I want a blower and I want it now.

[Jim B]

Of course I do. I have a tired 350 SBC that I plan to rebuild with my son-in-laws help. Always wanted a blower motor and it seems like this is the place to find out what I need. I am not quite in the "build" process yet, but am well into the "acquisition" process. I have acquired a T-body, front end, posi rear end, tires, wheels, windshield frame, rear coil overs, lake pipes, radiator and the metal for fabricating the frame. Oh, ...and the tired 350 with still ok compression from a 1984 Chevy Pickup which is destined to be sucking big air if I can make it happen. I know I don't need 600 hp or 500 even. How about a mild boost that gives me about 400+ or so? What do you guys think?

 

[old round fart]

A mild blower motor will give you more than enough with t buckets! You will like it!

 

[Jim B]

For that kind of mild boost, what do I really need to do when putting this motor together to prep for the blower? AND which blower? Luckily right now it is a blank canvas.

 

[Spanky]

Make sure your bottom end is sound (good bearings, 4-bolt mains are desirable) and watch your compression ratio. Keep it around 8.5:1

 

[Island Girl]

Blowers are an awesome aesthetic on a hot rod.

How functional it is, and what you expect to attain can cover a wide range between being essentially "looks only" and 8 second quarter mile times.

Engine wise, like Spanky said, the bottom end and rotating assembly is where you start.
The bane of roots blowers is their miserable adiabatic efficiency, and the incumbent predisposition to detonation, hence the need to make wise cylinder head and piston choices, as well as accounting for what's available for gasoline in your area.

If you look at a lot of turbo or centrifugal blower setups, they at least have intercoolers to cool the boosted air, but unless you have a marine setup, or space for some extra hardware where you can run a Superchiller, you don't have that cooling with a roots blower.

That extra heat in the combustion chamber pretty much mandates forged pistons and aluminum heads if you want to use the blower for a real HP increase, as opposed to just looking cool.

There's some episodes of "engine Masters" on YouTube where they take a very basic crate engine, (cast pistons, rods, crank) and put a blower on it. The power gain is notable, and at least for a few dyno pulls, it doesn't blow up.

I'd hardly consider that evidence of it being a sound idea for your T.

Building a shortblock for a blower, or any power adder really, is significantly more costly than basic stock, so before you start gathering parts, be sure you plan the whole thing out in advance. . . Work out a budget, . . for a blower motor that makes good HP and will last, it's a major investment.

If you want an idea of the cost difference, just look at what it costs for an Edelbrock crate motor with carb, versus the same motor with a blower. . . . granted that's new retail pricing . . . but the difference is what's important.

As you look at blowers, about the biggest you can fit on a SBC and still have the original HEI distributor is a 6-71 . . you might squeeze an 8-71 with a small distributor.

If you're looking at a used blower setup, be sure to have a reputable shop, experienced with blower builds, check it out . . old and worn out is worse than none at all.

Best of luck on the build,

Darlene

 

[rbsWELDER]

Spanky - How do you test for compression ratio?

 

[Spanky]

It's actually a pretty involved process, determining combustion chamber volume. Most people just estimate it based on the advertised cc volume for your cylinder heads and the type of pistons being used (dished, flat top, etc). Here's a link to a video that shows how if you really want to go there . . .

how to test for engine compression ratio - Bing video

 

[old round fart]

Way back in the ‘70’s when I built my avatar I was helping Pete Robinson with his SOHC powered top fuel car and his (and Hoyt Grimes and John Reed all dragster drivers) recommended I go to a junk yard and get a truck motor (they all had 8:1 compression back then) and run it til it blew up and go get another one. I didn’t listen but didn’t go to overboard. Stock connecting rods, forged pistons, ported and polished heads and 1:1 drive on the blower. Later I developed a water leak on the heads so I replaced them with stock 283 2 barrel heads and could not feel any power loss. Things happen so fast in a blown car you just can’t abuse the motor enough to need a killer motor. Drove mine for 9 years and over 100,000 miles! I would follow Pete’s advise and will follow it with my new car.

 

[Island Girl]

Just keep in mind that back in the 70's, we had 100+ octane gasoline, and trucks were not built as "sparingly", (cheaply) as they are now.

For a low buck, blower rig, I'd look at an older, 70's to early 80's) 454 with oval port heads, (not the tiny newer (gen5&6) truck peanut port heads).

Even the 2 bolt mains are OK to about 600HP.

You'd have awesome torque and great seat of the pants feel.

 

[Gerry]

Turbo's suck. Blow the thing and enjoy

 

[409T]

I'm building a blown 392 hemi right now. 8:1, 2 bolt mains, steel heads, 8% under driven, BDS 671 blower. Nothing special, just a good streetable engine. I would be thinking potential torque, not HP when trying to decide what components to use and how to build, but that's just my .02.

 

[RPM]

Be SURE to get a double crank key and a billet drive hub. It takes a lot of power to turn the blower.

 

[Island Girl]

Be SURE to get a double crank key and a billet drive hub. It takes a lot of power to turn the blower.

Better yet, while we're visiting the drive hardware, use a double keyed Fluidamper, not a solid drive hub for a street driven build, you'll feel the difference in reduced vibration.

 

[Jim B]

Good stuff. I will make note. Anything else I need to consider from the ground up with a blower?

 

[Island Girl]

Good stuff. I will make note. Anything else I need to consider from the ground up with a blower?

If you elaborate more on your budget, transmission plans, how you plan to use the T, we could be more helpful.

You could take a low buck rebuild with basically stock parts and slap a used 6-71 on it and have a blower motor . . . how long it might last is another thing entirely, but it wouldn't likely be very long before you break it or detonate it to death.

Or . . . . you could plan a good forged rotating assembly, forged pistons designed for blower use, modern aluminum heads with great flow and far better cooling, a blower tuned cam, and have some serious HP that you could depend on for years to come . . .

Think about if you want a lot of torque at lower rpm range that feels great to drive on the street, or do you want to have top end HP that works for you on the strip?

So many variables and options that you need to consider before you start spending $$$$ . . .

Darlene

This is mine coming home from its dyno runs . . .

 

[HenrysT]

As stated earlier, you can get a bone yard motor and slap a blower on it and cross your fingers every time you step on the loud pedal or you can put some insurance in like putting ARP studs and/or bolts, polished rods etc. and not worry about it, except for the speeding tickets. All this machine work , blue printing, studs is just like insurance. Like the old Fram commercial... "You can pay me now, or pay me later"

 

[fletcherson]

A blower is a big investment if you only want 400 hp.. maybe a little street charger, like weiant 177... I think they advertise 400 or so hp on a basically stock motor but you are still looking at 3k for the blower kit alone. You can get good power without one, it just depends on what you want and how deep your pockets are. Do your research, if you want big hp, don’t cut any corners, build a forged, balanced, rock solid motor with the blower in mind. I love blown engines. I built a iroc z with a centrifugal charger back in 97...I spent close to three grand then and the engine was already built.

 

[PotvinGuy]

Decide what you want before buying: a screamer or a cruiser. A screamer needs serious parts. Now I've been running a 671 on a crate SBC for years, but I drive like granny going to church...most of the time. I'd suggest underdriving a 671; while cruising it just makes hot air. Timing: low CR can use lots of initial. I run 20 initial, 15 speed and 15 vacuum, with boost retard. If you don't have boost retard, you might lower those numbers. Knocking can't be heard on our cars at high speed and high load, and it will bust up your motor.

If you can find a B&M 250 blower, it looks great on a SBC:

 

[Indycars]

Are those valve covers clear ???

 

[Jim B]

If you elaborate more on your budget, transmission plans, how you plan to use the T, we could be more helpful.

You could take a low buck rebuild with basically stock parts and slap a used 6-71 on it and have a blower motor . . . how long it might last is another thing entirely, but it wouldn't likely be very long before you break it or detonate it to death.

Or . . . . you could plan a good forged rotating assembly, forged pistons designed for blower use, modern aluminum heads with great flow and far better cooling, a blower tuned cam, and have some serious HP that you could depend on for years to come . . .

Think about if you want a lot of torque at lower rpm range that feels great to drive on the street, or do you want to have top end HP that works for you on the strip?

So many variables and options that you need to consider before you start spending $$$$ . . .

Darlene

This is mine coming home from its dyno runs . . .

NICE! Way more motor than I plan to build. What did it dyno?