First intake manifold porting - advice?

[SS454]

I apologize if this has been covered many times before, but I'd just like to see if I could get some advice on my first ever attempt at porting.

Intake is a Weiand Action Plus dual plane.
Engine is a 461 ci BBC, 280H cam, stock (afaik) 820 iron cylinder heads with 2.06/1.72 valves.

Engine made 370 rwhp @ 5100 on a chassis dyno.

The goal is to let it breathe a bit better on the top end so it doesn't fall off so quickly. Since I road race my car, there are times where I hold gear and run it upwards of 6000 rpm.

In stock as cast form:




I already did some plenum mods. Divider cut down, and some blending.



My main question is in regards to the floor of the ports. When I lay the gaskets on my heads, the gasket/ports match pretty well. But as you can see the intake manifold ports don't match the gasket very well at all. I was thinking of reshaping the exit of the port to more closely match the entry of the cylinder head, which would mean removing material from the floor, and then blending about 2" into the port. I do not want to do any porting deep into the port, or reshaping the radius as there would be too much of a risk to completely bugger up the port to port distribution. Should I do a bit of "gasket matching" or just leave it?

Thanks

[rally]

Bigger is not always better, be careful. You tube might have some good intake porting videos. Weiand intakes were designed pretty well.

[FC-Pilot]

Not to be a "Debbie Downer" I would not do too much more to that intake. If you try to open the bottom parts of the ports to better match the heads than for the ports coming from the lower plenum side the turn on the floor will be even tighter. Also, the bottom bit of overhang may not be a bad thing. Playing with porting the plenum can be tough unless you know where you need to move the fuel for better fuel distribution. I am not much of a porter, so I don't screw with intakes too much unless it is going to go on the dyno first where I can see if I messed anything up or not. Anyway, that is just my two cents.

Your best porting efforts would be on the heads in the bowls. Your time spent there could really be something you could easily see in track times and on the dyno.

Paul

[JoePorting]

Porting the manifold isn't going to do anything. The small intake valve is the bottle neck.

[mag2555]

All around power wise you would be better of having just notched that Plenum divider a little and then running a large Carb like a 950 hp with high gain boosters!

[rebelrouser]

Not an expert but if you put an intake on a flow bench you will find a lot more air runs across the top of the runner, it looks like you already may have smoothed the radius where the air turns from the carb flange, which is the biggest thing you can do without causing problems. The runners work best if you have a straight taper, if you make the runners fit the gaskets you will have a runner then a big bulge where you matched the gaskets, not a good thing. I usually texture the floor and sides blend the radius where the carb flange meets the runners and call it a day. You may check how the runners flow, I find most dual planes have a big difference between runners on flow, and their is not much I have been able to do to fix them. I have did some OEM cast iron intakes for some pulling classes that had to use the OEM manifold. I opened up the plenum with a mill and radiused the top of the runners and did a little work where the runners met the plenum to try and equalize the flow. Never had a manifolds to compare with but the pullers had me do several, so they must have worked fairly good.

[Newold1]

I think you are good where you are at. As others said leave the intake/head transition alone.

I would say careful carb selection and set up and tuning will be very important as carbs do not like to be tossed back and forth to begin with and off/on throttle smooth acceleration is more important on a road race car.

If the engine is still not pulling hard past 6000 rpms look at addition of a carb spacer and obviously spend a lot of work with timing and A/F numbers under acceleration.

[PRH]

IMO, the more likely source of the power falling off sharply is the “h” in your “280h” cam.

Put a nice smooth solid cam in it and it will go over 6k with ease.

[SS454]

Well I think it's obvious the popular decision is to leave the port runners alone, so I think i'll leave it as is.

I am running a FiTech EFI, but did have a Holley 3310 750cfm carb on it before.

I have dynoed it with the carb, then with a 1" open spacer, then with FiTech. I have also changed the valve springs which were installed very poorly and had very little seat/open pressure, and during the swap have greatly improved that, checking install height and spring rates on every single valve.

All of this has made very little difference on the top end. Peak power has always been around the same, and the drop off has always been about the same as well. The cam is wrong for the engine, but it's what I have, so I'll work with it. Plan is to take it to the dyno again next year, see if there is any diffs. Power will likely be diff as I went from an M22W 4 speed to a T56 Magnum.

[Newold1]

Was the 280H Comp cam degreed in when installed? It's about +4 as ground and if it's in past 0 it's pretty anemic for that big block at 230 degrees duration at .050" trying to go past 6000 rpms. You can try crutching the cam by maybe installing it at -2 -4 degrees but the lower rpms may get a little soft. You could also go to a set of 1.8 rockers and get some more lift which will slightly increase duration and may help raise the peak.

Which CFM FI TECH unit do you have on the engine?

Shop around, you appear to have the engine partially apart anyway. Find a camshaft on the used market if need be and get the right camshaft in your engine. THIS IS YOUR LIMITER AS IT SITS NOW ! NOT CHANGING IT WILL NOT FIX YOUR PROBLEM !

[SS454]

Was the 280H Comp cam degreed in when installed? It's about +4 as ground and if it's in past 0 it's pretty anemic for that big block at 230 degrees duration at .050" trying to go past 6000 rpms. You can try crutching the cam by maybe installing it at -2 -4 degrees but the lower rpms may get a little soft. You could also go to a set of 1.8 rockers and get some more lift which will slightly increase duration and may help raise the peak.

Which CFM FI TECH unit do you have on the engine?

Shop around, you appear to have the engine partially apart anyway. Find a camshaft on the used market if need be and get the right camshaft in your engine. THIS IS YOUR LIMITER AS IT SITS NOW ! NOT CHANGING IT WILL NOT FIX YOUR PROBLEM !

The cam was already installed when I bought it, so I really don't know if it was degreed or not.

I have the FiTech 1200 hp 8 injector unit. All their systems have the same 835 cfm TB, the diff is the injectors. I know it's overkill, but the plan was to be able to use the same system on a completely different engine.

I 100% agree the cam is the limiting factor. I'd likely go with a Howards HFT 231/235 @0.050 .544/.553 110LSA if I were to swap. That or a Lunati 60203. I really don't want to put a lot into this engine as my dream/plan is to build a 509 BBC in the future.