What compresion pistons should be used.

Old 05-31-2010, 03:08 AM
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Join Date: Dec 2008
Posts: 34
Default What compresion pistons should be used.

I am looking to convert my gas Blown BBC to alky, After reading a lot of the topics that I find on this website. I am being to think that along with all the other stuff I am getting ready to do that it might be a good idea to replace my pistons as well.
Current engine set up:
BLOCK - 4-bolt main 427 seasoned block bored .030 oversize. Block is hot tanked, custom honed, dry decked, line honed, new cam bearings installed. Brass freeze plugs installed. The Outside of the block is painted with your choice of factory colors.
CYLINDER HEADS - New RHS™ Pro Action cast iron rectangular port cylinder heads castings feature 320cc intake runners. Stainless 2.250 & 1.88 valves. New perf valve springs which will handle up to a .600 lift cam. (Larger cams or solid lifter cams will require optional valve springs at extra cost.) Stud girdles installed.
PISTONS - Forged supercharger pistons. 7.3 to 1 static
RINGS - Premium Speed-Pro moly rings.
RODS - P.A.W. 6.135" high performance connecting rods which have been shop-peened, checked for straightness. Resized on the big end and fitted with high performance 3/8" chrome moly rod bolts for maximum strength and performance.
CAMSHAFT - Your choice of a new P.A.W. / SSI hydraulic cam to match application.
LIFTERS - New P.A.W. hydraulic flat tappet to match your cam.
CRANKSHAFT - Factory steel crankshaft precision finished at .010 under on both mains & rods journals and machined for dual keyways!
BEARINGS - New Clevite M77 - Top quality rods and mains bearings.
TIMING CHAIN SET - New P.A.W. double roller timing chain set.
GASKETS - Fel-Pro engine gaskets set along with a pair of SCE ICS Titan copper head gaskets with stainless O-ring wire.
OIL PUMP - New P.A.W. high-volume oil pump to provide maximum protection.
PUSHRODS - New P.A.W. 3/8" chrome moly high performance pushrods.
BALANCED - Electronically balanced rotating assembly, pistons pressed on to rods. Advise salesman if using flex plate or flywheel.
DAMPER - Special damper for use on supercharged engines with dual keyway.
ROCKER ARMS - New P.A.W./SSI long slot rocker arms.
SUPERCHARGER - Complete 6-71 supercharger 8% over driven
HEADERS - 1 7/8 primaries to 2 1/4 colletor. 2 1/4 out the back through Supper 44 Off Road Mufflers
CARBS - 2 Demon 650 Blower Carbs
TRANS - Built 700R4
REAREND - Currie 9"+ 35 spline Axles Detroit locker 5.13 Gears
IGNITION - MSD 6AL Box, MSD Distributor, and Mallory Coil
While tuning on a chassis dyno in a 6000 lb truck, @ 5000 rpm 3rd gear it made 344 hp and 378 lbs torque. The guage was showing 10 lbs of Boost. This is turning 39.5 x 18 Super Swamper Boggers. We were not going of all out HP. I just wanted to make A/F ratio was safe. I am sure to a lot of you I am not making crap for HP and Torque, but this is my first experience with Blower engines and bought the engine preassembled. Trying to make it better as I go.

Now to the mods in the near future.
Hilborn EFI with FAST XFI system
ALCOHOL for fuel
ARP Head studs.

Now my question, with the information that I have posted above I am looking for input on 3 subjects,
1 How much Horse power will this bottom end hold safely.
2. Should I get higher compression pistons to go with the alcohol
3. Based on pistion choice and alcohol does anyone have a educated guess on amount of HP this combo should produce.

I know that it is accepted that you should loss 25% HP and Torque through drive line for drag cars, but I am also wondering due to the weight of my truck and the added Transfer casuse. Shouldn't I lose more and maybe that is why my original numbers were so low.

Please help me. I am getting ready to spend a crap load of money in this project and I wan to do it right and also have as much HP and Torque I can get relieablly. I have read many alcohol posts that say they are running 11 to 1 or even higher is some cases with Blown Alcohol engines. If that is static compression, then I am thinking that 7.3 is WAY to low. Especially when you consider some of the posts say that they are running over 20lbs of boost all day. Understand that this truck is still driven on the street some, so I know I am not building an all out race engine, but still want to get as much as I can out of the engine for what my useage is going to be. Limited street, lots of mud and mild trail usage. This is just a big TOY to me. Thanks for your help, if I am stupid or headed completely off base Please don't hesitate to tell me. Tell me the truth. I want to learn the right way, not the Cheap way. Cheap always cost more in the long run.Thanks again
Mudmut is offline  
Old 05-31-2010, 11:54 AM
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Join Date: Sep 2007
Posts: 4,140

I do not know anything about blowers so I'm of no help.I'm sure someone will chime in with an answer though.

If not, you can also try yellowbullet.com .I'm sure someone there will have some experience with what you are trying to do..as long as it doesn't bother you to be called "phuckstick"..they call everyone that.

Good luck.
Tod74 is offline  
Old 05-31-2010, 01:02 PM
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Join Date: Nov 2008
Location: Phoenix AZ
Posts: 116

I tend to stay at 8.2 for pump gas drivers, 9.5 for gasoline weekend warriors and 11.5 or maybe a little more for methanol race stuff. These are just my own baselines, we all have different methods.

Trail cruising to Mud racing is quite a big span to build around. I would probably just leave it at 7.3 and spin the blower a little harder. Trail cruising a blown alky setup may be a thing of the past once you find out how much fuel it actually takes to drive around.
ccperf721p is offline  
Old 05-31-2010, 02:30 PM
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Location: Fountain,MICHIGAN
Posts: 856
Default comp

The 11.0 to 11.5 is PERFECT for a Blown Alcohol Combo!
I Need to reread you Post,but I would think that 1100-1200 HP is Not out of the Question!
G 8)
I have a 439" BBC right now that makes 1450HP.Its 11.2 Comp.Alu/Rods,Venolia Pistons,Merlin 345 Iron Cyl.Heads,745-760 Roller,Mert Mag 6-71 Stripped S/Charger,Bird Injector,110 Enderle Pump,Mallory Super Mag 4(4.3 amps).
Maybe this will give you some Help?
bbchevy is offline  
Old 05-31-2010, 05:28 PM
Join Date: Jan 2006
Location: MN
Posts: 86

When you chassis dyno, you want to run that in 4th or high gear.. If you ran it in 3rd yor #s will be lower from the final gear ratio of 1 to 1... With a 4x4 chassis and driveline expect a 28 - 30% loss with 5.13s. We have a dyno-jet at the shop where i work.

With a blown alky deal dont skimp on the ignition. Get a MSD Mag 20 at the min. On our 540 big chief stuff we went from a 20 to a 44 and picked up 125 hp at the wheel in my chassis. But thats all out high dollar stuff.
obsessedtruck is offline  
Old 05-31-2010, 07:23 PM
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Join Date: Jan 2006
Location: La.
Posts: 2,890

Sorry to be the dog in the wood pile, but you are not making $'s and sense on this one. First you have a $9,000.00 motor, now you want too spend $8,000.00 on a EFI, now another $1,500.00 to $2,000 on changing the pistons, which you cannot do without tearing the motor down and rebalancing it. That makes it a $20,000.oo motor which you may or may not be happy with. Alcohol likes lots of compression, your street blower will only put out 6 to 8 lbs. of boost even with over drive on that big of a motor. I know you are obsessed with running the blower and that's cool. My suggestion is if you want too run EFI is too take the rotors out of the blower, and it would still look like you are running a blower and run it on gas, that's one suggestion the other is to sell your holly carbs and put Quadrujets on the system that you have, for less than a $1,000.00. I lived in Az for over 20 yrs. and had friends that belonged too a desart hillclimb/rock crawling club. No one ran holly's because they simply did not work, but Quadrujets do. I'm talking about 45 degree inclines up and down hill over rocks and bolders, etc. In Flagstaf Az. they have at the cinders a hill called $100.00 hill, and when i was there no one made it with holly carbs.

zipper06 is offline  
Old 05-31-2010, 08:48 PM
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Join Date: Dec 2004
Location: austin texas
Posts: 729

alky, 12.5 to 1 and a blower makes a fun ride, but not a streetable one. You really have to figure out what you want, before you end up with a pile of junk gernaded parts and a empty bank acount.
kwkracing is offline  
Old 05-31-2010, 09:33 PM
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Join Date: Dec 2008
Posts: 34

Thanks everyone for your advice.
Understand about the dyno, we were a little concerned with wheel hop going in a higher gear due to the high sidewall of the tires I am running. They create a lot of vibration at high speed. Very aggresive tread.

Don't worry about being the dog in the pile on this. That is why I asked the question. The more I read the more questions I have so I ask and hope to get straight forward answers. Which most tend to give. I appreciate that. I don't have a problem with having a 20,000 dollar engine, if when I spend that money it will be right. I understand that what I am trying to do is odd and very expensive. I love the blower, I don't think that I am going to get rid of it.

I know that I will not get any kind of fuel mileage out of the engine on alcohol, that is why I am planing to use a 32 gallon fuel cell. Thanks for your info.

Thank you sir for your advice. That is sort of what I am trying to do here before I get home and spend a bunch of useless money. What I am wanting is something very different from the norm, I want close to 1000 Hp that I can take to the trails and not worry about the fuel leaning out, If I so want to though I want to be able to drive it to a VERY close show, just to have something different than the masses.

Now the question is if I leave the bottom end alone, what sorta HP can I see. Sounds like it will be better to change pullies or get a larger blower.
Sorry to be a pain the butt over this, just trying to get all the info upfront.

kwkracing, I hope that you will be available for consultation when I return, looks like I will probably need someone to keep me sensable.
Thanks again everyone hope to hear more from you.
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