Valve to cylinder wall clearance,Shrouding Question?
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- Rommel Racing
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Valve to cylinder wall clearance,Shrouding Question?
Now I did do a search on this and did find lots of info on here,but I still have a few questions.
I have a friend,who bought a used 396bbc(.060 over)that had a set of GM 990 cast iron rectangle port heads on it. I told him that those heads were way to big for the little rat,and suggested he find some Brodix 270cc BB-O oval port heads to use instead.
So he happened to find a brand new set of the Brodix 270cc oval ports that a guy had for sale and bought them.
Now I have them here and I'm mocking up his engine and find that there is only .020-.025" clearance between the intake valve and cylinder wall @.600 lift.
So I'm thinking,dam that's close the intakes are 2.25" and the bore is 4.155",and from searching on here I realize that the valve is over the 53% rule.
That being said I mocked up the iron 990 heads (which had 2.30" intakes) and found it had been running with only .005" clearance
Now after finding all this out,I searched for more info and found this build on Superchevy's website,where they built a 408bbc with the Brodix heads and 2.25" valves .
http://www.superchevy.com/technical/eng ... index.html
and this follow up
http://www.superchevy.com/tech/0106sc_h ... index.html
I suggested to my friend that we just build a 496bbc,but he says he has already spent to much money on this little rat and is afraid his wife will divorce him if he keeps spending more!
Anyhow what do you guy's suggest.
Sorry for the novel,
Steve
I have a friend,who bought a used 396bbc(.060 over)that had a set of GM 990 cast iron rectangle port heads on it. I told him that those heads were way to big for the little rat,and suggested he find some Brodix 270cc BB-O oval port heads to use instead.
So he happened to find a brand new set of the Brodix 270cc oval ports that a guy had for sale and bought them.
Now I have them here and I'm mocking up his engine and find that there is only .020-.025" clearance between the intake valve and cylinder wall @.600 lift.
So I'm thinking,dam that's close the intakes are 2.25" and the bore is 4.155",and from searching on here I realize that the valve is over the 53% rule.
That being said I mocked up the iron 990 heads (which had 2.30" intakes) and found it had been running with only .005" clearance
Now after finding all this out,I searched for more info and found this build on Superchevy's website,where they built a 408bbc with the Brodix heads and 2.25" valves .
http://www.superchevy.com/technical/eng ... index.html
and this follow up
http://www.superchevy.com/tech/0106sc_h ... index.html
I suggested to my friend that we just build a 496bbc,but he says he has already spent to much money on this little rat and is afraid his wife will divorce him if he keeps spending more!
Anyhow what do you guy's suggest.
Sorry for the novel,
Steve
-3400lb stock suspension 67 Camaro
-10.5-1 compression pump gas 540bbc.
-th-400, 4200 stall 9" convertor
-12 bolt 4.10's
-29.5x10.5 Hoosier radial slicks
- Best on motor only 9.59/142.24mph
-10.5-1 compression pump gas 540bbc.
-th-400, 4200 stall 9" convertor
-12 bolt 4.10's
-29.5x10.5 Hoosier radial slicks
- Best on motor only 9.59/142.24mph
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- Rommel Racing
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Oh ya, sorry about that.Unkl Ian wrote:What application does he want the motor for ?
This is just going to be a street/strip combo,going into a 69 El Camino.
The pistons are old TRW closed chamber slugs with 43cc domes,so it should have around 10.25-1 compression with the 119cc Brodix heads.
We were also planning on running a solid street roller as well.
Thanks again,
Steve
-3400lb stock suspension 67 Camaro
-10.5-1 compression pump gas 540bbc.
-th-400, 4200 stall 9" convertor
-12 bolt 4.10's
-29.5x10.5 Hoosier radial slicks
- Best on motor only 9.59/142.24mph
-10.5-1 compression pump gas 540bbc.
-th-400, 4200 stall 9" convertor
-12 bolt 4.10's
-29.5x10.5 Hoosier radial slicks
- Best on motor only 9.59/142.24mph
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Here is a great thing to do to help your situation out.
As already posted, grind an "eye brow" in the top of the block.
With the cylinder head on as on your picture, take a sharp wire/scribe bent in a "J" shape that will allow you to reach up from the bottom of the bore and scribe a line in the top of the deck that is blocking/shrouding your intake valve. Once the line is scribed on all of your cylinders, remove the head and grind this relief in the block. Take care to not grind below the top ring.
This procedure, will increase air flow into the cylinder.
Best of success.
As already posted, grind an "eye brow" in the top of the block.
With the cylinder head on as on your picture, take a sharp wire/scribe bent in a "J" shape that will allow you to reach up from the bottom of the bore and scribe a line in the top of the deck that is blocking/shrouding your intake valve. Once the line is scribed on all of your cylinders, remove the head and grind this relief in the block. Take care to not grind below the top ring.
This procedure, will increase air flow into the cylinder.
Best of success.
- Rommel Racing
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- Location: British Columbia,Canada
Valve to wall clearance?
So,other than reworking the top of the cylinder notch,do any of you have any problems with the .025" clearance we have between the valve and cylinder wall?
When,I questioned Brodix about this they recommended a min. of .070".
I can't see any witness marks on the cylinder walls from when it was running the 2.30" valves and having only .005" clearance,so is it safe to say it should be fine?
Anyone know what the factory valve size was on a L78 396bbc?
When,I questioned Brodix about this they recommended a min. of .070".
I can't see any witness marks on the cylinder walls from when it was running the 2.30" valves and having only .005" clearance,so is it safe to say it should be fine?
Anyone know what the factory valve size was on a L78 396bbc?
-3400lb stock suspension 67 Camaro
-10.5-1 compression pump gas 540bbc.
-th-400, 4200 stall 9" convertor
-12 bolt 4.10's
-29.5x10.5 Hoosier radial slicks
- Best on motor only 9.59/142.24mph
-10.5-1 compression pump gas 540bbc.
-th-400, 4200 stall 9" convertor
-12 bolt 4.10's
-29.5x10.5 Hoosier radial slicks
- Best on motor only 9.59/142.24mph
- Wolfplace
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Re: Valve to wall clearance?
=Rommel Racing wrote:So,other than reworking the top of the cylinder notch,do any of you have any problems with the .025" clearance we have between the valve and cylinder wall?
When,I questioned Brodix about this they recommended a min. of .070".
I can't see any witness marks on the cylinder walls from when it was running the 2.30" valves and having only .005" clearance,so is it safe to say it should be fine?
Anyone know what the factory valve size was on a L78 396bbc?
Been a while but I am reasonably sure it was 2.19
I would be a little concerned at 25 thou mainly because the damn bores are not always where you think they are unless it was blueprint bored
I find them off a substancial amount in a lot of cases so your 25 thou may not be that in all cylinders
If you know you have 25 thou everywhere my opinion it should be fine but a bit more would not upset me,,
I think you were very lucky with the 5 thou clearance you had, that's scary
Here is a pic of a 402 block I am doing with the relief's, pretty simple deal
Mike
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Lewis Racing Engines
4axis CNC block machining
A few of the cars I have driven & owned
A tour of my shop
The Dyno
And a few pics of the gang
"Life is tough. Life is even tougher if you're stupid"
John Wayne
- nhrastocker
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How close are the exhaust valves to the bore? Have you considered using offset dowels? The exhaust valves are not so sensitive to being near the cylinder wall. The valves are to big for that bore and grinding a relief in the bore is not as good as using the right size valves. But I guess that you are stuck with the stuff you have so I would offset the heads and grind reliefs. If the seats are cut smaller than the valves you could always cut the valves down a little. Erland.
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Thanks for the tipBrian Rock wrote:If you put the reliefs in the top of the bore, be aware of where your ring gaps are when you install pistons. Especially the oil ring scraper rails!
Yeah, I learned that one the hard way.
The 318 Mopar motor likes reliefs too, if installing 2.02 intake valves...I was able to get away with no reliefs but I bet its pretty close right now-and the flow is being hurt. Might not have thought about the ring gaps as the pistons get pop in, Thanks again.
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