SBC/6-71 Blower Motor Questions for the motorheads here

[Curly]

I have decided to build my first blower motor for my project. I want it to be dependable #1, All out HP is NOT a priority, and it should look like an early motor. I figure 6500 RPM and 5-7 lbs boost is the tops for this mostly street driven motor. Here is some of the things that I have collected and the question about them...

1. 350 010 block (2 bolt main)...is a 2 bolt going to be sufficient?

2. A pair of 1968 307/327 032 heads (70cc chamber, 1.5" / 1.72" Valves and no accesory bolt holes) Will valve diamter kill this motor? What style valves should I run?(severe duty, open up the exhaust side to 1.6"...)

3. Stock 350 Cast crank -10/10. Will a cast crank live up to this?

4. A set of TRW Forged Blower pistons mounted on a set of Pink rods ala floating style...I think these should do just fine.

5. Cam selection:Hydraulic .447/.447 gross lift, .222/.222 @.050, 114 degree lobe angle.

6. Induction: Weiand Intake, 6-71 and 3 Rochester 1 3/32 2G's (840 cfm total). Should I be looking for the 3 of the 1 1/4" carbs?(1143 cfm total) or use 1 1/4" outboards and 1 3/8" primary for a total of 1197 cfm?

Any other tidbits of info that I should know about building a blown motor? So far I get the same answer from everybody that I ask...Make sure that your bottom end is strong...nice info but not very helpful http://www.jalopyjournal.com/ubbthreads/images/graemlins/crazy.gif

[Roothawg]

First of all I think,(now this is my opinion) that you need to spend the money on your short block. You need to have a steel crank, buy a SCAT crank, they are cheap.

Secondly, you need to have good rods and rod bolts. A blower is a big air pump so it will continually be pumping, even when you are just cruising.

Thirdly, the heads need to be able to scavenge the cylinders or you will just have a great big intake manifold instead of a blower. I would say 2.02/1.60 at the very least.

As far as carbs....I don't know.

I am no expert but these are the things that sent up a red flag for me.

[porknbeaner]

Root is right about the crank.
Your boost doesn't sound too extreme you don't really start haveing fuel supply problems until you get up above 10 lbs of boost.
Big valves are good and I prefer open chamber heads especially if I'm building a streeter.

Your cam should have no overlap, good wide lobe separation, I normally call the cam grinder and ask for a blower specific cam.

Your 2 bolt block should hold up OK, but you should make arrangements for the future when you decide to boost the c#$p out of it. Huffing is an addiction just like running nitrous, the more you do the more you want to do. You will want to run more boost in the future.

So take the block and find yourself a set of 4 bolt caps. Fit the caps to the block and have it align bored. The two bolt chebby has thicker webs than the 4 bolt block so you will end up with a stronger block.
O ring the block (not the heads), that way you'll be able to run more boost if you want. And if you change heads you won't have to have them O-Ringed you'll already be set.
Shoot for a static compression of 8:1 or less.
Polish everything, the rods the lower end.
I've probably missed something but this will get you started.

[Fat Hack]

Also, carburetion and ignition are VERY critical. Don't be afraid to run "too much carb" as far as what works on a normally aspirated engine. Two Holley 600s should work out well for ya.

You want the mixture a little on the fat side...a lean condition in a blower motor spells a quick and violent death! Tuning the carbs and sorting out the final combination will be a meticulous task, but a very neccessary one.

Make sure your ignition system is up to the task as well...lighting off the squeezed mixture will take a reliable, healthy spark. Buy the best wires and coil you can afford. Run the gap a the outside of the allowable range, and buy cooler plugs.

Also very important...WATCH YOUR TIMING AND ADVANCE CURVE! Detonation is a killer, and you don't want any...trust me! You don't want any more than about 32 degrees TOTAL ADVANCE with a blower, and you don't need it comming in too quickly.

A good safety measure is a "blower window", usually located in your manifold at or near the base of the blower. Should a backfire or explosion occur, this 'window' is designed to pop out and hopefully save the rest of your motor from taking the brunt of the force. Always a good idea.

Of course, exhaust is a concern to be addressed while you're at it. Good, large tube headers are a must...backpressure can only be a BAD thing here...make it FLOW!!

[Curly]

Root,
Thanks, I was thinking of going with the SCAT crank as insurance but had the crank sitting here...it still needs ground so I might as well leave it there and spend the money I was going to use to grind the crank and put it towards the new crank.

The rods are the good GM pink rods and they have been polished and have a new set of ARP bolts in them.

[Curly]

[ QUOTE ]
Root is right about the crank.
Big valves are good and I prefer open chamber heads especially if I'm building a streeter.

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Does the small intake runner and valve idea of making more torque go out the window when putting a huffer on it? I read somewhere that the exhaust side is where you want to concentrate...big valves (forget the % rule of intake over exhaust of a normally aspirated motor) and large diamter primary headers. Currently 1 5/8 Speedway megaphone kit. In the future it will be a set of long 2" Zoomies

[ QUOTE ]
Your cam should have no overlap, good wide lobe separation, I normally call the cam grinder and ask for a blower specific cam.

[/ QUOTE ]

Crower shows a moderate boost cam (5-10lbs) as:
114 Deg, .232/.232 @ .050 and a gross of .459/.459
Mine is:
.114 deg, .222/.222 @ .050 and a gross of .447/.447

[ QUOTE ]
Your 2 bolt block should hold up OK, but you should make arrangements for the future when you decide to boost the c#$p out of it. Huffing is an addiction just like running nitrous, the more you do the more you want to do. You will want to run more boost in the future.

[/ QUOTE ]

You are probably correct on the "Need more boost" mentality...I tend to get a little overboard on stuff like this

[ QUOTE ]
So take the block and find yourself a set of 4 bolt caps. Fit the caps to the block and have it align bored. The two bolt chebby has thicker webs than the 4 bolt block so you will end up with a stronger block.

[/ QUOTE ]

Hmm was thinking of this and looked up the part number last night! Sounds like I'm thinking the correct way http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif

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O ring the block (not the heads), that way you'll be able to run more boost if you want. And if you change heads you won't have to have them O-Ringed you'll already be set.

[/ QUOTE ]

Great Idea! I'm putting that on the list of things to get machined!

[ QUOTE ]

Shoot for a static compression of 8:1 or less.

[/ QUOTE ]

Gotcha...Thanks

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Polish everything, the rods the lower end.

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I assume you mean the lifter galley and EVERYTHING! I might as well do the outside too since this is going into a car with no front sheetmetal except an empty model T grille shell!

Thanks!

[Curly]

Hack...you are a plethora of information! Was good to finally meet you at Broken Dreams last weekend. I tagged this as a favorite post. I knew that timing advance and "over carbed" were a couple of things I'd have more questions with. I heard a MSD with a retard curve was the ticket. Manifold has a pop off plate in place of a t'stat neck. I'll plumb the water into the 1/4 NPT holes on the rear of the manifold. I'm running the radiator in the bed. It should turn a few heads when done. Now that Hammerin' set the bar up a notch I went home from the cruise inspired and thinking. http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif

[Fat Hack]

Ha Ha...good stuff, Curly...wish I woulda gotten to talk to ya a bit more! http://www.jalopyjournal.com/ubbthreads/images/graemlins/cool.gif

[Roothawg]

I want to hear more about this topic........

[Scotch]

I still think you're going to see issues. It's seems obvious to me you want to he look but not "max performance", so, I'd drop static CR to 7.5, or even 7.0:1. I'd also underdrive the blower (BIG blower pulley) in the range of 30 percent. You won't make big boost, but you don't need to. You want it to live, not win races. Over-exhasut it, as was mentioned, with bigger exh. valves and oversize primaries on the headers. Be conservative with the timing, as was also mentioned. Use ARP studs on the main and rod bolts. Run wide ring gaps (.018-.020), and make sure you've got a good crankcase ventilation system (a vacuum pump would be best, but at least have several breather points on the motor, like 1 in each valve cover and one on the fuel pump blockoff plate).

Blower motors can be very civilized if you design them right. If you want to push it hard, that's another post, but if you want it to be reliable, fun, noisy, and bring lotsa looks, don't overwork it and don't expect it to be a top fueler. Blowers make heat since they're compressors...the molecules bump into each other and this friction causes heat. Heat kills engines. So, if you want a functional blower you can still rely on to get you anywhere, keep CR low, underdrive the blower, be conservative on the timing, run nothing but good gas, and don't wind it up too far.

Also- REMEMBER! The engine will swell when it heats up. Keep some slack in the blower belt when the engine is cold and you're setting it up. Between half-inch and an inch of slack on the longest portion of the belt is fine. Once the motor warms up, the blower will move up and take slack out of the belt. If you don't have enough slack, the belt tension will pull the crank up into the bearings and burn through them. You know this is the case when you see the top of the main bearings worn out after it lets go. Too tight of a blower belt will murder your main bearings.

Many late-model blower setups have spring tensioners to account for this growth. Old school setups do not, and this slack must be accounted for.

I've done quite a few blower setups for street and race on gas and alky with carbs and EFI. If ya get stuck, I'll do what I can to help ya.

Scotch~!

[Curly]

Huge smokey doughnuts in the middle of Woodward Ave. See this
http://www.jalopyjournal.com/ubbthreads/showflat.php?Cat=&Number=511652&page=1&view=collap sed&sb=5&o=&fpart=1

[Fat Hack]

Scotch is right on the static compression ratio for sure. It's easier to fight detonation and build a "mild supercharged" engine that will live if you start out in the basement as far as static compression goes.

(For running on pump gas, this is ultra critical...if you start out at what sounds low, say 7:1, then add a couple pounds of boost, you're already building cylinder pressure relative to that of an engine with a 9:1 static compression ratio. Go much over three to five pounds of boost, and you'll be looking for race gas...even with "only" 7:1 compression to start with.)

The added heat of a supercharged engine is going to require a cool, steady fuel supply...electric pumps with one regulator per carb and a return line to the tank aren't a bad idea.

To keep the engine alive, it will need an adequate cooling system as well. BIG radiator, free flowing water pump and appropriate fan(s) to do the job. Compressing air builds heat...above and beyond what the engine already produces...be ready to compensate for that!

[Tony]

I know i've posted this before somewhere..but i'll give you the skinny on what i have and mine is VERY streetable..

283 (all are 2 bolts), bored 30. Double hump heads (1.94 intake), mild port work.
8.1 pistons, stock rods with ARP bolts, shot peened. Steel crank (small journals were all steel).

I have a Lunati 'Bracket master' cam with around 500 lift.
2 500 carter's tied together (not progressive).
I did spend some time getting the carbs tuned right. I too like them to run a touch fat.
It keeps the motor a little cooler, and my headers from discoloring real bad.
It dosn't even foul plugs..i've had this set in there since the beginning of last year.

Dyers V 6-71 huffer running 27% under.
The blower is about 300ci, and my motor is only 288ci so thats one of the reasons it's under driven so much, plus the 8.1 slugs would be too much with much more.
It still makes boost, and when you step on it you KNOW it's blown..

The cooling system is very stout.
Walker Z-series rad, Stewart hi-flo water pump, stewart hi-flo thermostat and March under-drive pulley's (for better cooling, not the performance ones)
I didn't want any problems overheating if i was crawling through a show..
It has never gotten above 195 no matter how hot it is out.

Yet i'v had this thing out on the highway doing a steady 80mph with out even a burp..
It's been together 4 years this way, and i have not had one problem at all..

[Roothawg]

Hey packrat what kinda mileage do you get? Is it insanely bad?

[Tony]

When i had just the two 500's on an Offy intake i was getting around 10mpg or so and again, they were tied togeher..
Once i put the huffer on and fattened up the carbs it dropped to around 8ish.
I havn't checked it in a few years, just once to see the difference.

I know this year when we went to the Syracuse Nats, about 120 miles the way we went, i went through a full tank of gas, 16 gal.
So that works out to be around 7-8 mpg.

Not much worse than my '02 GMC at 10mpg, and a LOT more enjoyable to drive http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif