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downside of increased compression?
http://slantsix.org/forum/viewtopic.php?f=19&t=64501
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Author:  rich006 [ Thu Feb 13, 2020 8:58 am ]
Post subject:  downside of increased compression?

Is there any downside to increasing compression ratio? I mean aside from the inability to run regular gasoline if you go too far. Surely there must be some downside or the factory would have built it with higher compression from the beginning, right? I'm guessing increased wear on bearings, cylinder walls, etc that could shorten engine life. Thoughts?

Author:  Reed [ Thu Feb 13, 2020 9:11 am ]
Post subject:  Re: downside of increased compression?

Higher NOx emissions. Faster wear on mechanical parts.

Author:  DadTruck [ Thu Feb 13, 2020 9:37 am ]
Post subject:  Re: downside of increased compression?

Quote:
or the factory would have built it with higher compression from the beginning


possibly, but the slant was intended to be an economy vehicle, manufactured as 'economic' as possible.
the fact that the actual compression found is typically much lower than what the engine seemed to be
listed as having is likely the result of loose manufacturing tolerances and even poorer manufacturing capability/expectations.

the lower compression as Reed mentioned helped engine life as well as made the engine turn over and start easier.
Certainly would have help battery and starter life.

Author:  DusterIdiot [ Thu Feb 13, 2020 6:00 pm ]
Post subject:  Re: downside of increased compression?

The above comments have merits up to a certain point. Economics do play into the grocery getting utility engine...
literally a couple hundred bux could up grade you to a V-8 car so why spend more on a small mill that won't approach
the big block at the time without spending the amount of money to make a V-8 anyway.

Right now a fair amount of modern vehicles run in the 9-10:1 SCR range, and some high end vehicles are running
up to 12:1 on the street. Part of this is the available technology and engineering knowledge that wasn't available
when our engine was designed and 20 years before that the vehicles going to war were using even lower compression
and using high drive ratios to keep the engine happy on petro that was crudely refined by todays standards.

An issue that does occur with engine longevity is the fact that when an end user goes from driving a stock 1 barrel
car to a hipo slant...a lot of aggressive driving ensues and it hammers the drive and powertrain shortening the life
of the build...on the top end, the guys wringing all the power out of the engine to get across the line faster are beyond
the original design specs and safety margin of the engine and it will wear out from repeated 1/4 mile runs. Routine
maintenance and less abuse will help things last longer...(along with good engineering when thinking out the build
and rebuilding the mill).

You shouldn't have any problems keeping a 9:1 SCR engine together for 100K+ miles in a daily driver as long as you aren't
hammering it light to light, or pulling repeated hyperpak clutch dumps... :roll:

10:1 SCR if thoughtfully put together will last a similar amount

11:1 and 12:1 can be streeted but the build will not be an MPG car and may not last as long as you will
be racing it a bit to see what it really can do.

Designing with the DCR in mind and adjusting the cam specs along with matching to the drive ratios and rpm
will help decide how much knock needs to be supressed with higher octane, less timing, or other methods...

NOx is a product of high cylinder pressure and temps...which will occur but can be lowered through use of
EGR, timing, catalytic convertors...it isn't even considered in race cars, but if the car is to be smogged, you
may need to keep it all stock to keep the regulating body happy and get your registration renewed.

Keep asking questions, hone in on what you want to achieve and build for the here and now.
(...and be thankful the Ford Nucleon didn't get built, we'd have had a completely different discussion
on engine longevity...LOL)

8)

Author:  drgonzo [ Thu Feb 13, 2020 9:33 pm ]
Post subject:  Re: downside of increased compression?

Nucleon....I had to google that!

Author:  rich006 [ Fri Feb 14, 2020 5:26 am ]
Post subject:  Re: downside of increased compression?

DusterIdiot wrote:
NOx is a product of high cylinder pressure and temps...which will occur but can be lowered through use of
EGR, timing, catalytic convertors...

Keep asking questions, hone in on what you want to achieve and build for the here and now.


Would you ever consider adding a catalytic converter to a car that didn't come with one? Let's say one of your goals is to minimize the stink in your exhaust.

Author:  GregCon [ Fri Feb 14, 2020 5:35 am ]
Post subject:  Re: downside of increased compression?

Not bad arguments, certainly as theory, but it's been well proven in the real world that high compression has no 'visible' effect on reliability. There are way too many engines from all makers running 10:1 or more that last forever.

As for compression ratios, my daily driver is right at 13.0:1 which places it well into 'high end' territory. It burns regular gas in small amounts, puts out over 1HP/cubic inch, and is bone stock. I have 100K miles on it and I have no reason to think it won't go to 300 or 400K if I keep changing the oil.

Author:  Reed [ Fri Feb 14, 2020 8:21 am ]
Post subject:  Re: downside of increased compression?

rich006 wrote:
DusterIdiot wrote:
NOx is a product of high cylinder pressure and temps...which will occur but can be lowered through use of
EGR, timing, catalytic convertors...

Keep asking questions, hone in on what you want to achieve and build for the here and now.


Would you ever consider adding a catalytic converter to a car that didn't come with one? Let's say one of your goals is to minimize the stink in your exhaust.


Yes. I fully intend to install one or maybe even two on my 76 D100, but only after I convert it to fuel injection. Carbs and catalytic converters don't coexist well on the same vehicle.

Author:  GregCon [ Fri Feb 14, 2020 8:46 am ]
Post subject:  Re: downside of increased compression?

Yep. The converter will die soon enough if you run it on a carb'd engine then your smelly exhaust is back.

Reminds me of the guy who told me, back around 1977, that he was going to buy a cadillac converter so he could convert his Pontiac into a Caddy.

Author:  Reed [ Fri Feb 14, 2020 10:39 am ]
Post subject:  Re: downside of increased compression?

Although a few years back I got a 1982 Dodge Ramcharger that was built with a carb and a cataytic converter. I replaced the original catalytic converter with a new high-flow three-way converter and it seems to be holding up well, so far.

Author:  DusterIdiot [ Fri Feb 14, 2020 7:12 pm ]
Post subject:  Re: downside of increased compression?

Quote:
There are way too many engines from all makers running 10:1 or more that last forever.


I guess when the slant six time machine shows back up and they bring back proof that a Morlock actually
has a running 10:1 engine in 802,701 AD we'll take that as fact... until then we are looking at limited
examples that have survived about 80 years so far... :lol:

Most of any engines that will survive a human lifetime will be because they are maintained, cared for, and
not abused...

Author:  Thebearded1 [ Fri Feb 14, 2020 7:22 pm ]
Post subject:  Re: downside of increased compression?

rich006 wrote:
Is there any downside to increasing compression ratio? I mean aside from the inability to run regular gasoline if you go too far. Surely there must be some downside or the factory would have built it with higher compression from the beginning, right? I'm guessing increased wear on bearings, cylinder walls, etc that could shorten engine life. Thoughts?


Where are you planning to have the machining down for your head/block? I'm in MD too and will be looking to have a head done.

Thanks
Gene

Author:  Reed [ Fri Feb 14, 2020 9:39 pm ]
Post subject:  Re: downside of increased compression?

DusterIdiot wrote:
Most of any engines that will survive a human lifetime will be because they are maintained, cared for, and
not abused...


Thats what Eloi are for.

Author:  rich006 [ Sat Feb 15, 2020 3:36 am ]
Post subject:  Re: downside of increased compression?

Thebearded1 wrote:
Where are you planning to have the machining down for your head/block? I'm in MD too and will be looking to have a head done.


I have a couple of machinists' names. Both were personally recommended by good mechanics. I plan to visit their shops to get a feel for how they operate (and how interested they are in my project) before I make a decision. I'll start a new thread about my build. The reason I asked the question in this thread is because I saw a post on FABO where someone claimed that increasing compression has no downside. It sounded too good to be true.

Walt (Charlie's Machine, Wicklow Rd, near BWI airport)
410-760-5014

Woody (Mayo Rd, Edgewater, MD)
410-798-5806

I'm not sure if they have last names, LOL.

Author:  Thebearded1 [ Sat Feb 15, 2020 4:42 am ]
Post subject:  Re: downside of increased compression?

rich006 wrote:
Thebearded1 wrote:
Where are you planning to have the machining down for your head/block? I'm in MD too and will be looking to have a head done.


I have a couple of machinists' names. Both were personally recommended by good mechanics. I plan to visit their shops to get a feel for how they operate (and how interested they are in my project) before I make a decision. I'll start a new thread about my build. The reason I asked the question in this thread is because I saw a post on FABO where someone claimed that increasing compression has no downside. It sounded too good to be true.

Walt (Charlie's Machine, Wicklow Rd, near BWI airport)
410-760-5014

Woody (Mayo Rd, Edgewater, MD)
410-798-5806

I'm not sure if they have last names, LOL.


Great thanks! Yea the only downside I see is finding new pushrods if you mill the deck really far. But then again that may be easy, I just haven't looked. I'm just going to do a mild bump in compression to go well with a 2 bbl setup

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