BBC heads and 6-71 blowers

[bfr57]

Getting ready to build my first blower motor, a Mark VI BBC. I'm considering a pair of cast iron heads that are available locally for a fair price, I think. They are 781 castings, oval port, with extensive bowl work, porting, CC'd, and gasket matching. They come with Manley stainless 2.19/1.88 valves, 10 degree locks, but no springs for $300. How will they work for a street only, low boost 6-71 blower? I'm not after huge HP, but I don't need it choked either. OR, should I save my money and pony up for some aluminums?

[Adam's 55 Chevy]

781's are open chamber so as long as your pistons match a set of springs suited to your cam will run you about $250.oo max. Thats a total outlay of $550.oo. A set of ally heads with no work will cost approx 2k + depending on what you get.

For a first blower motor I am sure you will be happy with the iron heads and you can then save up for some ally ones and still recoup your $500.oo back in your own time.

[Madspeed]

dont forget that using oval port head needs an oval port blower intake.
after you goto square ports later you will need another intake
dont forget the extra 150.00 + in gasketts your loosing when you change those heads later as well as fluids sealers and cleaners.
not to mention it may be difficult to sell those heads after you use them. I personally would not use a set of heads without going through them again and thats a fair amount of cash.

If I was you id go with the Air Flow research heads and be done with it
Comp in the 7:1 range Hyd roller and get 800 hp EASY

Why build a blower motor and not boost it?

Hers a 1400 hp bbc Alky motor we run

[KsKustoms]

Personally I too like to get things done right the first time. AFR Heads will make much more power and save weight. If you have the money get the CNC chamber heads. They are the best bang for the buck. But just the standard As Cast heads will be much better then those Iron heads.

[bfr57]

I talked to local machinist who has built numerous race and street motors and didn't really care for the oval port GM heads either. I plan on using The Blower Shop blower and they don't make a manifold for ovals. He said the ovals can be made to work, but suggested Brodix Racerites because the exhaust ports are configured much like stock. I need that for my application as things are tight on clearance issues. Since he's a dealer for Brodix and The Blower Shop, he can cut some deals. What's the opinion on those Brodix heads?

[Madspeed]

Nothing wrong w Brodies
das Gud tu
the afrs are the best bang for the buck they flow Great for the cost allmost to great

[Madspeed]

I was thinkin. (ya I smelled smoke too)

If your gonna run a blower make the best of it
If you run heads that flow Big numbers you will make less boost,, And thats a good thing.
More boost = More heat = More detonation= less power
say you had oval port heads and your boost was like 15 lbs
say with that same drive ratio you installed heads that flowed 100 more cfm and your boost went down to 12 lbs or 10 lbs
you would still make more power than the 15 lbs.
Why?
because 1. pressure is heat
2. the boost is because of the restriction in the head flow
3. to make more boost takes more power from the crankshaft
4. you can add more timing because the intake charge is cooler
5. You are actually getting more charge in there from the free flowing heads

Make sure you also get a camshaft AFTER you get head flow numbers Comp figured out weight of car Rear gears and TQ converter figured out

Something else you should consider is Chamber design
This Is very critical.
If you go look at the LSX guys they are running boost on engines that are stock at CR of 10:1 on pump gas (not obsered boost)
I could ramble on for days Il let you soak that up a bit first

[Bandit]

I am replacing my 781's with Brodie Race-rites. It was a tough decision, because as you may know, the 781's are one of the best-flowing BB heads. Which means I probably won't see all that much of a power increase from the new heads. Hopefully I'm wrong and I'll get a heap more power.

In your case though, I think the Brodies would be more justified, because like others have said they will cope better with the additional heat and pressure in a blown application. Also, the improved scavenging effect of these heads with a blower will net a much bigger power increase than they would on a NA motor. Plus, they will help cut back on all that weight--you are adding the weight of a blower and accessories to an already heavy engine so losing that extra 50 lb. would be good.

I would shell out the cash for the big Brodies, I think your blower will like them.

[572SS]

I am replacing my 781's with Brodie Race-rites. It was a tough decision, because as you may know, the 781's are one of the best-flowing BB heads. Which means I probably won't see all that much of a power increase from the new heads. Hopefully I'm wrong and I'll get a heap more power.

In your case though, I think the Brodies would be more justified, because like others have said they will cope better with the additional heat and pressure in a blown application. Also, the improved scavenging effect of these heads with a blower will net a much bigger power increase than they would on a NA motor. Plus, they will help cut back on all that weight--you are adding the weight of a blower and accessories to an already heavy engine so losing that extra 50 lb. would be good.
I would shell out the cash for the big Brodies, I think your blower will like them.


Your right about the 049's and 781's being the best flowing STOCK GM Iron OVAL port heads. By todays standards that's not saying much! More than a few people will say the Vortech's are a much better all around head, I'm not one of them, yet!

Al

[NOPANTS-68]

be careful in the Mark VI block head selection. It was my understanding that not all cylinder heads were compatible with that block or was it the other way around? I know you can't strap the Mark VI heads (like the 572R rect ports) on the older blocks due to the cooling passages being way off. I looked at those heads for my Mark IV block and it was a no go. Hate to complicate things for you, but that's a lot of bread to drop to end up having an application error. The GMPP website tells you what parts work together and what don't.