Thoughts on raising compression verses peak cylinder pressur

[Mignon]

turbotoaster said:

For basic maths on what to expect i dont really know if it would work this way but to go from 7.8:1 to 9.0:1 is a 16.8% change, if that carried over to the power output at the same boost, that would equate to 656bhp then maybe the extra from better head/cams and ethanol to crack 700bhp.

CR doesn't even remotely work that way. For each extra full point of CR (i.e. 8:1 up to 9:1) you get about 2-3% more thermal efficiency (extra power) with diminishing returns as CR rises. However on a turbo engine you lose more in potential boost pressure/ignition advance related power than the extra CR gives.

[227bhp]

Mignon said:

turbotoaster said:

For basic maths on what to expect i dont really know if it would work this way but to go from 7.8:1 to 9.0:1 is a 16.8% change, if that carried over to the power output at the same boost, that would equate to 656bhp then maybe the extra from better head/cams and ethanol to crack 700bhp.

CR doesn't even remotely work that way. For each extra full point of CR (i.e. 8:1 up to 9:1) you get about 2-3% more thermal efficiency (extra power) with diminishing returns as CR rises. However on a turbo engine you lose more in potential boost pressure/ignition advance related power than the extra CR gives.

That would apply if you were using the same type of (pump) fuel, he's talking about using 85% Ethanol which would be around 108 Ron.

[227bhp]

turbotoaster said:

sorry if im missing things out.

22.6 46.6 70.4 92.6 112 126.5 136.3 139.9 143

143 is at .500" then reduce by 0.050" each time.

my current cams are 274 degree with 11mm 0.433" with hydraulic followers

Since the porting was done with stock size valves but i simply put 1mm overside valves in(there wasnt much material around the valve seat area for the stock size valves so the seats were simply cut for the large valves) and not reblended to take advantage of them then 130cfm is a guesstimated figure.

My new cams that arrived today are 280/276 with 12.5mm 0.500" but are also designed for mechanical followers so valve accleration is a bit more aggressive

Inlet valves will be 2.3mm larger and exhaust 2mm larger but this time the head will be ported with these valves in place to make maximum advantage of them, the data for that head is below

23.2 46.5 70.6 94.4 114.3 130.4 140.1 145.6 150.25 153.1

I can't really comment on any of that as there is too much guesswork and you've already bought your cams.

[stevieturbo]

Mignon said:

CR doesn't even remotely work that way. For each extra full point of CR (i.e. 8:1 up to 9:1) you get about 2-3% more thermal efficiency (extra power) with diminishing returns as CR rises. However on a turbo engine you lose more in potential boost pressure/ignition advance related power than the extra CR gives.

Again..people are doing crazy things with ethanol ! It just seems to love both boost and moderate-high CR's


And whilst the current turbo may have more life left in it, the point is the more modern units are simply more efficient. They make power more easily, over a wider range of rpm etc etc and being more efficient will do so with less boost.

So really there are potential gains everywhere for something you dont even need to delve inside the engine for. It's just a bolt on part ( with perhaps a little fab )

I like Precision turbos, but the BW EFR's are very popular too.

[turbotoaster]

Max_Torque said:

I still can't see 200kg of extra mass in a car the size of an elise with a feature content as bare as an elise/exige........

If we just compare stock for stock, there is 160kg difference between a k series s1 and a toyota s2(700kg/860kg)

The american car then has a turbo k20 and chargecooler setup installed so theres additional weight there.

My car is fully stripped of excess weight and pretty much everything has been taken out or lightened which has got it down to 650kg, I have put alot of effort in getting all the weight out of it

[turbotoaster]

Mignon said:

CR doesn't even remotely work that way. For each extra full point of CR (i.e. 8:1 up to 9:1) you get about 2-3% more thermal efficiency (extra power) with diminishing returns as CR rises. However on a turbo engine you lose more in potential boost pressure/ignition advance related power than the extra CR gives.

If we take any knock scenerio out of the situation the only example i can find of someone making a large change in compression with no other changes at all(same fuel, dyno, turbo, head setup) was a honda b18 engine.

this is moving from 9.0:1 to 13.5:1


for reference he ran his gt30 turbo to 19psi at this compression without knock, just ran out of turbo

[227bhp]

turbotoaster said:

If we take any knock scenerio out of the situation the only example i can find of someone making a large change in compression with no other changes at all(same fuel, dyno, turbo, head setup) was a honda b18 engine.

this is moving from 9.0:1 to 13.5:1


for reference he ran his gt30 turbo to 19psi at this compression without knock, just ran out of turbo

What fuel is it using? It's not petrol.

[turbotoaster]

227bhp said:

What fuel is it using? It's not petrol.

e85, the same fuel im talking about using

[227bhp]

If you're going drag racing with a floppy block and too much power you need to fill the block: http://www.hardblok.com/

[turbotoaster]

227bhp said:

If you're going drag racing with a floppy block and too much power you need to fill the block: http://www.hardblok.com/

Im not interested in doing that as it means i wont be able to hot swap liners when required

[227bhp]

turbotoaster said:

227bhp said:

If you're going drag racing with a floppy block and too much power you need to fill the block: http://www.hardblok.com/

Im not interested in doing that as it means i wont be able to hot swap liners when required

It isn't difficult to make them removable or just fix them in place and bore and hone like any other block. You make it sound like you're going to re-liner it every weekend.

[turbotoaster]

227bhp said:

It isn't difficult to make them removable or just fix them in place and bore and hone like any other block. You make it sound like you're going to re-liner it every weekend.

I have a rod stroke ratio of 1.45 and im spinning it to 9000rpm, the liner thrust faces take a battering, you cant buy oversize pistons for them so boring is not an option aswell as needing to pull the engine out to do it, liners i can remove and swap by hand means the block can say in the car.

Ductile liners very rarely crack from movement, hence the name, its only going to start being an issue if they move around enough that it causes head gasket breach, if they are fixed then I loose one of the benefits of the engine when i havent had an issue from that regard yet.

So i want to keep that feature, im taking it drag racing where I will be pushing it, if something happens I would live to be able to swap things out in the pits rather than going home.

My question purely relates to cylinder peak pressure(not average over the compression cycle) and whether the increase in static compression causes a higher peak while still maintaining the same torque demand, ive seen analysis to show that might the case but wanting to hear from someone like max torque who probably would have used combustion pressure sensors in his line of work to confirm/deny

[chuntington101]

stevieturbo said:

Here's a recent one at around 65psi boost with E85..although it's probably making 13-1400hp lol

https://www.youtube.com/watch?v=9Jr4OneRjq8&

Bl00by here! That things fast. And so much a sleeper as well. Anymore details on it?

Got to agree though E85 is an astonishing fuel! Just a real shame we don’t get it over here. It’s become the staple diet for ALL fast cars in the US. In fact some are even ditching their meth addictions in favour of some good old E! Lol

[turbotoaster]

chuntington101 said:

Bl00by here! That things fast. And so much a sleeper as well. Anymore details on it?

Got to agree though E85 is an astonishing fuel! Just a real shame we don’t get it over here. It’s become the staple diet for ALL fast cars in the US. In fact some are even ditching their meth addictions in favour of some good old E! Lol

it is good stuff, im hoping for some improvements with 9.7:1 compression, 40psi of boost and e85