Unreliable in boring engine?

[mattgo]

Just to start off, I don't know that much about cars.

But I was talking to my father yesterday and we were talking to each other how we could make the supra I just bought faster, I told him if boring the cyliner .4mm over and getting forged pistons and stronger rods. He said that it would be a bad idea because if you overbore an engine you take its quality away and lessen the engine dependability, making it an unreliable car to drive. Is that true?
I don't know if it's the same thing as a motorcycle but I always thought boring the cyliner and getting oversize pistons would create more power and make the engine stronger. I could be wrong so that's why I'm asking you guys.

I've tried searching about it but didn't find anything usefull to answer my question.

 

[gsxrwut]

well if you take it too far out you will end up sleeving it.. which inturn is stronger.. but u know once you move any thing over stock the actual reliablity and dependablity of milage kinda goes down.. lets say u do boar it over and change the connecting rods.. hg and pistons.. your probably wanting more power.. so your going to boost higher.. it will last with high hp numbers.. it really just depends how anal you are about working with your cars.. if you dont want to mess with it that much * i mean maintain it * then stay with the low hp numbers closer to stock and it will prolly work out better for you.. if you want to daily drive it and boot the shit out of it .. dont expect 100k miles out of it .. /.. just my 2cents

 

[johnathan1]

Ummm...I don't know of anyone who has sleeved a 7M, and I don't know why one would want to either. Most people bore out the 7M to straighten things out, not necessarily to make more power...and I don't see how boring out the cylinder a little bit would make the car "unreliable"...

When making power with an NA (non-turbo) engine, you make everything bigger, like boring out the cylinders for higher displacement...But with a turbo car, you don't go the same route to make power, in other words, you don't really need to make everything bigger, just up the boost, free up the intake and exhaust, and manage the AFR's.

So basically, you should spend money in other areas, because boring out the cylinders won't give you much of gain with the car in stock form...if I were you, I would just do all the basic performance upgrades (BPU's) like intake, exhaust, MBC (manual boost controller), and after that, you can either go standalone, or get a piggyback computer like the Apex'i SAFC-II (fuel management) which is best when coupled with the Lexus AFM, and 550cc Injectors... Ugh, I am rambling, just do some searching, and you will easily find ways to make more power with the 7M.

 

[levi1717]

if you are looking for hp and not too worried about reliablility then boring wouldn't be a bad idea would it? once you've got boost and fuel boring will still give you good horsepower won't it?

 

[cnewingham]

As long as everything is done correctly (build, fuel mgmt, tune) then you will be o.k. My block is .080 over which equates from 83mm stock to 85mm. Here is a pic just to show that it doesnt like my bores are that big but they are and there have been no issues with this block related to the over boring. You also have to remember it costs a nice chunk of change to get forged pistons made at that size.

 

[gsxrwut]

i only tossed sleved out there because i know on other makes of engines if you bore it out too far the cylinder walls become too thin and you need to sleve it to strenghten it back up.. i dono where the water jackets are in the 7m but it was just a thought..

 

[mattgo]

hmmm...interesting

 

[lowbudgettarga]

As long as everything is done correctly (build, fuel mgmt, tune) then you will be o.k. My block is .080 over which equates from 83mm stock to 85mm. Here is a pic just to show that it doesnt like my bores are that big but they are and there have been no issues with this block related to the over boring. You also have to remember it costs a nice chunk of change to get forged pistons made at that size.

Holy cow, I didn't know you could go that big on a 7m. did you achieve that first try? or did you go through a block or two before that with thin cylinder walls?

 

[cnewingham]

That is by far the max you can go. There have been a few that have built the 7m like this and the car Ibought happened to have this treasure tucked under the hood. It had HKS cams, ported head, HKS sport turbo kit, and a bunch of other goodies along with ROD KNOCK (previous owners stupidity)