compression ratios

[rob020]

hey guys,

anyone know what compression ratio i'll end up with if i put a tp magna head on an astron 1 2.6? someone said around 6-7:1... anyone got anymore accurate info?

also... if i put a 2.0 crank in my 2.6 block... that would lower the c/r even further wouldnt it? are the 2l pistons taller? are the conrods longer? would i have to shave a couple mill off my block?

also... if i put a astron 1 2l cam in the astron 2 head, what size whelch plug would i need to seal the hole in the back of the head.. ive got a spare 40mm one sitting here

thanks guys,
rob
p.s. im going for a efi turbo setup

[Billsy]

astron1 with astron 2 1-8 head ends up around 7.4:1

hey guys,

anyone know what compression ratio i'll end up with if i put a tp magna head on an astron 1 2.6? someone said around 6-7:1... anyone got anymore accurate info?

also... if i put a 2.0 crank in my 2.6 block... that would lower the c/r even further wouldnt it? are the 2l pistons taller? are the conrods longer? would i have to shave a couple mill off my block?

also... if i put a astron 1 2l cam in the astron 2 head, what size whelch plug would i need to seal the hole in the back of the head.. ive got a spare 40mm one sitting here

thanks guys,
rob
p.s. im going for a efi turbo setup

[havocgtr]

[quote="Billsy"]astron1 with astron 2 1-8 head ends up around 7.4:1


is that with flat top or dished pistons i'm guessing dished
got a simmilar question myself my 2.6 has flat top pistons and i'm putting a M4 head on it any idea on the c/r for dished?

[Superscan811]

Posted this EXCEL Compression Ratio calc a while ago.

M6/M7 heads are 70cc.

Astron 2.6L
Rods are 166mm
Stroke is 98mm
Piston Dia 91.1mm
Pistons sit 0.6mm below the block (35.5mm compression height)

Astron 2.0L N/A
Rods are 166mm
Stroke is 90mm
Piston Dia 84.0mm
Pistons sit 0.2mm below the block (39.9mm compression height)

Wiseco Forged pistons for the turbo 2.6L Astron
17cc dish
Pistons sit 1.1mm below deck (35mm Compression height)

Hope some of this helps.

Cheers.

[rob020]

im sorry, but my head hurts when i try to follow that...

so what happens if you put 2.6 pistons in a 2l or a 2l crank in a 2.6...
youd loose a fair bit of compression height wouldnt you?

[Superscan811]

so what happens if you put 2.6 pistons in a 2l or a 2l crank in a 2.6...
youd loose a fair bit of compression height wouldnt you?

You can't fit a 2.0L piston in a 2.6L block. Well actually you could but there would be about a 7mm gap between the piston and the bore.

A 2.6L block + 2.0L crank + 2.6L flat top pistons + M7 head = 2.4L engine with the piston sitting 4.6mm BELOW the deck and a Compression Ratio of 6.5:1.
Not a good combo in my book unless you are planning to constantly run VERY HIGH boost.

Figure out the amount of horsepower/boost/RPM you are expecting to run, that will give you a guide to what Compression Ratio you will need.
Once you have that figured out, work back from there as to what pistons/crank/head/etc.. you will need to achieve that goal.

Cheers.

[rob020]

hmm...

tp's dont have m7 heads do they... so if the head on my tr was an m7 head and i used that... are there any pistons out there i could use to bring compression back up to 7.5-8??

anyone out there made a 2.4? i just like the idea of a square bore/stroke... should be revvier shouldnt it?


i just want a 2.4 efi turbo


cheers,
rob


p.s. i never said anything about using 2l pistons but could there be a longer conrod out there we could use?

[havocgtr]

so what happens if you put 2.6 pistons in a 2l or a 2l crank in a 2.6...
youd loose a fair bit of compression height wouldnt you?

You can't fit a 2.0L piston in a 2.6L block. Well actually you could but there would be about a 7mm gap between the piston and the bore.

A 2.6L block + 2.0L crank + 2.6L flat top pistons + M7 head = 2.4L engine with the piston sitting 4.6mm BELOW the deck and a Compression Ratio of 6.5:1.
Not a good combo in my book unless you are planning to constantly run VERY HIGH boost.

Figure out the amount of horsepower/boost/RPM you are expecting to run, that will give you a guide to what Compression Ratio you will need.
Once you have that figured out, work back from there as to what pistons/crank/head/etc.. you will need to achieve that goal.

Cheers.

Funny i swear it said 2L pistons in a 2.6L the first time i read it aswell

[shuggy]

hmm...

tp's dont have m7 heads do they... so if the head on my tr was an m7 head and i used that... are there any pistons out there i could use to bring compression back up to 7.5-8??

anyone out there made a 2.4? i just like the idea of a square bore/stroke... should be revvier shouldnt it?


i just want a 2.4 efi turbo


cheers,
rob


p.s. i never said anything about using 2l pistons but could there be a longer conrod out there we could use?

think logically, if the flat tops sit low below the head (hence the low compression) then all you gotta do is get longer conrods with dished pistons.

this might be completely incorrect but if you think about it, if the rods are longer, then there is a dish to miss the valves, the piston sits closer to the head and therfore less gap therefore more compression

yea??

[Superscan811]

p.s. i never said anything about using 2l pistons but could there be a longer conrod out there we could use?

Sorry , it was late when I posted my reply, I obviously wasn't thinking too straight.

I've been looking around for a while for standard "off the shelf" parts that could be used for high and low compression engines as well as short and long stroke.
There are some 4.6L Ford rods that are 3.1mm longer that will fit
BUT
they require special bearings to be made. Thanks to Stealth dropping off the Crank and Rod to my brother, hopefully I will get a few sets of these bearings made up out of aluminium-bronze, so I can test them.

The Forged Rods are cheap, less than US$500 delivered (for a set of 8), are nearly 200g lighter than standard EACH, and can easily handle over 400hp. It looks like a good option if the custom bearings can be made cheap.

The other good thing about these rods is that you can either make a high compression engine using standard 4g54 pistons
OR
a low compression engine using 6G72 pistons (which are the same as the 4G54 piston, only 4mm lower in compression height.)

There are a lot of options with the 6G72 pistons with dishes between 1.4cc and 24cc, so instead of using a decompression plate and 2 head gaskets, you match up the piston for your desired CR and have fun.




The other option is either to Stroke or De-Stroke the engine.

Cheater is already making my high compression 2.4L Astron engine using standard rods, a 2.0L crank and a set of forged Celica pistons I picked up cheap from the US.
I can get some crazy compression ratios with this setup, 11:1 if I just bolt everything together and up to 14:1 if the block and head are shaved 1mm.

I'm also planning on a stroked 2.8L Astron engine which will be turbo'd. I already have the Shorter Rods and Forged Pistons. The rods are 3.4mm shorter, the bigend is 6mm smaller, 7mm narrower, OVER 300g lighter and can handle 450hp. If the 2.6L crank can be offset ground the 3mm needed to fit these rods, I'll be able to dramatically lighten the crank, so even on low boost, with a compression ratio of about 8.5:1, the engine should be very responsive.

If you can handle being called an idiot every now and again, are prepared to listen and to do a lot of research, you would be surprised at what options you can find.

Manufacturers' catalogs come in very handy, especially if they are in electronic format. It makes it easier to search for what you need.
Use Ebay as a research tool as well, not just Google.
You would be surprised at the depth of information you can find on some items. Often the sellers will post links to the manufacturer that are difficult to locate via Google.

I hope this gives you some food for thought.



Cheers.

PS: post your findings so other people can learn from both your triumphs and failures.

[Superscan811]

Here are some "SIDE by SIDE" pics of 3 standard pistons and a Forged Turbo piston.


Part of my ever growing collection of "TEST PARTS"





The 6G72 piston is for a SOHC engine and the TS Magna piston is for a M8 head.

Cheers.

[rob020]

those longer rods sound perfect... as soon as i can afford some forged pistons my bottom end should be
pretty bullet proof with both right? are the starion lead/copper (i think) bearings the best ones to use?

in the mean time... do you reckon id have more fun blowing up the stock astron 1 with my turbo setup as it is.
with a magna head on my block for low compression 7.5:1?
or the whole magna engine for 9.2:1?

wait a minute.. i dont wanna blow up the magna engine... thats the good one
i want to run 6-8 psi untill i get forgies... then hopefully 12-15 everyday... is that doable?
what should i do guys?

cheers,
rob

[panda]

are the starion lead/copper (i think) bearings the best ones to use?

Starion motor is a 4G63T, not an Astron, unless you live in the USA. ;)

[rob020]

yea, starquest g54b... didnt they change to lead/copper bearings in 87?

[panda]

yea, starquest g54b... didnt they change to lead/copper bearings in 87?

Better to ask the guys on the SQ forum in the States. www.starquestclub.com

[rob020]

lol... so just standard supercheap auto bearings are the ones to use then?


would a magna head on my sigma block make it too slow off boost?


cheers,
rob

[stealth]

why not just cc the head that you get then shave the the to suit the comp ratio
that you desire!
i have heard of 3mm being shaved of the magna heads with no problems at all
so work out what comp you want then do a couple of calcs
i think you will find it easyier to get some flat tops pistons from astron 2
then you will have no worries getting what you want (as its turbo'd)
acl flat tops are cheap as and if you putting bearings in pfhh why not
nice new rings and your all set to go
cheers stealth

[panda]

Stealth, whats the effect on cam timing with 3mm off the head ?
and can the cam tensioner still keep the chain tight ?

Sorry if I'm off topic. ;)

[stealth]

you need to change spring in tensioner and run
a adjustable cam sprocket eg:rollermaster timing
set no problems
or a cheater sprocket ,ask 81GL (nick) his 2lt
has these mods i believe
cheers stealth

[rob020]

gee.. the thing is i dont know what compression ratio i want (or should want)... thats why im asking what i should use... and the more money i spend on shaving heads the less money i have to buy a sexy turbo manifold off you

im using a magna head... wouldnt flat tops be too high compression?

could i use a 2l crank with flattops and shave 3mm off the block?


cheers,
rob

[stealth]

well how about when your picking up your manifold you bring the head
with you and ill cc it then you answer a couple of questions:
are your piston at zero deck ?
what bore size ?
what turbo?
and how much boost and ill tell what you got and what you want
cheers stealth

[COBWBS]

ok

Ideal motor is a 2.6 block, with 2.0 liter crank, and forged pistons, What rods??

And wats a decent pistion for turbo aplication??
i know RX22NV is using gapless rings.. No idea wat pistons

Wats a good comp ratio for 20 PSI up??

[rob020]

well how about when your picking up your manifold you bring the head
with you and ill cc it then you answer a couple of questions:
are your piston at zero deck ?
what bore size ?
what turbo?
and how much boost and ill tell what you got and what you want
cheers stealth

im in tas... i sure hope you were prepared to ship that manifold..

i havent opened either motor yet (i have an astron 1, an astron 2 and 2 2 litres at my disposal) but i was planning on running a chinese ebay special "t3 style" turbo.. 8-12 psi?

is there anything wrong with using a 2l crank with acl flattops and shaving the block to zero deck? (or .005 or whatever) as opposed to using longer rods? or did those celica(?) pistons have the added height required?

as soon as my megasquirt and edis kit gets here ill post up some pics

hey stealth... if i send you my crank pulley and a 36-1 trigger wheel could you put the two together? i might send you a cam sprocket too.. do i get a discount if i send you 3 and only want 1 back?



cheers,
rob

[rob020]

ok, i just put the magna head (its an m3) on the sigma, but ive kept the adjustable rockers and chucked in a 2lt cam... now i just need to run off to repco for a 35mm welsh plug...

so can anyone tell me what compression ratio i should have with an m3 head and dishies?

cheers,
rob


p.s. im very very disappointed with the person who sold me the cars definition of "new engine 36000kms ago".... number 4 cylinder makes me cry.... how oversize should i bore it? and should i do the wideblock or the narrowblock? ive got bellhousings for both

[stealth]

geez for some reason i thought you were local up here but anyway
yeah ill post it
why not use 186 red motor pistons i think that thay fit the 2.4 set up?
(someone might correct me)
mate a t3 at 8-10 psi (what fuel are you using eg;98)if so mate set it
at between 9/1 to 9.5/1 and have fun (its only low boost )
as for the comp question you should have cc'ed the head as there all different
these days ,do your dished pistons sit at zero deck ,what head gasket did you use
how thick was it ???????????????????
did you check your valve to piston clearances???????????
cheers stealth

[rob020]

grrr... 35mm is slightly too large to seal the water pump pulley hole... i'll just fill the old seal with rtv sillicone..


are they all different because it couldve been shaved?? could you assume it hasnt been shaved and put the figure somewhere in the right ballpark? im sorry, i just thought all astrons of the same era were the same.... i mean, the deck height shouldnt change should it? unless it has longer rods, or taller pistons... or a shorter deck...

thanks for being patient with my ignorance...


oh yea i used one of those acl graphite composite head gaskets, and heaps of permatex copper seal-a-gasket... i love that stuff



if 186 pistons work than that is what i shall use... should be easier to find forgies?


cheers,
rob

[rob440]

Hi ,
i am trawling the forum for info. I have a 2.6 astronII. My motor is carb at the moment and I have a efi conversion + haltech to install. My motor is stock but I want to have the option to increase power. I want a NA motor , I am looking to get some MORE compression. Is there a a head like a 2 ltr or something I can bolt on that will give me a high CR?

Rob

[stealth]

mate astron 1 heads have a small comp chamber around 55cc
astron 2 heads are anywhere form 68cc-84cc
hope this helps
cheers stealth

[rob440]

do you know are the valves same , ports? etc.
and an astronI head can bolt to an astronII motor?

using the comp calc downloaded from this post
changed the piston dome to 0
= 11.91

[stealth]

yeah you can get up to 11.7 to think its around that anyway
and yes a astron 1 and 2 are interchangeable BUT the inlet
manifold bolt pattern is DIFFERENT
only the bottom set of holes are in different postions also around
the thermostate
you can make a adaptor plat form astron 1 to 2 or 2 to 1
so not really a biggi
cheers stealth