aluminator with a supercharger

[engineermike]

9:1 @ 16 psi = 18.5:1
11:1 @ 10 psi = 18.5:1
9:1 @ 26 psi = 25:1
11:1 @ 18 psi = 25:1

See a trend there ?

Just curious as to your source because something tells me you’re taking this way out of context.

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[engineermike]

Correct. But 9:1 @ 25 psi is around the same power level 11:1 @ 15 psi.

9:1 @ 16 psi = 18.5:1
11:1 @ 10 psi = 18.5:1
9:1 @ 26 psi = 25:1
11:1 @ 18 psi = 25:1

See a trend there ?

Just curious as to your source because something tells me you’re taking this way out of context.

From the RPM outlet. Not taking anything out of context

Actually, as I suspected, you are taking the chart out of context. You were somehow equating the RPM outlet chart of "effective compression ratio" to "same power level", which absolutely is not the case. If it were, we could just run 18.5/1 compression, ditch the supercharger, and make the same power as 11/1 and 10 psi.

This isn't a ironed headed engine made 40 years ago that you need 7.5:1 cr for 8 psi @ 20 degrees timing. But as always, run what ya want. Cheers.

Correct, it's not....I'd say it's much closer in design to a modern Predator, Aluminator SC, Cobra Jet, or GT Supercar, which all benefit from lower compression ratio with their boost.

 

[SolarFlare]

This one is going the distance fellas, I feel it. GL to OP and the mathematicians.

 

[Jmtoast]

I sense Nerds

 

[wazslow]

If all you have access to is 93/91 octane, I would go with the lower compression option. If you have access to E85, I would choose the higher compression ratio.

 

[engineermike]

What you wanna start doing cam timing, ignition timing and all the other minutiae that determines EXACT cr's @ whatever psi ? Come on now. That chart gives a great general idea of what's going on. Not exact, but close enough.

I can certainly get into all the “minutiae”, as I do it for fun. As you see in my other posts, I’m modifying cam timing, GDI blend, and GDI timing and measuring effects on borderline knock spark timing.

But that’s not what we are talking about here. The chart you referenced very clearly said it is to determine “how much boost you can run”, whereas you attempted to use it as a power prediction tool. As a side note, the same page you quoted to support your point (that higher compression is always better), states the following “If you are building your engine from scratch, it is a good idea to try to build it with a relatively low compression ratio, such as 7.5 or 8.0:1. It is fairly easy to change the boost to get the best combination of performance and power, but it is extremely difficult to change the compression ratio, especially if you want to lower it. Additionally, you will make more total power with a low compression, high boost engine than you will with a high compression, low boost engine.” Again, this is the site that you referenced, not me.

 

[IrishStallion]

I’m buidling a 13.5 to 1 Yote on 8 psi....look out MF’s!

 

[engineermike]

... be my guest.

Thanks for giving me your permission, but no one is talking about doing the things you mentioned. That’s a straw man argument.

Secondly, you’re arguing with a direct quote from your own reference, so I suggest you take it up with them.

 

[engineermike]

I will admit that I haven’t driven a GT500, but I also haven’t seen any reports of them being “dogs...at anything under any sort of significant boost”.

 

[wazslow]

Don't you drive a NA Coyote?

 

[Andy13186]

I absolutely love my NA gen 3 coyote on e85, its insane for what it is. Whipple gen 5 on order though, staying on e85 with the whipple.

 

[IrishStallion]

Wildhorse is a badass look out...

 

[Sean709]

I think there is a happy medium if having to replace a short block on a motor that already has a tune and pulley combo I would stick with the same 11.1 in that case. I do like the fact of the older motors at 11.1 over the newer 12.1 for boosted cars. If I was going custom pistons I would shoot for 10.1 myself and just pulley 1 size down. Just my thoughts.

 

[Jackson1320]

I think there is a happy medium if having to replace a short block on a motor that already has a tune and pulley combo I would stick with the same 11.1 in that case. I do like the fact of the older motors at 11.1 over the newer 12.1 for boosted cars. If I was going custom pistons I would shoot for 10.1 myself and just pulley 1 size down. Just my thoughts.

Then just get a gen1 or gen2 f150 shortblock and your there.

 

[Sean709]

Then just get a gen1 or gen2 f150 shortblock and your there.

I just meant compression wise. Even with my combo if I had to go thru the short block I would spend the little extra on Something like manly rods and pistons and a ring pack designed for boost. If its apart anyway might as well.

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