbers.

Will, by deeper you mean something like a 3.5 or 3.73?