My high compression + boost concept

[MWP]

Agreed, its what im building my engine for.
5S-GTE with ~11:1 CR, smallish turbo, E85 and water-injection.

[Duk]

Agreed, its what im building my engine for.
5S-GTE with ~11:1 CR, smallish turbo, E85 and water-injection.

Sounds like a potential torque monster !
My next turbo engine will be a 7AFTE (NOT a 7AGTE) engine.
I'm looking to follow a similar method to the European car manufacturers (Audi, Volvo, Saab) of the last 10 or 15 years or so.
Keep pre-turbine housing exhaust sizes as small (no bigger than exhaust port size, but without using areas that allow large expansion of the gasses, and so slowing of the exhaust gas. So no excess increases in volume like at the collector, only to then speed the exhaust gas back up as it goes into the turbine housing's nozzle) and as consistent as possible to keep exhaust gas velocity, as well as out right flow, as high as possible!
Looking at European cars like Audi, Volvo and Saab of the last 10 to 15 years or so, they have churned out cars with their peek torque numbers in the low 2000rpm range, but then still go onto achieve 100hp/litre. This is while meeting emissions requirements and having plenty of safety built into the car (to help allow for dimwhits and sh!te batches of fuel).
With fewer noise and emissions requirements, plus the added tuning advantage of water injection, getting a really solid and broad torque curve from a small capacity, highish compression ratio turbo engine should be quite straight forward.

[Indelible]

"Looking at European cars like Audi, Volvo and Saab of the last 10 to 15 years or so, they have churned out cars with their peek torque numbers in the low 2000rpm range, but then still go onto achieve 100hp/litre."

you do realise toyota do it too just look at the vvti 1jz

"The adoption of VVT-i and the improved cylinder cooling allowed the compression ratio to be increased from 8.5:1 to 9.0:1. Even though the official power figures remained at 280 metric horsepower (210 kW) at 6200 rpm, torque was increased by 20Nm to 379 newton metres (280 lbf·ft) at 2400 rpm. These improvements resulted in increased engine efficiency that reduced fuel consumption by 10%. The adoption of a much higher efficiency single turbocharger than the twins as well as different manifold and exhaust ports were responsible for most of the 50% torque increase at low engine speeds . "

[Duk]

you do realise toyota do it too just look at the vvti 1jz

"The adoption of VVT-i and the improved cylinder cooling allowed the compression ratio to be increased from 8.5:1 to 9.0:1. Even though the official power figures remained at 280 metric horsepower (210 kW) at 6200 rpm, torque was increased by 20Nm to 379 newton metres (280 lbf·ft) at 2400 rpm. These improvements resulted in increased engine efficiency that reduced fuel consumption by 10%. The adoption of a much higher efficiency single turbocharger than the twins as well as different manifold and exhaust ports were responsible for most of the 50% torque increase at low engine speeds . "

Just trying to keep this factual (rather than some sort of pissing contest). Audi made 380Nm of torque at 2100 from their 2.2 litre 5 cylinder S4 way back in 1995, without any variable valve timing. Admittedly the peak power was 'only' 169KW @ 5900rpm. http://autospeed.com/cms/title_Audi-...3/article.html

The point is, back yard mechanics can apply newer styles of turbo philosophy and achieve similar results. But adding variable valve timing to an engine not originally equipped with it is pretty much unrealistic.

[Indelible]

hahahahahahaahahahaha whats not factual about my post

if thats what you think i was implying that vvti did that
the last sentence was the relevant part , just did the whole paragraph so it made more sense

"The adoption of a much higher efficiency single turbocharger than the twins as well as different manifold and exhaust ports were responsible for most of the 50% torque increase at low engine speeds "



1JZ-GTE single turbo VVTi 280 hp @ 6200 rpm
378 Nm @ 2400 rpm

1JZ-GTE twin turbo 280 hp @ 6200 rpm
362 Nm @ 4800 rpm

2JZ-GTE twin turbo 320 hp @ 5800 rpm
427 Nm @ 3600 rpm

2JZ-GTE VVTi twin turbo 280 hp @ 5600 rpm (limited)
454 Nm @ 3600 rpm


vvti isnt the main reason as to why the peak torque rpm decrease it was the turbo selection and exhaust velocity

they went from a twin turbo model to a better matched single turbo which bout the peak torque down from 4800 to 2400 rpm

notice how the 2jz kept its twin turbo setup and added vvti but peak torque rpm didnt change

and this was way back in 1996 , with only 8psi boost
not starting somethin just sayin

[Duk]

hahahahahahaahahahaha whats not factual about my post

if thats what you think i was implying that vvti did that

1JZ-GTE single turbo VVTi 280 hp @ 6200 rpm
378 Nm @ 2400 rpm

1JZ-GTE twin turbo 280 hp @ 6200 rpm
362 Nm @ 4800 rpm

2JZ-GTE twin turbo 320 hp @ 5800 rpm
427 Nm @ 3600 rpm

2JZ-GTE VVTi twin turbo 280 hp @ 5600 rpm (limited)
454 Nm @ 3600 rpm


vvti isnt the main reason as to why the peak torque rpm decrease it was the turbo selection and exhaust velocity

they went from a twin turbo model to a better matched single turbo which bout the peak torque down from 4800 to 2400 rpm

notice how the 2jz kept its twin turbo setup and added vvti but peak torque rpm didnt change

and this was way back in 1996 , with only 8psi boost
not starting somethin just sayin

I wasn't saying that you weren't being factual.
I started my previous thread a tad badly. It should have started with something like: "Adding another example of factory performance, Audi..............."

I think we are both agreeing on the importance of well designed and well specified turbo installations. I used European cars for my example because I'd seen a few of their turbine housings and exhaust manifolds and noticed how small they kept their ports and collector area VS what I had seen in Japanese cars that were a few years older.
I use to have an RB20det powered Silvia and the RB20's use exhaust ports that are WAY to huge for the capacity of each cylinder (if it used the same cylinder volume to exhaust post cross sectional area as a 4AGE head, the 2 litre 6 would have had 25mm diameter exhaust ports, but they were more like 35mm. Nearly twice the cross sectional area and so, much lower exhaust gas speeds) plus they used big T3 sized collector and then turbine housing. Turbo performance could have been hugely improved by shrinking the exhaust ports and using much small runners with a tiny collector before the turbine housings nozzle.
Even with just a Garrett GT28r (.64 A/R turbine housing), it's around town performance sucked.

[NME308]

Hi there guys,
Since my brother and I have already put some data together on another forum with similar boost/compression topic I'll borrow it...

Data shows somewhat convincingly that Compression and Boost follow a couple of basic principles:

A) For every point of compression you raise an engine you gain 3.2% power potential.
B) For every 1psi of boost you feed an engine you gain 3.5% power potential.
I use the words 'power potential' as these gains rely on tuning ability to take them from theoretical to practical!

To illustrate, consider the following example:
For a given engine combination in which nothing but compression is changed physically and of course basic fuel and ignition tuning.
12:1 compression being boosted 20psi gives 28:1 effective compression.
7:1 compression being boosted 45psi gives 28:1 effective compression.
Now just for arguments sake lets say for the 'control' fuel being used 28:1 effective compression is the highest level safely achievable in these motors before detonation creeps in.

As the 7:1 compression motor is 5 compression points less, it is already down 16% power potential on the 12:1 compression motor.
Since the 7:1 compression motor needs 25psi more than the 12:1 compression motor to see the same effective compression it is up 87% in power potential.
Taking the 16% compression loss away from the 7:1 motor leaves it with 71% greater power potential at the exact same 28:1 effective compression. In essence it takes 5psi more boost at any given point to make the same power with 7:1 compression than with 12:1 compression and each psi more boost from there is pure profit!

Note: Assuming the power adder of choice is turbocharging, the above example allows for tailoring the choice of turbo/s and configurations of such to maximise the potential of each engine combination.

For a more technical explanation of the above condensed information go to:
http://www.modularfords.com/forums/f...ressure-51059/
To add to the practical examples listed here check out the difference in output of this boosted engine at differing compression and boost levels:
http://www.k20a.org/upload/HondaRA168EEngine.pdf

Choosing compression ratio based on proposed boost figure does not work for me... I achieve my initial power goal, get bored and go looking for more...

Cheers from a couple of fellow old school thinkers,
Glen & Jason

That was in a discussion about high end alcohol race motors so if the difference between 12:1 and 7:1 seems too far removed for a daily driver (bahaha what am I saying my daily driver is 7:1 comp ) try a figure such as 11:1 and 8psi boost. Using the maths already established if we drop the compression to 8:1 you gain 20% power and torque by raising the boost to 16psi and the engine still has the exact same internal cylinder pressure! No need for exotic and or heavy engine internals to use high boost. Now back to the usual question of off boost torque and engine response which common myth suggests a low compression engine suffers a lack of- the difference between 11:1 and 8:1 in power and torque off boost is 9.6% (once again this MUST be properly tuned or the myth continues...). If we are talking a 4AGE Blacktop with factory 162hp as the starting point then I'd take the barely noticeable 9.6% loss off boost for the 300hp on offer with 8:1 vs 250hp with 11:1 personally.

Keep in mind that anything which can be done to prevent detonation and allow more boost in a high compression motor can also be done to a lower compression motor to allow even more of that lovely boost to be shoved in for even more tire shredding fun!

Cheers,
Jason

[Sam_Q]

I forgot that I posted this thread on this forum. I ended up finding out what would happen if someone tried my concept.

Acl performace sell pistons intended for a 20V engine at are about 10:1, not officially though- the stated figures are 8.5:1 but their wrong. Someone I know tried these with two different turbos and said it had awesome response and top end.

[Supra967]

^^ this. You've only got to look at the turbo F1 specs of the late 80's to see the massive power potential. Just got to control what you have in there. Nothing wrong with a high comp daily to save a bit of juice.

[NME308]

^^ this. You've only got to look at the turbo F1 specs of the late 80's to see the massive power potential. Just got to control what you have in there. Nothing wrong with a high comp daily to save a bit of juice.

Hi there mate,
I posted a link to the F1 specs of the late 80's. Not just any specs but those from Honda the most dominant engine supplier!
The compression ratio they used when allowed unlimited (read 70psi+) was 6.5 to 7:1 comp. Once the governing body had clamped the boost permitted back down to 2.5bar they raised the compression up to 9:1.

There is a rather unknown relationship to ignition timing and average engine power. These guys were still running 30 degrees of ignition timing to ensure complete burn in the cylinder which maximises torque and power. Running high compression on crappy pump fuel and pulling the timing real low to prevent detonation is at very best a poor compromise which is loosing HEAPS of power and torque over what should be available from a turbocharged engine!

Sam_Q pointing to mates who have done the high comp turbo thing and say it had awesome top end and response is rather misleading... Something objective like a dyno graph or drag strip ET and MPH figures would help people decide if such a route is really for them. Any turbocharged combo FEELS awesome to the pimp with his bum on the drivers seat...

Cheers,
Jason

[Sam_Q]

your right Jason, I will see if I can get something less subjective

[Duk]

^^ this. You've only got to look at the turbo F1 specs of the late 80's to see the massive power potential. Just got to control what you have in there. Nothing wrong with a high comp daily to save a bit of juice.

You also have to remember that the jungle juice they used as fuel was mainly made up from Toluene/Methyl-benzene. Apparently they had to actually heat the fuel in order to get it to burn properly (maybe even burn at all at low loads ).

When chasing outright performance, dropping the compression ratio so you can run more boost with ignition timing that is advanced enough to get the maximum heat energy out of the air fuel mixture without detonation is preferred, rather than having to use less advanced ignition timing than what the engine may want, so detonation is under control. That is, if ignition timing could be advanced more without detonation, the engine could make more torque.
However, how often are road cars using out and out power? Not very often. Certainly not as often as we like to think

http://www.motortecmagazine.net/article.asp?AID=2&AP=1 is a reposted article from the now dead Go Fast News website. In the article Vizard makes mention of really high compression ratios causing a really fast initial burn of the air/fuel mixture that then then fizzle out quickly as the piston starts to get towards the half way point of the stroke.
This sound quite plausible to me. A very tightly packed air and fuel 'package' requires very little time for the flame front to reach all of the combustible content within the combustion chamber. This gives huge initial pressure, but 1 where the combustible gasses are consumed very quickly. With a lower compression ratio, the flame front takes longer to move through all of the combustible gasses and so there is a more even, higher average combustion pressure over a longer period of time. There is also more combustion pressure available when the crankshaft is closer to 90* ATDC, where the most amount of torque can be developed.
Obviously we are talking about tiny fractions of a second here.

[Supra967]

NME - i've read a short bit of info on turbo F1, very impressinve, even if the engines only lasted a hand full of laps. My post was refering to yours by the way, sam got in before me

Duk - i'll have a read when i'm not running late for work. Right though, combustion chamber is where it all happens, numbers like boost or cr tend to means less once you set fire to the fuel. Mathematically and practically though, like Jason said, the gains from efficiency increases are well overshadowed by air mass increases. At the same time we aren't driving around in F1 cars

[NME308]

My post was refering to yours by the way, sam got in before me

Haha thats funny! You posted too slow and I in hindsite obviously posted too fast!

Cheers,
Jason