Help with high comp pistons.. 12/13 CR

[ben_p]

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=120383258133

Just seen these on the bay... good price (they have offered me non-maxis new and not in overbore for £370, which is good also)

Questions

1. Why wont these fit OEM rods, can I not modify them to fit? :/

2. Will these work with 428s?

3. What would be any gains/losses against OEM and the normal 12CR wossners as the MAXIs are 13CR

 

[Sean.]

chances are the bushes in the rods are different sizes.

 

[ben_p]

Could the OEM not be adapted?

 

[Fred@BTM]

13.3? never knew wossner did them

we used the 12.4's on stock rods

why you so keen to overbore?

 

[ben_p]

im not keen to overbore, just that all the pistons that have come up are overbore lol. (feck paying £550, when BB are doing them for £370)

 

[ben_p]

BB can do me a set of rods for £299.. hmmm £60 for 13:7:1 CR and forged rods..

 

[Fred@BTM]

don't bother with rods, some of them are terrible, stock rods balanced with ARP's will do 8000rpm all day long on NA

you tried Omega/accralite/je/iapel etc etc?

 

[ben_p]

Yeah i dont want to change the rods, as you say i can just fir ARP 2000 studs and im not looking to rev past 7850 RPM

The only reason I would use forged rods is if the 13CR maxi pistons wont run on OEM rods (and even then ive got to find out is 13 CR is good togo for on my engine)

 

[Fred@BTM]

you spoke to yoz abot the ones he's selling (also CODEGY is selling his too)

need new rings, but might work out cheaper?

 

[ben_p]

codegy sold his on ebay..the same person bought the cams and the pistons.. he left feedback for codgey..

But the next day he offered them on here to a lad, so he may of been ebay owned!

Total steel rings are £80 for 4 pistons, so they would have to be less than £290 to evem be cheaper than new!

 

[stan*]

13.3:1 isnt massive on the scheme of things, but considering your cams are relatively low duration, I would be tempted to stick with the 12.5:1 pistons. reason being you can over-comprees an engine, and the resulting "negative work" will sap power. you will likely find you will have to knock a bit of ign advance off when mapping to allow for det free combustion, which again saps output....its a pay off.
The other reason i would be tempted to to go with the others is that these maxi ones are a slipper design. so really piston ring wear will be higher.

 

[ben_p]

Sweet, cheers for the heads up stan*!

12:5:1 it is!

 

[Icarus]

12.5:1 will IMHO be far better for the cam spec and rev limit you will be running. Stan* is bang on, as is Fred regarding the rods - standards with ARP's are fine for the rev limit you want to run.

Calm down and stop looking for ways to spend money Ben ;-) Get the current lump running correctly first and all the associated issues solved so you've got a good base to work from!

Cheers
M

 

[ben_p]

Cheers!

I want power! lol, what i dont want to do is spunk £300-£400 quid on a map for this engone.. if my long term plan is high comp!

 

[Fred@BTM]

its a LOT of effort for an extra 10-15bhp dude!!!!

 

[Mark One]

13.3 is mega high. surely that's the kind of thing that'd need direct injection to avoid det at reasonable ignition advance.

 

[ben_p]

yea but i want to be faster than F15's, saturn rockets etc!

 

[Fred@BTM]

learn how to drive then

you're mad if you ask me, if the bottom end is fine leave it alone to be honest

by the time you do a high comp bottom end, balance it all, new bearings, seals, etc etc etc its going to cost you a lot!

better off spending the money on tuition than all that effort for 10-15bhp

 

[ben_p]

owww!

 

[Mark One]

yea but i want to be faster than F15's, saturn rockets etc!

did someone say boost?


....sorry my mistake

 

[stan*]

13.3:1 isnt THAT high, for a cam duration of say 300deg it would bring the effective/dynamic compression down a far chunk...and its this value that matters more than static figures.

I personally WOULD fit forged pistons, they are definately worth it....