Maximum static compression for a supercharged motor on pump gas

[4twennyAint]

I second the motion for methanol/water injection.  I raced for years with 9.8 : 1 compression under 15psi boost, but with a 50/50 blend of water / methanol I never had a problem using 93 octane.  And, I ran a full 38 degrees ignition advance.  Check out Snow Performance.  Without a methanol kit, you're not getting anywhere near the full power potential of your boost.

[Autoholic]

A blown 427 SOHC will not have problems making power down low. I bet your engine will make more power at 2000 rpm's than some of the new cars being sold today.

Leny, good luck and share some pictures of your build. I'm very interested in seeing a new blown SOHC being built. If you haven't found all the parts you need for your build, you might want to try and get a hold of Paul Munro. He's in Australia and he casts various parts for the SOHC, including new blower plenums. What vehicle are you looking to drop such a beauty into? If you don't plan on driving it all that often, you could just buy E85 or even E100 from a company like VP Racing or Rocket Fuel. Or just go straight to methanol.

[Qikbbstang]

You said it yourself: " I would want to use one to make power, not just to look cool."

               IF you want a serious blown/power adder motor.That adder dictates pretty much everything going in/on that motor is selected with that power adder in mind

[Tommy-T]

I built my 8-71 blown 452FE to look cool...and accidentally ended up making stupid power!:)

I chose an 8-71 over a 6-71 simply because you can turn it a little slower (making less heat) for the same boost. And, of course, it looks bigger too.

The best way for me to describe driving the same car normally aspirated vs. boosted is that now it pulls as hard in high gear as it did in second before. Crazy!

My car has 8.5:1 CP blower pistons. I have easy access to 100LL Avgas at $5 a gallon so I keep it handy. I also have a Snow water/meth system on it that starts injecting at 4lbs. and is fully "on" a 9lbs. I'm fairly confidant I could go with 91 octane California "moonshine" gas and water/meth, but I don't because I don't have to.

My car seems to like a fairly aggressive advance curve to run cooler around town but my Electromotive distributorless ignition has a linear programable retard feature. I give it 18 initial, 34 total by 3000rpm, then start pulling 2* per 1000rpm after that. Shift at 6K.

The Snow water/meth kit is a pretty easy install with the injectors in aluminum plates under the carbs. My pump and tank are in the trunk. I use the Snow "Boost Juice" from Summit $35 for 4 one gallon jugs, but you could mix your own distilled water and methanol for cheaper. The controller is kind'a tricky to get right...but seems to stay put once you dial it in. 
 

[Leny Mason]

Hi If I can figure out how to put some pictures on this sight I will, it is a 1964 Comet We are making a full frame for it now four link my rear tires are 17x33x16 on the rear I was going to straight axle it but I changed my mind now is the time to change it to a  Mustang two, We made the front fenders six inches longer along with the wheelbase, that made a lot more room in the engine bay for all the blower drive and distributor I am making a 90* gear box for the distributor  to get out of the way of the blower belt it started out as a nice one owner car. Leny Mason

[Autoholic]

What exactly are you doing for the distributor?  I believe the blown SOHC's used a distributor from a Ford flathead and then ran it off of the long timing chain, using the fuel pump gear. Maybe our members who know more about the blown SOHC's will chime in on how it was done.

I can't find any pictures of a blown SOHC that did this way, but the Suncammer I think did it this way.

[64bird410]

Depends on your ability to control your timing, afr, and octane. Essentially the big deal with "boost" is controlling cylinder pressure and "octane".  when dealing with factory engines and 9+ to 11:1 static compression ratio when adding boost the knock sensor is happy when dialing back the timing under high pressure conditions aka high load(lower rpm and high boost/throttle angle). Using water/meth has shown that you can get away with alot more timing with pump gas. Favor meth further away from the combustion chamber and then favor water closer to the chamber. Water can soak up alot of chamber / egt temp supposedly. When  Running enough water/meth there isn't a a big difference between 87 and 91 pump as far as the knock sensor is concerned. 

[Leny Mason]

Wow I have not seen that Car before the water pump is interesting, any way that distributor is the same one I have with blower belt on I only have about one quarter inch and that is a stretch, so I am using the Jim Bairillo's front  cover that came with the  Rotor Phase distributor then I found a 90* gear box 1 to 1 so I can get it out of the way, I will try to do some pictures . Leny Mason

[AlanCasida]

Thanks for all the input, guys. You are the best! Sounds kind of like I figured, I'll really need to plan on at least pistons for this.

[cjshaker]

I have easy access to 100LL Avgas at $5 a gallon so I keep it handy.
 

I'm a little jealous, Tommy. 110LL here in Ohio is almost $8 a gallon, and that's within 3 miles of a refinery. Seems odd considering gas is cheaper here, I think.

Does anyone know the longer term effects of running water through an engine? I know it turns to steam, but it seems that there would be some moisture left behind that would have to condense, and I'm curious how that would affect aluminum heads, cylinder bores, valve seating and rings.

[Faron]

N/M

[AlanCasida]

Thanks for everyone's input!

Here is a bit of information I got off of Blower Drive Service in their FAQ
The question asked was "What type of pistons and compression should I be running on my blower"

Their answer:In the last decade as the octane rating of gasoline decreases and the demand for more horsepower increase, there is more of a possibility for detonation. Forged piston made for blown systems are highly recommended. Also using 8.5 to 9.1 compression ratio and less blower boost will keep the engine cooler. When you run a lower compression engine and raise the boost levels, this elevates the temperature of the air charge to your engine, requiring you to buy higher octane gasoline to suppress detonation.
I am right at 9.0 now. If I run a slightly thicker head gasket or have the combustion chamber opened up a little on the heads I think I'd be right where I need to be. I have a bare pair of Edelbrock 76cc heads laying around. My machine shop has a service of opening them up to 88cc(stock MR). I'd have to check against a head gasket and of course talk with them but I might be able to open them up to maybe a 95cc or so and get down to about 8.5.

[Joe-JDC]

Alan, I would not increase the combustion chamber to get the lower compression.  Those heads are not the thickest of metal, and cutting them that much takes the temper out of the heat treatment.  It is much more wise to buy the proper pistons for the desired compression ratio and still have a useable set of heads for another build.  JMO, but 8.5:1 is safe, and a FE has enough torque to still be able to get out of its own way on the street.   My engine was built with ~8.7:1, and I ran 14 PSI on the street with boost timing retard.  Joe-JDC