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 blup58
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| posted on August 26th, 2003 at 10:17 AM |
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Compression Ratio Settings
G'day All
I need some advice from some of your budding technical and experienced people in relation to what compression ratio to run on my engine.
Engine Specs are as follows:
Cap acity: 2110cc
82mm forged scat crank 5.5 inch carillo rods 90.5 mm bore,
lightened flywheel and 8 dowelled, 2300lbs kennedy p.plate, Street eliminator heads, ported/polished, 42 x 37.5 manley valves, duals, 1.5:1 rockers,
chromoly pushrods, retainers K8 cam, as21 case, 48mm dells, deepsump, fullflowed, external cooler/filter, 30mm oilpump, berg linkage & pulley, 1
3/4 header.
Here is the thing - it is currently running at 10.2:1 compression
When I purchased the engine I got to take it for a run, now I don't think I would need to tell most of you but it was very fun, the holey crap
bar was gripped and gripped tightly.
This however is the basis of my dilemma, I want to drop the compression ratio to increase longevity of the engine but at the same time I wantto retain
that angry warrior feel the engine put out.
I know that I probably can't have my cake and eat it to but surely there has to be a good ratio that is an even trade off for this set up between
fun and longevity.
so has anyone out there got some suggestions on what compression I should run, to increase longevity but not lose too much of that Wahooooo!!!!
feeling.
I might just note that the car won't be a daily driver but more of a street weekend warrior. (Will hopefully run a couple of 1/4 miles but not
building it purely for this, additionally I have not decided on wether it will run on the track at weekends)
Any advice would greatly be appreciated.
Cheers
Brad
:bounce
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 Bizarre
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| posted on August 26th, 2003 at 10:43 AM |
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Do not race into this too quickly
Low compression does not mean longevity.
High compression does not mean hi temps.
There is HEAPS of info on this on the STF and is not ment to bag Gene Berg and his 6.5:1 motors.
A lot has changed since the 70's - fuel especially.
This is what sets a good engine builder apart from the amatuer.
First - does it run hot?
Does it ping?
Does it run on?
10.2:1 is NOT all that high
I am running just under 9:1 on a daily driver.
You really need to know deck height and head chamber and shape before a better person than i can tell you if it is ok.
Who built the motor.?
Why was the CR set 10.2:1?
My first guess would be to leave it where it is and make sure your timing is right and you run PULP.
Sounds a great motor
Futue te ipsum!!!
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Stanley
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| posted on August 26th, 2003 at 12:04 PM |
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Blup ? Where abouts in brisbane are you located. I know a guy you could talk to who's up on that sought of stuff.
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blup58
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| posted on August 26th, 2003 at 12:07 PM |
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Thanks for the feedback blue 74l.
To give answers to some of your questions.
I actually purchased the motor of Keith Haeusler in Picton. From what I can gather from other feedback KEith is really knowledgable with engines and
is a really nice guy. So assuming all his info was true, he said the motor never really ran hot and I think he generally ran it on Optimax.
Didn't notice an pinging or run on....(can you clarify what you mean by run on)
I know Keith has used it for a few runs down the 1/4 mile and had some good times (test driving it with the welded diff was interesting, especially
while try to do a u turn in the back streets of Picton)
Can't recall who built the engiine originally, but I'm sure I asked the question.
The motor has been out on an engine stand as I am in the process of a body of resto, but I'm not to far off a restored rolling chassi, so its a
matter of while the engine is out, should I get a mild recondition and drop the compression ratio.
Pardon my ignorance but what is STF??
Cheers
Brad
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blup58
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| posted on August 26th, 2003 at 12:09 PM |
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I live in the Tarragindi/Annerley area, five minutes south of the Big Smoke.
Cheers
Brad
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 vw54
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| posted on August 26th, 2003 at 12:12 PM |
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Thats the engine you got from Keith in Sydney
C/R ratio depends on what you want to do with the car and how often you want to rebuild the engine.
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Bizarre
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| posted on August 26th, 2003 at 12:14 PM |
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Yep - Keith has a few motors under his belt! :thumb
STF = http://www.shoptalkforums.com/
Go to
Speed and Drag
and also
The Tyde 4'rum
Also go to
http://www.aircooledtechnology.com/
and read Old Jake's thoughts on compression ratio
Run i mean - turn engine off but car keeps going. Can be a sign of a badly tuned motor
If ya like i could borrow it for a year or 10 and tell you how it goes?
Futue te ipsum!!!
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Dasdubber
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| posted on August 26th, 2003 at 12:25 PM |
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Seeing I am helping Brad with his body off resto thought I'd better chime in. Engine doesn't run on or ping (as stated already). Runs very
nicely considering the K8 cam (which is a nice streeter in my opinion).
Other points of interest would be that it will be mated to Brad's freshly rebuilt close ratio IRS trans so short quick bursts would be on the
cards with occasional longer trips (eg valla) - right Brad? And the fullflow system with external cooler (with fan) and doghouse shroud will help keep
cooling under control. Oil temp gauge will be installed to keep an eye on whats happening out back.
From the people I have spoken to, running around 9:1 would be conservative enough, bust still maintain that yeeeharrr feeling. I'm not 100%
certain though.
Alan
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blup58
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| posted on August 26th, 2003 at 01:35 PM |
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Thanks Blue74l - I'll check out those sights.
I'd love to let you borrow it, but unfortunatley I don't have any spares.......so at this stage I'll have postpone lending it to you.
I'm sure you understand.
Vw54 - I mentioned in my email above what it will generally be used for, not planning on having to rebuild too often, but the question is how often is
often.
I guess to guys that race engines every month or two might be standard, and for those daily drivers every half decade might be too often.
Hadn't really thought about it, every couple/few years would be O.K provided I get a lot of fun out of it during those years. But then again I
don't know what to expect re rebuild frequency.
any thoughts on what I should expect i.e. High comprssion = lots of fun = rebuild ????every year ????
low compression equals = just fun = rebuild ???every second or third year???
Alan - yep longest trip would probably be Valla, but more often than not longest trip would be to coast and back (say 200klms return)
We'll Alans made the call on compression people any one out there going to confirm or suggest another point of view?
Brad
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FirstName V LastName W
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| posted on August 26th, 2003 at 09:38 PM |
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Ah the old compression ratio delema. How much is too much. If your engine is not showing any signs of the previous mentioned, pinging or running on
than as it was said before you have a bloody good engine and probably more to the point it was a well balanced combination to start with. When an
engine builder builds a motor it is normally with a purpose in mind, he or she sets out to achieve something from that motor that they dont already
have in thier present motor. Generally an engine with that comp is built to throw you back in the seat and this is by the sound of it why you bought
the engine. For it not to ping with that comp is outstanding and must be due to the combustion chamber design and shape or you are using a high
octaine fuel or perhaps a little of both is involved. An experienced VW performance person would probably agree that the only two things that woud
show early signs of wear would be both the big and and little end bearings. Having said that I still dont think that the 10 : 1 or so comp that this
engine has would accelerate the wear on the components all that much so you should be able to with regular servicing maintain this engine for many a
years. If it aint hurting don't touch it you could upset the engines balance and dropping the comp would definately see a reduction in power.
Each to their own just remember what goes around come around.
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Bizarre
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| posted on August 27th, 2003 at 08:50 AM |
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I will say again to leave it if it is behaving. Pulling things down to do minor changes will only add a chance of upsetting things.
As well by changing things low compression motors "can" be dogs to tune which can lead to a quicker rebuild than not.
Rebuild frequency - who knows. My 9-ish to 1 1776 has 30thou on it in 2 years and is as strong as ever.
IF you want another option that will only cost more money - wait a while and save for a set of CNC 044's and set the CR then. Why - i have heard
SE's are old tech and not as good as the new CNC's.
Just a silly idea - NOTHING wrong with what you have.
Why not give Kieth a call.
I am sure he would have 2c to throw in
You SURE i cant test it for you??? :bounce
You can borrow my 1776 and see what a mild motor is like? :bounce
[Edited on 26-8-2003 by blue74l]
Futue te ipsum!!!
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Baja Wes
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| posted on August 27th, 2003 at 04:33 PM |
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You will find that an engine will handle high compression ratios if it is jetted rich to suit. This will mean you won't get the best economy, but
if you don't care don't worry about it.
Wait until summer and see what the motor thinks of the high CR. I think it will ping if laboured, unless it is jetted rich and the timing isn't
overboard.
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Oasis
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| posted on August 27th, 2003 at 04:46 PM |
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| Quote: | Originally
posted by blue74l
You SURE i cant test it for you??? :bounce
You can borrow my 1776 and see what a mild motor is like?
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If not, want to try my mild engine then?? Guaranteed to put you to sleep. Very relaxing.
"Tell him 'We've already got one'"
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