Exhaust port porting?

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MidTexCuda

MidTexCuda

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I was looking at the exhaust port on my heads today and noticed a lip on the top edge of the port. My header primary tubes sweep up off the flange not down so I was wondering if there would be anything gained by cleaning this area up or if it would ruin the head. What are your thoughts?
 

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I've not seen the rest of those heads (Bulldog?) but that should improve the flow. It even makes a difference on the Edelbrock RPM heads when you clean the CNC'd opening back into the port.
 
IQ thank you. I owe you a box of cigars or 12 pack for all the help you have giving lately. You know my sorry flow #'s should the exhaust be ported like the intake? Mine look stock.
 
Porting the exhaust properly should help a great deal. Here is an example from a RPM head we just did for a 505. First, out of the box flows and second ported. These were using a 2" pipe. In tests we have seen RPM exhaust ports go over 300cfm.

Lift............OOTB.............Ported

.100............57.................58
.200..........112................125
.300..........163................182
.400..........197................217
.500..........217................240
.600..........231................257
.700..........239................285

If yours are unported you could see a similar increase.
 
some work was done at least twice. here are the flow numbers form the second go round. most likely no pipe.
lift------D---E
.100--49.4/ 52.4
.200--94.2/102.9
.300-131.4/136.4
.400-157.5/166.2
.500-179.8/193.4
.550-189.7/201.4
.600-199.6/212.0
.650-208.3/219.5
.700-215.8/225.7
.750-220.7/230.6
I will get pics tonight of the exhaust port.
Because I may use these on my boosted engine any improvements to the exhaust will help a ton
 
Mopar exhaust ports actually flow really well. I would just smooth out the casting and match the upper part of the port to the exhaust header. Leave the floor alone. Messing with the floor of the port will only hurt your flow.
 
I'd agree with that considering a port job would include a gasket match.
 
A gasket match on an exhaust port is generally a messed up port job. I would never recommend gasket matching an exhaust port and certainly not dropping that floor to match the gasket.
 
it had copper gaskets--- not sure of the part number but the gaskets had about a 1/8" overhang into the port on the sides. I think I have some huge bugs to work out.
 
I would not do that much. You don't want to make a trumpet out of it, and you don't want to lose anything off the short side or the sides.
 
I am either going to clean them up and sell them or use them on my procharger build. Thats why I was curious about fixing that area of the head. Dont want to make the anymore unsellable.
 
In either case porting the exhaust side isn't going to do that much by itself. I'd leave them alone.
 
I have been sick the past couple of days so I have had time to day dream on my build. I have a question:
I am going with a 2.375" primary tube on my sc build and was looking at how to fit those pipes. My plan is to not make adapters but to make my own flanges. That being said I have not touched the heads with the prior roof issue and was planning to keep the same square shape. Can I make the head port opening more of a D shape? has anyone ever done this?
 
IQ52 said:
A gasket match on an exhaust port is generally a messed up port job. I would never recommend gasket matching an exhaust port and certainly not dropping that floor to match the gasket.
Click to expand...

Nice to read that!

I have been reading up on porting and plan to do my heads and I have read that in a couple of places.
 
Talked to an old friend today. He said the port opening area should match the valve area and that you can safely increase the port opening to +15% of the exhaust valve area.
does this sound about right?
 
The exhaust gases are supersonic & hot because of the cylinder pressure. They have an entirely different behavior than the intake charge. The goal is to kep them moving and hot. You are better served keeping the port area smaller and raising the roof to help it turn than anything else. That gives the least surface area for thermal trasfer and the port acts as a nozzle between the cylinder at the later part of the combustion cycle where the pressure within the cylinder is still fairly high and the cooler and larger volume header primary tube. That can help scavenging which is much more significant to complete cylinder filling than the pressure differential created by the piston moving down on the intake stroke. The step between the header flange and port does not hurt you in the least.
 
I was only going to open up the last 1/4" to 1/2" up. That opening is 1.810w by 1.246h area of 2.255. My 1.81 valves have an area of 2.572. Was going to take the ramp out of the top and open the sides a tad. Would this be the wrong direction?
How I understand your post is that having a smaller opening than my valve opening going out of my head into my collector then into a big pipe is a good thing because it keeps the flow going better based off the thermal properties of expanding gas. And if I do want to increase any part of the port focus on raising the roof in the port and leave the dangling wedge in place?
also is the scavenging need as great with a boosted engine?
 
Remove the wedge.

On our RPM heads with the 1.78 valves and flowing 285 cfm, the port is 2.49 sq in. vs the 2.498 sq in of the valve. The RPM heads that made 787 HP naturally aspirated on the 451 engine have a 1.81 valve (2.572 sq in) vs the port opening of 2.467 sq in. I have not run a turbo charged engine myself but those that I have associated with, who were making 1,700 HP to the rear wheels, said to put the best flowing exhaust port on your engine that you could.

We've been through this crap with a bunch of diesel engine guys. They keep adding boost on the stock head using twin turbos and make 900 HP. We ported the head, used a single turbo, stock cam and made 1,400 HP. Of course the owner failed to upgrade the valve train and blew the engine apart at 1,400 HP.

We will be finding out soon as we are in the process of building a 572 ci, all aluminum, twin turbo wedge. I can promise you the heads will be made to flow everything we can get out of the exhaust.
 
Yes - remove the wedge. Don't make it wider. Don't revise the roof or bowl. Just take out the lip. It's less of an issue with boost but as IQ said - a better flowing port will only help with any boost, and if it's a turbo, the smaller, hotter, and faster you keep the port the faster boost will develop. There is a HUGE difference between "best flowing" and most efficient. They are not the same animal. Best flowing on a bench, any bench, may not be very efficient. Three reasons for this are you have to flow it backwards, the material moving through the port is not exhaust gasses but standard atmosphere at ambient air temp and full of water, and last you're not pushing the gasses at 1300psi - you're sucking at 10" or 28" of mercury. IMO the exhaust port is best shaped in relation to the percentage of intake flow needed. Flow benches are much better at predicting the intake flow although the lower the test pressure the more vague the result.
 
Thank you all. I am trying to get my new window opening established so I can cut my flanges and build my pipes over the long weekend. Should I get a gasket that fits the port or is atad bigger. If bigger by how much?
Thanks again
 
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