I have scrapped the idea of building another Henry-J and decided to just make this one a little scarier to put down the "1320"! The fact is I have built a lot of hard small block chevy's through the years and would be proud of most, but I want to go blown this time. Never done it and dont know the doo's and don't's of said piece of machinery. I do know the crank will have to with stand a shit load load of abuse but a man could sink a fortune in the crank and rods in the blink of an eye. I am not trying to skimp on it but would not like to get divorced over the bill $$$. LOwer compression pistons?? Cast crank out of the question???? Forged piston's???? HEADS oh the HEADS???? HELP!!!!!!
Figure out what your actual budget will be....and spread the money out..........look around for whats sitting around that you have not used and sell the items to help finance your new direction..you can find good things at swapmeets sometimes....atleast buy forged pistons and build a balanced assembly....Good Luck, Littleman
If you can find a set of 454 castings for heads they have very small intake valves. 1.74 I think, never the less you have a shit load of room for BIG exhaust valves. A little runner work and some pocket porting and you are done. And they are a large CC head so it will help on that compression. The problem with a blown drag engine is the large amount of force put on the bottom end all at once. Hypereutectic pistons will work but make sure you clearence the bore and the rings for the added growth of the piston. Depending what you are planning on as far as horsepower Eagle, Scat and other offer I beam rods that will withstand 600 horse. Anymore than that I would go H beam. Go full float with the pins. And detail the shit out of the block. Remember nothing will work at all without oil. This is where you should spend some of that money saved from the pistons and rods. Make sure to find a machinist who understands heat growth in a engine before you have him do any work on your shit. Forged crank for sure. Magnuflux a used crank at the biggest crank shop in town. I take mine to powermotive here in Denver they do locomotive/industrial cranks. Their machine shows all the cracks.
Tell us more about what you plan to do....how much money do you have available? is the car going to be used on the street? what trans setup and gearing is in it now? My take on it is that a blower will increase torque, and will let you make more power at lower rpm. This will require a strong crank, and strong pistons, but the rods will be loaded more in compression than in tension, so they don't need to be super duper high rpm rods if you won't turn high rpm. Heads need to flow very well (both intake and exhaust). Cam still needs to match the RPM band you will run, which should be coordinated with the drivetrain in the car. If it's a low buck setup then I suggest getting off the shelf low compression blower pistons, stock rods with good bolts and normal prep, steel crank, and balance it and put it together properly, but don't go overboard spending money on every little "trick" you can think of. Buy the best flowing heads you can afford. A roller cam would probably be a good idea, they generally give more lift for the same duration compared to a flat tappet.
Use a widely available forged factory crank, there's no need to get exotic and pricey. A good set of rods isn't terribly overpriced, but you will have to step up for the pistons. $600 for a set of JE blower pistons is about as cheap as it gets. In addition to the dish, blower pistons have slightly different ring gap placement or dimensions. Be careful using a bargain priced chinese rotating assembly, unless your machist specifically uses one brand and knows what to look for. I'm doing this exact build for a blown 350 in the garage (OT project). First it fried the original cast setup after 18 months huffed, now it's going back together right. Probably $1500 of parts in the rotating assembly, ain't SBCs a beautiful thing?
How about the Speed Pro TRW-L2441F pistons? $400 for a set. I've been running the 454 version of these for years....seem to work ok.
I would buy a cheap forged crank, some heavy H-beam rods, use a 4 bolt with a short fill, and some TRW L2441 pistons. Use a good oil pump and you have a bulletproof bottom end. Stud everything. Remember the blower puts a ton of strain on the crank snout - a good balancer is a must and have double keyways machined and installed. Factory large chamber heads work fine - but get heavy casting heads, not the later lightweight jobs. Put all your work into the exhaust port. I personally would invest in a set of Dart Iron Eagles or Canfield aluminums. Cost the same to rebuild stock stuff. I wouldn't use a factory forged crank with the price of new forged stuff. Sure its made in china, but if its from a good dealer/manufacturer like SCAT, I wouldn't worry about it. Run a larger blower like an 8-71 on alcohol and go reallllly fast with little parts breakage. Alcohol is very forgiving.
your rods are extremely important blower compression will destroy them pretty easy. spend all your money on your bottom end, then you can upgrade the top end as the money comes. Ross, TRW, and diamond make good forged blower pistons. H beam rods, or if you wanna pull revs use aluminum rods but they will have considerably quicker fatique. a good crank also, and if your using a 4 bolt block get billet caps it will cut dont on the flex of the block and keep the crank from walking around. A solid roller cam is great for blower setups, it wont float the valves or try to flatten the lobes under load. good flowing heads titanium valves, keepers and reatiners, beehive springs.it will lighten the valvetrain and allow you to make more efficent power at high revs and under cylinder load. First spend all the money on the bottom end, you can upgraded the rest later like i said.
If it is a drag only motor, the best thing you can do is to run methanol. Most engine failures are due to detonation. Heat and cylinder pressure along with too low of an octane fuel are your enemy. Methanol burns nice and cool and wont detonate like gas. Obviously methanol is not ideal for a driver however. Like the others said, a steel crank and forged pistons would be a good idea.
My 2 ccents... A friend and I rode a 6-71 huffed dragster deep into the 8's on our spare short block. It was a bone stock GM crate short block. On the next-to-last race of the season, it spun a rod bearing, we snapped in a replacement and are still running it. Race parts? Only if you have the money to burn.
You never know the edge untill you go over it.... That means, you never know what parts will fail untill they do. My motor runs 120+mph quarters and has stock rods (ARP bolts) and 2 bolt mains. But, Pontiacs have bigger mains than a Chevvie and I don't rev it past 5500 rpm. I did drop big coin on a set of custom pistons. I run 7 lbs of boost with 7.8 compression and aluminum heads to keep those pistons alive. Bottom line...build her as stout as you can, but that still might not keep you from scattering parts on the track. You just never know.. Pay VERY close attention to your compression ratio, boost , fuel mixture and timing and your pistons should live a long and healthy life. I'll still spot you a carlength at teh HAMB Drags this year. Holler if you need any help. -Abone.
I like the stock GM parts thing too....the 454 blower motor in my 55 has all stock GM high perf internals, the exception being the TRW blower pistons that replaced the original stock GM installed TRW forged high compression pistons. 70k miles or so on it, one overhaul to replace rings.
I'll take that car length!!! It may not be done by then though so I may need two!! I have a 700R4 tranny behind it now and intend on making it a street-able drag car. I like the fourth gear of the tranny so may have to send it off or get one built for this kind of torque. The budget is two thousand this year and another two thousand next if needed next spring!! The 671 kit itself is $2700 off the shelf new, and from what I hear is the safest way to get one without worrying about it being worn out. My intention is to do as told build the lower end from a good core four bolt 350 I have here now. What kind of compression ratio is too much and why a small intake valve? Wouldn't that restrict the flow in or am I missing something?
yeah, a small intake valve would restrict flow. Blower motors work just fine with typical "big" heads. Compression should be around 8:1.
Check out HRE.com forums. Best info and people around for supercharged/injection/alky stuff. They do charge a fee to join, but it's cheaper than making a big $$$ mistake on the engine.
the large amount of force put on the bottom end all at once. Backwards: compared to the same ft/lbs. of torque and cylinder pressure developed by a NA motor, the pressure spike is smaller and spread over a longer interval in crank degrees. The reason for choosing a head casting with small-ish intake valves is to permit as large an exhaust valve as you can fit without re-locating the guide centers, etc. If you can find one, the pre-1964 1.94" intake valve allows a 1.65" exhaust and still has an excellent intake port. You can shorten your exhaust timing considerably by running 1.6 or higher exhaust rockers. A 6-71 is a very primitive device, and produces more heat than power compared to anything else you can name. If the Jimmy is for looks - just remember you're paying for it. if you want real power, get an ATI Procharger from SD Concepts. More details: http://victorylibrary.com/mopar/blower-engine5.htm
A 6-71 is a primitive device, but if you run 8 psi or less the heat really isn't an issue. Go over 10 psi and then you might want to consider a more efficient blower. But this is a traditional board after all....and 6-71 was the hot ticket in the pre-1964 world.
Here is a good book , street supercharing by Pat Ganahl, I've been running a 671 on a 350 chevy for years it is just a big air pump.
Thanks for the help. I can start keeping my eye out for parts and start reading up on the whole damn thing. I have the start up money for it now but didn't want to go all in without having some idea of "HOW IT WORKS" ( I love that show). I did want to keep the big blower look but is there any other companies besides DRYER or WIEAND that make a more efficient blower than the 671 with the old big blower look? I don't like the short housing long snout look of the newer ones I have seen. Do I need to spend the money on the blower then build the engine around it or build the lower-end then keep my eye out for a good huffer? If looking for a used one what are the things that should steer me away from one I am looking at?
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