Oversized piston query??

7th October 2009, 23:05

Thinking of rebuilding engine over winter and toying with the idea of putting 80mm high comps in the block. Anyone put bigger pistons in before and does this cause any other problems like overheating????.............hhmmmmmmmm

7th October 2009, 23:09

the cylinder walls are really thin so dont get too much machined out

7th October 2009, 23:12

80 or 81 is as much as you can go with the wall thickness. Overheating isnt really an issue, the only problem you may find is if in the future something happens and something gets in the bores and scores/marks them, then the bottom end will be useless as its overbored to its max.

You dont gain much from the extra size really. Go 79mm Imo

8th October 2009, 20:39

ok, what else would you need to upgrade in the bottom end? rods and bolts presumably, but what about bearings and seals? Ive also got a modified head and will eventually be running throttle bodies when the credit crunch decides to ease off

I read on another thread that the crank is strong enough..........discuss ={

8th October 2009, 21:13

Can do quite abit to the bottom end to make it better matey.....

Stronger rods, Uprated rod bolts, Lightened and balanced, Knife edging, Baffled sump, Competition bearings,

Can also go with different crank/rods.... 1800cc. How deep are your pockets.

8th October 2009, 21:36

not as deep as they used to be, lol

whats knife edging? thinking of running a dry sump eventually
know someone who preps rally and track cars-although mainly old fords- but will make me one up if i ask him

8th October 2009, 22:36

anybody??

where did you go sax-oli?

8th October 2009, 22:45

dont go massive if you dont need to imo.

Although bore wall issues tend to be more when theres high inlet temps from massive compression with boost.

Standard cranks (with or without a little bit of work) have been known to take a shit load of abuse.

8th October 2009, 22:53

not intending on running boost. just throttle bodies.
cheers though mate

9th October 2009, 11:12

knife edging the crank is a process which re-profiles the crank counterweights, so that when they pass though the oil in the sump less of a decelleration force is experienced by the crank. This in theory allows the crank to spin more freely while usually reducing the weight of it too.

9th October 2009, 21:39

aahhhhhhhhh!!

gotcha. Never heard of this before

10th October 2009, 13:09

ive heard knife edging can cause problems with the oil circulation around the crank. that was on the old fords right enough dont exactly no if its the same with the tu engines. but if your going to be running a dry sump do see any problem

10th October 2009, 15:14

Quote:

Originally Posted by sax-oli

80 or 81 is as much as you can go with the wall thickness. Overheating isnt really an issue, the only problem you may find is if in the future something happens and something gets in the bores and scores/marks them, then the bottom end will be useless as its overbored to its max.

You dont gain much from the extra size really. Go 79mm Imo

is 79mm standard bore size as i've herd its 78mm?

10th October 2009, 21:52

Quote:

Originally Posted by boabVTR

ive heard knife edging can cause problems with the oil circulation around the crank. that was on the old fords right enough dont exactly no if its the same with the tu engines. but if your going to be running a dry sump do see any problem

has anyone else heard of anything like this??

as i say, ive only just heard of this so im a bit of a knife-edging virgin

--break me in gently--

10th October 2009, 21:52

dont know what original bore size is tbh

10th October 2009, 21:59

Original bore is 78.5iirc If the bores are good on the rebuild and can be honed within tolerances of the new pistons then i would just keep the same. Youll get a bit more cylinder space with the bigger bores though, so a bit more power.... its totally up to you.

10th October 2009, 22:02

you wont gain much from overboring. More can be got from stroking the engine as you can get to 1796cc. With throttlebodies and the right cams you will get over 200bhp.
The dry sump can reduce parasitic losses so may gain 1 or 2 % bhp. Its expensive though

10th October 2009, 22:14

Quote:

Originally Posted by KamRacing

you wont gain much from overboring. More can be got from stroking the engine as you can get to 1796cc. With throttlebodies and the right cams you will get over 200bhp.
The dry sump can reduce parasitic losses so may gain 1 or 2 % bhp. Its expensive though

whats involed in this then? shorter rods and new crank maybe, but what about the case? have you got to get it widend for the bigger crank?

Do you know anyone that can do all thats involved??

10th October 2009, 22:18

Yup shorter rods and bigger o/a crank so the pistons reach the top of the crankcase. Pugsport/cituning Do kits iirc.

Big ££££ for 200bhp t/b'd route matey.

10th October 2009, 22:42

ive heard its fairly expensive and a supercharger could be a better way to go. not so keen to turbo it as s/chargers have more usable power and most people do the turbo route. Could be wrong though- you tell me....

its a bit of a project car so this is going to be a long drawn out process over a couple of years and i want to make it my own rather than just doing what everyone else has done.