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The mkiv Supra Owners Club

upgrade pistons?!


L33
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since blowing my engine up and stil buying parts for a rebuild im not sure what pistons to go for.

 

im not going for a huge spec, so far ive bought some hybrids ( dont start argument on this please) some 550 cc injectors, already have full bpu except a boost controller which i will be buying shortly and proberly running about 1.3 bar of boost, and getting a emanage unit.

 

now is that spec going to be fine to run standard pistons, valves and springs or do i need to buy uprated? obviously dont want to spend the huge figures on the above if its really not needed. very unlikely i wil be upping the power much more than this any way in future. looking at uprating the head gasket to for a hks one.

 

ive yet to strip the engine to source the problem but have been suggested it could be damaged pistons so im going to buy new any way while its all apart

 

cheers Lee

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They say stock internals are good for around 550-600bhp, this was the intended output for the Supra anyway so it makes sense. Uprating the internals is basically future-proofing if you intend to use that setup. Many run that kind of setup with stock internals. Id personally recommend a good strip down, clean, re-hone, new rings, oil pump, shells etc all the usuals. At least you then have a sound engine ready to take the figures that Mr T initially intended.

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ok cheers 4 the comments! have to assess the damage and hope i wont need bigger ones to save my pennys!

 

and head gasket i think thats gone to causing part of the engine problem so i thought a hks one would be a good move to prevent again?

 

hoping to have her back near the start of next year or end of this one :)

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and head gasket i think thats gone to causing part of the engine problem so i thought a hks one would be a good move to prevent again?

 

I've yet to hear of a head gasket failure on a MkIV. At least one that wasn't caused by having no coolant and massively overheating the engine or something. The stock headgasket is a very good multi-layer metal job, the only reason to change is if you go for aftermarket pistons that are designed with a thicker headgasket in mind - for example the JUN pistons I have give the standard compression ratio with a 1.6mm headgasket, so I went for a HKS 1.6mm one. Otherwise I would have used a stock one.

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again thanks for the info and i wil just get a new stock one then!

 

as i said not to sure what the problem was, thick white smoke was coming out the exhaust, and oil had appeared to have come out the top and covered the engine bay. inital thought what a oli seal in a turbo.

 

on the day it happened my revs dropped and limited to 4 k just b4 it blew smoke.

 

5 spark plugs have been melted so no longer has the arm over the "spark" bit. 5 cylinders were low on compression, one read 0, and one went off the scale then read 300 or so. one is fine. the elctrical connectors to the coil pack have got hot and just crumbled and broke

 

wasnt a turbo that had blown from a quick inspection, so not really sure yet what it could be, rough ideas were head gasket, yet were no obvios signs, but oil has leaked from lower down on the block behind the front tensioner. failing that could have some damaged pistons? not to sure, been buying bits to prepare for the worst when i take her in, but tryin to get better bits also like bigger injectors etc.

 

this happened on a sat, yet the thursday b4 it came out the garage after haveing double decat, plished intake pipes, polished intake manifld and silicone hosing fitted. could of been dodgy work that messed every thing up? not really sure.

 

when i do take it in i wil be making the 2 hour trip to toyota gt to try and sort this mess! as no where round here has a clue and have done nothing but mess my cars up b4 and now possibly this one to yet there is nothing else close

Edited by L33 (see edit history)
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5 spark plugs have been melted so no longer has the arm over the "spark" bit. 5 cylinders were low on compression, one read 0, and one went off the scale then read 300 or so. one is fine. the elctrical connectors to the coil pack have got hot and just crumbled and broke

 

Sound like you want a new engine to me. Would probably work out cheaper than a full rebuild.

 

Sounds like your front main oil seal blew, the viscous fan would blow oil everywhere.

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If you are stripping the engine it would be madness NOT to rebore and re piston it UNLESS the bores were 100% perfect. Unlikely in a high mileage engine, or one that's seen any traumas. Wiseco, in my opinion, are the best of the cheap forged pistons, and Tomei and Cosworth (via JUN) make high end ones. Stock pistons should be adequate on a well mapped car on hybrids, but forged ones would be nice, and would allow further mods at a later date. Don't underestimate the cost of a proper basic engine rebuild!!

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Sounds more to me like the BPU work caused a lean condition and you've detonated the engine to death. A leaking FMS wouldn't cause the spark plugs to blow their tips off. The oil may have come out of the PCV or intake filter if you have an aftermarket pod one. Oil gets into the intake tract due to enormous ring blowby thanks to the detonation destroying them.

 

I also notice you say "one the day it happened my revs dropped to 4k so clearly you were giving it some beans at the time, thus reinforcing my theory that the engine detted to death.

 

If you think you are fitting stock size pistons with no rebore to a car with 5 fubar cylinders, think again. The amount of metal flying around in there is going to have scored the bores and maybe damaged the cylinder head as well.

 

What silicone hoses did you have fitted? What peak boost did you see? Can you give us a photo of the engine - overhead shot around the inlet manifold and head :)

 

-Ian

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Sounds more to me like the BPU work caused a lean condition and you've detonated the engine to death. A leaking FMS wouldn't cause the spark plugs to blow their tips off. The oil may have come out of the PCV or intake filter if you have an aftermarket pod one. Oil gets into the intake tract due to enormous ring blowby thanks to the detonation destroying them.

 

I also notice you say "one the day it happened my revs dropped to 4k so clearly you were giving it some beans at the time, thus reinforcing my theory that the engine detted to death.

 

If you think you are fitting stock size pistons with no rebore to a car with 5 fubar cylinders, think again. The amount of metal flying around in there is going to have scored the bores and maybe damaged the cylinder head as well.

 

What silicone hoses did you have fitted? What peak boost did you see? Can you give us a photo of the engine - overhead shot around the inlet manifold and head :)

 

-Ian

 

i was doing a fair rate put it that way.

 

before the smoke the boost gauge rocketed off the scale, and is only running standard boost?!

 

i have bought another engine and so call only done 39k miles but is damaged and a load of other dodgy stuff so i been trying to get my money back, yet they have been refusing so its going through court.

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I'd say you either got runaway boost because the wastegate closed suddenly for some reason (maybe a shiny silicone hose coming off the actuator) or a shiny silicone hose came off the FPR or MAP sensor and the fuelling went lean at the wrong moment. There may be a common factor :eyebrows:

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I'd say you either got runaway boost because the wastegate closed suddenly for some reason (maybe a shiny silicone hose coming off the actuator) or a shiny silicone hose came off the FPR or MAP sensor and the fuelling went lean at the wrong moment. There may be a common factor :eyebrows:

 

ive had a look and doesnt appear that any silicone hosing has come off, i was tld to check that first!

 

been mentioned about the amount of metal that could be rubbing against the pistons so i need a rebore etc, well apparently that would make a obvious noise. sounds odd but before i took the spark plugs out for a compression test the car would idle fine for about a min then the thick smoke would start out the back, yet stil idle fine?! it was thick white smoke. yet no sign of water loss r oil in intercoler pipe

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