I have a 403 that I am looking to install this summer. It has been rebuilt with .030 Arias flat top pistons and currently has stock reworked 403 heads and a cam that is a little above stock. I have a set of BBO C heads and SBO #5 heads. I am wondering if a large power increase is possible with the swap of either. I don't want to dig into engine but I am looking for simple power increases and also to see if it is worth it.

Both the C and #5 heads are currently stock. I am not opposed to getting work done to either set to wake up the engine some more. I know if I put the C heads on I have to find a intake to port match and I have read that if I put the #5 heads on it is best to have stock pistons with the combo due to extremely high compression ratios.

Which head swap will benefit the engine best and what other factors do I need to consider to do so? Anyone have any of the above combo's, any input on power gains or if it is worth the $$?

 

What are the piston specs, dish, flat top etc?
What car is in going in?

 

87 Cutlass
Arias Flat top
Displacement: 408.03
Bore: 4.380
Stroke:3.385
Compression: 9.60
Comp. Height: 1.620

 

If you already have flat top pistons, I would go with the C heads. Get an RPM intake to match the ports and you should be good to go.

Keep the heads at 80cc (stock)and worst case scenario you'll have approximately 9.58 to 1 compression with your bore and stroke combination. This is with a .030 deck hgt, and .041 compressed head gasket.


I would say that should be a pretty good motor

 

I am guessing the C heads are 80cc. I don't know if any work has been done to them previously. I should have noted that I do want to switch cam also. Just want more sound for the engine.

Current cam specs:

Adv. Int/Exh Duration : 280/290
Int/Exh lift : .497/.496

I keep hearing that the RPM intake is the best to be ported, what about the Holley Dominator intake?

 

X2 on the C heads. They were used on the 400 BBO, why wouldn't you want them on a 403 SBO (assuming the flattops for CR, as you already have).

 

Power increase guestimates? Is it worth the $$ ?

 

x3 on the c heads. Better flow will allow you the potential to make more power.
For example, your 403 with 4A heads and a stockish intake probably only has about 85% volumetric efficiency. Using a .500lift cam on a 112 with 224 236@ .050 with, oh say.... peak horsepower of 5500rpm You're in the 325 hp range.

Allow it to breathe better, say getting it up in the 95% volumetric efficiency range could possibly get you in the 350-375 hp range.

If you use a cam that gets peak horse around 6000 rpm, you could get 400+ horse out of it.

For the 425 horse scenario, your heads would have to be able to flow around 240 cfm at the .500 lift of this cam and your valve. The C castings fall short of that.

The edelbrock heads claim 250-275 cfm at .500, but they don't fit small blocks with a stock fuel pump.

Also keep in mind that these are estimates that I pulled out of my behind .

Some quick math: I just flowed my heads last week. 240cfm intake 180ex was the result at .600. My cam is not .600 lift, it's .500 lift.
So deduct 20cfm right there
Now we're at 220
that is just the head. Flowed with intake manifold showed an 8% loss. Which is actually really good.
deduct another 20cfm
now we're at 200.
What about carburetor and air cleaner now?
Whack off another 20 for good measure.
Now It's 180.

Required intake flow(the WHOLE PACKAGE) for 425 horse is 225 cfm at .630 lift .

I hope this wasn't confusing.
Do this same math on stock 4A heads that probably flow 190 (wild guess) and then deduct the previous 60cfm estimate
You're at 130 cfm for the package.
Not good.

 

The factory 4A heads have an awful exhaust port and huge chambers. Any of the decent pistons like your Arias, Diamond or KB pistons require stock, #8 or BBO heads. Otherwise compression will be sky high. X4 on the C heads. PM Cutlassefi for cam suggestions.

 

Don't think the Dominator can be ported that much, go with the RPM.
I'd do an Erson TQ40 for your combo. 284/296 adv., 220/228@.050 with .504 lift and it'll be easy on the valvetrain. And yes, you'll hear it.

 

J-(Chicago) thanks for the scenarios and in depth info. Really gave me some inside on what is possible. I would love to get in the 400 hp range. The Edelbrock heads are out of the budget for the 400+ hp. I just have to make sure these C heads are stock since they can't be modded up too much.

It's obvious that the C heads is the choice. Would appreciate members advice on what to do to the heads for max results. Is anyone running a 403 with BBO heads?

Cutlasefi cam recommendation has the .500 lift. I definitely would like to milk as much power that I on a reasonable budget before I swap engines.

 

I would say go for the "C's"

The 4A heads on the 403 are 79cc IIRC and the C's are 80. You said you put flat top pistions in there, so in this case, the C's are better choice IMHO

 

4A are supposed to be 84cc, mine were around 86cc.

 

The best choice is to go with the C-heads for the engine's current set up. I have to find out exactly what the cc specs are and figure out what i can do to them and then figure out what to do. Like I stated I am not trying to drop to much $$ into the heads and definitely not looking to buy Edelbrock heads.

 

IIRC the Edelbrock heads are "C" heads

 

181 intake cc and 130 exhaust cc volumes, but I think u r looking for chamber volume.

 

Yea, I am looking for chamber volume. I have been doing research on specific head specs but I am seeing a variety of specs. I can't find no one running BBO heads on a 403 either.

If I am hearing correctly, I can't mill the stock heads at all for this application. Is that correct?