| Author |
Message |
JPB6061
Samba Member
Joined: August 23, 2024
Posts: 40
Location: MI
|
 Posted: Mon Dec 30, 2024 4:57 pm Post subject: Deck Height, Squish and Performance Effect |
 |
|
Got a set of nice dual port heads but with only 40cc chambers.
92 x 76 "A" forged Mahle pistons.
If I don't buy new heads with say 55cc chambers, how bad would the 2021 run with the 40cc chamber and a .137" deck height which would give me 9:1 CR? I've thought about dished pistons as a solution, but haven't found any type 1 specific 92's. I could mill dishes in mine, but am a bit skeptical about final piston deck thickness.
Empi Web Cam 86B, Dual 44's.
We've built v-8's with .100" deck and no apparent issues, N/A tunnel ram with nitrous and twin turbo. I've read a lot on here about squish, preignition, detonation, etc. and other than the oft-quoted Gene Berg trope have not come across anyone posting current real-world examples.
As per usual, costs are spiraling out of control and I'm curious if anyone has some input here! |
|
| Back to top |
|
 |
b-man
Samba Member
Joined: May 20, 2008
Posts: 653
Location: So Cal
|
| Posted: Mon Dec 30, 2024 5:41 pm Post subject: Re: DECK HEIGHT, SQUISH AND PERFORMANCE EFFECT |
|
|
Build it and report back with your real world results.
Or buy new heads with the proper chamber size and set the deck to .040”.
Had the same quandary myself, my build changed from a 9:1 1835 to a 9.5:1 2276. I sold my 50cc heads and bought 60cc heads.
_________________
1956 Dove Blue Panel
1966 Velvet Green Single Cab
1957 L41 Black Oval Window Beetle
Last edited by b-man on Mon Dec 30, 2024 5:48 pm; edited 1 time in total |
|
| Back to top |
|
|
Glenn 
Mr. 010
Joined: December 25, 2001
Posts: 79687
Location: Sneaking up behind you
|
| Posted: Mon Dec 30, 2024 5:44 pm Post subject: Re: DECK HEIGHT, SQUISH AND PERFORMANCE EFFECT |
|
|
I'm rebuilding a 2054 that has 42cc heads. Deck will be .109" so he gets 8.7cr.
He doesn't want to spring for new heads since he didn't expect to spin a rod bearing with only a few hundred miles after he bought the engine from someone else.
_________________
Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
Member #1009
#BlueSquare
עַם יִשְׂרָאֵל חַי |
|
| Back to top |
|
|
Alstrup
Samba Member
Joined: July 12, 2007
Posts: 7862
Location: Videbaek Denmark
|
| Posted: Mon Dec 30, 2024 5:48 pm Post subject: Re: DECK HEIGHT, SQUISH AND PERFORMANCE EFFECT |
|
|
Not good, but doable. The engine will respond basicly like a hemi, which means that it will need a lot of timing to make a decent burn. You will alsa have to have some decent spark capacity.
Dont expect any major torque- or hp out of it.
_________________
https://www.thesamba.com/vw/forum/viewtopic.php?t=435993 |
|
| Back to top |
|
|
Brian_e
Samba Member
Joined: July 28, 2009
Posts: 4057
Location: Rapid City, South Dakota
|
| Posted: Mon Dec 30, 2024 6:12 pm Post subject: Re: DECK HEIGHT, SQUISH AND PERFORMANCE EFFECT |
|
|
Here is a long post about it from a while back.
Read jimmyhoffa's post half way down.
https://www.thesamba.com/vw/forum/viewtopic.php?t=761948&highlight=
I have had very similar experiences going from .110 deck down to a .040 and dished pistons on a 2276cc. I can no longer recommend dishing pistons though. Mine ran cooler, idled better, WAY better throttle response, and needed a smaller main jet with the tight deck.
If you have NO money left, just build it. But if you can swing the heads, there are lots of options out there with good chambers that are 60cc.
Dave will be along shortly to call us all rocket scientists, and accuse us of reading chevy books. Tight deck isn't just a chevy thing. It applies to any internal combustion engine. It has been proven to work better since the '50's.
Myself and others have done the A/B comparison, and it does make a noticeable difference in multiple areas.
Brian
_________________
So more or less the lazier and stupider you want to be, the nicer quality parts you need to buy.
-Modok
Narrowed beams, Drop adjustable spring plates, Bus disk brake and IRS kits.
www.type-emotorsports.com
Type E Engine Parts and Supplies
https://type-emotorsports.com/collections/engine-parts |
|
| Back to top |
|
|
txoval
Samba Member
Joined: January 23, 2004
Posts: 3847
Location: The Woodlands, TX
|
| Posted: Mon Dec 30, 2024 6:20 pm Post subject: Re: DECK HEIGHT, SQUISH AND PERFORMANCE EFFECT |
|
|
Can you convince him to change the cam? Way cheaper than heads
Run .06 at 11:1 and an 86C
I guarantee you will sell the 86b quickly |
|
| Back to top |
|
|
modok
Samba Member
Joined: October 30, 2009
Posts: 27700
Location: Colorado Springs
|
| Posted: Mon Dec 30, 2024 8:16 pm Post subject: Re: DECK HEIGHT, SQUISH AND PERFORMANCE EFFECT |
|
|
| JPB6061 wrote: |
| how bad would the 2021 run with the 40cc chamber and a .137" deck height which would give me 9:1 CR? |
This one is easy, the answer is very simple
Run it just like that, or get different heads.
Not possible to dish the pistons enough or open the chambers enough to get tight deck.
How bad would it be? depends what you compare it to, but, still pretty good. I mean, what is the goal anyway?
Far as anybody with "real world experience" just use the search feature.
Last edited by modok on Mon Dec 30, 2024 10:14 pm; edited 2 times in total |
|
| Back to top |
|
|
sled
Samba Member
Joined: February 16, 2005
Posts: 6256
|
| Posted: Mon Dec 30, 2024 8:45 pm Post subject: Re: DECK HEIGHT, SQUISH AND PERFORMANCE EFFECT |
|
|
“Buy once, cry once”
There are tons of benefits to proper deck height
Those heads would yield 9.6:1 on a 1600 with .040 deck….kinda sound like door stops to me 
_________________
drive your split. |
|
| Back to top |
|
|
74 Thing
Samba Member
Joined: September 02, 2004
Posts: 7642
|
| Posted: Mon Dec 30, 2024 10:17 pm Post subject: Re: DECK HEIGHT, SQUISH AND PERFORMANCE EFFECT |
|
|
| Brian_e wrote: |
Here is a long post about it from a while back.
Read jimmyhoffa's post half way down.
https://www.thesamba.com/vw/forum/viewtopic.php?t=761948&highlight=
I have had very similar experiences going from .110 deck down to a .040 and dished pistons on a 2276cc. I can no longer recommend dishing pistons though. Mine ran cooler, idled better, WAY better throttle response, and needed a smaller main jet with the tight deck.
If you have NO money left, just build it. But if you can swing the heads, there are lots of options out there with good chambers that are 60cc.
Dave will be along shortly to call us all rocket scientists, and accuse us of reading chevy books. Tight deck isn't just a chevy thing. It applies to any internal combustion engine. It has been proven to work better since the '50's.
Myself and others have done the A/B comparison, and it does make a noticeable difference in multiple areas.
Brian |
Brian, why do you no longer dish the pistions-too thin? |
|
| Back to top |
|
|
Brian_e
Samba Member
Joined: July 28, 2009
Posts: 4057
Location: Rapid City, South Dakota
|
| Posted: Tue Dec 31, 2024 11:18 am Post subject: Re: DECK HEIGHT, SQUISH AND PERFORMANCE EFFECT |
|
|
| 74 Thing wrote: |
| Brian, why do you no longer dish the pistions-too thin? |
I know if 2 engines now that broke the AA hyper pistons that were dished about .055". I know both were not the best tuned, and were pinging and lugging up a long hill when it happened.
On the other hand, I have 30k+ miles on my 2332cc in my bay with big dishes in the AA pistons, and it has been fine. Long hot, hard miles. I have probably 10-12 more with dishes out there that have been just fine, but 2 did break.
I think it is kinda like the old "that guy could break an anvil in a sandbox" kinda thing. Same goes with transaxles. Some guys can make a stock box last forever with a 2332cc, some guys can destroy a build box with a 1641cc. Lots depends on the tune, and driving habits.
With the availability of good quality heads, with correctly shaped, large volume chambers, there really shouldn't be a need to dish pistons anymore.
Brian
_________________
So more or less the lazier and stupider you want to be, the nicer quality parts you need to buy.
-Modok
Narrowed beams, Drop adjustable spring plates, Bus disk brake and IRS kits.
www.type-emotorsports.com
Type E Engine Parts and Supplies
https://type-emotorsports.com/collections/engine-parts |
|
| Back to top |
|
|
BFB
Samba Member
Joined: November 03, 2014
Posts: 2747
|
| Posted: Tue Dec 31, 2024 12:12 pm Post subject: Re: DECK HEIGHT, SQUISH AND PERFORMANCE EFFECT |
|
|
| Glenn wrote: |
I'm rebuilding a 2054 that has 42cc heads. Deck will be .109" so he gets 8.7cr.
He doesn't want to spring for new heads since he didn't expect to spin a rod bearing with only a few hundred miles after he bought the engine from someone else. |
WHAAAAA??? Oh the sacrilege! Im surprised the guys arent forming a mob to have you disbarred. Heh heh
I personally think this “040” deck gets made to much out of, is the tight deck better? Sure. But how many engines built with a good deck run around mistuned, probably a lot, and thats worse. I know ive torn down several engines and sure yall have too that had well over .1 deck and had obviously ran for a long time, im pretty sure i measured a few at about .17.
So i dont think .137 is going to be detrimental but it were me, id split the difference and run .1 with 9.9:1 cr
_________________
"how am i supposed to torque the rear wheel nut to 250 ft lbs??? " - clonebug
An interesting thing happens in forums where everyone starts parroting the same thing and "common knowledge" takes over.
Most experts aren't. |
|
| Back to top |
|
|
Alstrup
Samba Member
Joined: July 12, 2007
Posts: 7862
Location: Videbaek Denmark
|
|
| Back to top |
|
|
Rome
Samba Member
Joined: June 02, 2004
Posts: 10591
Location: Pearl River, NY
|
| Posted: Tue Dec 31, 2024 3:30 pm Post subject: Re: DECK HEIGHT, SQUISH AND PERFORMANCE EFFECT |
|
|
[quote="modok"]
| JPB6061 wrote: |
Not possible to dish the pistons enough or open the chambers enough to get tight deck.
|
People might lob tomatoes at me for this suggestion, but it might be an alternative for improvement- and certainly for discussion: How about machining the heads for semi-hemi chambers? That usually removes several cc of head material, and should allow the PO to run less deck height. Though if the heads already have only 40 cc chambers, maybe there is not enough thickness to the chamber to sustain removing more material safely from the SH. |
|
| Back to top |
|
|
Alstrup
Samba Member
Joined: July 12, 2007
Posts: 7862
Location: Videbaek Denmark
|
|
| Back to top |
|
|
94touring
Samba Member
Joined: October 24, 2020
Posts: 530
Location: Tulsa - OK
|
| Posted: Tue Dec 31, 2024 6:12 pm Post subject: Re: DECK HEIGHT, SQUISH AND PERFORMANCE EFFECT |
|
|
| BFB wrote: |
| But how many engines built with a good deck run around mistuned, probably a lot, and thats worse. |
Well, then let's say the same amount out of tune WITH a huge deck height, so double the bad. I was one of those guys actually. Bought a turn key 2110 and drove it awhile and was never impressed. Then added a wideband and saw how out of tune it was. Tuned it best I could and it was better but still underwhelming. Then decided to change things up and redid the top end. Granted I upped compression, ported heads w/ matched manifolds, 92TW, and 1.25 rockers, but I also went from a massive 0.1+ deck height to a .040. It was easier to tune and ran the same head temps as before and with over a full point more in compression. Went from underwhelming to hey this is rather whelming!
[/quote] |
|
| Back to top |
|
|
oprn
Samba Member
Joined: November 13, 2016
Posts: 14864
Location: Western Canada
|
| Posted: Tue Dec 31, 2024 6:54 pm Post subject: Re: Deck Height, Squish and Performance Effect |
|
|
What in the engine going to be used in and for what? Drag racing? Weekend warrior? Daily driver? Rock crawler?
How high would it be with a .040" deck and those heads?
Maybe you could use a high CR with the right fuel and application? 12/1 or 13/1 works for methanol or... heaven forbid... propane/natural gas.
_________________
Our cars get old, we get old but driving an old VW never gets old! |
|
| Back to top |
|
|
txoval
Samba Member
Joined: January 23, 2004
Posts: 3847
Location: The Woodlands, TX
|
| Posted: Tue Dec 31, 2024 9:31 pm Post subject: Re: Deck Height, Squish and Performance Effect |
|
|
| change the cam…but it would be nice to get more details on the heads. |
|
| Back to top |
|
|
modok
Samba Member
Joined: October 30, 2009
Posts: 27700
Location: Colorado Springs
|
| Posted: Tue Dec 31, 2024 10:23 pm Post subject: Re: DECK HEIGHT, SQUISH AND PERFORMANCE EFFECT |
|
|
| Rome wrote: |
People might lob tomatoes at me for this suggestion, but it might be an alternative for improvement- and certainly for discussion: How about machining the heads for semi-hemi chambers? That usually removes several cc of head material, and should allow the PO to run less deck height. Though if the heads already have only 40 cc chambers, maybe there is not enough thickness to the chamber to sustain removing more material safely from the SH. |
That would be fine choice IMO.
Some would say you are further ruining the heads, but maybe this is just how they will retire from racing. |
|
| Back to top |
|
|
BFB
Samba Member
Joined: November 03, 2014
Posts: 2747
|
| Posted: Tue Dec 31, 2024 11:07 pm Post subject: Re: DECK HEIGHT, SQUISH AND PERFORMANCE EFFECT |
|
|
| modok wrote: |
| Rome wrote: |
People might lob tomatoes at me for this suggestion, but it might be an alternative for improvement- and certainly for discussion: How about machining the heads for semi-hemi chambers? That usually removes several cc of head material, and should allow the PO to run less deck height. Though if the heads already have only 40 cc chambers, maybe there is not enough thickness to the chamber to sustain removing more material safely from the SH. |
That would be fine choice IMO.
Some would say you are further ruining the heads, but maybe this is just how they will retire from racing. |
I thought about mentioning hogging out the chambers earlier, not necessarily semi Hemi cutting them though, but i figured to get where OP would need to be he’d need to remove about 5cc and thatd be more than most ppl are willing to go. Not to mention all the pissing and moaning about how the engine wouldnt run.
Most ive pulled out was 11cc out of some 42cc empi heads cut for 94’s. Look like boosted LS heads.
Do whatever works , it ain’t rocket science its just a damn 4 stoke engine
_________________
"how am i supposed to torque the rear wheel nut to 250 ft lbs??? " - clonebug
An interesting thing happens in forums where everyone starts parroting the same thing and "common knowledge" takes over.
Most experts aren't. |
|
| Back to top |
|
|
Vanapplebomb
Samba Member
Joined: November 03, 2010
Posts: 5572
Location: Holland, MI
|
| Posted: Wed Jan 01, 2025 6:56 am Post subject: Re: Deck Height, Squish and Performance Effect |
|
|
I have found a tight deck to be really helpful. Somewhere in the range of 0.030 - 0.050 inches seems to be the sweet spot. I tend to go on the tighter end, 0.030 - 0.040 inches.
The engines tend to run cooler (even with slightly more compression) and tune up better. Larger than 050 seems to cause a lazy response to changes in tuning. By the time 0.080 rolls around, it’s a lazy engine that tunes up more vaguely. Overall just less responsive.
One thing I do when running close to 030 is to rock the pistons in the bore when checking. I measure clearance at the top and bottom the cylinder while applying light pressure to the back side of the piston skirt with a wood or plastic dowel. This takes up any clearing play and tips the crown out to give you a better idea of how close the piston comes to the head. On bigger bores with shorter skirts, you can see a few thou difference between that and measuring over the pin.
_________________
1800 Type 4 Berrien 295
http://www.thesamba.com/vw/forum/viewtopic.php?t=487021 |
|
| Back to top |
|
|
|
