New to supercharging, need some pointers

[jaded13640]

Hi, I've been using fuel injection (Enderle Bird) and methanol for many years but I've never had the opportunity to do a supercharged application until now. We've got Duster bodied tube chassis car that weighs right around 2600 pounds. Loose converter, hopefully it's appropriate for the situation, and we picked up a stripped 671 and an additional Bird with the "K" series barrel valve. It's been suggested that it'll need to at least be respooled or just use the cube. We use iron 440 Block, bored and stroked to 500" and Stage V Hemi conversion heads. We'd like to see some low 8s and maybe an accidental 7 would really make my life complete.

I understand that a good blower cam, like a good nitrous oxide cam, is rather specific to supercharging. We have a very aggressive solid roller that I need to see what the specs are...maybe it'll get us by.

My first question to the blower guy was "what compression ratio should we use?" He said that with methanol you can go all the way up to 18:1 but he suggested we'd maybe want to stick around 12:1 and start by spinning the blower 25% overdrive. Fine with me if that's correct.

So those are the question I need to start with, you guys may need more info but I need to start by know what compression ratio will be the most friendly so I can get pistons and rods ordered. We're going to need lots of parts and we also don't yet have a blower intake. So if anyone has some good used stuff we can use, let me know.

Thank in advance,

Wayne

[GlennLever]

Compression wants to be high. the way you get there is an argument. I like running static pressure low and let the blower do the work to increase you compression. finial compression of 18:1 might be a little low.

cam is important, however if there is not a bunch of over lap between intake and exhaust, you can try it out. You will want to change the cam at some point.

[jaded13640]

Excellent, thanks for the response. So you think with a stripped 671 and 12:1 would be a little low? If so how much? Your personal opinion on it is fine. Thanks for the cam info too.

Wayne

[Paul New]

I’m not a Hemi guy but, what I say is 12-1 is too high if your just starting out high static compression does not give you much of a tuning window and you will need it!

[jeff/21]

we ran 9.2-1 20% over littlefield 8-71 496 BBC on alky 1500 hp on dyno 9000 rpm on the straights using chart gave use 22-1 with the boost.
so 12 -1 seems a high but ran 13-1  6-71 30% over on a drag race 406 small block never dynoed

[dreracecar]

10.2 to 10.5 is a good starting point for compression for alc, and fairly easy on the starter.  People will tell you that cam selection is a "Black art", it really isn't, Too hot or wild of a cam will eat up the valve train, save that for those that can afford it or is running a class that demands it. Let the blower and magneto do the work

[jaded13640]

excellent info! I'm cool with lower compression if that's the ticket.

I forgot to mention before, we need a hemi pattern blower manifold....I'm having a hard time understand why of all combinations THEY would be scarce but I'm not seeing any yet. Ideally used so save some money.

Wayne

[GlennLever]

What is really important is the finial compression ratio. If you start with a higher static pressure you ask the motor to do more work, and the blower, does not work as hard.

If you start with a low static pressure you are asking more of the blower. Not a problem just a different way to look at it.

671 is a smallish blower which might need some help ......

[Supercat]

We are running a 477 Buick blown alky. 671 to start and get the bugs out then we have the 871 when we are ready for it.
We are at 11.25 to 1 with a .070 head gasket.
Like many have said let the blower do its job add in fuel and good spark an have some fun.

[jaded13640]

And that reminds me of the other question I forgot to ask. I've always used the good Felpro gasket for NA, what do you guys that run blowers use for head gaskets?

Wayne

[Supercat]

Copper head gaskets.

[Draw 3D]

My little SBC has 11.5:1 compression ratio and in my opinion, if you start with low compression, you're going to have to spin the blower much faster and at a certain point, it will become the less efficient, and, the intake air will get heated more and that's not what you want to do.

[dreracecar]

My little SBC has 11.5:1 compression ratio and in my opinion, if you start with low compression, you're going to have to spin the blower much faster and at a certain point, it will become the less efficient, and, the intake air will get heated more and that's not what you want to do.

   All blowers have a maximum boost they obtain till they start to cavitate, they are not linear and boost does not increase the more OD/rpms you give it.  Blower OD is to regulate when full boost is achived  say 5 over comes in at 60' while 25 over- 10' but on both runs saw a max boost of 22#

  Lower static lets the motor work easier from the start and then power on once the car gets rolling and has the rpm to handle the increased load the blower provides. Higher static puts more load on the drivetrain at the hit.
  But as Glenn mentioned-- find out which way works for you, I run what works for me and haven't change the basic combo in 24 years

  Alc maintains a 64* cooling charge into the intake port, If you are running gas then the intake charge must be cooled

[Draw 3D]

Alc maintains a 64* cooling charge into the intake port

Don't think that is correct, temp at the intake port would be determined by amount of pressure and amount of air compressed mixed with the alcohol.

[dreracecar]

Then why is it the my Intake manifold is cold after a run???