cutlassefi

I’ll be doing two 403’s, one with iron heads, one with new Edelbrocks. But some other differences as well. However both will have RPM intakes, and all roller valve trains.
I’ll post both sets of build specs in the coming days.

69OldZman

Patiently waiting. This should be informative.
Thanks for doing this.

joe_padavano

Mark, when you are really looking for something to do, try a short-stroke 400 vs a long-stroke 400 vs a 403, built as closely the same as possible. By the way, which iron heads?

cutlassefi

Here are the build specs for each;
Build 1)
#5 mildly ported irons
Hyd roller, 227/234@.050, 108lsa, .576/.573 lift
10:1
RPM intake
QF Hot rod series 750

Build 2)
Out of the box Gen III Edelbrocks
10:1
Hyd roller 233/238@.050, 110lsa, .587 lift.
RPM intake, minor port matching
Holley Terminator TBI

Both will be blowing thru my 1 3/4 dyno headers and 2.500” exhaust.
Should have results in the next 7-10 days.

BangScreech4-4-2

I didn't know Mark takes requests () but I would love to see this too.

deadeyejedi

Subscribing

cutlassefi

That would be an interesting comparison for sure.
But I don’t see it happening, mainly because I’d have to use flat tappet cams in all three to keep it legit. Can’t do a roller for the .921 block. Like a lot of others, I’m not doing flat tappet builds anymore. Sorry.

Bernhard

The difference in power levels would be interesting. In my opinion what engine placed first second and third would not be a surprise just the max HP/TQ and power curve.

1. 403
2, 400 E
3. 400 G

joe_padavano

I would agree with that ranking, assuming all three used the same heads. There will be a difference in the intake, naturally.

cutlassefi

And the same compression(I’d use bb heads on all three, which would necessitate a piston change on the 403) cam, and carb size. Lots of potential costs and variables here guys.
I can get solid roller lifters for a .921 block but they’re very pricey, about $1500.00. Not sure I want to bite that bullet either unless someone wants to buy that build. Just sayin.

Duh

Just use 842 lifter blocks. Yes they will be 45°.

cutlassefi

You have one you want to donate?😉

Duh

If you want to pay for shipping from NJ I just might have one in my garage. It does need some work.

cutlassefi

Well ok then. Once I get thru the dozen or so I have in the works now, I may take you up on that.
Thanks!

Fun71

Pffft, do a windowed 403 vs. a SMW 403.

Sorry, been holding back for days and I just couldn’t help myself.

Bernhard

The amount of over bore on the 403 might also be a variable?

cutlassefi

Of course, everything is.
But I believe Joe’s point is to see how those differences affect power and tq, with the rest of the parts being essentially the same.

jmcghee

Tried Google but cant find an answer . Are the GenIII heads just big block heads?

cutlassefi

They’re the newest ones.

jmcghee

So best I can tell these are big block heads you installed on this engine.

Fun71

Using big block heads on a 403 cubic inch engine makes sense.

olds 307 and 403

Yeah, they are the 77cc large valve version. You can bolt them on a small block but you need a 4.125" bore minimum to clear the valves.

OK65Cutlass

Hey Mark, how do the intake/exhaust ports compare on those heads?

cutlassefi

Hmm not exactly true. The chamber is only about 4.100 wide to begin with.
They didn’t change the valve centers vs any of the earlier designs.

olds 307 and 403

Good to know. What would you recommend as a minimum bore size?

cutlassefi

Just that, 4.100. The small block version should be right around 4.00, mine are.

cutlassefi

The irons would be significantly smaller than the Edelbrocks. And the Edelbrocks are larger than a regular big block head as well.