Compression, dynamic/static, question...

[PQ]

Originally Posted by Supercharged SS

How do you think the trans is going to like that? Start saving. You won't make 16 psi without major changes to the blower. It's just not as simple as changing the pulley.

I guess I should have said I'd like to be able to. In case I do end up with the Whipple I wanted later. lol The tranny is already in the works. I have a hook up for that thank God. haha

Originally Posted by BullF-16

Excellent thread here! I know i laid awake at night when planning my current engine. I knew i would eventually be twin turbo (happening as i type this)

One of my concerns was dish volume on my pistons. I knew the general consensus here was keep CR in the 10s Vs going low at 9:1. I basically chose middle of the road with -23cc Wisecos. I calculate this puts me right at 9.5 CR.

No E85 or race gas for me, just 93 octane blended with Torco for an in tank octane of about 96. Plus the car will be tuned with the meth. Planning on 20psi so nothing crazy. The PT6766s should feed this motor nicely.

Again, great read. Now should I have Pat G spec me another cam......Nah, this should be fine for a while!

Damn.

The meth makes so much sense to me now. I'm glad I have learned these things.

[old motorhead]

Originally Posted by PQ

Longer duration cam would keep the compression down a bit?

You can get the dynamic compression ratio where you want it with intake duration, lobe seraration angle, and ground in advance (or retard).

[SSBUSDRVR]

Excellent thread here!

Yes now you got to go and mention TTs. Mind is now sidetracked. lol

This is so freaking cool. It's like pandoras box for us dummies. hahaha

Yes bought a book and took an online class didn't help much so subscribed to this class. Anyone want to buy an EForce?

[jessrayo]

This is a great thread, I wish I would have found it sooner. Now where do I begin.... Ted summed up one point very well in one post, it is all about the octane. The graph posted by the OP is a specific graph for the efficiency of a fuel of some specific octane, from my personal experience it looks like about 89 or 91 to me.

While changing the boost does not change the actual compression ratio of the engine, the air is actually compressed in the process of making boost and the posted chart shows what the equivalent compression of the air would be if it was provided by compression ratio rater than a combination of compression ratio and boost. It is a guide to help you not exceed the fuels limitations. That is why if you have more boost, you generally want less compression. The air is already compressed some by the blower before the piston even starts to compress it.

Each fuel has a peak efficiency, the more you can compress it before it spontaneously detonates the more power you can get out of the fuel. It can be a fine line, more compression makes more power right up to the point it destroys your engine. That is the red area in the chart. If you boost the octane of the fuel you get a completely different chart with the green and yellow areas being larger.

This principle of peak compression providing peak power is then combined with the simple idea that if you can get more air and fuel in the engine at the proper ratio you will have more power. There is no replacement for displacement, bigger is better, and all those phrases. You need more air and gas to make power period.

Ultimately you will only make as much power as you can get fuel in the car at the proper AFR. Usually, you run out of air. If you run a 427 instead of a 376 you will not be able to make as much total boost because the blower will be pushing against less restriction, so you may want to raise the compression a little to get max efficiency from the fuel.

Air is pretty easy to compress but it has some interesting thermal properties related to compression, most of these work against the ability to make power so some engineering is necessary. For instance if you double the pressure and in the process of doubling the press you end up with double the temp, you don't actually have any more air, you just have the same amount of hot air under pressure. Unfortunately, a by product of every compressor is heat so if there isn't a way to offset this heat you don't actually get more air molecules in the engine you just have hotter air under pressure that makes the fuel less stable.

The physics of making peak horsepower are very complex and this thread is digging into some of the engineering conundrums related to boost and compression ratio.

[zebra]

Originally Posted by JANNETTYRACING

There are so many variables the simplest way to size a blower is by HP target.

700-750 RWHP would be a high end for a 2300.

A 2.9 would be better suited for 800 RWHP and a 4.0 would be better for 1000 RWHP.

Hope this helps.

yeah, i completely understand that. what i asked was what you thought the limit was with the blowers we have (since budget is an issue & working with what we already have is preferred over buying something else)
i know if i was starting over, i'd probably get a Whipple (that i wanted in the first place but was told not to hold my breath waiting to see if they even decided to make)

Originally Posted by IRPQ

I'd like to run it up to 15-16 psi on drag strip days. Toss a smaller pulley on for everything else. So I think 10:1 would be a good fit to be safe.

Ya, fuel pump and injectors is first no doubt.

Longer duration cam would keep the compression down a bit?

a bigger pulley would turn it down... but we know what ya meant

and more duration split/overlap would lower the dynamic CR

Originally Posted by jessrayo

...
For instance if you double the pressure and in the process of doubling the press you end up with double the temp, you don't actually have any more air, you just have the same amount of hot air under pressure. Unfortunately, a by product of every compressor is heat so if there isn't a way to offset this heat you don't actually get more air molecules in the engine you just have hotter air under pressure that makes the fuel less stable.
...

one of the linked articles touched on that as well. that's where boost becomes a little better than compression because you can keep the air cooler by boosting to a specific cylinder pressure than relying more on mechanical compression.

that is if i understood that article right

[PQ]

Originally Posted by zebra

if i understood that article right

I believe you did.

[zebra]

why don't you just Whipple Bonnie's car & call it a day?

[JANNETTYRACING]

Originally Posted by zebra

yeah, i completely understand that. what i asked was what you thought the limit was with the blowers we have (since budget is an issue & working with what we already have is preferred over buying something else)
i know if i was starting over, i'd probably get a Whipple (that i wanted in the first place but was told not to hold my breath waiting to see if they even decided to make)

The limit of a Blower will be based on 2 factors, Max Rotor Speed, and rotor size.

We have taken the Maggie to Pretty impressive power levels with some design changes to enhance flow.

The Limit of What you can do with any combination will still always be Octane if using Pump gas.

Ted.

[zebra]

let's call it 91 octane @ 4000' (about as good as 92 at sea level). no faster than 18k on the cathedral-port blower, forged 383 LS1 (3.9"b x 4"s) with AI port work on 862 heads & healthy cam. 90mm or 102mm TB, either one - if i need to bore out the snout & upgrade, i will.

what i'm going for here is if 700+ to the ground is realistically possible... or is this going to top out in the mid-600s?

[JANNETTYRACING]

Originally Posted by zebra

let's call it 91 octane @ 4000' (about as good as 92 at sea level). no faster than 18k on the cathedral-port blower, forged 383 LS1 (3.9"b x 4"s) with AI port work on 862 heads & healthy cam. 90mm or 102mm TB, either one - if i need to bore out the snout & upgrade, i will.

what i'm going for here is if 700+ to the ground is realistically possible... or is this going to top out in the mid-600s?

Auto or Manual, Truck or Car?

You will have to lower the compression to run the blower that hard and IAT is going to be the bigger challenge.

Sorry If I am only giving you bits and pieces, there is just too much to cover in a thread, a Phone call would speed up the process big time.

Ted.

[Pro Stock John]

Increasing cam overlap would have the effect of reducing or maybe achieving lower cylinder pressure right? More charge/force would exit.

[SSBUSDRVR]

So what does the EForce TVS spin at on 3.25 pulley? Is it really worth dropping down to 3.0 or 2.75 or will the IAT increases really defeat the purpose and or belt slip become an issue. Had none on the 3.25.(leaning now towards 9.5 compression 415-418) Old Cam had around 7 degrees of overlap.

[dan0617]

Originally Posted by Pro Stock John

Increasing cam overlap would have the effect of reducing or maybe achieving lower cylinder pressure right? More charge/force would exit.

yes. Which is why static CR is almost meaningless although in the performance world it is discussed the most. Many people don't understand the definition or concept of dynamic so they talk static. SCR should be about the last thing you determine, it is the final mechanical adjustment to get the DCR where you need it for your selected boost, cam, ci, fuel octane, iat, etc, etc, etc.
,
That overlap helps pull the charge in at higher rpms on an NA motor. Too much overlap kills the cylinder pressure (and the part throttle drivability) at low rpm. On a boosted motor you want to control cylinder pressure some other way, because the blower is taking power and raising air temps to make boost and overlap is wasting it. So you then lower the IAT, up the octane, retard the timing, or lower the SCR to control the cylinder pressures and temps.

[zebra]

Originally Posted by JANNETTYRACING

Auto or Manual, Truck or Car?

You will have to lower the compression to run the blower that hard and IAT is going to be the bigger challenge.

Sorry If I am only giving you bits and pieces, there is just too much to cover in a thread, a Phone call would speed up the process big time.

Ted.

2000 FRC in signature (manual), but i'll try & find a time when i'm off work & you're still open to call.

Originally Posted by SSBUSDRVR

So what does the EForce TVS spin at on 3.25 pulley? Is it really worth dropping down to 3.0 or 2.75 or will the IAT increases really defeat the purpose and or belt slip become an issue. Had none on the 3.25.(leaning now towards 9.5 compression 415-418) Old Cam had around 7 degrees of overlap.

assuming you've still got the 1:1 in the back, at 6000rpm, the blower would be up about 13,850. going down to a 3.0 will start making a 6-rib setup harder to keep from slipping. as for the IATs, i don't have much of a calculation or guess on that