Over bore???
- Thread starter S3 Paul
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A slight overbore will increase capacity slightly, so that has an obvious advantage. Not sure if 1mm would need a different head gasket or not?
I know if i were doing it, i would get as large as i could before it was cost prohibative.
I know if i were doing it, i would get as large as i could before it was cost prohibative.
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Well cost of pistons is almost the same,
I want the car to be if you understand me like standard only better, By that i mean no running problems like over heating. need of extra oil cooler radiator...
Some say the advantage of the extra 100ish cc would be less than that gained by say 1psi boost increase. yes i understand more power off boost will be a goodthing and that advantage will be across the rev range.
But the difrence in costs of going from stock bore and pistons with uprated rods and a over bore with new pistons will be about 500
I want the car to be if you understand me like standard only better, By that i mean no running problems like over heating. need of extra oil cooler radiator...
Some say the advantage of the extra 100ish cc would be less than that gained by say 1psi boost increase. yes i understand more power off boost will be a goodthing and that advantage will be across the rev range.
But the difrence in costs of going from stock bore and pistons with uprated rods and a over bore with new pistons will be about 500
Ah so you are not looking to bore anyway. I assumed you were overboring anyway so the cost difference would have been negligable
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Ye. well most say dont do it on here,
Most tuners say... do it. bigger is best,
maybe the members on here see the cost and the tuners see the power.
I just dont want to build something i will regret as i cant afford to do it twice to be honest.
Most tuners say... do it. bigger is best,
maybe the members on here see the cost and the tuners see the power.
I just dont want to build something i will regret as i cant afford to do it twice to be honest.
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Ye. well most say dont do it on here,
Most tuners say... do it. bigger is best,
maybe the members on here see the cost and the tuners see the power.
I just dont want to build something i will regret as i cant afford to do it twice to be honest.
Most tuners say... do it. bigger is best,
maybe the members on here see the cost and the tuners see the power.
I just dont want to build something i will regret as i cant afford to do it twice to be honest.
If you original bores and pistons are servicable , then i would re ring the the OE pistons with some decent rods, then you are set for a safe 450 ish BHP/Torqe.
Increasing the diameters of the cylinders has it plus and negative points. If your increasing the size you will have a larger volume and if you do not have increased air flow through them you will actually lose torque at the lower engine over the rev range. The Volumetric efficiency of the cylinders will drop unless you are able to utilise the increase in volume within the cylinders. I done a project a little while ago on increasing bore size and gas flowed heads, if done right you can see and increases of about 10 - 15 bhp and 10 - 20 lbs. I do have power and torque graphs at each increase in diameter.
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So with the set up i have ( hybrid turbo, 3inch down pipe and decat...) would some mapping make it worth the over bore or would i need to be looking at a gas flowed head and the like?
Im not looking to fit a cnc head just yet if at all as it will add another 1500 to the build which i cant justify for the power im after.
Im not looking to fit a cnc head just yet if at all as it will add another 1500 to the build which i cant justify for the power im after.
Turbo cars or any car loves air, more you can increase the volumetric efficency of the engine the more potential power it will have ( the ability to draw air into the cylinders ). Most modern engine use about 90 % of the volume within the cylinder, so if you think your increasing the volume you are going to be decreasing that value even further.
However if your hybrid turbo spools up earlier in the rev range then you shouldn't see any decrease and should see and increase in low down power/torque with a custom map to alter the fuel ratio for the added air that will be in the cylinders.
I done my project on a naturally aspirated car and in the lower rpm it was slight down on torque but once in the high rev range the power was increasing consistantly to the maximum rpm and had a peak power of about 18bhp and 15lbs over the standard engine
However if your hybrid turbo spools up earlier in the rev range then you shouldn't see any decrease and should see and increase in low down power/torque with a custom map to alter the fuel ratio for the added air that will be in the cylinders.
I done my project on a naturally aspirated car and in the lower rpm it was slight down on torque but once in the high rev range the power was increasing consistantly to the maximum rpm and had a peak power of about 18bhp and 15lbs over the standard engine
NA vs FI is a world apart. volumetric efficiency can be dramatically changed by altering teh ratio of stroke to bore (under square vs oversquare), whilst this is still important to the character of the engine dynamics with a turbo engine you are not relying on those characters to fill the bore with air by creating a vacuum and "drawing air"....you have ****** great turbo pushing it in sometimes at pressures higher than your tyres!
If you bore a turbo block and lose torque you have done it wrong. you can actually lose overall available torque across the curve by big porting everything (inlet, TB, valves, exhaust ports). you have a big port head anyway (BAM/AEB S3 heads) , leave it alone unless you are really looking for a massive top end and are fitting a much larger Inlet manifold. It does just fine with stock cams and stock ports and bang for buck is an expensive option. get your valves done as you won't want the heads dropping off at higher revs and temp.
your stock block is bored at 81mm.
It can take 83.5 but you are sailing very close to the edge.
83mm is a good compromise. It also gives you the option of using readily available 2l gasket kits.
Coupled with a longer 92.8mm crank and you can have a nice 2008cc block, otherwise a stealthy 1.9l. (a lot less hassle than the stroker as well!)
personally I think the 1.8t engine benefits from it as it lacks driveable torque at low revs. but it depedns entirely on your driving style. It you are rev limit bouncer then you probably won't see any difference as the top end figures are more limited by the port sizes and flow restrictions in your turbo, exhaust and head/inlet as someone else mentioned.
If you like to tootle around town with your kids in the back and get sick of dropping into first gear when you go round very slow corners then you should see a useful (but not mindblowing) increase in torque.
your stock pistons are bulletproof. re-ring and hone will see you a long way.
If you want to change the dynamics of the way your engine delivers power an give you potential for spooling much larger turbos more effectively in the future then bore it
If you bore a turbo block and lose torque you have done it wrong. you can actually lose overall available torque across the curve by big porting everything (inlet, TB, valves, exhaust ports). you have a big port head anyway (BAM/AEB S3 heads) , leave it alone unless you are really looking for a massive top end and are fitting a much larger Inlet manifold. It does just fine with stock cams and stock ports and bang for buck is an expensive option. get your valves done as you won't want the heads dropping off at higher revs and temp.
your stock block is bored at 81mm.
It can take 83.5 but you are sailing very close to the edge.
83mm is a good compromise. It also gives you the option of using readily available 2l gasket kits.
Coupled with a longer 92.8mm crank and you can have a nice 2008cc block, otherwise a stealthy 1.9l. (a lot less hassle than the stroker as well!)
personally I think the 1.8t engine benefits from it as it lacks driveable torque at low revs. but it depedns entirely on your driving style. It you are rev limit bouncer then you probably won't see any difference as the top end figures are more limited by the port sizes and flow restrictions in your turbo, exhaust and head/inlet as someone else mentioned.
If you like to tootle around town with your kids in the back and get sick of dropping into first gear when you go round very slow corners then you should see a useful (but not mindblowing) increase in torque.
your stock pistons are bulletproof. re-ring and hone will see you a long way.
If you want to change the dynamics of the way your engine delivers power an give you potential for spooling much larger turbos more effectively in the future then bore it
S3 head is already big port. useful having a spare to do your work to and then swapping them over. less down time!
I am still 99% sure that is not the case. If you look at the inlet mani gasket for the AGU/AEB, its a different part numbe than for the AUM/AUQ/AMK/BAM... the rest of the 1.8T range (150/180/210/225) share the same gasket, and i know for a fact the AUM is small port.
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I have been told the S3 BAM head i have is small port. as there is only one engine code that has the large port head shockingly though it isnt the BAM,
Before this car i had a mk3 golf vr6 with a super charger on and i loved the lasy power . low down grunt,
I like to potter round alot of the time but then at other times i like to power out of corners and enjoy making the haldex work.
So if im after a slight increase in the power ( lowdown and elsewhere if i can) money aside, would people over bore? I would like the lump when done to be able to take 400+ maybe 450 but thats it. no more, i may change the turbo and head IF i dont sack the lot off after its done and go for an S4
Before this car i had a mk3 golf vr6 with a super charger on and i loved the lasy power . low down grunt,
I like to potter round alot of the time but then at other times i like to power out of corners and enjoy making the haldex work.
So if im after a slight increase in the power ( lowdown and elsewhere if i can) money aside, would people over bore? I would like the lump when done to be able to take 400+ maybe 450 but thats it. no more, i may change the turbo and head IF i dont sack the lot off after its done and go for an S4
Look at it this way...How long will you keep the car? If a short time, dont waste your time or money...save it for a new car. if you plan to keep it for ages then go for it. a 2.0T would be a better base expecially with a built head and bottom end..Chuck a 2871R on that, or a GT30 and you will be flying.
I stand corrected, you are right about the BAM head.
either way I wouldn't worry about its ability to flow
bore it, you will at least get a clean block to start from. 2.0l stroker is the way forward if you can be bothered and have a spare block.
codes and info for those with too much time on their hands (courtesy of Michael Ghia - clubgti)
either way I wouldn't worry about its ability to flow
bore it, you will at least get a clean block to start from. 2.0l stroker is the way forward if you can be bothered and have a spare block.
codes and info for those with too much time on their hands (courtesy of Michael Ghia - clubgti)
