Author Topic: Valve clearance  (Read 2502 times)

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Gregwill16

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Valve clearance
« on: December 03, 2020, 01:47:55 PM »
What is the safe maximum intake/exhaust valves that will work with a 4.155" bore?

My427stang

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Re: Valve clearance
« Reply #1 on: December 03, 2020, 01:51:06 PM »
What is the safe maximum intake/exhaust valves that will work with a 4.155" bore?

Haven't chased the max, but on a CJ valve spacing have gone 1.70 and .625 or so lift
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Ross

- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, Erson SFT cam, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 461 cid FE, headers, Victor Pro-flo EFI, Comp Custom HFT cam, 3.50 9 inch

blykins

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Re: Valve clearance
« Reply #2 on: December 03, 2020, 02:25:18 PM »
What is the safe maximum intake/exhaust valves that will work with a 4.155" bore?

2.200" intake valve is safe.  Exhaust valve will depend on cam lift.
Brent Lykins
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Gregwill16

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Re: Valve clearance
« Reply #3 on: December 03, 2020, 05:02:53 PM »
Thanks guys I was thinking I may be in a pickle. Brent you will be spec'ing the cam anyhow so I'll spill the details and see.
This is a fresh, well done C scratch 462 shortblock that was being built to run on e85. So it has SRP 261501 pistons, which means I either need to run e85 or go with MR heads, to get compression down. The heads are fresh but it sounds like the 1.73 exhaust may be an issue?

blykins

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Re: Valve clearance
« Reply #4 on: December 03, 2020, 06:03:45 PM »
I don't think I'd go the E85 route.  If you want it to be a driver, E85 is hard on stuff. 

Maybe mix some pump/race gas 50/50? 
Brent Lykins
Lykins Motorsports
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www.lykinsmotorsports.com
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Gregwill16

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Re: Valve clearance
« Reply #5 on: December 03, 2020, 07:07:27 PM »
I agree Brent. I looked into the e85 route and doesn't seem bad, but I could replace the pistons and go with different heads much easier and spend less $.
So is the 1.73 exhaust a no go on 4.155" bore? If not, I guess I could drop down to a 1.70 exhaust valve and be safe.
Furthermore, the modern performance engine seems to be dish pistons and small chamber heads. So would there be much performance difference between this setup versus changing to dish pistons and CJ heads?

blykins

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Re: Valve clearance
« Reply #6 on: December 03, 2020, 07:21:19 PM »
Probably so.  A flat top or a dish is going to be more efficient than a dome.  I generally try to stay away from domes if I can help it, as they add weight and also get in the way of flame travel.   I would much prefer a small chamber and a dish, but you work with what you have. 

If you changed pistons, you're looking at rechecking the crank balance at least, but it would open you up to using any head under the Sun. 

I have never ran a 1.73 exhaust valve on a 428 bore, so I can't say with certainly.  There's a point where the exhaust valve gets real close to the cylinder wall and it may not take much lift to do that with a 1.73.
Brent Lykins
Lykins Motorsports
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WConley

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Re: Valve clearance
« Reply #7 on: December 03, 2020, 08:35:53 PM »
I've run a 1.72 exhaust (C3AE-J Low Riser head) on a +.030" 390 short block in the past.  I had to notch the bores to clear a roughly CJ-spec hydraulic cam with about .500" lift.  Sure, I bet there was plenty of valve shrouding but they were a nice set of heads and the engine ran very well!

Intakes were 2.19 and they had no clearance issues.
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My427stang

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Re: Valve clearance
« Reply #8 on: December 04, 2020, 07:40:59 AM »
 No real benefit of a huge valve in that bore, but I misread the question., I thought you asked only on exhaust.  I ran 2.15/1/70 in the last one, 2.20/1.70 on the one before that, both 4.155 and plenty of room. 

Here is a picture of when a 1.67 exhaust contacted the wall of a standard bore 390, as you can see , physically impossible to happen in an assembled motor.  Intake had a ton of room with a 2.15 valve.  That's a different head and valve size, but the exhaust valve is .06 smaller but the bore is .105 smaller

If I were you, I'd set a head on and look, and even better clay it up for radial clearance after.  Might not have to spend any money





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Ross

- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, Erson SFT cam, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 461 cid FE, headers, Victor Pro-flo EFI, Comp Custom HFT cam, 3.50 9 inch

Gregwill16

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Re: Valve clearance
« Reply #9 on: December 04, 2020, 08:19:37 AM »
Thanks for the information and pictures guys. Ross the math definitely says it should easily work. Clay is a good idea, also hoping my cheap phone boroscope will fit through the spark plug hole to have a peak at projected max lift.

My427stang

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Re: Valve clearance
« Reply #10 on: December 04, 2020, 08:49:59 AM »
I think likely too, like I said we went 1.70 and the cam was actually over .630 before deflection,  but a couple of thoughts

Depending on the head, you start losing real estate between valves, and of course the ability to shed/absorb heat. Less of a concern on a naturally aspirated motor than an un-natural one LOL, but an exhaust valve cools itself when closed, so losing  material between the valves is never optimal.

Also, the clay isn't really as much for the wall, best to do that with the block bare.  The clay would be best to check the pistons, radial clearance can vanish quickly and often is not intuitive where/when it gets tight.

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Ross

- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, Erson SFT cam, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 461 cid FE, headers, Victor Pro-flo EFI, Comp Custom HFT cam, 3.50 9 inch

cammerfe

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Re: Valve clearance
« Reply #11 on: December 04, 2020, 06:24:29 PM »
I don't think I'd go the E85 route.  If you want it to be a driver, E85 is hard on stuff. 

Maybe mix some pump/race gas 50/50?

Brent, it's completely outside the scope of this thread, but I'd be very interested in the 'why' of your statement that E85 is 'hard on stuff'. Perhaps, in politeness, it'd be better to open another thread?

KS

blykins

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Re: Valve clearance
« Reply #12 on: December 04, 2020, 06:53:25 PM »
I don't think I'd go the E85 route.  If you want it to be a driver, E85 is hard on stuff. 

Maybe mix some pump/race gas 50/50?

Brent, it's completely outside the scope of this thread, but I'd be very interested in the 'why' of your statement that E85 is 'hard on stuff'. Perhaps, in politeness, it'd be better to open another thread?

KS

Ken, the main issue is that it's hygroscopic and if it gains moisture, it will then possess acidic properties that break down aluminum, rubber, etc., etc.

If you use E85, it's best to use it with fuel pumps that are hard anodized and are compatible with alcohol. 

If carbs sit for a period of time with the bowls full, you can get oxidation inside.   If you use it, it's best to drain the bowls and probably just go ahead and drain the tank/cell after use. 

Brent Lykins
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Custom Roller & Flat Tappet Camshafts
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Barry_R

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Re: Valve clearance
« Reply #13 on: December 04, 2020, 07:55:46 PM »
I have not tried maxing out exhaust valve sizing on a 4.1xx bore with an Ed head
I can tell you that a 1.720 will scratch up the cylinder wall on a 4.070 even though it looks like it clears.
Exhaust valves apparently move a lot on the way down.
You have a bit over .040 extra radius, so you'd get the same results at 1.800 - a 1.750 should clear safely

Gregwill16

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Re: Valve clearance
« Reply #14 on: December 04, 2020, 08:19:43 PM »
Thanks for the input Barry. Trying to use what I have without putting anything in machine shop jail. The only thing I'm dreading now is MR heads forcing the use of headers in my Mustang.