methanol blown small block Chevy help

[theyob]

Hi there

im after some advise, I am currently in the process of building a 355ci small block Chevy running a 6-71 blower with mechanical fuel injection (for drag racing), My main question is what static compression should i be looking at running, Ive just purchased some nice aluminium rods but cant make my mind up on what compression pistons to use, Im planning on using methanol as fuel, I do have a set of nice JE pistons that will give me 12.7-1 compression, Would this be to high? Im new to running this combo so any advise would be greatly received, Any advise on running a combo like this also gratefully received! Please see below spec of my engine

355
4030 BORE
348 STROKE
5.7" RODS
9.00 DECK HEIGHT
64CC HEADS

Many thanks fpr your time

Mat

 

[patprimmer]

What boost or drive ratio do you intend.

If you want maximum power, use a high OD ratio, like 40% or so and low compression like 10:1.

Many get away with say 10% OD and 12:1 compression, but this route makes less power than high OD and lower compression.

You can run as much as 11:1 with high OD ratios if you run enough extra fuel to cool the charge to avoid detonation, however you will get very short bearing life vs 10:1.

If you are new to this, run 10:1 and about 15% OD until you learn the tricks of tuning MFI on methanol, then turn up the OD.

What fuel pump do you have.

What fuel control system do you have.

I know most drag racers disagree, but I think unless you are running a lot of nitro methane, good steel rods are a much better choice than aluminium.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[cheapcharlie]

a little knowledge is indeed a dangerous thing . take everything I say with a grain of salt. static c/r of 13/1 and higher are doable with wedge type cyl heads boosted on alchol. I suspect when you do the math after carefully mesureing the piston to deck,gasket and combustion chamber volume if you have a true 12.7/1 static c/r with the pistons you now have.since I have no experience running boost and you and pat have the same inernet as me it seems to me you would be better asking someone running a simalar combination....but why would you listen to someone who can,t even spell? I sure like drag racing myself ahd I WISH THE YOU BEST. Jerry (younger gang racing)

 

[patprimmer]

I have campaigned a 350 SBC with a 6:71 and Enderly MFI.

We reliably ran high 7s low 8s with a 2600 # door car.

A site more accepting of home done drag racers is HRE.com but there is a modest annual fee. They are a specialist forum for drag racing, MFI, exotic fuels and superchargers.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[theyob]

Hi

Thanks for the replys, I think ill take yr advise pat with the 10-1, and run more OD, This set up really is new, i really know very little about running this combo and have gone diving in witout really thinking i dont really know what im doing!.....so its going to be a very large learning curve, Can you explain to me what the main funcyion of the "pill" is....does this pill determain the amount of fuel that flows back to the tank? and under what cercurmstances do i change "the pill" I guess its all to do with weather conditions? Got any tips on how much fuel to run etc? is it a case of trial and error by going the old route and whipping a spark plug out? You will have to excuse my lack of knowledge, But im really just trying to learn as much as i can.

Thanks for your time

Mat

Heres a moc up pic

 

[theyob]

oops...excuse the typos and spelling errors!

 

[patprimmer]

The Pill controls the amount of fuel returning to the tank at open throttle.

If you are rich you put in a BIGGER pill to LEAN it off.

Guess work won't really do.

Start with the 10:1 and say 15% OD. That gives you some margin for error without getting a melt down.

On alcohol, you read plugs differently.

You do not look for coloured deposites on the porcelain. You llok for signs of heat on the ground strap and the threads.

Perfect tune will give discolouration up to 3 threads at the most extreme point and on the ground strap to the start of the bend.

Cadmium plated plugs are best as the heat burns of the plating making it easy to read.

It is best to get your system flowed by an expert before you start.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[patprimmer]

You change pill a little to fine tune for weather.

You change it a bit more for serious changes in altitude.

You change it more still for changes to the blower.

A:F ratio shows more on the threads.

Spark advance shows more on the earth strap, but a change to one affects both to some degree.

What pump.

What hat.

What nozzles and where.

What bypasses. Main pill bypass and idle poppet, or more like high speed poppet, port nozzles, pump sizer bypass and pump saver poppet bypass.

Some bypasses have a spring loaded poppet valve to control by pressure. Some have a pill or jet, some have both.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[thundair]

theyob
I agree with patprimmer that you need to school yourself with building and tuning a blown alcohol motor. Richer is always safer but not better.... so be safe.
I would disagree a little about using steel rods as they will transfer more kinetic energy into the crank and block webbing.. check out this forum

http://speedtalk.com/forum/

Cheers

I don't know anything but the people that do.