18 psi would be best on 9:5 or 9:1 compression? If on 9:5 or 9:0 what would be the difference?

 

I think most would go with the 9.5 or 9.1 on a super charger. But its more towards the 9.5

 

You need to consider your dynamic (boost) compression ratio in the calculation and the octane of the fuel you intend to run at full boost. Altitude can also play a factor in the calculation. So let's play with some numbers:

18 PSI with 9.0:1 CR at 2000ft = 19.62:1 dynamic CR
18 PSI with 9.5:1 CR at 2000ft = 20.73:1 dynamic CR

now for comparison I run my car at
19PSI with 8.9:1 CR at 2000ft = 20.00:1 dynamic CR

I produce ~900RWHP through a TH400. I lower my boost on pump gas to keep things safe but I'm Turbocharged. I just click a button to lower the max boost. So as you can see I can run higher boost but keep my dynamic CR value lower than a person running 9.5:1

I'm biased but I'd go with the 9.0:1 Static CR. It just gives you more flexibility later on. Now if you plan on running C16 in that puppy then I'd say you can run pretty high static CR without too many issues.

Not sure if I answered your question but I guess we need more detail on what you plan to do. What you want to do in the future.

 

i know expert guy with 408 C.I.D he say that with high compression you will get stuck 700 - 800 rwhp .
he say after 700 rwhp you need booost to extra power
the more booooost the more Horse power what do you think about this
his done 20 psi on 408 vett F1c on 5000 rpm 700 rwhp and he say the engine compression shoud be betwen 8.8 and 9.3 C.R to play with 18+psi on F1C or F1 serias

thanks
navy

 

All depends on your goals and setup!

I run 8.5:1 compression and 17 psi on 91 octane pump gas with just an intercooler...

If your gonna be running pump gas i think you should go with 9:1 that will give you more leway when you are running pump gas!

you have to decide:

less boost - more compression?
more boost - less compression?

meth?
intercooler?
street, track, both?
power goals?

ect........

 

General guideline on boost versus HP. And CR versus HP.
With every lb of boost I add about 37 Crank HP.
If I go from 8.9:1 to 9.9:1 I'll about 16 Crank HP.

So it's logical to add more boost but up to a point. There's a whole lot of things to consider like the efficiency of your supercharger pushing air at a higher PSI. Overdriven superchargers depending on the manufacturer can be all over the place.

In general terms give up static compression ratio and increase the boost. That gives you the most HP output.

 

my car for street with meth i hope see 880+ rwhp

 

Ok. So what if you're a little guy like me that plans to run the neighborhood of 10-12 psi. I was planning on running PRC stg 2.5 6.0l heads to drop the CR to about 9.7:1 and run the stock bottom end with a custom ground blower cam. Hoping for 500whp. Any opinions?

 

DISCLAIMER: A lot depends on efficiency of the setup and the volume of air that the compressor develops but use this below for a general guess:

Assuming 9.7:1 I figure the 6.0L will put out about 400 crank HP worst case. Now add on top of that 12PSI which would be about 727 crank HP. Assuming 20% losses and you should see 581RWHP. 10PSI would be 672 crank HP with a 20% loss being 538RWHP.

 

Awesome thanks

 

I am hitting 18 psi at 9.3:1 with methanol. Making 840 rwhp through a 4L60E, pig *** rich, and low timing. Once I get the reluctor wheel fixed, we should hit 900+ rwhp with the tune leaned up a bit and more timing added.

 

Is 39:1 under boost high?

 

I'm just lookinf for a street rod that goes to the track once or twice just to see what she does. Don't want to run meth or anything. Just 500~ reliable street horses. Guys at TSP said that the stock bottom end of my LS1 with their prc 6.0l stg 2.5 heads and a custom cam on 10 psi of boost would get me there pretty easily.

 

why ! tha meth keep save for your engine , Regardless your engine 500 or 1000 hp street,dragrace cars .

meth = save

 

I'm just now studying FI and I'm way over my head FI+Meth+my lack of knowledge= nasty algebra problem

 

No lmfao!!!

 

I agree on meth = safe! very cheap insurance for a very expensive setup plus it cleans the hell out of my windshield! LOL

 

I calculated that I would make 809RWHP on the dyno at 17PSI. That day on the dyno I made 824RWHP. I also calculated that I'd make 911 RWHP @ 21PSI but only made 907. So on actual dyno testing:
17 = 824 RWHP
18 = 882 RWHP
21 = 907 RWHP

It all depends on the dyno the day the compressor efficiency how big the motor is to start with what you rev it to and your losses through the drivetrain.

Compared to the Top fuel guys out there running 45.5 PSI on Nitro I'm sure we all look pretty silly with these little mouse motors. I have fun with it and that's all that counts. Cheers to the big boys out there.

 

what about you live in sea level and your looking for close to 800-1000 HP.
but i thikn the 800hp would hook better right?
oh and ofcorse all on pump gas

 

If you live in Brownsville at Sea Level then I'd say you have bigger problems. Unless your parking garage is on stilts! LOL....

I really don't know how to calculate octane to dynamic compression ratio. I can tell you this. I make around 976 Crank HP at 14PSI. I've run on the street lots of time at 14PSI with no issues at all on pump gas. I won't push it beyond that.