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9:5 and bout 200psi is what I'm finding with the 10:5 ratio. Will the dynamic really change a whole lot with duration changes on the cam?
 

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How does it have more air and fuel?

The high static/longer duration engine held the intake valve open longer.... Hows that work?


Btw... The high dynamic high boost engine wins.

And if you guys wanna start talkinsome bullshit about 6:1and 7:1 motors again please dont... Ill get a headache.


Dynamic compression being equal, the low static compression engine wins.

Isn't that the goal of a boosted engine? We can achieve high dynamic compression ratios without boost. But a boosted engine can swollow a larger volume of charge causing more expanded volume and more HP.
 

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How does it have more air and fuel?

The high static/longer duration engine held the intake valve open longer.... Hows that work?


Btw... The high dynamic high boost engine wins.

And if you guys wanna start talkinsome bullshit about 6:1and 7:1 motors again please dont... Ill get a headache.
Correct, first prize to you sir! The high dynamic high boost engine wins! But just to make sure we aren’t confusing some readers it must be noted that the high dynamic high boost engine is neither of the two options presented in my example earlier. The high dynamic high boost engine will always win provided the following criteria can be met:
· Fuel octane is high enough to prevent detonation
· The engine can handle the elevated combustion pressure
· The competition’s lower compression engine must not be allowed to exceed the maximum boost that the high dynamic high boost engine can handle
The high dynamic engine will be a high dynamic low boost engine on pump gas. It is my OPINION that the high dynamic high boost engine should only be entertained by class racers who have run out of options for increasing power via other means such as volumetric efficiency and, my personal favourite, increasing boost to name a couple.

My explanation of low dynamic compression in a high static compression engine - (Working backwards using our compressed volume of 50cc we find that 8*50cc=400cc. We have now effectively reduced the starting volume of the cylinder, that’s how.) appears to form the basis of your question to Regal Rocket. You have not provided a reasoned rebuttal for my explanation of dynamic compression to support your view that holding the intake valve open longer while the piston attempts to compress the charge will actually allow more air and fuel to enter the cylinder.
As for the headache such discussion could cause, should it be entered into – one explanation is that the pain felt is due to the brain forging new neural pathways as one learns to think in a completely new way.
 

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Dynamic compression being equal, the low static compression engine wins.

Isn't that the goal of a boosted engine? We can achieve high dynamic compression ratios without boost. But a boosted engine can swollow a larger volume of charge causing more expanded volume and more HP.
Top Fuel comes to mind as an example.

The lowest compression, most powerful, double boosted engines on this planet.

I'm too am a believer in the low comp more boost theory.

My current turboed E85 build will have a predicted 8.5 to 1 comp.

I expect it to be lame out of boost but wont be scared to open the bottle if it's not spoolin' at a transbraked 4000 plus rpm...:-D
 

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I'm having a very similar debate with a fellow turbo Focus owner. We're doing 2 different builds: his 2.0L is 9.0:1 static with stock cams (202/189 dur. @ .050", .354"/.317" lift, 112 +0 LSA) and my 2.0L is 10:1 static with Crane 224-0014 cams (236/226 dur. @ .050", .435"/.410" lift, 112 +4 LSA). I figured our discussion will actually fit well with the example given in this thread of the 2.0L. He has a stock head (~240 CFM @ .400" lift) and I have a ported head (~280 CFM @ .400" lift). Other than that, we have the same setup down to the same size turbine housing a/r on the same GTX2867R turbo. We're both looking to run about 20psi which will be about the edge of what that turbo can push within it's efficiency map.

With his intake valves closing at 33* ABDC @ .050" lift and mine closing at 46* ABDC @ .050" lift, our dynamic compression is within about .2 of each other dispite having a full point of static compression difference. His way is the more traditional way of doing it where as mine is a little outside the box. We've been going back and forth about who will make more power, who will be faster at the track, and which setup will spool the turbo quicker.
 

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Dynamic compression being equal, the low static compression engine wins.

Isn't that the goal of a boosted engine? We can achieve high dynamic compression ratios without boost. But a boosted engine can swollow a larger volume of charge causing more expanded volume and more HP.
The only way your scenario works out is if theres an octane limit.

Boost limited higher dcr engine wins.... Unlimited octane high dcr wins.

If the two engines in your scenario also have the same boost and octane.... Higher dcr engine wins.

Only way the lower dcr engine outpowers a higher one is if it can run a higher boost amount for a given octane. Even then its not a guarantee.

8:1 turbo engines are a thing of the past.
 

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Top Fuel comes to mind as an example.

The lowest compression, most powerful, double boosted engines on this planet.

I'm too am a believer in the low comp more boost theory.

My current turboed E85 build will have a predicted 8.5 to 1 comp.

I expect it to be lame out of boost but wont be scared to open the bottle if it's not spoolin' at a transbraked 4000 plus rpm...:-D
Because you're talking about an example where the fuel itself being used creates power and cylinder pressure compared to say, gasoline. And their objective is to be able to cram as much of said fuel into the cylinder without hydrolocking the engine, or pushing the heads off the block.

Your sole comparison is one out in left field, similar to if we started talking about diesel engines with 19:1 static and 70 psi of boost. They're non comparable due to the fuel being used.
 

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Even the best fuels are octane limited.
Methanol and C16 too have their limits when combining dcr and scr.
If boost levels in drag racing are ever going to see the hundreds of psi that say tractor pullers are making then it will only be possible with pulling timing or lowering scr.
8:1 and lower turbo engines are a thing of the future...:-D
 

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My dynamic is 9.2 my static is 9.1 ,my cubes is 427 , t4 turbos 1.05 a/r 77mm turbine , e85 , 335 cfm @.650 lft, 13 degrees timing ,1.42 60ft (3100 rpm 3.5-4 lbs boost) , 3.72 330ft ,5.57 @131 on 9.5 lbs of boost w/a 26 x 8.5 tire.. any pro and cons with my set up ?
 

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Dynamic higher than your static????
 

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Oh really?
The only way you build an 8:1 boosted engine these days is if you put so much fuel in the motor...any more static compression would hydrolock the motor.

Some of the baddest blown alcohol engines on the planet are 12:1 with 60+ psi of boost from a screw.

Helping a friend with his 481x and its a "low"compression version... 10.8:1

Again 8:1 compression boosted engines are a thing of the past.
 

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thats what it says on the wallace calculator ,, but that is with boost calculated into the equation
The dcr im referencing is before boost...

Youve got a long way to go on yours... Turn it up already. Hehe

And quit pussy footing around with the timing. Your car should be running 4.90's
 

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The only way you build an 8:1 boosted engine these days is if you put so much fuel in the motor...any more static compression would hydrolock the motor.

Some of the baddest blown alcohol engines on the planet are 12:1 with 60+ psi of boost from a screw.

Helping a friend with his 481x and its a "low"compression version... 10.8:1

Again 8:1 compression boosted engines are a thing of the past.
John,

I know a few screw blown PX engine builders. None of those engines are 12:1. NONE.

And I remember the discussion we had about your friend's 481X. You called me about it.

And I RESPECTFULLY disagree with your 8:1 statement. That is all.

Travis Quillen
 

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Im sure in certain Apps its still gonna be something to do.... I havent found one yet...

Vances X had 12:1 with the pistons that were in it as delivered... Guy claimed he ran a screw on it.

Barker over at AJ tried to get us to leave em in it.....

Montgomerys mod motor picked up when the dynamic got driven up with the smaller cams.

Ive had 3 LS engines pick up power by changing cams around so they ended up with higher dynamic numbers.

Didnt mean to sound like an ass if i did.... Given the threads context of street oriented applications is what i was basing my opinion on albiet maybe a touch too adamantly.
 

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What about in classes where you are limited in turbo size? Wouldn't you want to use more compression and more fuel to pull as much out of the limited setup as possible?
 

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8:1 a thing of the past???

News to me!!!

Damn come to think of it where in the hell does that even leave me?...

My daily drive is a 1976 Celica with a 7.0:1 compression 3TC 1.8L Toyota 4 cylinder pushrod donk.
No porting, factory cast 3SGE Beams pistons, standard rods, 230 and 219 @ 50 cam.
Re-used standard head bolts and an ebay no name fibre head gasket.
Blow through home built 650cfm carb.
Borg Warner S200 turbo with custom modified .5 turbine housing (home job...)
I have no intercooler although I do spray 50/50 water meth pre turbo.
It drives as it races as it dyno's on our middle of the range Australian 95 octane fuel (typically we have 91, 95, and 98 octane).
Last time I put it on the chassis dyno 12 months ago it went 270RWHP at 22psi. Sure I use a lot of boost but it is a standard head from the late 1970's so flow is somewhat meagre...
I have slowly crept up on the tune and now can safely push 35psi boost and it is an animal by comparison to running 22psi boost. Within the next couple of months I intend to dyno again and see how it goes now.
Best quarter mile is a 12.6 @ 102mph as I backed off at half track and cruised due to lean fuel issues with my blow through carb and it was running 25psi boost. Also I hope to get to the track again within the next few weeks (flaming atrocious local weather permitting...) as I am confident the carb issue is under control again!

With 40 degrees ignition timing the car responds just fine in traffic to and from work each day. Off boost performance is better than my work vehicles or wifes Nissan Pulsar.

I absolutely LOVE my low compression engines! :p

Cheers,
Jason
 
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