AFBCamaro

Hey guys I am starting my 6-71 GMC blower project. Tell me what you think. Especially what you think i will make for HP/TQ.

I just finished rebuilding a good original GMC Diesel blower to put on my 305 small block (lo3).

Just for the fun of it my car is running mid 14s with the untouched original 305 TBI heads.

Here is my setup. The engine is original full cast bottom end. Im getting a good set of 882 cylinder heads (76cc) which flow great and i am doing my own porting work and concentrating heavilly on the exhaust side. Stock valves are 1.94 and 1.5 and im changing the exhaust to 1.6 valves. The estimated compression ratio will be around 7.7.

It have headers with true dual exhaust and i will soon add some cutouts on each exhaust pipe for the track.
I estimate around 10-11psi running the blower 10% underdriven.
The blower will rider on a port matched bds intake manifold. Two carter 625cfm carburetors 3.42 posi in the rear and a 700r4 for about two weeks(est) till it blows I already rebuilt a th350 for when the 700r4 goes.

After it is well tuned for the street I will go to the track to get some times with it in street trip(stated above).

And then im going to take a risk on one run and run the blower 1:1 :-O
I will open the exhaust cut outs. chill the blower and the intake manifold and make a pass. Might even consider a 50 shot of nitrous oxide for cooling effect. Run 118 octane gas and around 26 deg of total timing.

What do you guys think? Any and all comments/suggestions welcome..

Take care guys I will update this as I go on.

mw66nova

iTrader: (13)

i am not sure how well those heads and valves sizes will work with the 3.73" bore. the problem is that the valves in it now MAY hit the side of the bore and the valves you put it in will PROBABLY hit the side of the bore. i would consider a whole build up, dished pistons and all, and go with a 305 sportsman s/r torquer head. or, find a set of 416's and port the crap out of those. get a valve job and 1.94/1.50 valves. then bolt your charger on top of that. i understand what your trying to accomplish with the big cc head, however i just don't think it will work with the small bore, unless you have the block chamfered (like willie's). and even then, you may still run into problems. if your seriously concerned about exhaust, maybe run a 1.6:1 ratio rocker on your exhause valve. however, boost is an interesting thing and has the ability to push alot of mass through very small openings. just somethings to consider. with the 58cc combustion chamber, build for about 8.5:1. then run 10lbs on that for the street. and go 1:1 at the track. you should see some good horsepower and TONS of torque. yes, that 700r4 will be gone in no time....have fun!

AFBCamaro

I definatly see your point, I have considered this posiblility myself. I am running a .450 lift on the intake and the exhaust right now, so i was thinking i might have been able to get away with it. But since I want to have this done by the end of august I will do as you say and install 1.6 rockers on the exhaust side to get a little more duration and lift out of my exhaust. This cam is an extremely blower unfriendly cam its got a lot of overlap but the situation is actually patched up quite nicely thanks to my rhoads variable duration lifters.

This is actually a budget buildup so I am staying with the stock LO3 305 Shortblock for now. (cast pistons scare me a little) I was building a 385 and sold all my rotating assembly to buy this blower. I originally bought a 144 B&M Blower and sold it before i put it on to buy the parts for this one(6-71). Its not as efficient at low speeds but ive been in a 4-71(smaller) blown car and the prodigious torque scared me. Later I will build a purpose built blower shortblock. (357sbc).

If i like the power the 305 pushes with the stocker shortblock I might get crazy and push the 305 to crazyness levels with a full forged shortblock 305, maybe a stroker 334? Maybe??

On the side of my car it says Little 305 so Im in it for the shock value simply because im just bored of conventional everyday build ups.

Hey mw66nova thanks for your reply any more would be apreciated. (from anyone)

What do you guys think I will run in the street trim and the crazy trim?

AFBCamaro

WOW this topic must be really boring. Im i not high tech enough for you guys :-)

Man i fell outdated. no centrifugal dual intercooled quad turbo setup for me :-(


ok then i will go into the nothingness of which i came!

mw66nova

iTrader: (13)

well, i have definetly decided to go with my 305 (or should i say: 310) build up so we will be 5.0l buddies. the plan is to run all forged bottom end with the exception of the stock crank (it's in extremely good condition.) flat tops with 416 casting heads. all-in-all about 9.22:1 compression.(very gasoline friendly) i however, will probably go with nitrous as my power adder as the nitrous can be turned on and off when needed. i am not making a whole lot of money and i am going for economy with durability. my parents are helping me out financially and then i will pay them back. it's kinda like a going away present before i move out.

if i were you, i would look into the comp cams nitrous cams, they are great for boost as well. jegs sells them. i wanna say they are like $180-190 for cam and lifters. they also work well with out poweradders.

my ultimate goal is to run either a procharger d-1sc or a 144 powercharger blow-through style. which is the main reason i am going with the forged bottom end.

hey man, have fun and be creative. oh, about the 334 stroker idea, that would make massive amounts of torque but they lack the ability to spin up quick and you will probably start loosing power after 4500rpms simply due to the fact of the small bore and the HUGE stroke. very hard to make upper rpm power. word from the wise, ditch your current heads and get some 416's. they are everywhere. any LG4 or L69 from 82-86(?) has them.

AFBCamaro

I was wondering would I be able to adapt a BOV to the 6-71 setup. The reason is that I know that the rotors take a small beating when I let off the throttle. Which I happen to do every time I shift. Besides if somehow I can adapt it to the blower it might sound kind of nice in between shifts. If I did this for now I would get a stock used one out of some unamed car

PS-my setup should push between 8-12 psi if thats any help
Thanks for your replies

83 Crossfire TA

iTrader: (2)

The rotors _should_ never touch. If you’re talking about a rattling when you let off the throttle, that’s probably some slack in the drive gears allowing a little clunking (most roots types have straight cut gears that cause some extra noise there… eaton claims that it’s gotten rid of it on the M112 that it uses on the Aston’s and Jags by using helically cut gears).

WRT to any damage that you think that you might be causing when you let off the gas to the _big, heavy_ rotors, don’t worry about it, they can take more then the rest of the setup will.

If you want to do something like that that would be cool, run a bypass so at idle/part throttle the blower is basically along for the ride. This should have a big impact on normal cruising and gas mileage. Newer eatons have a bypass built into the case and eaton claims it lets them use less then .5hp at normal cruising speeds.

AFBCamaro

I clearanced the rotors so they never touch, they are very close though. :-) I like it tight

I was concerned because alot of the street kabooms ive seen have been when right when the carburetors go from WOT to a sudden stop.

Its probably that at that momoent the rotors are still pushing at a high speed and suddenly when the blades get closed it causes a momentary lean. ??!?!

Can anyone explain this eaton bypass system. Ive believe ive read about it somewhere. I will be doing my research into this now. Maybe on how to cheaply implement such a bypass.