Compression ratio

falcon_ea-ed · 14-03-2005, 06:35 PM

I heard some decent power gains can be achieved from raising the compression ratio is this true? where can you get this done at/ how much does it cost.
any Info would be greatly appreciated.
My car is an EB2 S-Pac
Thanks,

Walkinshaw · 14-03-2005, 06:55 PM

can be done by 3 methods

1, decking the head
2, running flat top pistons
3, thinner head gasket

neither are cheap

Thanatos · 15-03-2005, 08:34 AM

IMO it's not worth changing the compression ratio and nothing else. The gains just don't justify the cost.

If a headgasket blows, or you are planning a rebuild or worked head, then do it at the same time, but the gains are very negligable, so don't go to too much trouble to do it.

Sox · 15-03-2005, 08:40 AM

I'm not sure what cost you guys are talking about here, skimming a head costs approx $40, and a metal gasket costs <$90.
For less than $150 you can raise CR by at leat 1/2 a point, which will certainly help throttle response and increase fuel economy.

Rick.

Thanatos · 15-03-2005, 08:47 AM

Quote:

Originally Posted by Sox

I'm not sure what cost you guys are talking about here, skimming a head costs approx $40, and a metal gasket costs <$90.
For less than $150 you can raise CR by at leat 1/2 a point, which will certainly help throttle response and increase fuel economy.

Rick.

As john said, not everyone is game enough to do the work themselves.

Not to mention the fact that, even if you do it yourself, it's a lot of trouble to go to for bugger all gain.

I still maintain that there's not a lot of point unless you have the head off for another reason ;)

EFFalcon · 15-03-2005, 08:43 AM

$150 + labour...
not everyone is game enough to do a headgasket change themselves.

Sox · 15-03-2005, 08:45 AM

Quote:

Originally Posted by EFFalcon

$150 + labour...
not everyone is game enough to do a headgasket change themselves.

Yep, add another $200 for labour, still not bad for the gains.
And it will complemant any cam upgrades in the furture.

Rick.

EFFalcon · 15-03-2005, 08:48 AM

personally i think that $350 is better spent on perhaps a exhaust upgrade, maybe cam change if thats done.
I'd wait for the headgasket to go or the head to come off for some other work before worrying about it (unless ofcourse u can do it all yourself)

Sox · 15-03-2005, 09:36 AM

Quote:

Originally Posted by EFFalcon

personally i think that $350 is better spent on perhaps a exhaust upgrade, maybe cam change if thats done.

This is debatable.
$350 spent on raising CR on it's own won't raise peak power, however it will increase low and midrange torque by a noticeable amount, anything up to 10nm.

Extractors/exhaust will cost at least $800, fitted. This will yield an improvement right across the range if decent extractors are used. Though realistically we won't see much more than 10kw increase.

So 10kw of power for $800 or 10nm of torque for $350.
You do the math.

Rick.

Walkinshaw · 15-03-2005, 09:40 AM

I think what the other guys are getting at may be that it may be adviseable to do headwork in one go. Instead of removing the head just to raise CR, why not plan ahead and with the head off, get it decked, ported, port matched, whack a new cam in all at once to save a bit of mucking arround and labour

Thanatos · 15-03-2005, 09:43 AM

Quote:

Originally Posted by Walkinshaw

I think what the other guys are getting at may be that it may be adviseable to do headwork in one go. Instead of removing the head just to raise CR, why not plan ahead and with the head off, get it decked, ported, port matched, whack a new cam in all at once to save a bit of mucking arround and labour

Exactly ;)

Sox · 15-03-2005, 09:50 AM

Quote:

Originally Posted by Walkinshaw

I think what the other guys are getting at may be that it may be adviseable to do headwork in one go. Instead of removing the head just to raise CR, why not plan ahead and with the head off, get it decked, ported, port matched, whack a new cam in all at once to save a bit of mucking arround and labour

Naturally.
Though my point is that there are gains to be had, and in the case where a head gasket is on it's way out (very common in E series cars), the job may be closer than anticipated, and then well worth doing.

Rick.

Thanatos · 15-03-2005, 09:55 AM

Quote:

Originally Posted by Sox

Though my point is that there are gains to be had, and in the case where a head gasket is on it's way out (very common in E series cars), the job may be closer than anticipated, and then well worth doing.

Hmmm, this sounds like exactly what everyone else has been saying!

Arguing just for the sake of arguing again, Rick?? :P

Sox · 15-03-2005, 10:03 AM

Quote:

Originally Posted by Thanatos

Hmmm, this sounds like exactly what everyone else has been saying!

Not quite matey, you said there is bugger all gain, which is clearly wrong.

Quote:

Arguing just for the sake of arguing again, Rick?? :P

Maybe it's just a case of you don't like being proven wrong.

Rick.

Thanatos · 15-03-2005, 10:13 AM

Quote:

Originally Posted by Sox

Not quite matey, you said there is bugger all gain, which is clearly wrong.

What i said is that the gains don't justify the head being taken off JUST to raise the compression ratio.

Quote:

Originally Posted by Sox

Maybe it's just a case of you don't like being proven wrong.

Rick.

Show me where i've been proven wrong??

The way i see it, everyone else has agreed 100% on this topic, including you in your previous post :P

Like i said, arguing for the sake of arguing ;)

EFFalcon · 15-03-2005, 09:44 AM

well judging by the fact that falcon_ea-ed isnt confident in changing a cam, i imagine a headgasket change is a little further out of reach. therefore waiting for the head to come off for another reason will in the end, save money.
unless u want to pay someone twice (also $200 for labour sounds a bit optomistic to me) then i'd suggest waiting and spending (saving) money for other things they may want.

Walkinshaw · 15-03-2005, 10:14 AM

For the effort of removing the head i think there is bugger all gain. If im going to the trouble of pulling the head I'd want to see some quite significant (+15-20rwkw combined with a suitable cam) gains.

Yagz · 15-03-2005, 12:53 PM

OK.

End result of this thread, and to answer the question of the original poster;

Yes, increasing the compression ratio will give you improved performance,

and,

NO it is not the cheapest bang for buck modification you could do unless you are willing to remove the head/change pistons yourself.

See, wasn't so hard, was it? :P

Walkinshaw · 15-03-2005, 01:11 PM

Quote:

Originally Posted by Yagz

OK.

End result of this thread, and to answer the question of the original poster;

Yes, increasing the compression ratio will give you improved performance,

and,

NO it is not the cheapest bang for buck modification you could do unless you are willing to remove the head/change pistons yourself.

See, wasn't so hard, was it? :P

BINGO. This was also said about 3x above......end of story.

falcon_ea-ed · 15-03-2005, 05:05 PM

thanks for all the replies- i understand that yes power gains are achievable but it dost cost some $$$ if you dont do the work yourself- better to wait till the head goes
Thanks.