6-71 small block choices... which is best?

[65TerrorCuda]

I've been perusing the 6-71's available for small block Mopars for a few years now, and want to know everyone's opinion who's owned or tuned a blower motor.
The brands I've found so far(that make complete 6-71 blower kits) are BDS, Hampton, and Dyers, from most expensive to least.

I've contacted these manufacturers but can't get a straight answer about the intake manifold differences. All they'll say is that it's a two piece welded intake, with the bottom half being a milled dual quad intake(Offy).
I'd like to find the lowest profile intake possible to keep the carb hat from knocking low flying planes out of the sky.

Some brands claim to have the best blower and say everything else is junk, while others offer 12 month warranties. Are they really that different?

[65TerrorCuda]

well sonny youll never find any of that stuff out no one ever put a 671 on a small block chryssler
their all 6 inch tall manifolds, you hav to hav a secont keyway cut in the crankshaft, lock out the timming on the destributor advance, run 1/2" fuel lines and sure, a single 750 4bbl is just fine
Now you'll probebly want to know how I logged into your account and such! Save it.
:flip:

[rumblefish360]

Yikes! Sounds like Mom or Dad got ya.
"no one ever put a 671 on a small block chryssler"
Bull!
Well, theres a few guys running around here with blown small block Chrysler engines. The first thing about biz is no one will ever say there second best. Why would they? If they did, you would ask who, which they'll never say and if they did, I would say there head was hit with a piston and rod assembly from a P.O.'d worker.
Then you would purchase the comptions and not theres.

"their all 6 inch tall manifolds"
Bull!
On the intake diff's, theres really none.
Theres no such thing as low profile blower intakes. There all low. Period.
The blower itself is the main thing in size. The blower case is the barrel part. There are size differences in super chargers. The smaller the number, the smaller the case. Holley offers smaller units not in the 6-71, 8-71 etc. size. There listed as 142 or 177 super chargers. There cases are a lot smaller. I have a freind that has a 142 under his hood in a Nova. Do not under estamate these little monsters.
DLI (Dick Landy) uses these superchargers with his stuff for a bolt on kit.
"you hav to hav a secont keyway cut in the crankshaft," Never seen that done, on several cars with blowers. No make exempt.
I have seen Olds, Buicks and Chevy big blocks. A Poncho and sevral small block Chrysler, Chevys.
"lock out the timming on the destributor advance, "
Not true. However, there is a valid point to that.
"run 1/2" fuel lines "
Not true again.
"a single 750 4bbl is just fine"
That depends on ALOT!
"Save it."
Save your money. Wise idea until you know what you need to know. Unlike someone else here, other than me, that didn't save there play time for later and study there spelling.

Oh, if you are 12, I commend you for trying to find out the facts and doing some research. Good work! No matter the age. Keep up the good work.

[sanborn]

I have no experience with supercharged SB Mopars. I do have experience with SB "off brands" spaning several years and several miles.

I have several questions/comments:
1. What do you plan to do with this engine? Is it street only, street/strip or race only?
2. What HP/Torque level do you want?

If you are wanting practically anything more than 500-550HP, consider the block you choose. You need something with 4 bolt mains and good cylinder walls. This takes you to "X" or "R" blocks real quick.

If you want more than 600HP, use only W2 or better heads. The same can be said for carburation. A single 750 Holley acts as a "restrictor plate". If you want more---use two 750s.

Gotta eat supper-----Be back later!

[sanborn]

Continuing on:
Crankshafts/ Rods---If wanting more than 600HP, consider aftermarket. You will need 4340 crank/rods. Mopar 1053 cranks aren't strong enough. Get good blower pistons with .220"+ top ring margin.

Ignitions---A locked distributor is fine, will work well even on the street. You need something like an MSD ignition system. You can use a mechanical advance distributor with some curve tayloring---but stay away from vacuum/mechanical.

Tuning---If at all possible, get the engine to a dyno with data acquisition. You will be surprised where the engine may want to run jetting wise, advance wise, hedder wise. Set the controls for 500-600 RPM/second. Less gain may strain the internals of the engine too much.

Oiling---Do not use full groove bearings, they may not take the strain. Enlarge the oiling passages for good flow especially to the connecting rods- especially if you want to go to 7000+RPM.

Now to brands of conversions---All three you mentioned have been around for years. All three probably produce good parts. Make sure you are comparing "apples to apples". There are "stripped" blowers and "non stripped" blowers. There is a significant difference in cost. Generally "stripped" blowers are for racing only, non stripped are usually for the street.

I've probably said everything needed up to this point. If you have other questions, I will monitor this thread.

[71dart666]

You ever checked out ATI prochargers? They arent a 6/71 blower that sticks out of your hood but instead are centerfugal superchargers. Though all my knowledge is limited to reading magazines ect.. they seem to be extremely potent power makers. I read an article ::covers face in shame:: in a Chevy mag where they supposedly got 760 hp out of a built 355 on pump gas... doubt it'd last very long but just imagine if you did the same thing to a 340 or 360 assuming the engine block would take it.

[rrunner69]

i was watching that show rides the other night and they used a similer style (BLOWER) on a ferd expedition bumped the hp from 240 to over 400 by bolting it on they used a shaker scoop off of like a cuda it was pretty cool all fit under the hood a little noisy with the blower whine what a waste of some good mopar parts

[Cliff Foster]

rumblefish have you ever heard of the Long Island Ducks? I play in a league that plays against them called the Atlantic league. We start in late april

[71dart666]

Just curious on a side note, what is the maximum power output that a small block say 340/360 can take? Not rods or crank but the bare block, I hear its about 600 or so ? What about the MP magnum blocks, are those any stronger then the old ones?

[rumblefish360]

Cliff Foster; Sorry to get back to you late. Yes, the Ducks play within 15 miles of me. There popular and well advertised here. They do well in selling tickets. Theres a huge difference in Major league ticket prices. It sucks. N.Y.ers like baseball. Not the price.
Let me know when you come to town. Lay me on your scheduale. (sp)

71dart666; Cast cranks have that 600 HP warning limit. I know you said block, but I have not met or seen anyone geting to that level. Dewme5 had a twin turbo set up w/12 lbs of boost and cracked the block. Read about here; ( http://mywebpages.comcast.net/dewme5/ )

[Cliff Foster]

email me at fittrainer@msn.com our season starts april 27th and ends at the end of sept

[71dart666]

Would 4 bolt mains help strengthen things up abit down there? Or is it just the block itself that gives out. Ive seen that other guy post on here hes got like a 71 cuda or something with twin turbos on a 408 stroker i beleive, I think he said he runs high tens.

[sanborn]

Mopar blocks vary a lot in rigidity. The stiffest are early 318 blocks, next are early 360s, then the early 340s. The weakest are the thin wall castings. The stiffness of a block is generally determined by the thickness of the cylinder walls.

Four bolt mains help the stiffness of the block some---but don't help as much as thicker cylinder walls. What generally gets a block is twisting forces---main caps don't help that much.

Four bolt mains really help reduce main cap "walk" that comes about under high torque applications. And, since four bolt caps are generally beefier, are not as prone to crack as a stock cap would be.

By all means, use four bolt caps if possible. But, strong cylinder walls are more important.

Now back to the eternal question--Will stock type blocks hold up under a supercharger? It all depends on how hard you stress it UNDER LOAD.

We have broken four bolt main X blocks in half with 650HP/ 550 ft. lbs. of torque. We watch our aluminum blocks flex every race(800 HP/600ft. lbs.). But, I am beginning to believe our kind of racing(dirt oval) is harder on an engine than any other type of racing.

What your engine will see under a supercharger will be different than what we put our engines through.

1. Depending on the overdrive and the efficiency of the supercharger itself, you may not begin to put out much boost until 5000RPM--about where your torque curve peaks. So additional boost only helps to maintain the torque at higher RPMs, not increase the total torque output.
2. That's why turbochargers are much easier on blocks, cranks, etc. Their boost comes at much higher RPMS and don't stress the components near as much. That's why turbos are favored by OEM automakers- it's easier on the components.
3. If you want a streetable combination, you will probably choose a camshaft with more lobe separation, like 110-112 degrees. The additional degrees of separation helps to reduce cylinder pressures(easier to drive on the street) and also makes the combination much easier on the components.
4. If you choose any cylinder heads other than serious race heads, your engine will be very limited on HP/Torque anyway.
5. Torque is what kills components, not HP.

I'm sort of wandering around with this response. I hope it makes some sense to you.

[rumblefish360]

sanborn; Clear and as allways, well writin.

[71dart666]

What about the new magnum blocks used with the crate magnum engines? Do those have any advantages over the older blocks? Id assume you'd want to keep it as close to original bore as possible then for strength right.
Also it would be better to run maybe a bigger suprecharger unit and kinda go for a topend rpm engine rather then a high boost lowend engine wouldnt it ?

[millerman340]

So, The 70 318 block is stronger than a 72 360 block? what about the main journal size any factor on that?

[kl89360]

Originally Posted by millerman340

So, The 70 318 block is stronger than a 72 360 block? what about the main journal size any factor on that?

i have heard before that the early 318 blocks will take a overbore of up to 4" from the stock 3.91 bore,if that were true and it will absolutly have to be sonic checked to know for sure,but in a forced induction case like this i would have to say the 318 bored minimal would be stronger than its larger bore brothers.the 318 main journal size of 2.50 is plenty plenty strong,the stock 360 is 2.81 and truthfully probably overkill.imho :baby0:

[kl89360]

oh yes and btw,ANYONE actually considering overboring their 318 to 4" should really think about what they are doing!lol! :chainsaw:

[sanborn]

I believe your best block is an aftermarket X or R block. There is no comparison in rigidity to a stock block.

But if you insist on a stock block; here is my preference in descending order:
1. (best) 318 "Industrial" block(w/poly heads)
2. Early 318 block(pre 70)
3. Early 340 block
4. Early 360 block(with 340 water jackets)
after those I would be very careful!

[PhilThePitcher]

could someone post up a link, i can't find any small block blowers, btw i have a 318

[73Cudaswap]

I totally agree with rumble fish on about every point he makes. He's dead on about small blocks and blowers, but one thing I think he might have missed is to pay very close attention to the specs given by the manufacturers. I personally prefer BDS, the tech support and quality of components is phenomenal. I saw an add the other day that a guy had, 1970 Camaro, 454 bored .60 running 11.5 to one compression pistons and a BDS 6-71, needless to say, really really bad idea. Blowers don't like high compression engines like that, they have a tendency to put parts in orbit, especially a street car setup. Do some checking around if it's really the way you want to go, especially since nothing sounds prettier than blower whine.

[tman32]

Originally Posted by 71dart666

You ever checked out ATI prochargers? They arent a 6/71 blower that sticks out of your hood but instead are centerfugal superchargers. Though all my knowledge is limited to reading magazines ect.. they seem to be extremely potent power makers. I read an article ::covers face in shame:: in a Chevy mag where they supposedly got 760 hp out of a built 355 on pump gas... doubt it'd last very long but just imagine if you did the same thing to a 340 or 360 assuming the engine block would take it.

As far as the power goes. I really like the 671 dyres. And it is in a 340 and the block does take it no problem and low and behold it is on pump fuel.

[sanborn]

Let me provide a little info---it's not about a Mopar but a GM---but the same basic info will apply to any OHV engine.

My son "had a wild hair" and just had to have a 671 on his GMC pickup. So this is what he built:
---.030" 350 GM engine, early stock block with billet 4 bolt mains(the weak point in my opinion).
---215CC Dart iron heads, properly prepared, stainless valves, moderate port work.
---Winberg Billet crank, Carillo rods, Dished CP blower pistons(8.2 to 1CR), balanced, etc, Total Seal rings.
---Usual block prep, enlarged oil passages, etc.
---Two 750 Holleys(Stealth prepared)
---MSD ignition (locked advance)
---Comp roller, roller lifters, stainless rockers, Isky "Tool Room" springs, Del West super 7 locks, retainers, etc.

This is a "street cruzer" engine, not a drag engine.

Now comes the dyno work----
After fire up, breakin with two hours of run time, retorque, check valve lash, etc., he could begin some dyno work. The dyno is a Superflow w/latest data acquisition.

Initial runs showed 620HP with power fairly flat up to 6500, it fell off above 7000. Not bad!! Blower was running one to one ratio. 15 lbs. of boost at 6500.

Realized the carbs were not opening up all the way. Linkage was corrected, power went to 649HP, kept pulling to 7000. Boost was 17 lbs. at 7000.

Talked to this carb guy, he recommended changing the MSD box to a 7A. WOW! what a difference! Power was better all the way up---to 694HP. Boost was still 17 lbs.

Tried three different sets of headers, found the 1 7/8" primary step, 2" secondary step worked the best. Went up on ratio, got to 20 lbs. of boost---found it didn't produce any more power. We suspect the heads are acting as a "restrictor plate" and not allowing any more air to be forced into the combustion chamber. Backed the ratio back down.

So that is where he stopped!

Since then, he replaced the old used rotors with a new set, set the rotor timing clearance. Another big difference, now he gets 20 lbs. of boost with 5% underdrive. Another thing, changed the rockers from a true 1.48 ratio(at valve) to a 1.52(at valve). The engine is much stronger.

He also built a methanol supplement injector system. The thing gets absolutely brutal---unsafe unless the driver is very experienced. The methanol cools the charge, condensing the air thereby forcing more into the combustion chamber.

Remember, this is a "cruzer". He got 16.3 MPG(interstate) on a recent 800 mile trip. He uses 50% 93 octane and 50% VP 110.

The truck is a 87 GMC(his grandfather's), weight is 4250, Nascar full float 9" Ford rear, Nascar truck arms, coil over rear, full four puck Nascar disc setup on front/rear. Trans is GM 350(built by someone in Alabama). Fuel cell and dual batteries in rear of bed. 50/50 weight distribution.

I am posting all this info to help inform. This is what he did---and these are the results. You should expect like results with a SB Mopar---provided you use like components.

Roots type GMC blowers are neat. I used one over 30 years ago on the street. They are some hassle---but what isn't in life. If we didn't want hassle---we would be driving electric cars---or riding a bicycle. Good Luck!!!

[moeflo]

A little on the blower styles. Since the roots types always are compressing air, they are always making heat. The centrifugals operate much more like a turbo. During normal operation they are just along for the ride. They build boost with RPM. i ran a 9lb intercooled ATI (little P600B) on a bone stock 302 ford. It had a 9lb. pulley set up. It would provide something between 9-10 lbs. total. If nailed at, say, 1500 RPM, boost started to show at around 2700-3000 RPM (about 2-3 lbs) By 4500, it was 8, with the total in by 5K. They are so much easier on the engine than a roots type, if long-life is a concern. I put that one on at 117K, retired the car at 197K motor and blower still good. Always on pump gas and stock timing. (BTM's are a must w/o intercoolers, on centrifugals). Low end performance is not an issue with these. Assuming you can wait for 2500 RPM to come around. And, nailing it in second at 1500RPM, it would start slipping the tires at about 3500, and at 4-4500 RPM it would just blow them off. Stock everything other than 3.55's

They lack the looks and romance of a roots (but, not the noise). So it's just personal taste. Just don't rule out this type due to precieved lack of low-end.

[sanborn]

Hey Moe, how have you been doing?

I'm sorry I failed to answer some of your messages. I guess I am the "Forrest Gump" of computers. I didn't even know I had a "private message" section to go to!

[moeflo]

Originally Posted by sanborn

Hey Moe, how have you been doing?

I'm sorry I failed to answer some of your messages. I guess I am the "Forrest Gump" of computers. I didn't even know I had a "private message" section to go to!

Doing good. How are the various projects going? Is the flathead up and running? Yea, check those PM's,

[sanborn]

Moe,
Had to push the FH/40PU back in the corner. Wife wants her 289/40Sedan finished first. I will get there---sooner or later!