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Bub Samba Member
Joined: June 10, 2004 Posts: 1156 Location: Central Washington
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Posted: Wed Feb 07, 2024 10:02 am Post subject: 36hp deck height / compression / cam setup.. |
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Ok guys-
hopefully in the next couple days I have all the scraps here to put this back together. I built this engine a couple years ago with 40hp/ 83mm big bore kit and it has run fantastic- almost 8k miles. BUT, it was just an experiment that I knew I didn't intend on leaving as-is forever. So I re-thunk the final build I wanted to have. I'm going down to 80mm p/c's for better cooling and less blow-by.
But give me some opinions on these specs :
64x 80 stock internals.
Original heads just rebuilt w/ 32.5mm intakes
WW Cam
WW 32 PBIC's
*might take 3-4lbs off the flywheel.
So, the 80mm p/c's end up with slightly less deck than the 83's.
I'm getting .025" deck height , ~ 46-47cc volume in the heads.
That deck is pretty tight- but? Can I get away with it on a 36hp @ 7.5:1 with the cam and intake specs ? Compression is fairly conservative, I had it @ 8.4:1 with the 83mm pistons/ stock valves and never had any issues.
And even if I can get away with it- how much is a flycut on the heads going to get me if I shim the deck to .040 and bump the CR up?
With what I have- what would you do?
oh yeah, and I had this wacky idea I may try on a spare exhaust.
_________________
hitest wrote: |
Had a girlfriend once who shall we say, nearly arrived at the mere sight of a semaphore in action- easy to please she was... |
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esde Samba Member
Joined: October 20, 2007 Posts: 5993 Location: central rust belt
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Posted: Thu Feb 08, 2024 7:37 pm Post subject: Re: 36hp deck height / compression / cam setup.. |
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I have spoken to many 36hp enthusiasts, and they have all generally said the same thing, which is to not be afraid of raising the compression. On my zwitter engine, the heads are cut a little more than 2mm which gave just over 8:1 (stock stroke and bore). Alstrup understands the cam-compression relationship very well, as he has built so many of these engines. I'd wait for him to comment
Shaving the heads on a stock engine does create a few obstacles: intake and exhaust will need to be narrowed, and pushrods shortened. It's just time if you can do the work yourself.
*edit* I see the dual carbs, so nix the intake narrowing. _________________ modok wrote:
Bent cranks are silent but gather no moss. I mean, ah, something like that. |
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Bub Samba Member
Joined: June 10, 2004 Posts: 1156 Location: Central Washington
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Posted: Fri Feb 09, 2024 12:24 pm Post subject: Re: 36hp deck height / compression / cam setup.. |
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I probably wouldn't even be bringing it up- except there isn't a single machine shop within 130 miles that can flycut a head.
So I am kind of screwed.
I do have a place I can get another set of heads already done- to the specs I want, but it's another $700.
As it sits with the .025" deck and 46cc chambers I'll be running 7.5:1. So, ...what am I missing out on with this fairly conservative setup?
3-4hp? maybe FIVE! I"ll admit it's a large difference in this case.
Just had a big huge flood mess in my basement yesterday so doesn't look like the $700 for better heads is in the budget. So Maybe I'll just run it like this for the summer and revisit it next winter if I feel like it's worth it.
Good news is I found a running 36hp locally for $250 and the guy is dropping it off in a few minutes. Why! Yay! Because . _________________
hitest wrote: |
Had a girlfriend once who shall we say, nearly arrived at the mere sight of a semaphore in action- easy to please she was... |
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Braukuche Samba Member
Joined: September 03, 2004 Posts: 11027
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Posted: Sat Feb 10, 2024 8:38 am Post subject: Re: 36hp deck height / compression / cam setup.. |
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Bub wrote: |
I probably wouldn't even be bringing it up- except there isn't a single machine shop within 130 miles that can flycut a head.
So I am kind of screwed.
I do have a place I can get another set of heads already done- to the specs I want, but it's another $700.
As it sits with the .025" deck and 46cc chambers I'll be running 7.5:1. So, ...what am I missing out on with this fairly conservative setup?
3-4hp? maybe FIVE! I"ll admit it's a large difference in this case.
Just had a big huge flood mess in my basement yesterday so doesn't look like the $700 for better heads is in the budget. So Maybe I'll just run it like this for the summer and revisit it next winter if I feel like it's worth it.
Good news is I found a running 36hp locally for $250 and the guy is dropping it off in a few minutes. Why! Yay! Because . |
My old machinist called it quits recently. It’s getting harder and harder to find anyone to do anything outside of boring 1600 based stuff and even that, finding competent shops is near impossible. _________________ Go Reds! Smash state!
Retirement is here!
1956 Ghia
1959 SO-23 Westfalia
1960 double cab
1960 Baja Bug
1963 stretched double cab
1962 Golde sunroof Ghia
1963 356 B coupe
1963 Notchback
1967 21 window less rusty now |
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esde Samba Member
Joined: October 20, 2007 Posts: 5993 Location: central rust belt
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Posted: Sat Feb 10, 2024 9:29 am Post subject: Re: 36hp deck height / compression / cam setup.. |
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Braukuche wrote: |
Bub wrote: |
I probably wouldn't even be bringing it up- except there isn't a single machine shop within 130 miles that can flycut a head.
So I am kind of screwed.
I do have a place I can get another set of heads already done- to the specs I want, but it's another $700.
As it sits with the .025" deck and 46cc chambers I'll be running 7.5:1. So, ...what am I missing out on with this fairly conservative setup?
3-4hp? maybe FIVE! I"ll admit it's a large difference in this case.
Just had a big huge flood mess in my basement yesterday so doesn't look like the $700 for better heads is in the budget. So Maybe I'll just run it like this for the summer and revisit it next winter if I feel like it's worth it.
Good news is I found a running 36hp locally for $250 and the guy is dropping it off in a few minutes. Why! Yay! Because . |
My old machinist called it quits recently. It’s getting harder and harder to find anyone to do anything outside of boring 1600 based stuff and even that, finding competent shops is near impossible. |
I didn't want to learn to machine cases, but I tired of sending them on a thousand mile round trip, so I bought a Bridgeport and 36hp line bore set up. Now I'm in the same situation with a bunch of 36hp heads.... and about to purchase some seat cutters and valve guide hones. 25 years from now I'll be the "old guy that doesn't do them any more".
It sucks, but for me it's the only economical way to keep working on these things. _________________ modok wrote:
Bent cranks are silent but gather no moss. I mean, ah, something like that. |
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