General head questions

[SadbutTrue]

Just had a handful of random questions about ensuring you buy the right cylinder head for a given engine.

1) I noticed Trick Flow heads differentiate between 1.46" and 1.47" spring O.D., and also have an option for both o-ringed and non o-ringed heads? Whats the advantage or application for each?

2) If you purchase a set of heads with 7/16" head bolt holes, and need 1/2" bolt holes (ie buy a set of heads designed for a 302 and try to use them on a 351w), is it advisable to have the hole enlarged? Or does this compromise the head at all?

I know I had a few other questions but they're escaping me at the moment. Thanks!

 

[SadbutTrue]

Just had a handful of random questions about ensuring you buy the right cylinder head for a given engine.

1) I noticed Trick Flow heads differentiate between 1.46" and 1.47" spring O.D., and also have an option for both o-ringed and non o-ringed heads? Whats the advantage or application for each?

2) If you purchase a set of heads with 7/16" head bolt holes, and need 1/2" bolt holes (ie buy a set of heads designed for a 302 and try to use them on a 351w), is it advisable to have the hole enlarged? Or does this compromise the head at all?

I know I had a few other questions but they're escaping me at the moment. Thanks!

figured out about the spring size (1.47 is just their single spring size, 1.46 is for the double spring). the other questions still loom though. Also, if I were to machine the heads to accept the larger bolts... how much would that typically cost?

 

[brianj5600]

I would seriously ask these questions to each manufacturer. They all have tech lines or just e-mail the tech department. I have done the e-mail thing and just cut and pasted the bulk of the letter. The things that are specifc to each company edited.

 

[BarnStang]

You should still be able to get the heads with the 1/2" bolt holes, and use the washer kit. Do they still offer that?T Hat's what I put on my 93. Also opted for the O ring groove. My future plans had been to add boost with a turbo probably. THe head gaskets for the O ring heads are expensive. At least they were when I put them on 20 years ago. Oh, if I remeber right, the O ring heads from summit only came with the larger head bolt holes. I think I could only get the smaller head bolt holewith non O ring heads. Was a long time ago so I'm not up on what you can get today. Check Summit and the trick flow site. I needed to get guide plates and hardened pushrods.

 

[mrmustangman357]

oringed heads are for extremely high performance/boosted applications (RACE) and don't really apply to the world of street engines. You will find the VAST majority of aftermarket heads are drilled 1/2" already. if you wanted to run them on a 302 you buy bushings to run them. Drilling the heads from 7/16 to 1/2" never caused a problem since I remember

 

[rbohm]

1) I noticed Trick Flow heads differentiate between 1.46" and 1.47" spring O.D., and also have an option for both o-ringed and non o-ringed heads? Whats the advantage or application for each?

as you found, the larger spring diameter allows for an internal dampner to be installed. but a larger diameter spring also allows for a higher spring rate while keeping the same wire diameter, and this allows for a more aggressive cam design than a smaller spring diameter does.

2) If you purchase a set of heads with 7/16" head bolt holes, and need 1/2" bolt holes (ie buy a set of heads designed for a 302 and try to use them on a 351w), is it advisable to have the hole enlarged? Or does this compromise the head at all?

if you buy a set of heads with a 7/16" head bolt holes, you can drill them out to 1/2" with no problem. however you need to make sure the drill is centered in the opening, or drill slightly oversize.

 

[SadbutTrue]

What are the rules for milling heads?

Trick Flow makes a big deal that their heads can run the 2.02 valves with stock pistons. How much leeway does that leave? The reason I ask is I did some basic calculations... assuming the gasket was .06" thick (i think I heard that around here at some point, please correct me if I'm wrong) and my 72 351w has an 9 compression ratio (conservative... if anything it might be less, which makes the #'s friendlier as far as milling goes)... i should have about .07" between the top of the piston's travel and the block. Counting the gasket, that means I have over .13" of room not even considering any space that may exist between the top of the piston's travel and the lowest the valve will get.

Essentially, it looks like there shouldn't be any problems milling at least .025-.030" off the bottom of the head, which according to Trick Flows site, should effectively reduce the combustion chamber size from 61cc to around 56 cc (their website says the 'rule' is .006" of milling = 1cc, and as you go farther the rate at which you shrink the combustion chamber should increase).

Doing that would produce a compression bump of roughly 4-5 tenths of a point (again, if my calculations are right). Which, even for the worst case situation with my 72 351w would get me into the low 9s... not great, but it'd do. And its possible my crate engine was rebuilt to earlier specs (Autozone just lists their 351w's as 69-74, its possible they just stick 69/70 style pistons in all of them) which might mean I'd be at closer to 10:1.

Basically, it seems like it ought to be a lot cheaper to mill the heads down and get to the low-mid 9s in compression instead of buying new pistons and tearing down the whole rotating assembly, which is pretty new and is working great at the moment. Plus, after looking at AFR's website which has that 'most comprehensive cylinder head comparison ever'... it seems to make little sense to me to go to a $1500 set of AFRs when Trick Flows made only 5 horsepower less than them on the same 331 stroker (and you can get used Trick Flows for half the price).

So... on that note... how far can you usually mill the heads without affecting piston to valve clearance? What minimum piston to valve clearance is recommended?

 

[D.Hearne]

You can mill up to .040 before having intake fitment problems, mainly the intake bolts moving toward the centerline of the engine (I went thru this in milling my Canfields .060, inn which the chambers lost 7 ccs volume, 64 to 57) Do not mill the intake before checking the fit (after milling the heads) It's possible, the intake won't need milling, I've had two out of three engine combos that didn't need intake milling. The stock head gaskets are around .040-.042 thick (compressed) As for piston to valve issues after milling, if that's a problem, it's also a problem before the mill operation. .030-.040 mill isn't a whole lot in piston to valve clearance.

 

[SadbutTrue]

You can mill up to .040 before having intake fitment problems, mainly the intake bolts moving toward the centerline of the engine (I went thru this in milling my Canfields .060, inn which the chambers lost 7 ccs volume, 64 to 57) Do not mill the intake before checking the fit (after milling the heads) It's possible, the intake won't need milling, I've had two out of three engine combos that didn't need intake milling. The stock head gaskets are around .040-.042 thick (compressed) As for piston to valve issues after milling, if that's a problem, it's also a problem before the mill operation. .030-.040 mill isn't a whole lot in piston to valve clearance.

Well, I'm assuming that Trick Flow's claims that it won't be a problem are accurate. Hopefully the .030-.040 isn't enough to create a problem.

 

[D.Hearne]

You didn't mention the cam specs. That's got a lot to do with this too. When I milled my Canfields .060, they were going on a stock reman roller 5.0 short block with Silvolite flat tops (albeit the 1.585 versions) with a B303 roller, and 1.7 rockers. I never checked the clearance, but I doubt the valves came anywhere near the pistons, not even on the 7500 rpm freeway blasts.

 

[D.Hearne]

I don't even have problems with them on my 331 with the Z303 & 1.7's either. (at 7000 rpms) Those SRP's have .003" deck clearance

 

[SadbutTrue]

You didn't mention the cam specs. That's got a lot to do with this too. When I milled my Canfields .060, they were going on a stock reman roller 5.0 short block with Silvolite flat tops (albeit the 1.585 versions) with a B303 roller, and 1.7 rockers. I never checked the clearance, but I doubt the valves came anywhere near the pistons, not even on the 7500 rpm freeway blasts.

Around .520 lift, hydraulic flat tappet, with probably 1.6 ratio rockers. Never really heard of people getting a whole lot more power with 1.7s, so I dont plan to stress the valvetrain. Compcams 274XE is the one I've been looking at. Lunati and Crane have similar grinds but the Compcams one seems the best overall.

Trick Flow says up to .540 lift their heads will work with any stock piston.

 

[D.Hearne]

Well the lift is only one factor in piston to valve clearance in cam grinds, you also have the actual valve timing events to consider too. With a head mill, and that cam, & those heads, it would be best to clay the pistons before firing it up.