gday all,
just a question, when i build and engine and the block needs to be bored out (scratches etc) do i get oversized pistons or standard pistons and oversized rings?
Do oversized pistons even exsist?
Another question, in a street motor is it worth the extra money for 'race' piston or just use the standard ones?
Combo is at this stage: Red block, blue crank, blue rods, mild cam (27/67 or 1800- 5300RPM) probably yella terra head or ported 161 head, running on straight gas.
Steve
Oversized Pistons or rings?
Started by
_73LJWhiteSL_
, Oct 10 2006 06:46 PM
15 replies to this topic
#2
_CHOPPER_
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Posted 10 October 2006 - 06:51 PM
Rings and pistons need to be matched to the bore size. The first oversize is normally 0.020", so you need +0.020" pistons and rings. Stock pistons have been known to crack around the ring lands in stock engines that haven't been thrashed, so something like the HQ race pistons would be good. Only thing is, I'm not sure if they are available for anything other than 202's. I don't see anywhere you have stated the size of this Red block, is it the 173?
[EDIT] I need to learn to type better!
[EDIT] I need to learn to type better!
Edited by -CHOPPER-, 10 October 2006 - 06:53 PM.
#3
rodomo
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Posted 10 October 2006 - 11:07 PM
Why not stick a blue head on it too and be done with it?
I am having thoughts with my LJ of using the original red 173 block and all the bits off the blue 2850 to get around rego dramas.
I am having thoughts with my LJ of using the original red 173 block and all the bits off the blue 2850 to get around rego dramas.
#4
FastEHHolden
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Posted 11 October 2006 - 12:00 AM
you can go out to 80 thou over (no typo) I have a 186 block bored 80 thou (and stroked 1/4 inch..its a 210 )...but it doesn't leave much in the bore.
Buy your pistons and give them to the machinist to measure.
Buy your pistons and give them to the machinist to measure.
#5
_[BOTTLEDUP]_
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Posted 11 October 2006 - 03:42 AM
If the block needs boring then you will need to buy oversized pistons. As FastEH has mentioned, get the pistons BEFORE the block is bored, and get the machine shop to bore & hone the block to suit.
Putting in better quality pistons is definately a good idea, although what is available for a Holden 6 isn't a 'race' piston by today's standards. Precision Motorsport and ACL both do good performance pistons for the Holden 6, if you can get them with the thinner rings, these have less drag on the bore and better ring seal at high revs. Moly coated top rings are desirable but not essential, I always get file back rings so I can get the end gaps exactly correct.
I'd also get new cam bearings installed at the same time, and get the mains tunnel line honed.
Putting in better quality pistons is definately a good idea, although what is available for a Holden 6 isn't a 'race' piston by today's standards. Precision Motorsport and ACL both do good performance pistons for the Holden 6, if you can get them with the thinner rings, these have less drag on the bore and better ring seal at high revs. Moly coated top rings are desirable but not essential, I always get file back rings so I can get the end gaps exactly correct.
I'd also get new cam bearings installed at the same time, and get the mains tunnel line honed.
#6
_jklumpp_
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Posted 11 October 2006 - 12:12 PM
My engine is at the machinist at the moment having all this done, so i can confirm, oversize pistons & rings (.030" oversize), line bore the block (I have been told this should be done to any red 6 that is being rebuilt), polished black motor rods, and everything is being balanced.
The ACL "Race" piston only comes to suit a 202 (made for the HQ's), so you can only get a 'Duralite' for the other engine sizes - My engine is semi-race, and my engine builder reckons the Duralite will be fine.
The ACL "Race" piston only comes to suit a 202 (made for the HQ's), so you can only get a 'Duralite' for the other engine sizes - My engine is semi-race, and my engine builder reckons the Duralite will be fine.
#7
_73LJWhiteSL_
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Posted 11 October 2006 - 07:13 PM
Sorry guys i should clarify. No I am not rebuilding the 173, I have a (supposedly) low miles 202. I was told it has only done around 35,000 Ks. I DON'T want to bore the block at all if i don't have to, prefer to keep it at 202ci.
I was comtemplating ACL Race pistons, rather than using the standard ones.
I was definately planning to get the engine and crank (i assume the crank can be balenced by itself and the engine balenced as a whole?) balenced up so it spins up nicely.
I have comtemplated the blue head option, but i am planning to stick a hot red head on, and modify a VK EFI Manifold to fit a 9 port head.
Steve
I was comtemplating ACL Race pistons, rather than using the standard ones.
I was definately planning to get the engine and crank (i assume the crank can be balenced by itself and the engine balenced as a whole?) balenced up so it spins up nicely.
I have comtemplated the blue head option, but i am planning to stick a hot red head on, and modify a VK EFI Manifold to fit a 9 port head.
Steve
#8
FastEHHolden
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Posted 11 October 2006 - 07:34 PM
Your 202 will need a careful measure to see if new pistons will have the correct clearance..it will need a hone for new rings.
If it was me I would modify a 12 port head (bigger valves) and leave the manifold alone....This manifold developes positive pressure when used in conjunction with the black 12 port head....something i am sure you will lose by trying to stick it on a red head.
If it was me I would modify a 12 port head (bigger valves) and leave the manifold alone....This manifold developes positive pressure when used in conjunction with the black 12 port head....something i am sure you will lose by trying to stick it on a red head.
#9
rodomo
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Posted 12 October 2006 - 01:17 AM
Why not stick a blue/black head on it and be done with it?
#10
_jklumpp_
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Posted 12 October 2006 - 01:18 PM
agree with ^^^, wouldn't a 9 port head with EFI would be a backward step...I would think you'd definately want a 12 port head for the best result with EFI? especially as the EFI was designed for the 12 port - I would imagine it hard to modify the EFI to suit 9 port, and even if you did, you'd lose effeciency of flow?
#11
_73LJWhiteSL_
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Posted 12 October 2006 - 06:30 PM
I'm happy to hone the 202, i just don't want to bore it if i can avoid it. Correct me if i am wrong, but if you bore it out as far as it can go, and damage the bore, you need to replace the whole block right? Also bored out engines tend to run noticabley hotter? Is that correct?
With the VK EFI thing i am sure the manifold will work better than the redline manifold i am running at the moment cause the EFI inlet is more balenced. And it shouldn't cost too much to get a couple of manifolds and give it a go. I am pretty sure dad will be able to get someone to do the work for me farly cheap.
I am not keen to stick a 12 port head on, cause unless i am incorrect it means new extractors, and if i put my new motor in and have problems its not as easy to ripp it out and stick the 173 back in. I have to change extractors and muck around a lot more than if i was runing 9 port heads on both the new motor and my exsisting 173... it is a daily remember
The other disavantage i was told is you can't stick unleaded valve seats in blue and black heads cause it goes through into the water jackets. Can anyone confirm that one?
Steve
With the VK EFI thing i am sure the manifold will work better than the redline manifold i am running at the moment cause the EFI inlet is more balenced. And it shouldn't cost too much to get a couple of manifolds and give it a go. I am pretty sure dad will be able to get someone to do the work for me farly cheap.
I am not keen to stick a 12 port head on, cause unless i am incorrect it means new extractors, and if i put my new motor in and have problems its not as easy to ripp it out and stick the 173 back in. I have to change extractors and muck around a lot more than if i was runing 9 port heads on both the new motor and my exsisting 173... it is a daily remember
The other disavantage i was told is you can't stick unleaded valve seats in blue and black heads cause it goes through into the water jackets. Can anyone confirm that one?
Steve
Edited by 73LJWhiteSL, 12 October 2006 - 06:33 PM.
#12
FastEHHolden
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Posted 12 October 2006 - 06:44 PM
You are correct about boring engines..you have the possibility of rebore should something go bad...but you can sleeve them too...my big beef with boring too far is the heat.
fair enough argument re extractors..but you could get a stock blue at the drop of a hat...the VK efi manifold is certainly better than the 3 runner cain or lynx...it will be interesting to see your results.
Blue and black heads get modded (gas seats) everyday..never heard of them breaking thru..it happened to me on a set of YT 308 heads...you just loctite them to seal them.
fair enough argument re extractors..but you could get a stock blue at the drop of a hat...the VK efi manifold is certainly better than the 3 runner cain or lynx...it will be interesting to see your results.
Blue and black heads get modded (gas seats) everyday..never heard of them breaking thru..it happened to me on a set of YT 308 heads...you just loctite them to seal them.
#13
makka
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Posted 12 October 2006 - 06:45 PM
the overboring only becomes a concern when you get somewhere around 60thou, if its a stock bore engine you should be able to get away with a 20tnou overbore.
#14
_73LJWhiteSL_
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Posted 13 October 2006 - 06:36 PM
Thanks for the answers guys.
As i said above i want to avoid boring unless it is necessary, which means i can bore it a few time if i need to, which in theory means the block should do me quite a few years.
I don't mind if i spend a little bit of money on a modified EFI manifold to get it to fit a 9 port head and it doesn't work much better, but i think it will work better, even if its not as good as with a 12 port head.
thanks again
Steve
As i said above i want to avoid boring unless it is necessary, which means i can bore it a few time if i need to, which in theory means the block should do me quite a few years.
I don't mind if i spend a little bit of money on a modified EFI manifold to get it to fit a 9 port head and it doesn't work much better, but i think it will work better, even if its not as good as with a 12 port head.
thanks again
Steve
#15
rodomo
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Posted 14 October 2006 - 10:24 AM
I had a look in "Steve's Garage" and saw the dyno sheet. Definately time for something bigger.
#16
_73LJWhiteSL_
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Posted 14 October 2006 - 05:50 PM
That was before the gas went in by the way. Also it was with really clogged air filter... which i didn't realise at the time
I reckon its got maybe 10 kws more with the gas system. 
Steve
I reckon its got maybe 10 kws more with the gas system.
Steve
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