XE Pistons and Rods

[chappers1.3]

Hello.
Next step on the ladder of Modifications and i need help/advice again.

I'm thinking of buying a some 86mm XE Forged Mahle Pistons and Rods for my project engine which is a C20NE. I want to do this because i want to raise the compression ratio from standard but dont want to buy 500quids worth of gear. I have looked into this abit and various engines and the C20SEH & C20XE ones are not dished like the C20NE pistons so i am thinking will increase the compression. I looked at the Comp Ratios of the SEH, XE and NE engines and these are:

C20NE = 9.2:1
C20SEH = 10:1
C20XE = 10.5:1


Bore is 86mm and Stroke is 86mm on all 3 engines, they are identical, this means the pistons must raise/ lower the comp ratio??

Does anybody know if the XE piston/rod setup compatable in an 8v? Will they fit the crank? will the pistons hit the head/valves.

I dont want to use SEH setup firstly as the XE setup should in theory be alot stronger and handle the power - SBD say the Early Forged XE parts are good for around 250bhp so will definately suit my needs. and secondly SEH engines are old and i cant find any pistons for sale... and i have had issues with a SEH in the past!

does anyone know or could they guess-timate the Compression Ration after i did this if its possible? i am estimating it will be about the same as the XE if its all the same size etc?

Cheeers guys.

[M7VLJ]

the xe pistons will fit into an 8v block for sure but im not to sure on the valve clearance. in theory it should raise the compression but this all depends on the head design too, id be interested into looking at this.

are there any valve pockets on the 8v pistons????

cheers
matt

[chappers1.3]

there are some pockets on the face of the pistons yes, they are about 3mm deep, however i am unsure if these are needed for the valves, as the SEH pistons do not have any pockets and the head fits fine and the valves clear on them.

It may also be worth mentioning at this point - I have the Big Valve head taken from the 1.8 early injection engine, think it came off a 1.8 Mk1 astra?

In essence i think it should fit, it is just the valve clearance issue, and making sure my compression will not be something rediculous like 13:1..

If it works though it could be a very effective way of getting alot more power out of the 8v block using standard GM parts.

[craig green]

Tom Stickland documented an 8v build using XE bottom end a few years ago. He had the XE pistons crowns machined though.

www.tomstickland.co.uk

[chappers1.3]

yeah i have seen that tom strickland website, he is using the XE bottom end though so i take it that he will be using the block, crank, rods and pistons in that setup.

I want to use, 8v block, 8v crank and bearings, but only using the xe rods and pistons.

I spoke to Vauxhall and they are useless, they cant tell me any specific details at all about anything other than we as the manufacturer cant recommend anything if for use in another engine!!

Meanwhile, I have now turned my thoughts to another issue which i haddnt thought of b4, will the conrod big ends fit my 8v crank, and which big end bearings should i use? NE or XE ones? or are they the same?

in essance the engine blocks are the same, they have the same stoke and bore, but there must be some tiny differences apart from oil passageways and water jackets.

I might write to total vauxhall and ask them to investigate 4 their tech section.lol.

Cheers

[craig green]

It will all fit within an 8v block. I'd be tempted to use a stronger XE crank tbh, assuming you are using carbs?

The compression will be too high though. You could lower it to your target CR by machining the piston crowns & custom work to the squish areas in the head.

Tbh I'd say you need to read up on engine blue printing. There are books.

Yes it WILL bolt together but there are important factors to consider & get right in order for it to be worthwhile, otherwise you may aswell bolt in a std SEH or XE.

[chappers1.3]

Yes i am planning to use some R1 carbs on a custom manifold.

so, by putting these pistons in i will push my CR up too high then!? i thought it might have done but wasnt sure how much - any ideas?? above 11:1??

I dont really want to go down the route of changing the squish areas on the head.. for the costs i'd imaigne it'd be as much as fitting an XE, and heard that it is not best practice to machine the crowns on the XE pistons because the face is abit thin?? or can you?

If i can get the compression right by skimming the pistons i might concider it..

but yeah, i neeed to read some books on blueprinting...

[craig green]

Might aswell use an XE head & cams, then theres no need for any machining + the outcome will be higher bhp than the 8valves & single cam.....

Tom Stickland managed to skim the pistons & run it with an 8v SER head.

[Will F]

Waste of time IMO

Just fit an XE, more reliable, easier to work on (as its all from one engine and not a multi-hybrid)

;)

[chappers1.3]

yep, i know that it would be easier to just plant a XE lump or head in but i aint got one....I do however, have some XE pistons and rods (or will shortly anyway). And i have done too much work to this 8v engine to just start again, even though it might be cheaper and the gains are higher when modified.

From looking at many websites and reading pages, i think maybe this is possible now - Doing some maths at the moment to try and find out how much i need to skim off the piston crown, I have access to lathes & milling machines so doing it isnt a problem, jsut working out how much to take off to get the CR at something between 10.5-10.6:1

from looking at Tom Sticklands Equations Excel sheet, i have totally confused myself http://www.tomstickland.co.uk/astra/mods2/engine/compression_ratio.xls (http://www.tomstickland.co.uk/astra/mods2/engine/compression_ratio.xls) coz he is referencing 5 different ones, but it gives me some areas/ideas where i should be looking etc

for starters i know, the Max Chamber volume = 499.5cc (1998/4), the compression ratio as standard is = 9.2:1, so divide these and you get 54.2cc after compression. which is made up of the Head CC, the piston dish, squashed headgasket and gaps to the piston rings.

i think i need to do some exact measurements myself, but if i find the CC of the Head, i should be able to calculate the deck height i need - which should give me the right compression ratio.

by using this http://www.johnmaherracing.co.uk/enginecalc.htm (http://www.johnmaherracing.co.uk/enginecalc.htm) calculator i work the deck height to be 1.19 (but thats assuming the pistons are flat tops i imagine)

More tomorrow i think, if you guys have any other thoughts let me know.

Cheers

[chappers1.3]

hello again, bit more info...

I have measuerd the CC of my 18e head using clear plastic sheet, some vaseline and a syringe full of water, did this a couple of times and these are the figures I got per cylinder..

Cyl No1 - 34cc
Cyl No2 - 34.5cc
Cyl No3 - 33.5cc
Cyl No4 - 35cc

I am going to do some more accurate measurements with a smaller syringe, this was done with a 50ml jobbie and only measures in 1ml devides but i did it 3times on each chamber to give an average.

Now - on a NE engine, the standard CR is 9.2:1....... this is with a 43cc head volume, looking tho Migweb and this site i found info to say that for every CC extra/less it changes the CR by 0.1. This leads me to think, if i put this head on my engine I would end up with a CR as follows

Cyl No1 CR - 10.1:1
Cyl No2 CR - 10.05:1
Cyl No3 CR - 10.15:1
Cyl No4 CR - 10.0:1

Now, I know that the CC of the ports are meant to be balanced to stop one Cylinder pinging or under performing in relevance to others, so instead of taking material out of the head face or re-cutting the valve seats deeper, i was thinking of matching each piston to its respective chamber as they will are going to need machining anyway. I am not sure how much i need to take off each piston yet as i have not put them in yet to measure the deck height, but on the whole what do ppl think about this idea?? I cant imagine it would cause too many issues..

Also - any views on what would good CR on a 8v engine, I have a 18e camshaft that has a 297degree duration with 11.75mm of lift?!with a long duration cam you can run higher static CR so i was thinking about 10.8 or 10.9 ish??

Cheers

[Stuart]

Id be more inclined to calculate what 1cc change does than reading it...

[chappers1.3]

I will calculate it of course... these are initial thought and estimates.

What is the highest CR any1 is running on a NA engine? What cam is being used?

[chappers1.3]

Sorry, please ignore that last post about 1cc being the same as 0.1 cr.... its not - i'm talkin ****..... :mad: so back to the excel spreadsheet for some more number crunching.

its a nightmare this... as soon as i get the secret formula tho - i'll be laughing... and i'll share it with you all.....:thumb:

cheers 4 your patience!

[Stuart]

its rather easy :p

the CR calculation is in the 1.4 tuning guide. rearrange a few things and then you can work out what fraction of cr will require X cc coming off the head... then use the diameter and work out howmuch needs skimming off. (rough rule of thumb there as the head is dome shaped)

[Stuart]

just done a few rough calcs assuming 86mm*86mm bore stroke...
0.5cc per cylinder = 0.1CR change

[chappers1.3]

Here is where i have got to so far on my calcs... the table is quite complicated as thought about quite a few different variables that effect the volume and i think will effect the overall CR.

These variables are:
- Overall CC of the cylinder using a 18e head compared to the NE head - my head is 5cc less than the original NE head, so this means the max cyl vol is also 5cc less.
- Overall CC using different Piston pocket depths - same reason as above, using the standard NE piston as a base then working from there....
- Gasket thickness - 1.1 and 1.3mm, tom stickland says 1.1, other ppl say 1.3
- The 4 x XE valve cutouts on each piston - i am using combined 1cc for them as, this is going to be measured properly tonight.
- Deck Height 0.1mm increase for the XE pistons in the NE block (this is also going to be used as my margin of error on the calcs)


The only thing i havent measured yet is the NE head, this is worked out backwards from the pistons, gasket, deck height, standard CR and cyl cc...... i am hoping to get it measured tonight but it needs a proper clean up, but the table might change depending on my findings.... and it assumes a gasket thickness of 1.1mm is applied!


Any ideas, bits i missed, thoughts, comments, general questions or advice would be sweet!!
...
Cheeers.

[chappers1.3]

Nope - it didnt work!!! damn internet computer!! lol

i will try and find some way to show u my workings!!

[chappers1.3]

found out by measuring the C20NE Head that its 43.5cc per bowl..

this means my 18e head has 9.5cc less vol than the standard head.

tell me if i'm boring any1.... i think its fasinating all this measuring cc, cr n whatnot.... keeps me wel busy thro the day!!

only thing is, that with all of my workings, i am gettin some well odd figures for the standard Engine..

Total Cyl CC = 499.5cc
Head Volume = 43.5cc
gasket vol - 6.61cc
piston dish - 11.25cc
deck height = 0.5mm = -2.9cc

so 499.5/58.46 = 8.54:1....... what am i missin coz it shud b 9.2:1?????

HELP????!!!

[chappers1.3]

we ok, cambridge helped me - cheeers mate!! :)

just 4 ur info, and if any1 needs a calculator for working out CRs or anything i have 1 and i dont mind sending out. PM me ur email n i'll send it you, took me 2 days to get it working right....

To sumarise -
You cant use XE rods n pistons in an 8v block with a 18e head..... :cry: because the CR is too high - i worked it out to come to 12.4:1, so this would mean you'd have to skim 2.75mm off the piston crown which no1 has done b4 - SDB dont know if its possible, Chris Astley doesnt either, the most i heard of is tom stickland who took 0.8mm off!! or use a 1.77mm thick Cometic Headgasket but u'd still need to skim about 2mm off the piston to get it down to 10.7:1... so we wont be trying that....

You can however, use the XE pistons n rods with the c20ne head (43.5cc)and u get about 10.4:1....

Putting the 18e head i have (34cc) on the C20NE with standard internals (11.25cc piston dish) works, gives about 10.7:1, but you have to use the 8v rods which arnt as strong apparently, and u cant jsut use the XE rods coz 1 has a floating pin, the other is heat fitted i think? anyway, u cant mix match.

SO - next option is LET pistons.... or custom made 1s.... LET it is :thumb:

Does any1 have any??? that they want to swap for some weight ballanced XE forged pistons?

I am advertising them in the For Sale list.

Chaps!!!