Given the range of lettered heads from Oldsmobile over time, I would like to know the stacking order, from best to last place, for the heads used on big block units. thanks for the clarification.

 

“Best” needs a specific definition.

Best in what respect?
Intake flow rate?
Exhaust flow rate?
Availability?
Affordability?

 

The reality is that other than the J heads, the differences are so small as to be in the range of manufacturing tolerance. There are many published lists of Olds port flow numbers. The problem is that these lists never tell you the sample size. Are these the numbers for ONE port? The average over one head? I guarantee that none of these lists have tested enough different heads to build a statistically valid sample size. Given the variability in sand casting at that production scale, expect the numbers to vary +/- 10% over the production lot.

 

Old wives would put this order, 1966 Toro "B" heads as #1, Probably 70 W30 "F" next, then 68 455 "D" heads, then "C"'s with big valves, however it is a crap shoot because like Joe said, there isn't enough difference in each casting to make a difference. But my old wife doesn't really care how they line up.

 

The best production 455 head would be the F or H or D head due to the fact the heat cross over does not get into both exhaust bowls. Now if you have the means to properly fill the heat cross over in it would come down to which combustion chamber volume you prefer, of course leaving the J head out due to its small runner volume.

 

Hi,

Like it has been said all pretty close, with that said I have heard A's are good as no bump in the exhaust ports for air injection, but again just hear say.

Regards,
Jim

 

Any Big valve head that is pre valve rotator.

so A, B, C, D, or E if it’s non rotater as the E came both ways.

they dropped intake port roof in the area under the valve spring seat to accommodate the deeper spring pocket.

E, F, G, H, and K are deep spring pocket

A has best flowing stock ex as there is no egr bump in the roof.

 

First, it's not an "EGR bump". The bumps are to accommodate the the air injection reactor (A.I.R.) tubes. Exhaust Gas Recirculation wasn't used on Olds motors until the 1973 model year, and that system was entirely contained in the intake manifold.
Second, without back-to-back flow data, there's no way to know if the bumps help or hurt flow. The infamous "Dent the header" episode of Engine Masters should tell you that. As an aerospace engineer, one thing I've learned is that subsonic flow is NOT intuitive. A bigger port may or may not flow better.

 

you can call it whatever you want when it’s NOT tapped and plumbed for the air lines.

i know what it’s for… my statement stands

I have enough flow bench data on Olds heads to prove this . The CC volume is different because of the lower port roof.

are you saying this is wrong, that the roof of the intake port isn’t lower on rotater heads?

 

Then post your flow results. It’s been my experience that grinding the “EGR” hump does absolutely nothing. The ex port is crap to begin with in its stock design. That’s why they raised the floor in the aftermarket heads.

 

since it’s absolutely nothing like you say, you must also have the data to show that?

It’s no big deal, but it isn’t absolutely nothing as the majority of ex flow is along the roof of the port.

seems like you guys are infatuated with the ex port for some reason…no comment on the intake?

 

Heres what I got on the intake @ 28 inches on a 4.155 bore SF 600 on a stock G casting head:



.200 122
.300 172
.400 196
.500 209
.550 215
.600 220
.700 226

What does a good exhaust port allow for, in your opinion.

 

Port volume has no direct relationship to flow. Talk about flow numbers (CFM) not volume. And CFM depends on inlet and outlet conditions also (shape and pressure drop), so that variable needs to be normalized. Collecting data is easy. Collecting meaningful data that can be compared is more difficult.

 

I never said it had a direct relationship to flow. Why it matters on a 455 is because the engine is port limited.


it’s just way to small. Every CC helps in the case of the 455.

the MCSA on a big block head is right before the seat, not the pushrod area like most think it is, so when the roof is lowered , for the spring pocket, it reduces MSCA.

which limits the engines breathing and where max pwr rpm occurs.

 

Pardon my ignorance, but did any of the factory heads come with fully divided middle exhaust ports? ie flush center divider.

​​​​​​….

 

That’s typical of a rotator head port. Non rotator head will be 8 to 10 cfm more from around .400 through .600” plus maxing 233 or 235 on the outboard port .

was than an inner or outboard port?

 

Middle two intake runners.

 

I haven't seen that myself.

 

K, notice how the flow starts out pretty good then fall off real quick. That 30deg factory seat and transition sucks.

If someone is staying with the factory big valve, it’s much better to start with a small valve head and install the big valve using a 45 seat.

wakes them right up.

 

The same G head flowed @ 28 inches flowed this after porting, 2.100 valve, middle port.



.200 156
.300 213
.400.251
.500 270
.550 274

298 @ full lift.

 

K heads, stock 2.07” int with a decent 30deg seat. Minor pocket port from 1” before guide to seat. Upstream of that not touched.

@28”

.100” 93
.200” 158
.300” 205
.400” 239
.500” 250
.600” 254
.700” 262

port does not stall or back up

When a 45 seat is used, from around .400” on up,numbers are even better. Still with no upstream work. Seat, bowl, guide and the MSCA is the biggest bang for time spent when keeping with factory valve size

 

bccan, Have never seen a full separationof the center exhaust ports on any big or small block Olds heads; it takes (about) 0.200" mill cut to attain that or build up with weld.

 

I've seen a chart here that shows the 'A' slightly outflows all the others on the intake and 'E' is slightly less than the others on the intake.
All the rest were about the same. Many past posters claimed grinding off the 'EGR' bump was worth a lot of power. However if Mark says its not worth it I would defer to him.
Exhaust flowed about the same on all of them except the 'J' which was a lot worse.

 

It is worth it to remove that bump in the port roof because the flow bias is along the port roof. You dont have to be a professional or expert to see it needs to go

Even on basic ex port rework for a street engine, the three things that get done are , that bump gets removed, the valve guide area outer casting cut back and the seat transition leading to the seat gets worked.

Think about it,, if there was a chunk of casting flash that big stuck in the port roof, hanging down, from a bad casting …..would you leave it? Of course not

it all adds up