[J Druin]

I am building a 400 with a set of the 72cc Speed Master heads. The block has been decked .011 to get it squared and will be .040 over. I am going to get the Icon pistons but not sure if I should get the flat top with 4.5cc or the dish with 14 cc. I know with the aluminum you can get away with higher compression but I want to make sure I will have no worries running on 93 oct. Doing some calculations I think it will be around 10.7 to 1 with the flat tops or about 9.6 to 1 with the dish pistons. What do you guys think?

[mgarblik]

Based on the limited info you provided, here are a few numbers. If you were making 400 HP at 9.6 CR, you would make 404.43 at 10.7 CR If you were making 500 HP at 9.6 CR, you would make 505.54 at 10.7 CR. 10:1 would be a better target and very safe . Many will tell you you can easily run 11-11.5:1 on pump gas with aluminum heads no problem. And they are absolutely right because lots of new cars do that every day. But they have computer controlled engine management systems with knock sensors, O2 sensors and port or direct fuel injection. An old Pontiac with a carburetor and no electronic controls can do it too. But you better know how to tune it just perfect. Too fine a line for my taste. BTW, my numbers came from a Wallace calculator of CR vs HP.

[Frank T]

J-
Do you have a cam picked out? That will help guide the piston selection.

Frank T

[steve25]

In short I think your making a bad choice in regards to building a 400 or so cid motor that's not a flat out high comp ( over 12 to 1 ) full race motor with those heads!

Let look why!

A stock late 1960s 4 bbl 400 motor with its true stock 9.5 compression and the 068 Cam made a peak torque number of 445 at 3600 rpm.

This came about by way of the Cam, the compression and in big part the 2.2 square inch minimum port area that the iron heads had in them.

Your pick of the speedmaster heads with there 215 cc Intake runner compared to the at best 155 CC Intake runner of the iron heads means that these new heads have some 28% greater minimum port area then the iron heads.

Keep in mind that the minimum port area to a factor of like 85% controls port velocity, and the amount of port velocity at any given rpm controls the amount of torque produce.

Concider things in a Apples to Apples view if you run those heads your down on that iron head peak Torque number by at least 20 percent and to get back to that original 445 ft pounds of peak torque your going to need to now rev the motor up to 4600 rpm to get back to that 445 ft lbs of original torque!

It's very hard even with a under 11 to 1 comp 400 cid motor to not loose on the bottom end of the power band with what you trade off in terms of top end power.

The only ways around this are
1) greater CID.

2) much higher compression.

3) higher rpms.

4) more gearing.

5) A combo of all 4 of these factors.

And last, but to a smaller effect much more valve lift to run more air thru the port at any given rpm to build more average port velocity which in turn makes more torque!

So depending on your goals for the car, it's weight and it's gearing, if you do not have these heads yet I would be looking at the two different aftermarket D port heads that are out there since there port volume comes in at about 187 CCs which means that your only dealing with a minimum port area gain over the iron heads of some 18%.

Pontiac new 100% what they where doing back in 69 and 70 when they made the 400 cid RA4 heads at a volume of 185 CCs and made 3.90 rear gears a minimum, with 4.33 gears the option!

If your stuck running the a aftermarket 187 CC head, or worse yet a 215 CC head on a 400 then you had better run a hydro roller Cam with atleast .580" lift and stuff in 11 to 1 comp with the needed electronics to keep the motor alive.

Even to this day I chuckle big time when I think back on the edelbrock add from 1996 when they came out with there 215 CC Round port heads.

They did a dyno test on a 400 motor with there Cam , new head and Manifold combo that made a tad over 420 hp if I recall right, where as even back then you could build a 9.6 comp 400 with stock iron heads and the lesser standard perfromer Intake that could make that same level of power but at a far lower rpm!

In terms of a 10.5 to 1 400 motor with any aftermarket head and a 068 Cam I defie anyone to produce a dyno sheet where such a combo puts out more the the stock 445 ft lbs of torque @ only 3600 rpm, a rpm where a true street rear geared, non 5 speed trany 400 cid motor needs it most!

Also we have just talked about the effects of these bigger aftermarket heads Intake ports, but in terms of the Round port heads they also have far bigger Exh ports which have the same velocity effect change with there greater minimum port area as the Intake side does!

[Frank T]

Steve25-
Great-great post! I didnt buy those Speedmaster heads back in Dec. for this exact reason... too big for the street.

Can you post the part numbers and flow rates for the following heads you reference...
" I would be looking at the two different aftermarket D port heads that are out there since there port volume comes in at about 187 CCs which means that your only dealing with a minimum port area gain over the iron heads of some 18%."

Ive read you do alot of head porting, so can you post your favorite stock head number castings to go onto a street 400 with flat tops that are common and affordable?
AND/OR
What you find most important in a stock casting (chamber, valve size, port size, etc), again for a street 400/flat tops.
I think that will help alot of folks (including me).

Thanks
Frank T

[Murf]

Steve, what size should an engine be to make the best use of 215 cc intake ports?

Thanks
Mu


Sent from my iPhone using Tapatalk Pro

[Steve C.]

For interest you can find interesting reading on the subject....

Calculating Optimum Port Area from Valve Size

https://www.cartechbooks.com/techtip...ht%20on%20this.

Calculating Port Cross Sections

https://hotrodenginetech.com/porting-pointers/

Two calculators of interest:

http://www.wallaceracing.com/ca-calc.php

http://www.wallaceracing.com/runnertorquecalc.php

Call Edelbrock and find out the as cast port entry size and runner length. Maybe someone here can post it.

.

[Murf]

Originally Posted by Steve C.

For interest you can find interesting reading on the subject....



Calculating Optimum Port Area from Valve Size



https://www.cartechbooks.com/techtip...ht%20on%20this.



Calculating Port Cross Sections



https://hotrodenginetech.com/porting-pointers/



Two calculators of interest:



http://www.wallaceracing.com/ca-calc.php



http://www.wallaceracing.com/runnertorquecalc.php



Call Edelbrock and find out the as cast port entry size and runner length. Maybe someone here can post it.



.

Thanks for the links, Steve! I hope I can get to where I understand it.

Murf


Sent from my iPhone using Tapatalk Pro

[Steve C.]

Not directly related to the OP topic but of interest....

"Many feel the 215cc intake port of our Performer RPM is too large for the street, but we've found that the long connecting rod and big crankshaft throw associated with the Pontiac V-8 tend to make them less sensitive to port volume. The RPM is a great head for street engines, and I pushed for a large intake port when developing the Performer D-port-one much like that used in our Performer RPM."

"He continues, "We determined that a majority of buyers would be installing the Performer D-port on street-driven 389, 400, and 455-inch engines, however, and that some of those would need to be emissions-legal. We ultimately decided on an intake port with less volume than the Performer RPM, which tends to promote port velocity and can improve low-speed throttle response, while remaining 50-state emissions compliant."

https://www.hotrod.com/articles/hppp...ylinder-heads/

The D-port version ended up being 204 cc intake runner volume.


.

[J Druin]

Well, this won't be strictly a street more of a mild street/strip with 3.73 gears, 2004R 4 speed and at least a 2500 stall. Also the cam I plan to run is a Howards Hyd Roller with 226.6, 236.6 @.050, .560 lift on a 110 LSA. This is a car I had years ago that I ended getting back in parts and overall rough shape. The previous owner decided he was going to redo the car and basically just tore it apart, pulled the intake and heads off the engine and let it set. When I had it back in 2002 it ran a best of 7.96 and consistent 8.0's at 3680 lbs. Same 400, .030 over #62's ported and a hyd flat with 228, 236 @ .050 and .470 lift. So, we will see if the Speed Master heads out of the box and a roller will pick it up much. Oh, it also sounds like I should go with the flat tops.

[Steve C.]

If these Speedmaster heads have a similar exhaust-to-intake flow ratio as the Edelbrock RPM heads and used in conjunction with headers and a efficient exhaust system on the car you might consider a cam with less duration on the exhaust side.

.

[Murf]

Originally Posted by J Druin

Well, this won't be strictly a street more of a mild street/strip with 3.73 gears, 2004R 4 speed and at least a 2500 stall. Also the cam I plan to run is a Howards Hyd Roller with 226.6, 236.6 @.050, .560 lift on a 110 LSA. This is a car I had years ago that I ended getting back in parts and overall rough shape. The previous owner decided he was going to redo the car and basically just tore it apart, pulled the intake and heads off the engine and let it set. When I had it back in 2002 it ran a best of 7.96 and consistent 8.0's at 3680 lbs. Same 400, .030 over #62's ported and a hyd flat with 228, 236 @ .050 and .470 lift. So, we will see if the Speed Master heads out of the box and a roller will pick it up much. Oh, it also sounds like I should go with the flat tops.

Please keep us informed & good luck!

Murf