Stock, stroker or ghetto capacity increase? ( supra 7m gte pistons bmw rods )

[A80Avant]

what are these for?

[Jamo]

If it was a road car I would go for a stroker without question. If you are going to use it for any sort of racing, circuit work or drag racing I would stick with the standard stroke. Your always going to be up in the higher revs so its should always be on boost. Therefore you would just be running higher piston speeds for no real gain as you would be out of its low down torque advantage.

exactly what I said

BTW 83mm gaskets aren't a problem, OEM canbe overbored to 83mm or 034 even though not my favourites sell 2 off the shelf gaskets that work with 83mm pistons.

[A80Avant]

034 does up to 82.5mm gasket. couldnt find the 83mm although i thought they did

[QuattroFever]

Edit: already covered. Tapatalk is hard to follow

[Audi_CQ]

If it was a road car I would go for a stroker without question. If you are going to use it for any sort of racing, circuit work or drag racing I would stick with the standard stroke. Your always going to be up in the higher revs so its should always be on boost. Therefore you would just be running higher piston speeds for no real gain as you would be out of its low down torque advantage.

At any RPM up to the strokers limit (~8000+) a stroker will be stronger then a 2.2. For a 2.2 to have more HP then a 2.5 you have to rev it past 9000-9500.......
All of the most powerful engines(1000hp +) in Norway are 2.5+ and I quess it's a reason why they use strokers

[Rusty]

Do people use skimmed 7A pistons at all? Not heard of it being done, so there must be a reason it's not commonplace...

[Error404]

they're not forged as far as I know

[x6rs]

654hp 764nm in engine on e85

7a engine, std 7a pistons, std rings(old rings)
everything standard 7a except gasket, rods and fuel....

did i mention its from sweden


so i guess using std 7a pistons isnt a problem.. 10.5 in cr, just use e85..

[Mcstiff]

they're not forged as far as I know

Correct.

[prj]

So, some more info for you guys from this car, as I did a post-dyno touchup on it, because it had bad fuel pump wiring and was tapering fuel. We relayed the pump and re-tuned the top end.

For reference, here is the URL to this car's page on my blog:

http://prj-tuning.com/?p=69

And here are some logs.
Because there is no restrictor on the boost hose there are pulsations of the intake visible on the boost graph, there is also a small oscillation when you come on boost, which only appears if you load it from really down low, don't get on my neck for it, I mapped most of it out later, and the car feels perfectly smooth now.
3rd gear:


4th gear:


We can see that we have 2 bar at 3300 in 3rd and 2 bar at 3000 in 4th.
You can also see how much timing it can safely take (there is no knock at all), due to the lowered compression ratio.

Not bad for a ghetto 500 quid engine build.

Btw in 6th on motorway, you dip the throttle and instantly have 2 bar.

[A80Avant]

i presume looking at the IAT these are logs done on the road, as on the dyno you had 45C temperature+, right?

how come with 8:1 compression you only get to around 19deg of timing? i would have thought you could go more than that!

fuel good?

also, what are the EGTs on these runs?

[prj]

This was done at airfield.
Dyno was pretty useless, only tuned the map a bit down low.
Iat was 50+ on dyno most of the time, so impossible to map anything.

Keep in mind that this is only upto 6600 rpm, at about 7200 it is running 23+ degrees.
We don't know what the actual CR is

But also, if you look at the timing, then at 3000 rpm and 2 bar it is not knocking with 12 deg. Usually most turbos that push so much boost do it at 4000 rpm with same timing.

No idea about EGT, but it is low with that amount of timing.
These are not 100% final logs. I have too many logs, so I just took two that I could definitely identify.

P.S.
This map is safe. It is a street car and the guy really likes to push it, so we are 3 degrees away from strong knock threshold in many places.

[A80Avant]

good stuff.

i was hearing knock on my 3071 @ 16deg and 2.1bar and was eliminated @14deg. comp.ratio close to 9:1, but IATs around 20C and lamda around 0.78 on hard boost

on the 3076 i always kept it around 12-13deg out of safety. we will see what it does on the dyno in 2 weeks.

EGTs scare me a bit with the smaller hotsides, but lower boost and higher timing will keep things cool..

[prj]

Anyway, discussing logs is not on topic.
I just posted these to show how well a K26/K27 #6 turbo spools up on this ghetto build.

Usually it is 2 bar at 3800 rpm in 3rd, on this car it is 3300-3400 rpm. 400-500 rpm earlier.

So a similar effect to a stroker for a fraction of the price.

[A80Avant]

very nice.

what is the estimated cc now on this car?