exhaust valve to cylinder head/block clearance issues sr-71

405 Views 6 Replies 3 Participants Last post by the_partman, 20 d ago

the_partman

Discussion Starter · 22 d ago

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ust wondering what the minimum exhaust valve to bore/ block clearance can be and safely not have interferance issues.?
reason being i have a sr-71 on a 4.39 bore and had exhaust valve collision . so long story short i "eyebrowed " the tops of the bores i got ok clearance but i can only come down the bore .200 from deck as my top ring runs too .270 and i do not want to get too close to that area. i have .026 clearance now . my only other option i think is grind the valves too a smaller diameter . .
what you guys think thanks

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bob460

· #2 · 21 d ago

What's interesting is Kaase's 521ci dyno mule made over 900hp and went to 7500rpm......no issue with smaller ex valve with 4.39 bore.

Maybe call Kaase and see what they think.

Cheers, Bob

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the_partman

Discussion Starter · #3 · 21 d ago

bob460 said:
What's interesting is Kaase's 521ci dyno mule made over 900hp and went to 7500rpm......no issue with smaller ex valve with 4.39 bore.

Maybe call Kaase and see what they think.

Cheers, Bob

ya i talked with roger about it . jon kasse was not there himself and would like to talk to him about it .
roger had no for sure answer for me . ge did say he would like .030 on the side of valve to block clearance (my question is that enough is all . he said it is ok if valve is ghosting on the block .which seems crazy but what do i know

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Stevem

· #4 · 21 d ago (Edited)

I looks like you have even less, or about as much exh to intake valve clearance.
Is that the case?

The exh valve is canted and bore clearance should increase as the valve opens right?

How much valve lift is .200” down the bore?
If you needed to sleep better at night by a .005” reduction of that valves OD you would not effect the overall flow, so don’t let that stop you.

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the_partman

Discussion Starter · #5 · 21 d ago

Stevem said:
I looks like you have even less, or about as much exh to intake valve clearance.
Is that the case?

The exh valve is canted and bore clearance should increase as the valve opens right?

How much valve lift is .200” down the bore?
If you needed to sleep better at night by a .005” reduction of that valves OD you would not effect the overall flow, so don’t let that stop you.

well maybe thats what i will do is just grind the valves 5 thou .
ya i eyebrowed them down another .025 and i only gained like 1 thou i have one bore i only have .024 clearance i checked tripple checked with wire guages most bores i have .027 and .028
well .200 though down bore i have aprox .550ish lift hard to measure exactly but pretty close the valves goes into the ring travel "zone about 100 to .150 again i did not measure exactly but gives a rough idea .i do no that before eyebrowing the clearance was like way to freaking tight .

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Stevem

· #6 · 21 d ago

Well even if you had to live with .015” of hot clearance between the valve and the bore I could very well live with that, but as always its the PTVC that you need to be very concerned with.

I have at times been forced into running as little as .060” clearance but you had better not have any valve float taking place and a rev limiter on the motor if your valve springs are iffy!

If you just can’t live with that tight a clearance then you could go for offset cylinder head dowls I suppose as long as your intake valves are not doing the same thing.

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the_partman

Discussion Starter · #7 · 20 d ago

Stevem said:
Well even if you had to live with .015” of hot clearance between the valve and the bore I could very well live with that, but as always its the PTVC that you need to be very concerned with.

I have at times been forced into running as little as .060” clearance but you had better not have any valve float taking place and a rev limiter on the motor if your valve springs are iffy!

If you just can’t live with that tight a clearance then you could go for offset cylinder head dowls I suppose as long as your intake valves are not doing the same thing.

intakes are fine they are way off the side of bore. i have .130 ptvc so thats good and that is with advanceig cam 4 degree .
it is the bore to valves clearance i hate to grind new valves but this engine is apart because of this happening in the first place ..

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