Performance 2T-ZE design

[Radar]

The dynamic compression changes a shit load depending on your inlet closing time!
The static compression is yes a preset, but it doesn't take into account ANYTHING else.
Dynamic compression determines your cranking pressure.
Depending on how much static compression I run & the inlet closing timing will effect how much cranking pressure I have.
There are things called general guide lines that people work towards..
There is a point for every cam where there is ideal compression and this is what I'm trying to find out through cranking pressure?
Does this make a little more sense to you now?
'Theoretical'? 'Magic'? wtf are you on about?

[NME308]

Hi there,

Sounds like you are going to build a real screamer there!

I am not a big fan of all the math etc, although it is interesting to see how all the elements of an engine can affect each other. The amount of variables not covered in your calculations should occupy the next couple of years of your spare time yet!

Swing your engine specs into this calculator: http://www.rbracing-rsr.com/comprAdvHD.htm - add some boost (make it heaps as it sounds like you are going for broke!) then refer back to your hot rod quoted article previous page. Now tell me what you are going to be running for fuel?

The piston engine is a truely remarkable mouse trap with a well noted knack for defying mathmatical principles! A good engine builder/tuner with many years of trial and error experience will be able to beat a computer hands down every time... In your quest to get the very last bit out of a 2t then you will need the very best head/port design around, and as someone mentioned earlier the yanks have been there and done that. I would be buying a head from one of the 3 main 3tc gurus (wont matter if it is for 2t or 3t) in USA and buy their intake manifold as well as they will be the key to this thing specially since you have shown your hand by buying a race cam!

A cam of 254 @ 50 in 1600cc's says you will have to drive it like you stole it to get your jollies from it - punting around the road while attempting to enjoy this creation will most likely see you on first name terms with your local magistrates court!

Cheers,
Jason

[Radar]

I've sat at home for the last year smoking and reading..
I honestly knew nothing before I started reading about how things work, that's why I've been sticking to the maths and asking lots of questions.
The cam I'm thinking will be putting me in the ball park of 4000-9000 which is chill..
I've been assuming with the wide LSA and higher static compression and boost at every RPM the idle shouldn't be too rough?
**But assuming is the mother of all fuck ups**
"As a general rule, the best available pump gas will work with an 8.0:1 dynamic compression ratio.
Erb's 8.0:1 dynamic guideline is for classic, old-school, all-iron engines"
According to that Calc:

With 10.5:1 SCR I'll have an 8.7:1 DCR! (178.2psi)
Basically I want as little boost as possible with as much compression as possible!
So this is what I'm trying to find out, how much dynamic compression (cranking pressure) I can run safely while still adding 10psi boost.
Only end up with a 14.6:1 dynamic boost CR which isn't huge when it comes to the turbo boys?
I hope this makes a little more sense what I'm trying to find out?
Really bad at explaining things so my apology's

[NME308]

The topic high compression and boost is hotly debated...
Some burn up engine bits trying it...
Some have good success and are happy with it...
There some of the modern desing combustion chambers which will tolerate far more compression (I should say pressure) than the old school stuff - and unfortunatly a 2t falls heavily within the old school! :

The long and short of it is however that the quality of fuel you run will dictate the amount of timing your engine can handle without damaging detonation occurring. Most engines with plenty of compression i.e. N/A to turbo conversions have to pull large amounts of timing out of the curve to avoid detonation. On an engine dyno this does not necessarily show up as a disadvantage, however in the real world where your engine is not under the most load it can bear (such as the purpose of a dyno) then engine acceleration is key. The more timing you can feed an engine (within certain technical limits) the more power you can make - and when not on a dyno the measure of 'power' is how fast you can accelerate the mass of your vehicle. Timing is just as important as the amount of boost pressure being fed into the engine! Brother and myself have taken our race car from 10.2 sec quarter mile to 9.6 all on the same 20lb boost just creeping up with the timing.

If you are prepared to run your engine on race fuel such as Martini ST1400 109 octane unleaded or E85 'pump' fuel if it available in your area then your 10lb boost should make for a cracker of an engine! I believe however if you want to run on regular 98 octane say that the amount of timing you could run would restrict the engine's ability to make 'power' badly.

I settled for a mild specced 3t with 7.0/1 compression feeding in 11lb boost drinking 95 E10 fuel running 35deg timing locked these days. The cam has 220 intake and 230 exhaust @50 with 110 lobe separation. It is an absolute cracker to drive with power from just off idle allowing me to accidentally bag the tyres up cracking the throttle open in the first 2 gears without clutching it or such.

If you are not prepared to shout this thing better than decent fuel I would look at starting with a couple of points lower compression so you can actually have a timing curve that runs BTDC instead of zero or ATDC!

My 4cents worth!

Cheers,
Jason

[Radar]

Cheers for the input Jason I see where your coming from for sure!
Timing and fuel type are huge players in making a high compression boosted engine work.
Why I've opted for coil pack per cylinder setup and vapor LPG injection.
The vapor have boys see some seriously good results and the injectors are reliable as compared to liquid injectors.
Plus you benefit from latent cooling (freezing) and high octane of 104+ from the LPG.

Ok lets look at it like this:
8.5:1 = DCR 7.11:1 (136psi cranking pressure) and with 12psi a final CR of 12:1 advance timing

/

10.5:1 = DCR 8.7:1 (178psi cranking pressure) and with only 6psi a final CR of 12:1 retard timing

So what is the difference between the two?
They are both reaching the same end result one just does it with more boost? and one needs more timing advance?
Will they both produce the same amount of power? Will one have higher peak HP while the other has more overall HP?

[NME308]

Cheers for the input Jason I see where your coming from for sure!
Timing and fuel type are huge players in making a high compression boosted engine work.
Why I've opted for coil pack per cylinder setup and vapor LPG injection.
The vapor have boys see some seriously good results and the injectors are reliable as compared to liquid injectors.
Plus you benefit from latent cooling (freezing) and high octane of 104+ from the LPG.

Ok lets look at it like this:
8.5:1 = DCR 7.11:1 (136psi cranking pressure) and with 12psi a final CR of 12:1 advance timing

/

10.5:1 = DCR 8.7:1 (178psi cranking pressure) and with only 6psi a final CR of 12:1 retard timing

So what is the difference between the two?
They are both reaching the same end result one just does it with more boost? and one needs more timing advance?
Will they both produce the same amount of power? Will one have higher peak HP while the other has more overall HP?

If we are running with the above scenario I would be using the lower compression and higher boost.

Why?

Because while both scenarios end up with the same dynamic compression ratio, the two methods radically different

Depending on just how far your reading has extended you probably know that boost pressure alone does not give a true indication of how much extra oxygen (power potential) an engine is receiving. For the purpose of this discussion we'll forget the technicalities...

10.5Cr with 6lb: The dynamic CR is the result of the amount of fuel and air which is effectively being compressed at the top of the chamber plus the extra 6lb being pressed in during the process.

8.5Cr with 12lb: The dynamic CR is also the result of the amount of fuel and air which is effectively being compressed at the top of the chamber plus the extra 12lb being pressed in during the process.

The 10.5Cr scenario has fewer CC's of volume available for air/fuel mix at TDC compression hence requiring fewer lb's boost pressure to achieve the dynamic CR.

The 8.5Cr scenario has many more CC's of volume available for air/fuel mix at TDC compression so it required more air/fuel to be pushed in with the higher boost pressure to achieve the same dynamic CR - More air fuel in the chamber = more power potential!

Now of course if your combustion chamber and fuel were detonation resistant enough possibly with the assistance of water methanol injection then the 10.5Cr engine WITH 12lbs boost would kick butt!!!

Cheers,
Jason

[Radar]

Thanks heaps man for the explanation,
I've just been reading about thermodynamics and how much temp raises with every shade of compression higher.
With boost your just increasing the amount air into the cylinder to create the same pressure but its at a much lower heat during final combustion i.e. less chance of knock
but the price you pay for power is poor fuel economy!
So basically it's hunting for the ideal compression to start with, so fuel economy doesn't go down the shitter and knock doesn't occur while still making power!
Boost has the bonus of the compressed air being passing through an intercooler, you can't cool air in the cylinder as easy.
There for less compression + more boost is the ideal way to go if your chasing reliable power!
10.5:1 is very doable but I'll need the need the octane to do it!
So it's better to err on the side of caution and maybe stick to maybe 9.5:1...?
It will make a little less cylinder pressure than the std 2T (DCR of 7.9:1) but now when I add 14psi to bring it up to a final compression of 15.5:1 with much less chance of knock and making more power??

[Radar]

My question is before I go and spend lots of money on a motor that may not work, should I maybe do a rough build and just run it until it dies?
My thinking is:
Machine down stock rocker towers to get 1.4 rocker ratio
Install new cam with .365 valve lift and .014 lash (both in/ex)
Install new shorter double valve springs
Shave head to bump compression up to 9.0:1
OR
Lower the compression ratio with a thicker HG to allow the valve lift?
Install a SC14 supercharger boosting at 7~12psi through a R33 stock intercooler depending on the compression ratio.
Just for fun and it'll give me a great idea of how the motor will behave..
So I'm curious to know how much valve lift can the stock pistons take before I'll crash into them?
Or even better if someone could tell me how to work how much valve lift and clearances and stuff? (other than the clay onto of the piston way)
Cheers