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Engine dilemma
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Author:  Drekkus [ Sun Apr 19, 2009 10:50 pm ]
Post subject:  Engine dilemma
I've been given a 1100 engine which I'm going to rebuild to replace my current one.40 thous over currently.
I was going to aim for a CR of around 10.1 so I was trying to work out what pistons (60 thou) to go with - dished or flat top.I have a '295 head on my current engine which had been reconditioned when I bought it so I was going to look at using that.That was until I measured it and its had 120 thou taken off it.I guess to get the compression up but 120 thou sounds a bit too much to trust.
It hasn't blown the head gasket in the couple of years I've had it on so do I go with it or look for another head.It would be a shame to waste it but even more of a shame to put pistons in to suit then have to change it all.
I've got a few months to decide as I'll be doing the gearbox first.
Author:  sgc [ Mon Apr 20, 2009 9:22 am ]
Post subject: 
At 120 thou off, that head is really thin. 90-100 is about the accepted maximum safe shave, I'm surprised you could get 120 off it without breaking into the rocker oil drilling.

Anyway, unless the chambers have been opened up significantly (which is not really necessary on a '295 as they're pretty damn good to start with) you'll need to run dished pistons to keep the CR under control. At 60 thou over and with a 6cc dished piston you're looking at nearly 11:1 static CR, put flat tops in and it's 13.5:1 :shock:

First thing I'd be doing with that head is cc'ing the chambers to see if they're standard. It's unlikely you're going to be able to do much with it unless they're enlarged.

Good luck with it, I'm interested to know how you get on :)
Author:  Drexxle [ Mon Apr 20, 2009 2:10 pm ]
Post subject: 
Lucky you got a 295, slightly better than a 202 which is the common use head.

Dont use flat top pistons if you intend to drive it daily, the dished pistons are dished for a reason, to help with a centred combustion. Not to mention keeping your compression ratio's down a little as mentioned in the previous post.
Author:  Drekkus [ Mon Apr 20, 2009 3:12 pm ]
Post subject: 
sgc wrote:
At 120 thou off, that head is really thin. 90-100 is about the accepted maximum safe shave, I'm surprised you could get 120 off it without breaking into the rocker oil drilling.


Unless I've measured wrong it is that much and I have compared with a standard head.
Maybe I've got lucky so far but will that hold.Also whats the chances of the valves hitting the block.I know it does have oversized valves.


sgc wrote:
you'll need to run dished pistons to keep the CR under control. At 60 thou over and with a 6cc dished piston you're looking at nearly 11:1 static CR, put flat tops in and it's 13.5:1 :shock:


I thought it was lower than that.I probably need to go through some calculations again.
BTW whats the dish cc on the Hypatecs?


sgc wrote:
First thing I'd be doing with that head is cc'ing the chambers to see if they're standard. It's unlikely you're going to be able to do much with it unless they're enlarged.

Good luck with it, I'm interested to know how you get on :)


I will cc it all this time.At the moment I'm starting to slowly get everything I need together and I'm trying to work out if I need to factor in another head.
I know that it had had new valves, valve guides, springs and inserts done.I was told who the work was done by and I'm suprised that they would take so much off it.
I'll just put it down to the learning experience if I have to get another.
Author:  gafmo [ Mon Apr 20, 2009 3:53 pm ]
Post subject: 
Drekkus wrote:
sgc wrote:
At 120 thou off, that head is really thin. 90-100 is about the accepted maximum safe shave, I'm surprised you could get 120 off it without breaking into the rocker oil drilling.


Unless I've measured wrong it is that much and I have compared with a standard head.
Maybe I've got lucky so far but will that hold.Also whats the chances of the valves hitting the block.I know it does have oversized valves.



What head did you compare it to...Another 295 Head :idea:
Author:  sgc [ Mon Apr 20, 2009 3:59 pm ]
Post subject: 
Drekkus wrote:
whats the chances of the valves hitting the block.I know it does have oversized valves.


The valves in a '295 won't hit the block in an 1100 regardless of oversize. With a really thin head such as yours there might be a risk of the valves hitting pistons but only if you're running a high-lift cam or 1.5:1 rockers.

Drekkus wrote:
I thought it was lower than that.I probably need to go through some calculations again.
BTW whats the dish cc on the Hypatecs?


My spreadsheet says:
(2.543"+0.060" bore) x 3.296" stroke = 287.4cc swept volume per cylinder

28.3cc std chamber vol - 0.120" skim = approx 18.3cc <--- [edit] I think this might be a little out since the chamber's not a perfect cylinder..

18.3cc chamber + 6.0cc piston dish + 3.5cc gasket vol + maybe 1cc piston-deck, ring land, etc = 28.8cc total combustion chamber volume

Therefore

(287.4cc + 28.8cc) / 28.8cc = 10.97:1 static CR

I don't know what's in the dish of a Hypatec, I've never measured one.
Author:  sgc [ Mon Apr 20, 2009 4:01 pm ]
Post subject: 
gafmo wrote:
What head did you compare it to...Another 295 Head :idea:


I thought they were all 2.75" thick from face to face.. ?

Probably not a good idea to compare thicknesses between heads, unless you know your reference head hasn't been skimmed itself.
Author:  drmini in aust [ Mon Apr 20, 2009 5:57 pm ]
Post subject: 
Valves won't hit the pistons, they don't reach full lift until pistons are 1/2 way down the bore.
At TDC with a sporty roady cam, valves won't be lifted more than .080".
Author:  Drekkus [ Mon Apr 20, 2009 7:02 pm ]
Post subject: 
[/quote]

What head did you compare it to...Another 295 Head :idea:[/quote]

With a 202 head.Same thickness aren't they at 2.75" thick as well ?
Anyway it measured at 2.75 and the 295 at approx 2.63" or a touch under 67mm
Author:  drmini in aust [ Mon Apr 20, 2009 7:05 pm ]
Post subject: 
All A series heads were ~2.750" thick when new. Give or take .010" or so...
Author:  Drekkus [ Mon Apr 20, 2009 7:07 pm ]
Post subject: 
sgc wrote:

28.3cc std chamber vol - 0.120" skim = approx 18.3cc <--- [edit] I think this might be a little out since the chamber's not a perfect cylinder..



Ahh, I was working off 60 thou being 2.6cc and so 120 thou being 5.2cc giving 23.1cc.
Author:  sgc [ Mon Apr 20, 2009 9:10 pm ]
Post subject: 
Drekkus wrote:
sgc wrote:

28.3cc std chamber vol - 0.120" skim = approx 18.3cc <--- [edit] I think this might be a little out since the chamber's not a perfect cylinder..



Ahh, I was working off 60 thou being 2.6cc and so 120 thou being 5.2cc giving 23.1cc.


That's probably more in the ballpark. My calcs assume the chamber is a perfect cylinder, which it obviously isn't.. and I haven't got any empirical measurements at the moment to adjust it ;)
Author:  Drekkus [ Mon Apr 20, 2009 9:56 pm ]
Post subject: 
sgc wrote:
Drekkus wrote:
sgc wrote:

28.3cc std chamber vol - 0.120" skim = approx 18.3cc <--- [edit] I think this might be a little out since the chamber's not a perfect cylinder..



Ahh, I was working off 60 thou being 2.6cc and so 120 thou being 5.2cc giving 23.1cc.


That's probably more in the ballpark. My calcs assume the chamber is a perfect cylinder, which it obviously isn't.. and I haven't got any empirical measurements at the moment to adjust it ;)


Working off my calculations you end up with 9.55 :1. Obviously I would still have to cc it all but my main concerns were whether or not the head is going to be usable/reliable and what "ball park" configuration I would need to get a decent compression.
Author:  sgc [ Mon Apr 20, 2009 10:01 pm ]
Post subject: 
Drekkus wrote:
my main concerns were whether or not the head is going to be usable/reliable and what "ball park" configuration I would need to get a decent compression.


I would think at -120 thou reliability is going to be questionable, but if you've had no gasket issues while you've been using it then that's the proof. As for ballpark configuration, forget flat tops -- they're going to kick the CR too high for pump fuel unless you're running a race-style cam.

As far as I know, +.060" is the largest overbore you can get 1100 [edit] dished [/edit] pistons for -- I'm considering another bore on my car which is +.060 already, and I'll either have to find another +.040 block or use GR's +.080 flat tops and take some volume out the chambers.

Keen to know what you end up doing ;)
Author:  Drekkus [ Mon Apr 20, 2009 10:45 pm ]
Post subject: 
sgc wrote:
Drekkus wrote:
my main concerns were whether or not the head is going to be usable/reliable and what "ball park" configuration I would need to get a decent compression.


Keen to know what you end up doing ;)


It will be a couple of months before get around to it as I'm doing the gearbox first.I don't have the money at the moment to do both at the same time.By that time maybe some other option will have presented its self.
At the moment I'm looking at working with what I've got.Collect things as I can afford it.Have a RE13 cam and most of the stuff for the gearbox so far.
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