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

[RL]

I think you better get professional help. Porting without a flowbench and knowledge of the heads will leave you with a holed head.

Things to look for is that every wall in the exh is thin, at least a lot thinner than the int, so you must be very knowledge and deliberate with porting anywhere in there.
Running inlets without filling the ports will make this a dog down low and a total rev master only. There is no way such a small engine (351) will be happy anywhere near the 7000rpm you propose.
We run 400s with filled ports, and the last one I did made 596hp on pump gas in a street engine at 6850rpm.

I don't know if you can see this page if you aren't logged in, but here is my modified 4V heads.
http://www.flowbenchtech.com/forum/view ... f=25&t=841

[thomas butt]

Concentrate your efforts on the short sides, intake and exhaust but more importantly look at the intake manifold of choice I bet there's more to be found there than in the heads.

-right now, i have an Edelbrock 2831 that will need to be opened up. The ports are tapered with a lot of plenum volume. Its a Nascar manifold with a 4150 opening. The outside dimensions of the runners at the flange are 2"x3". Plenum is deep. Flanges will have to be milled 1/2" because its made for high port heads.

[wyrmrider]

Perhaps you want to make the ports smaller instead of the manifold bigger
viewtopic.php?f=1&t=43423
are you going to fill the ex?
and why fool with an old Iron head in the first place, is this some matching number build thing?

[BigBlocksOnTop2]

Concentrate your efforts on the short sides, intake and exhaust but more importantly look at the intake manifold of choice I bet there's more to be found there than in the heads.

-right now, i have an Edelbrock 2831 that will need to be opened up. The ports are tapered with a lot of plenum volume. Its a Nascar manifold with a 4150 opening. The outside dimensions of the runners at the flange are 2"x3". Plenum is deep. Flanges will have to be milled 1/2" because its made for high port heads.

You will have to elongate all the bolt holes too. Big project that you are getting into. Better stuff is out there.

[thomas butt]

Concentrate your efforts on the short sides, intake and exhaust but more importantly look at the intake manifold of choice I bet there's more to be found there than in the heads.

-right now, i have an Edelbrock 2831 that will need to be opened up. The ports are tapered with a lot of plenum volume. Its a Nascar manifold with a 4150 opening. The outside dimensions of the runners at the flange are 2"x3". Plenum is deep. Flanges will have to be milled 1/2" because its made for high port heads.

You will have to elongate all the bolt holes too. Big project that you are getting into. Better stuff is out there.

It's one intake to use. I could just get a tfs track heat 351c or an edelbrock torker

[BobbyB]

I am interested in these heads too. How much better are the new aluminum ones than the old iron with stuffers? What happens to both with stroker cranks?

[RL]

I am interested in these heads too. How much better are the new aluminium ones than the old iron with stuffers? What happens to both with stroker cranks?

Basically, the 4V has a lot of faults, and the new heads correct those problems to bring it up to a more modern design so the ports are cast pre filled - that's why none of the new heads have that ridiculously large port any more -.

Increasing capacity increases the air flow demand for each incremental point in the rev range, so the velocity is higher for the same rpm, and it's the velocity that will tell you where each head will make it's best power. Small port will make power earlier, large latter. Basically, cam depending, if you had the same heads on a 351C and a 417C, the 417 will make the same power as the 351C just at a lower rpm - maybe 1000rpm earlier -.

[thomas butt]

I hope to keep most of the factory port and fill just a small portion of the floor and side (1/8") if at all. Here is a 2014 Corvette LT1 for an example of a large port small block. It does 460hp @ 6000 & 465tq.

[cab0154]

at 7000rpm at 360-380" I would leave them alone and concentrate on compression and cam. at 358" and 7000 with ported clevelands (340 on the intake side) and 10:1 at 3000lbs it went 98mph in the 1/8th. it just didn't need all that head. now with a 408 and 14:1 and 7500 its running 111mph. I think porting on those is a waste of time if you aren't going to run a bunch more stroke, rpm and compression. and if you don't know what you are doing you are likely to do more harm than good. if it were mine, I would cc the chambers, make sure all the seats and guides are good, use a good valve and VJ, concentrate on my valvetrain and cam and let it eat.

and if you think you are going to treat a 4v canted valve Cleveland head like a big port inline LS head and have good results, good luck. like I said above, I wouldn't port or fill in anything. just run it. see how it runs. you might be surprised. I wouldn't even port the intake much. the low comp 358 ran 98mph with one of those intakes unported on motor. if you ran 12:1, a solid roller, decent springs, and opened up the intake a little bit while keeping taper in it, I would bet it would go over 100 in the 1/8th on motor at 3000lbs and 358". and a 377 would likely pick up more.

[thomas butt]

at 7000rpm at 360-380" I would leave them alone and concentrate on compression and cam. at 358" and 7000 with ported clevelands (340 on the intake side) and 10:1 at 3000lbs it went 98mph in the 1/8th. it just didn't need all that head. now with a 408 and 14:1 and 7500 its running 111mph. I think porting on those is a waste of time if you aren't going to run a bunch more stroke, rpm and compression. and if you don't know what you are doing you are likely to do more harm than good. if it were mine, I would cc the chambers, make sure all the seats and guides are good, use a good valve and VJ, concentrate on my valvetrain and cam and let it eat.

and if you think you are going to treat a 4v canted valve Cleveland head like a big port inline LS head and have good results, good luck. like I said above, I wouldn't port or fill in anything. just run it. see how it runs. you might be surprised. I wouldn't even port the intake much. the low comp 358 ran 98mph with one of those intakes unported on motor. if you ran 12:1, a solid roller, decent springs, and opened up the intake a little bit while keeping taper in it, I would bet it would go over 100 in the 1/8th on motor at 3000lbs and 358". and a 377 would likely pick up more.

The LT1 head was just an example of how big GM ports are these days when guys were talking about using port stuffers. I am no expert by any means but would like to use the 4v heads as they were designed and just a small amount of fill …1/8" if needed.

I will take your advice and just stick to a good valve job.

[RL]

I hope to keep most of the factory port and fill just a small portion of the floor and side (1/8") if at all. Here is a 2014 Corvette LT1 for an example of a large port small block. It does 460hp @ 6000 & 465tq.

One thing you must never do if you fill the floor of a 4V, is to put any filler on the side of the port between the pushrod and the SSR.

Unfortunately that LT1 is probably not a comparable engine because it's cam limited. Basically they use small cams for driveability, and a large ports for top end performance. It's not really the same as an efficient racing port with the correct cam when ultimate speed is sought. Also looking at the outside of a port is very misleading as to what size actually is.

[cab0154]

at 7000rpm at 360-380" I would leave them alone and concentrate on compression and cam. at 358" and 7000 with ported clevelands (340 on the intake side) and 10:1 at 3000lbs it went 98mph in the 1/8th. it just didn't need all that head. now with a 408 and 14:1 and 7500 its running 111mph. I think porting on those is a waste of time if you aren't going to run a bunch more stroke, rpm and compression. and if you don't know what you are doing you are likely to do more harm than good. if it were mine, I would cc the chambers, make sure all the seats and guides are good, use a good valve and VJ, concentrate on my valvetrain and cam and let it eat.

and if you think you are going to treat a 4v canted valve Cleveland head like a big port inline LS head and have good results, good luck. like I said above, I wouldn't port or fill in anything. just run it. see how it runs. you might be surprised. I wouldn't even port the intake much. the low comp 358 ran 98mph with one of those intakes unported on motor. if you ran 12:1, a solid roller, decent springs, and opened up the intake a little bit while keeping taper in it, I would bet it would go over 100 in the 1/8th on motor at 3000lbs and 358". and a 377 would likely pick up more.

The LT1 head was just an example of how big GM ports are these days when guys were talking about using port stuffers. I am no expert by any means but would like to use the 4v heads as they were designed and just a small amount of fill …1/8" if needed.

I will take your advice and just stick to a good valve job.

I am certainly not a head expert, but I know for a fact you can go at least 6.80s with them in unported form. with compression and cam I would think 6.60s at over 100mph could happen pretty easily. considering what the ported iron 4v heads did on the low comp 358 and what my rhs 215s with a bowl blend on a 347 with some compression and cam went. I just think you wont have the ci and rpm to use port work. also, imo those things need to be ported by someone who has done them before, and at that point you might as well spend the money no some much nice aluminum stuff.

[thomas butt]

at 7000rpm at 360-380" I would leave them alone and concentrate on compression and cam. at 358" and 7000 with ported clevelands (340 on the intake side) and 10:1 at 3000lbs it went 98mph in the 1/8th. it just didn't need all that head. now with a 408 and 14:1 and 7500 its running 111mph. I think porting on those is a waste of time if you aren't going to run a bunch more stroke, rpm and compression. and if you don't know what you are doing you are likely to do more harm than good. if it were mine, I would cc the chambers, make sure all the seats and guides are good, use a good valve and VJ, concentrate on my valvetrain and cam and let it eat.

and if you think you are going to treat a 4v canted valve Cleveland head like a big port inline LS head and have good results, good luck. like I said above, I wouldn't port or fill in anything. just run it. see how it runs. you might be surprised. I wouldn't even port the intake much. the low comp 358 ran 98mph with one of those intakes unported on motor. if you ran 12:1, a solid roller, decent springs, and opened up the intake a little bit while keeping taper in it, I would bet it would go over 100 in the 1/8th on motor at 3000lbs and 358". and a 377 would likely pick up more.

The LT1 head was just an example of how big GM ports are these days when guys were talking about using port stuffers. I am no expert by any means but would like to use the 4v heads as they were designed and just a small amount of fill …1/8" if needed.

I will take your advice and just stick to a good valve job.

I am certainly not a head expert, but I know for a fact you can go at least 6.80s with them in unported form. with compression and cam I would think 6.60s at over 100mph could happen pretty easily. considering what the ported iron 4v heads did on the low comp 358 and what my rhs 215s with a bowl blend on a 347 with some compression and cam went. I just think you wont have the ci and rpm to use port work. also, imo those things need to be ported by someone who has done them before, and at that point you might as well spend the money no some much nice aluminum stuff.

-Definately. One day I will splurge for aluminum heads. I want to mess around with iron for now. There is a little potential for these and i like using what is there (factory iron) for now.

I was thinking of a 408 with a 9.2 deck and even do a 400. I like the 400 and would just have to work a little harder getting headers to fit. Got a manifold to work to. I might use a production reman as well. I know they have cast pistons but would relegate the rpm to under 6,500 and have the builder install ARP rod bolts & main studs, clearance the mains .030". Then would be able to utilize those 4v heads a little more and possibly get in the 6's. I checked the compression and with dish and heads shaved to 56c your looking around 11:1 comp

[RL]

-Definately. One day I will splurge for aluminum heads. I want to mess around with iron for now. There is a little potential for these and i like using what is there (factory iron) for now.

I was thinking of a 408 with a 9.2 deck and even do a 400. I like the 400 and would just have to work a little harder getting headers to fit. Got a manifold to work to. I might use a production reman as well. I know they have cast pistons but would relegate the rpm to under 6,500 and have the builder install ARP rod bolts & main studs, clearance the mains .030". Then would be able to utilize those 4v heads a little more and possibly get in the 6's. I checked the compression and with dish and heads shaved to 56c your looking around 11:1 comp

For a 408C to make power at 6500 you will need a port csa around 2.8" sq, so they will still have to be filled. Unfilled probably 7850pm peak power

[mag2555]

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!