2.20 1.73 valves in 4.08 bore 390

[DWKgalaxie]

I am building a 390 that I am planning to to a 445 Scat stroker kit in. I haven't pulled it down yet to see where it will clean up in the bore. The heads I have, and as everyone knows it's about impossible to get aluminum heads, are ProMaxx shocker 200 with 2.20 intake and 1.73 exhaust valves. I am planning on running a Comp Cams 284H hyd flat tappet with .584 Int lift and .588 Exh lift. I have a set of PRW alum adjustable rockers 1.76 ratio. I was wondering if anyone thinks I am going to run into a valve to block interference issue? I saw a thread where it was discussed, but when I read it, it's as though I'm looking at a CIA document with some words redacted. It looks like Jay replied back in 2012, a couple times saying he had no clearance issues in a 4.08 bore. I don't recall him saying what lift he was using, but with the .584/.588 lift I plan on using, it looked like I was going to be ok since the lift was just this size. Some people have told me I had to go up to a 428 bore of 4.13 or 4.16 that the 462 scat stroker kit uses. Going that big of a bore in a 390 block probably means it will have to have sleeves in every hole. If it does look like there will be an issue, probably on the exhaust valve, which surprised me, does clearancing the the bore involve any more than very carefully grinding an area at the top of the bore, and I did see Jays comments on how far down to go, in a way that looks like GM did on there 396 big block? This is going to be a bracket/street car 64 Galaxie fastback. I would appreciate any help you guys can give me on this.
Thanks, Dave

[frnkeore]

It will depend on if the PrMaxx uses the same valve spacing and the same center offset as the LR, of 1.98 c/c and .17 offset to the Ex side.

If so, it will clear by .015 +/-.010 Or just barely but, the valve inclination is 13°, meaning it just doesn't drop straight down. Depending on valve drop distance (seat to head surface) it may or may not clear. Just what you wanted to hear, right?

So, the real answer is to install the head w/o the gasket and measure the valve drop to the cylinder. If it hits, grind accordingly.

If the heads have the wider MR spacing, it will not clear a 4.08 bore.

[Phil Brown]

It will depend on if the PrMaxx uses the same valve spacing and the same center offset as the LR, of 1.98 c/c and .17 offset to the Ex side.

If so, it will clear by .015 +/-.010 Or just barely but, the valve inclination is 13°, meaning it just doesn't drop straight down. Depending on valve drop distance (seat to head surface) it may or may not clear. Just what you wanted to hear, right?

So, the real answer is to install the head w/o the gasket and measure the valve drop to the cylinder. If it hits, grind accordingly.

If the heads have the wider MR spacing, it will not clear a 4.08 bore.

Just don't grind that notch farther than where the top ring will run up the bore 😳

[DWKgalaxie]

Thanks guys, that info is of some help. I did measure with a digital caliper across the intake and exhaust valves and that distance is 4.05". So by over boring to 4.08 or 4.09 that allows for clearance, BUT when I take into account the amount of offset that the centerline is offset then the problem may show up. Knowing that grinding the bore is ok, of course not going below where the top ring travels, that puts my mind somewhat at ease. Since I am only planning to run .588 exh lift I am also hopeful that I won't have the interference issues that more lift could cause. Thanks again for your replies, I'll let you know how it goes, and if I run into any issues with these ProMaxx heads that you guys have very varied opinions about. I understand all of your thoughts and feelings about buy pure American, I'm about as adamant as you are but these times of, we might as well say zero availability of a lot of parts, make us bend our rules a bit sometimes. Besides these guys are 55 miles from me, so if I have a problem I can talk with them in person, and I figure if they work out, I was at least helping the local guys feed their families that work with Jason at ProMaxx.

[frnkeore]

If you can and have a flow bench, not to far way, have one chamber flowed.

I looked at their web site, about a year ago and they have flow numbers listed but, only for the small valve set. Under the info for the big valves, it doesn't say they flow more, I don't know why they wouldn't list the flow increase, seems odd. Maybe they've changed it now? I haven't looked in a long time.

[DWKgalaxie]

For these shocker 200 FE heads, the flow chart they have now shows for .600 lift, 331cfm intake and 254 cfm exh flow. But you are correct, it doesn't really, specifically say if these numbers are for the 2.09/1.66 or 2.20/1.73 valves. For advertising purposes you would think they would show numbers for the larger valves as they would be bigger numbers. I guess where I am now in this, I need to go ahead and order the 445 kit and put one cylinder together to find out where the top ring travels to, so that I can notch the bore, after I've had this block cleaned bored, blah blah blah, and it is ready for this hand fitting. Ahh if it was easy anyone and everyone would be running an FE. Oh, and on the subject you mentioned if the the valves have the wider MR spacing, I don't know how to check that other than just measure from the top of the intake stem to the top of the exh stem, center to center. I don't know that spec, and I can guarantee Jason at ProMaxx will not either. If you or anyone knows that spec, I'd love to know, so that I can check.

Thanks again for your reply and all the info. You really have been a big help.
Dave

[Nightmist66]

I once checked a set of iron CJ heads we have laying around here that either have 1.73" or 1.75" exh. valves on my old 4.080" 390 block. I did not have a head gasket installed, I just slapped it on to get a quick looksee. These heads were not milled to death, either. IIRC, it only made it a short bit past .400" before the exhaust jammed into the cylinder. A head gasket installed will help you more due to the valve angle.

So, I am currently at a 4.085" bore and using custom Edelbrock heads with 2.200"/1.650" valves. I did some unshrouding work for the large valves. These heads have been milled to death on purpose so I could go from a 70cc chamber to a 53cc chamber. I degreed the last cam I ran which was exactly .700" lift on intake and exhaust. And at around .720" lift is when both the intake and exhaust valves would hit the cylinder. Had I not decked the heads so much, I think quite a bit more lift would be easy. Another option you have is angle mill the heads about 1-1.5°. This will bump compression and increase the valve to bore clearance. However, I personally wouldn't run an exhaust valve bigger than a 1.650" in a 390 bore due to shrouding and I don't think there will be any gain even with angle milling. If you have the heads though, and everything clears, I guess run it. 

[DWKgalaxie]

That's some good info to work with. Thanks Nightmist66. The head gaskets they recommend are FelPro 1020 that are .041 thick. Ok, blast away. Everyone always has different opinions on head and intake gaskets based on hard learned experience. I've owned 5 FE motors but this is the first I've been into. I've been into a bunch of small and big block Chevys and always ran FelPro with good results. But that's apples and oranges, I know. From what you said head gasket thickness will help with the interference issue compared to no gasket, which makes sense, so .041 thickness may help some. These are 72cc heads and the pistons I will be running are dish top that are supposed to end up with 10.3 compression. I don't need any more than that, which is about stock, on this street and sometimes bracket car.
Thanks again
Dave

[frnkeore]

I can't find the valve stem size for these heads but, here is how you find the valve c/c distance:

With just the valves installed (no springs), with calipers, measure the distance from outside to outside of the pair of valves, then subtract the valve stem diameter, that give you the c/c distance. Intakes are usually .001 larger than Ex.

i.e. If your outside to outside measurement is 2.352 and your stems are .372, 2.352 - .372 = 1.98 c/c that will be a LR valve spacing.

The MR c/c spacing, is 2.100, that would be 2.472 - .372 = 2.100

As I said before, the offset of the valves, in the chamber is .170 for the LR. It's a little less for the MR @ .150. Both towards the Ex side.

I looked all over the ProMaxx site, and couldn't find a flow chart for either valve size. There was a icon for it but, clicking it didn't do anything.

[My427stang]

If you have the block and heads, why not bolt them on and look through the bottom?  You can see the intake, the exhaust will likely hit at some point, but you can measure the drop.  FYI these are C8AE-H with 2.15 intake and 1.67 exhaust.  Exhaust did hit but not until very deep. Not the same as your heads without knowing valve spacing, but didn't take too long and you can check all 8

[DWKgalaxie]

Those pics are great! Thanks Ross My427stang. I'm hopeful mine will clear by as much.

Dave

[Rory428]

To be honest, those seem to be pretty big valves to try to squeeze inside a .030" over 390 bore. And even if, they somehow do not contact the cylinder wall, I have to wonder if the shrouding of the larger valves will actually be of any real benefit. By comparison, the valve sizes on my TFS heads are 2.19" and 1.625", which is actually smaller than stock CJ exhaust valves, but with larger intakes. I have to believe that TFS thought a better exhaust port, with a smaller valve, was a better choice for smaller bore FEs. Since the Pro Maxx are basically an off shore bootleg copy of the older Edelbrocks, I have to wonder if they even tried and compared the larger valves to see if there was any real advantage, in a smaller bore, or just did it to say they have bigger valves, even if they are of no actual benefit.

[My427stang]

To be honest, those seem to be pretty big valves to try to squeeze inside a .030" over 390 bore. And even if, they somehow do not contact the cylinder wall, I have to wonder if the shrouding of the larger valves will actually be of any real benefit. By comparison, the valve sizes on my TFS heads are 2.19" and 1.625", which is actually smaller than stock CJ exhaust valves, but with larger intakes. I have to believe that TFS thought a better exhaust port, with a smaller valve, was a better choice for smaller bore FEs. Since the Pro Maxx are basically an off shore bootleg copy of the older Edelbrocks, I have to wonder if they even tried and compared the larger valves to see if there was any real advantage, in a smaller bore, or just did it to say they have bigger valves, even if they are of no actual benefit.

So .005 radially isn't much different from a TFS, but as said before, depends on valve spacing with the Pro Maxx heads.  Shrouding is interesting, to be honest, the only time I have seen shrouding as a primary issue, meaning more important than port and valve job, is in the chamber with the small chamber 352 heads.  With that setup, Tommy T gained quite a bit of flow by opening the chamber.  Now, not saying cyl wall shrouding isn't a thing, of course it is, but the ports on some heads are so bad that port performance likely makes more of a difference at normal valve lifts.

I do agree though, at some point there are diminishing returns.  Assuming these are the heads he is planning to use, I'd bolt a head on and measure clearance to the bore, on each valve, at max valve lift.  If they don't hit, run them, a 330+ CFM head will still do well through most of the valve travel.  Although again, no idea on that Promaxx, but on those iron, the exhaust will walk toward the wall until it hits, so it may not be as bad at lower lifts

Last comment, I don't think TFS went small because the exhaust was good.  I have ZERO proof, but I think they wanted an awesome intake port, and then ran out of room.  The TFS is one of the best out there, but it is pretty lopsided on the exhaust port

I would however pour the Pro Maxx intake port, if it's very big, I would pick an intake lobe and lobe timing to pull harder on a port if street/strip, especially with a 445

[e philpott]

I'm pretty sure the Promaxx is a Low Riser valve spacing even though it doesn't say, it's just a full CNC porting from Keith Craft on the existing head

https://promaxxperformance.com/product/shocker-200-ford-fe/