Head Port Advice Old 409

[Powertrip]

Stock rods + HEAVY pistons + RPM = Blown up 409, repeat.

[Ishiftem]

Rpm was definitely not a friend of the 409 especially as heavy as the pistons were back then. Even with better stuff today, hp and rpm will break the stock block. I keep this one under 7k. The 74 degree deck and short deck height really hamper these things as far as an intake and head package. The Z-11 with its raised ports helped but still was inferior to the mystery motor and its production counterpart, the BBC.
I’m still using a dual plane 2x4 intake and 50 year old carter AFB carbs. This winters project is turning a factory 2x4 intake into a short tunnel ram. The narrow valley and self imposed height restriction for hood clearance really make for less than an optimal deal, but it should help. I hope?!?!

[Tuner]

I wonder what you could do with this or an Offy 360 2x4 casting.
https://www.ebay.com/itm/409-Chevy-Offe ... 0008.m2219

[Ishiftem]

Tuner!! I don’t think the 4x2 would work. The offy 360 is a good starting point but the runners would still have to go. They are super short and the opening are directly across from each other so what any one runner is doing heavily disturb the runner across from it. I only have 50 bucks into the factory 2x4 so it makes a good sacrifice for the cause.

[Tuner]

I didn't meant to use the 4 x 2bbl carbs, just perhaps the manifold as a starting point. I understood you are going to cut and build a one-off of some sort, so I thought some aftermarket swag might be a better sacrifice than throwing anything virgin 409 in the volcano. Water jet some plates and build from scratch? I reckon the remains of whatever manifold you start with just becomes an adapter to the heads and whatever you do is going to be a welding and machine work project.

Have you done any significant welding on nearly 60 year old aluminum intake castings? I have had a couple of horror dramas with cracking during cooling unless the whole manifold is uniformly heated in an oven to very near welding temperature. They were Ford intakes, so I don't know if an alloy difference or ? might make it easier with GM intakes, perhaps someone has insight about this. Unless rules dictate you must start with a casting, I would have a few pairs of plates water jet or plasma cut so I could recover from oops!! or start over when the path becomes more clear as work progresses. (unless you are like me and everything is always just perfect the first time )

[Ishiftem]

This thing has a chunk broke off it (i have the piece) and a crack so it really doesn't have much value and I swear, GM must of made more these things than any other 60s aluminum intake. The things are everywhere. Before ebay when a 340 horse 327 intake or z-28 intake were $375, the 409 intake was a $100 if that. Then two people in the middle of nowhere who never saw a swap meet started bidding the things up to $250 and $300. I don't have a lot of talent so even if I mill everything off, I'll still have the port location, gooseneck, and distributor pad already in place. I plan to make it look cast when finished except for the top. That way, I can still run in some NSS races if I choose that don't allow a total sheet metal piece. As for welding, I have seen more than one of these made where they made the new runners by layering weld after weld. Not a fan of that but I think it shows they can be welded. Besides, Santa has seen my welds and he is getting me a grinder for Christmas! There is one person who makes a short tunnel ram for these things but I know of one person who made more power with a modified factory intake, another who made more power but only after loading the inside with epoxy, and another that lost a few tenths putting one on. Plus they are $1600 bucks. I have a friend who will do all the machining for me, and my engine builder gave me free use of his flow bench so I can put a head on it and try different runner lengths and angles so I am not completely guessing. So I should have a lot less than $1600 into it. I have more time than money and I like doing things myself for better or worse. If it doesn't work I'm still keeping my Edelbrock just in case!

[JoePorting]

If these were my heads, I'd go with a slightly larger intake valve. Probably around 2.30". The main goal here is to redo your valve job. I'd find someone with a Sunnen VGS-20 and use the #17258 intake cutter. It's a 5-angle cutter that should improve your flow numbers by around 15 CFM or more at each lift range. The angles are 35/45/60/75/82. The top 35 degree angle is .100" wide which really gives off good flow numbers, and the 75/82 degree lower cuts also have the effect of improving flow while opening up the throat to the max giving super good high lift numbers.

When you port, port right up to the bottom of the lower 82 degree angle. Don't cut into the valve job. That really messes up the flow numbers. Sunnen also has a 82 degree bowl hog cutter. To get the most out of a valve job, I found if you extend the lower 82 degree angle, you can get another 3 to 5 CFM. But again, don't cut into the original valve job, just cut the 82 degree angle right up to the existing 82 degree angle.

In terms of the top 35 degree cut, leave a slight ledge just about .030" high into the chamber. I know you'll want to cut the ledge down to improve flow. But every time I tried that, I lost about 5 to 10 CFM. The flow bench really likes that slight ledge just above the 35 degree cut.

[mt-engines]

If these were my heads, I'd go with a slightly larger intake valve. Probably around 2.30". The main goal here is to redo your valve job. I'd find someone with a Sunnen VGS-20 and use the #17258 intake cutter. It's a 5-angle cutter that should improve your flow numbers by around 15 CFM or more at each lift range. The angles are 35/45/60/75/82. The top 35 degree angle is .100" wide which really gives off good flow numbers, and the 75/82 degree lower cuts also have the effect of improving flow while opening up the throat to the max giving super good high lift numbers.

Why such a large valve?
Why not a #5065b? the steeper angle will open up the throat.

[Ishiftem]

Doesn't seem like there is enough meat left without sinking the valve. The face of the valve sits about flush now.

[mag2555]

Port wall thickness on GM castings with no core shift or internal rust will average out to .180", so if you go by the fact that for a given valve size to begin to produce the flow numbers it can, then the valve bowl throat to valve size percentage needs to be a minimum of 85.

Is short I do not think you will beable to make good use of a bigger Intake valve size then what you are running now!

[Ishiftem]

Plus there is only .033 between the intake and exhaust valve as it is!

[CGT]

Why such a large valve?

Exactly. This is a head showing signs of reversion, bigger valve with the same vj certainly isn't gonna make that any better.

Why not a #5065b? the steeper angle will open up the throat.

Exactly again. Good all around cutter that would likely clean up that reversion. Would probably sink the vj some and with that ssr or lack of thats probably not ideal, but I think it would still be a net positive.

[Mike Caruso 6250]

Rpm was definitely not a friend of the 409 especially as heavy as the pistons were back then. Even with better stuff today, hp and rpm will break the stock block. I keep this one under 7k. The 74 degree deck and short deck height really hamper these things as far as an intake and head package. The Z-11 with its raised ports helped but still was inferior to the mystery motor and its production counterpart, the BBC.
I’m still using a dual plane 2x4 intake and 50 year old carter AFB carbs. This winters project is turning a factory 2x4 intake into a short tunnel ram. The narrow valley and self imposed height restriction for hood clearance really make for less than an optimal deal, but it should help. I hope?!?!

Great Job

[Ishiftem]

Thanks!