Dead bottom end

[Dekerf1996 27]

Ok I have established my bottom end is now dead, low compression and possible bore wash.

Now what are my options? It's going on a stage 2 charger build with cams

Standard rebuild, with slight overbored?

2.9 rebuild with forged pistons?

Is it worth using forged pistons on a standard build?

Should I lower the compression whilst I am at it?

[Sump_slammer 23]

I spoke to stealth about this yesterday. Standard pistons are fine no need for fancey pistons. Only problem is if you get a re bore you need bigger pistons. So probs just go 2.9 with standard pistons. Would be the cheepest way. Altho if your getting it bored out youll need a tourque plate which you can buy from bar tek to make sure everything stays as if the heads bolted on so they dont machine it on the piss. With 8 psi if you want to go all out arp rod and head bolts. But even then they arnt needed.

[Sump_slammer 23]

So 2.8 bored to 2.9 with standard 2.9 pistons bored with a torque plate lol had to read it though again

[vwjetta99 0]

Why would you use standered C/R??if you are doing F/I you need to lower Your C/R..go with 9.5 C/R..

[Sump_slammer 23]

Theres no point if its only 8 psi. Ive spoke to stealth racing and ns tuning and they said theres no need. Plus with a supercharger if its vortech you cant run a v1 or v2 over 8psi because its on its limit. If you go turbo on the other hand yea go for lower compression ratios because you'll end up winding the boost up past 10psi then it'll start to strain the bottom end and can risk detonation. When they map it with standard internals they will just go a little more easy on the timing and fuel. But the amount you'll gain for a set of £800 pistons is hardly worth it at low boost.

[Dekerf1996 27]

Ah didn't know you could use standard 2.9 pistons in it.

Thanks for the info about the torque plate never heard of it before.

Was wondering about fancy pistons, but no point with a sc setup, so would really mean going turbo on her, which is a bit much for a daily car.

Think I will try and keep her fairly standard, might get away with a hone and new piston rings, if not it looks like finding some decent 2.9 pistons and an overbore.

Do you know how much I have to get it bored to?

[daveyboy 897]

I've got a 2.8 lump that I'm gonna put up for sale. The head is off it but it will come with the bottom end. I took the head off because the gasket went. The head has been skimmed and is ready to go back on. The engine was strong before I pulled it out. The reason I pulled out is I got a 2.9 engine cheap and put that in instead. Let me know if your interested

[Sump_slammer 23]

I new I saw the specs on here somwhere. This was a quote from united motorsports.

Factory 2.8 is 81mm bore - 2792cc

Factory 2.9 is 82mm bore - 2861cc

83mm bore will give 2931cc (2.9)

84mm bore will give 3002cc

The bore size alone on these engines makes ~no difference to output on these engines.

[vwjetta99 0]

Theres no point if its only 8 psi. Ive spoke to stealth racing and ns tuning and they said theres no need. Plus with a supercharger if its vortech you cant run a v1 or v2 over 8psi because its on its limit. If you go turbo on the other hand yea go for lower compression ratios because you'll end up winding the boost up past 10psi then it'll start to strain the bottom end and can risk detonation. When they map it with standard internals they will just go a little more easy on the timing and fuel. But the amount you'll gain for a set of £800 pistons is hardly worth it at low boost.

 

that makes no sense.i run a V1 with a 12 psi pully,I blew my headgasket pushing 8psi..when I built the motor I did lower C/R pistions.if he is going to rebuild it for F/I then why not lower the c/r??

[Sump_slammer 23]

12 psi on a v1? I was told on a charger like a v2 not to go past 8psi by the people who supply the kits and who tune them. They also said no neeed to lower the compression. Im just going off what the people who tune these every day tell me as im building a bottom end atm myself. So how has your v1 held up at 12psi? I was told 8 was there limit. Did you have to get a uprated core fitted to the supercharger so you can go up on the boost? I saw a chap at london volksfest who had a vf9 vortech and said it was on 17psi?? But with a 5 psi drop through the intercooler.

[Sump_slammer 23]

Also if you blew you head gasket at 8psi with standard compression I imagine it was on its way out, because ns tunning told me in the 15 years they have been fitting the vortech chargers they have never fitted a spacer plate. Stealth say theres no need to on low boost apps. Im just voicing what the pro's have told me. If he wants to go low comp he can do it, im just saying how to build a engine without it spiraling out of control cost wise. We would all like a low comp bottom end with h beam rods all studded out but it adds up. Im just saying a cost efficient way thats been proven to work. Do what ya want.

[vwjetta99 0]

http://www.c2motorsports.net/

 

this is the company who sells all the upgrades for the superchargers.

all im saying is if he is going to rebuild his motor,and he planes on going f/I ,then why not do it right??if he is buying new pistons anyway,then get ones for f/I....I don't like having to tear my motor back apart because something failed(headgasket)..

[chrisvr6t 19]

Lower the c/r for piece of mind and just to make it that bit safer, and go for a rotrex charger

Sent from my iPhone using Tapatalk

[Dekerf1996 27]

Thanks for all the comments and discussion

So 2.8 bored to 2.9 with standard 2.9 pistons bored with a torque plate lol had to read it though again

 

So I can get some used 2.9 pistons and make an odb2 2.9 what's the gains?

 

I've got a 2.8 lump that I'm gonna put up for sale. The head is off it but it will come with the bottom end. I took the head off because the gasket went. The head has been skimmed and is ready to go back on. The engine was strong before I pulled it out. The reason I pulled out is I got a 2.9 engine cheap and put that in instead. Let me know if your interested

Thanks will bear that in mind, will speak to the machine shop once I get the engine apart (hopefully next week)

I doubt I will be going with low comp pistons as they will add so much to the build, because then I will go turbo and this car is just my daily, if it was anything else it would be different, but I have a mk2 polo that I am building for my bit of fast road fun :-)

[Sump_slammer 23]

The gains are you dont have a worn out block. If the rings are gone chances are you need a overbore.

I was telling you a cheep real world way of doing it without ending up spending £3000 rebuilding a bottom.

May aswell use low comp piston and build it over the top. At least it wont break.

[Dekerf1996 27]

Sorry I was wondering if there were any proven numbers on the 2.9 conversion, that's all, as all I had heard was 2.9 odb2 corrado's go really well but never heard about the exact gains. It sounded by your knowledge you might know.

As for rebuilding my bottom end, looks like if my block is damaged I will go down the 2.9 route

[Lukey. 381]

I should think you would gain the same difference between a 2.8 and 2.9, about 15bhp