Compression Ratio

mazdamanik · 27-05-2005, 10:58 AM

Just wonderig how do you go about lowering compersion ratios of an NA motor ready for a forced induction setup? i heard someone say all you gota do is change the headgasket but i really dont think it could be that easy?? im asking because im seriously cosidering doing work on my NA engine for a supercharger?

twilightprotege · 27-05-2005, 11:18 AM

easiest way - thicker head gasket.

best way - new pistons

Cosmo Dude · 27-05-2005, 09:12 PM

Yep, easiest way is a thicker gasket but that will only lower the compression. It won't equip the engine for high boost or allow the correct ignition timing.

chicaboo · 27-05-2005, 09:23 PM

My Daddy always taught me that farking with the headgasket thickness can throw out the timing aspect between the cam gears and the pulley, is this true?

twilightprotege · 27-05-2005, 09:30 PM

only if the belt is the wrong size. if you use the same size belt then you're fine.

chicaboo · 27-05-2005, 09:33 PM

Do the belt tensioners accommodate the extra slack or tension well enough without slipping or rooting a bearing?

mazdamanik · 27-05-2005, 10:00 PM

ok thanx guys....if im gunna do it forgies will be going in i would say but thanx for the help now i know

chicaboo · 27-05-2005, 10:11 PM

About the rods, is it possible on the BP, FP and FS to remove the sump and take the crank, rods and pistons out that way without removing the engine?

twilightprotege · 27-05-2005, 10:27 PM

yeah you can do that fine.

twilightprotege · 27-05-2005, 10:28 PM

ps gav, like your new sig!

chicaboo · 27-05-2005, 10:32 PM

I figured it looks about right so I might aswell go with it, and people were complaining about the OLD sig...

W.A.I. · 30-05-2005, 09:46 PM

I m just wondering, for a NA car, running with lower compression ratio, what would it result to?

chicaboo · 30-05-2005, 11:24 PM

Probably less power, and higher fuel consumption... You would probably need to advance the ignition to get around it?

twilightprotege · 31-05-2005, 07:10 AM

less power, retard the ignition.

NA you never ever want to lower the comp ratio

BigMal · 31-05-2005, 10:33 AM

If you are replacing the pistons you will reaally want to hone the bores or
more likely bore and hone the block. The rings wear into the bore over time
and if your motor has a fair bit of mileage on it there will be a lip at the top.
You dont want badly sealed new rings that let a good part of your boost blowby
and be wasted. Take the head off and do things right.

27-05-2005, 10:58 AM	#1
mazdamanik Senior Member Join Date: May 2004 Location: Rathmines Car: Was an Astina now a Commohore :-( Posts: 903 View Photos By: mazdamanik	Compression Ratio Just wonderig how do you go about lowering compersion ratios of an NA motor ready for a forced induction setup? i heard someone say all you gota do is change the headgasket but i really dont think it could be that easy?? im asking because im seriously cosidering doing work on my NA engine for a supercharger? __________________ You can't race what you can't catch!!

27-05-2005, 09:12 PM	#3
Cosmo Dude コスモ Join Date: Dec 2002 Location: Location: Vic Car: Mazda '95 Astina I4, '86 B2K and '10 3 MZR-CD Posts: 7,888 View Photos By: Cosmo Dude	Yep, easiest way is a thicker gasket but that will only lower the compression. It won't equip the engine for high boost or allow the correct ignition timing. __________________ My 'stina Hatch

27-05-2005, 10:00 PM	#7
mazdamanik Senior Member Join Date: May 2004 Location: Rathmines Car: Was an Astina now a Commohore :-( Posts: 903 View Photos By: mazdamanik	ok thanx guys....if im gunna do it forgies will be going in i would say but thanx for the help now i know __________________ You can't race what you can't catch!!

30-05-2005, 09:46 PM	#12
W.A.I. Junior Member Join Date: Apr 2005 Location: Queensland Car: BA Hardtop Posts: 171 View Photos By: W.A.I.	I m just wondering, for a NA car, running with lower compression ratio, what would it result to? __________________ W.A.I.

31-05-2005, 10:33 AM	#15
BigMal 1ST BA TURBO MEMBER Join Date: Mar 2002 Location: Sydney Car: BA Astina Turbo Posts: 4,195 View Photos By: BigMal	If you are replacing the pistons you will reaally want to hone the bores or more likely bore and hone the block. The rings wear into the bore over time and if your motor has a fair bit of mileage on it there will be a lip at the top. You dont want badly sealed new rings that let a good part of your boost blowby and be wasted. Take the head off and do things right. __________________ If you want wind in your hair add a Hairdryer !!!

27-05-2005, 11:18 AM	#2
twilightprotege Driving a faster car now! Join Date: Oct 2003 Location: Work, always at bloody work... Car: Lotus ....... . Posts: 5,217 View Photos By: twilightprotege	easiest way - thicker head gasket. best way - new pistons

27-05-2005, 09:23 PM	#4
chicaboo Senior Member Join Date: Sep 2004 Location: Logan prefecture Car: Touge monster Posts: 7,585	My Daddy always taught me that farking with the headgasket thickness can throw out the timing aspect between the cam gears and the pulley, is this true?

27-05-2005, 09:30 PM	#5
twilightprotege Driving a faster car now! Join Date: Oct 2003 Location: Work, always at bloody work... Car: Lotus ....... . Posts: 5,217 View Photos By: twilightprotege	only if the belt is the wrong size. if you use the same size belt then you're fine.

27-05-2005, 09:33 PM	#6
chicaboo Senior Member Join Date: Sep 2004 Location: Logan prefecture Car: Touge monster Posts: 7,585	Do the belt tensioners accommodate the extra slack or tension well enough without slipping or rooting a bearing?

27-05-2005, 10:11 PM	#8
chicaboo Senior Member Join Date: Sep 2004 Location: Logan prefecture Car: Touge monster Posts: 7,585	About the rods, is it possible on the BP, FP and FS to remove the sump and take the crank, rods and pistons out that way without removing the engine?

27-05-2005, 10:27 PM	#9
twilightprotege Driving a faster car now! Join Date: Oct 2003 Location: Work, always at bloody work... Car: Lotus ....... . Posts: 5,217 View Photos By: twilightprotege	yeah you can do that fine.

27-05-2005, 10:28 PM	#10
twilightprotege Driving a faster car now! Join Date: Oct 2003 Location: Work, always at bloody work... Car: Lotus ....... . Posts: 5,217 View Photos By: twilightprotege	ps gav, like your new sig!

27-05-2005, 10:32 PM	#11
chicaboo Senior Member Join Date: Sep 2004 Location: Logan prefecture Car: Touge monster Posts: 7,585	I figured it looks about right so I might aswell go with it, and people were complaining about the OLD sig...

30-05-2005, 11:24 PM	#13
chicaboo Senior Member Join Date: Sep 2004 Location: Logan prefecture Car: Touge monster Posts: 7,585	Probably less power, and higher fuel consumption... You would probably need to advance the ignition to get around it?

31-05-2005, 07:10 AM	#14
twilightprotege Driving a faster car now! Join Date: Oct 2003 Location: Work, always at bloody work... Car: Lotus ....... . Posts: 5,217 View Photos By: twilightprotege	less power, retard the ignition. NA you never ever want to lower the comp ratio

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