Looking for a few tips on porting 351c 4v heads

[thomas butt]

On of the keys to making power with these heads with even 408 cid under them is what I touched on in my other post.
You need to use the exh blow down period and the cams over lap portion and the proper header collector size to produce a early yank on the intake charge and get that moving !
This will somewhat off set the too large intake port area that you will have with even 408 CID under these heads!

2" or 2 1/8" primaries seem to be what guys are using that make good power with these heads. Accufab makes them. I will get a custom cam for this build from one of the top guys that work with Clevelands. There seems to be a few out there that know how to cam these heads to make them work right!

[cab0154]

even with a good ported set the exhaust port is still junk. the 408 with the ported heads, mid 260s/upper 280s @ .050, low .700s lift, and 1 and 7/8" headers has an 8k rpm shift point. if the cam is right you don't need a huge primary. talk to chris straub about a cam.

[RL]

Mag2555 and cab0154, you guys know your stuff.

Basically if you don't fill the heads you have to be very smart and knowledgeable to use compromised design to fudge over the faults, like a large port, so it's a bit easier with the correct ports.

I've tried numerous pipes on these engines, and 2-21/8 was too big for us on a ¼ mile - you'll loose at 60ft - it will be like a wet sponge - and gain mph. You would have to drop gear and rev the nuts out of it.

Our 1200hp 400cu Prostocks use smaller than 2" with a 4 into 1 spinning at 10,500rpm

You generally see large pipes patching over a engine that has a faulty design combination.

[groberts101]

Mag2555 and cab0154, you guys know your stuff.

Basically if you don't fill the heads you have to be very smart and knowledgeable to use compromised tuning to fudge over the faults, like a large port, so it's a bit easier with the correct ports.

I've tried numerous pipes on these engines, and 2-21/8 was too big for us on a ¼ mile - you'll loose at 60ft - it will be like a wet sponge - and gain mph. You would have to drop gear and rev the nuts out of it.

Our 1200hp 400cu Prostocks don't use 2" with a 4 into 1 spinning at 10,500rpm

Right. If you have to use such a large pipe and throw huge duration at it to make bigger power?.. the motor will be be a peaky little bitch. Close ratio trans will be needed with super short gear to make it all work.

But if you get the ports closer to right?.. you can size everything much more realistically and it will make gobs more average power even though the peak number will be down.

I've done several sets of these heads through the years too and Knightengines hit the nail on the head. A 351 cid engine making anything close to 650 horsepower at just 7,000 rpm with iron stock location ports, and without any fill is a big fat pipe dream.

[thomas butt]

-all options on the table regarding header size, stroke, fill. I would like to minimize fill. Maybe a stroker 400 to 425" or...

[cab0154]

if you are only going to run 11:1 compression, I would just leave it a budget deal with unported heads. a 1.875 header with a 3.5" collector will be fine with the right cam. that would get you into the mid 6s in the 1/8th on motor and leave you some $ to set up the rest of the car/trans/converter/rear end/suspension. you can throw a lot of $ at them and only pick up .2 and you will still have iron stock heads. especially if its a stock block deal. honestly, the stock 4 bolt main blocks leave a lot to be desired since they aren't splayed.

I personally wouldn't even run a 4" stroke on a 9.2 deck, let alone a 4.25. I mean, you can, but its going to be 28oz balance because the counter weights are small because youll be sitting with a 6" rod. then you will have to keep it around 7200 anyway. after talking to a couple of guys about my 9.2 deck Windsor I ended up at 3.85" stroke, a 6.200" molnar ford beam offset rod and a 1.075" c/h because I am going to run it on the street and want it to live and have enough counterweight to internally balance. but that's just me.

[cab0154]

Mag2555 and cab0154, you guys know your stuff.

Thank you sir!

[smeg]

I've done several sets of these heads through the years too and Knightengines hit the nail on the head. A 351 cid engine making anything close to 650 horsepower at just 7,000 rpm with iron stock location ports, and without any fill is a big fat pipe dream.


Sorry, been done and a while ago too. Take a look at the CD/A record. 355 cubes, over 700 Hp, with cast iron, stock location, no filler, single 4 750, 4V iron Clevo heads. But oops, my bad, not at 7000 that is for sure.

[cab0154]

I would assume closer to 9k with a 3.5" stroke. the ported stock 4v heads I measured were pretty close to a 3" cross section at the pinch.

[mag2555]

I am going to dig out some flow info on a set of 2 bbl C heads I did many years ago, and as I recall the motor made a easy 620 HP.
I used over sized custom 2.11" Intake and a 1.77" exh, the Intake side hit 290 cfm at .500" and if I recall right the exh side topped 230 @ .650"
The exh side on the 2bbl heads are light years better than the 4 bbl heads and there terrible expansion rate that they have compared to there throat area!
The reworked exh ports on the 2bbl heads I did had about 25 minutes worth of work to them not including the valve job for the over size valve.
I will post more info on this tonight!

[thomas butt]

I am going to dig out some flow info on a set of 2 bbl C heads I did many years ago, and as I recall the motor made a easy 620 HP.
I used over sized custom 2.11" Intake and a 1.77" exh, the Intake side hit 290 cfm at .500" and if I recall right the exh side topped 230 @ .650"
The exh side on the 2bbl heads are light years better than the 4 bbl heads and there terrible expansion rate that they have compared to there throat area!
The reworked exh ports on the 2bbl heads I did had about 25 minutes worth of work to them not including the valve job for the over size valve.
I will post more info on this tonight!

What about the chambers? I have a set of 2v heads yet open chamber heads. Besides compression I thought cc heads have a better chamber. Didn't it take a lot to get the intake port to 290?

[DaveMcLain]

I am going to dig out some flow info on a set of 2 bbl C heads I did many years ago, and as I recall the motor made a easy 620 HP.
I used over sized custom 2.11" Intake and a 1.77" exh, the Intake side hit 290 cfm at .500" and if I recall right the exh side topped 230 @ .650"
The exh side on the 2bbl heads are light years better than the 4 bbl heads and there terrible expansion rate that they have compared to there throat area!
The reworked exh ports on the 2bbl heads I did had about 25 minutes worth of work to them not including the valve job for the over size valve.
I will post more info on this tonight!

What about the chambers? I have a set of 2v heads yet open chamber heads. Besides compression I thought cc heads have a better chamber. Didn't it take a lot to get the intake port to 290?

From what I've seen the 2V intake port is about the right size but it is shaped terribly bad. The short side is very tall and abrupt and there is not enough material in the casting to fix it with even a stock valve from what I've been told....

[mag2555]

If I had to make a anology to the amount of intake port rework I would compare it to the amount of time that it takes to get a iron SBC 461 head up to flow numbers in the 240 + range @ 28".
Yes, the short turn needs to be layed back a good amount to get these numbers and there is just enough meat there to do that and be safe from blowing out!
Had these heads not been of the thin wall casting that they are hitting 320 cfm out of them could be done and I guess if you had the bucks for a red hot oven weld job 8 times over then one could go that route!
The big valves that I had made up also ate up a lot of chamber volume.

[RL]

The 2V is also a bit tricky to get to 600hp - 540hp is pretty common -, but the 4V isn't that bad.

From memory someone sells alum int port stuffer that you bolt in - I had to cast my own in the 90's -, and there used to be SS exh flange plates that had a folded section that covered that dead area where the floor drops away - you could make these -.

[mag2555]

Dave I pulled out the info on those 2BBl C heads for Ya.
Here's the flow numbers with the intake being first and the exh next.
.100". 71.9. 51.9

.200". 154. 111.8

.300". 226. 160

.400". 271.3. 193.8

.450". 278.5. 210

.500. 286.6. 219

.550". Exh. 224

.600". Exh. 228

.650". Exh. 232.7
The intake port is a 1.83" throat with 3.24" minimum port area which is 9% less that the minimum port area in a stock 4 bbl C head.
The exh port had a measly 1.456" throat!
The overall exh to intake ratio with .500" on the intake and .550" on the exh was 78 %
A standard 3 angle valve job of 30/45/60 was used on both valves.