Head porting

[gradon]

My Borla header came with two gaskets: 1 regular size and 1 for larger ports. I just found the larger one and the exhaust openings are 1 13/16" and the intake openings are 2 1/8"x 1 7/16". Putting the gasket up to the head I can see 1/4" all the way around the exhaust ports and about 1/2" on just the bottom of the intake ports. Did Borla include this gasket for those that do some porting or is there some other head out there that has intake ports that low(I got the header that fits the 92-96). Now Dino, I see that you basically opened you exhaust ports to about 1 7/16" and that your intake ports are 1.654" x 1.417" (1 2/3"x 1 7/16"). Anyhow I've heard/seen the warnings not to touch the floor of the port and know about leaving a lip on the exhaust port. I'll be doing the port and polishing next week and wanted to know what was up with this gasket(do I buy another regular gasket or will it be fine to have a gasket used on a head whose intakes aren't opened as much as the gasket is?).

[4point6]

Maybe the Hesco aluminum head? Their website says they made it with extra material left for more porting. I have a 7120 and an 0630 head in my basement, both measure intakes up about the same (rough measurements 1.38" x 1.61").

[1bolt]

there's the Renix era (86-90) head which have lower ports, but no others all the HO ports are higher. The 0331's exhaust ports are "smaller" (they raised the floor of the port to increase velocity).

A little known fact, the 0331 head has higher ports than any other 4.0 head, both the exhaust and intake. The fact that some castings were prone to crack and the fact that the exhaust has a smaller cross section have lead most people (understandably) to ignore it... What we all may be overlooking is that the smaller exhaust ports might actually be an improvement, due to increased gas velocity (faster moving exhaust gases) resulting in better scavenging.

The exhaust port and even the intake ports, need to be "good enough" in cross section, after which design (or porting if the design is poor), and velocity are far more important.

Interestingly there are race engine builders out there who fill in exhaust ports (usually the floor just like in the 0331 head) because the port is bigger than needed for CFM, and not optimal for velocity.

Meaning the Piston has no problem pushing spent gases out the Valve but when the piston nears TDC the gas flow out the vavle is slow and lazy... Smaller well designed (or ported) ports have the effect of siphoning (called scavenging) or sucking the last bit of exhaust out leaving a mild vacuum inside.

Guess what that does for you? Yeah, it helps SUCK the intake charge in when the intake valve opens as the piston travels downward... Making the engine more efficient because the exhaust is helping the next intake of fuel and air.

This is why "long tube" headers are so good for torque, they also increase the velocity of the exhaust and maximize the scavenging effect.

Borla definitely didn't include a gasket specifically for HESCO's gilded Aluminum head. Throw the bigger gasket out and use the smaller one, if you're gasket matching look for the other head porting thread in here, from a week or so ago.

[gradon]

I've been reading up on porting for a while now and did purchase the deluxe porting kit from Standard Abrasives. I smoothed out the 99+ intake that's on my 96 back in June. I'm going to yank the head off the 94 block on Monday and start working on it. Today I looked around for that second gasket and was curious as to what application Borla deemed it necessary to include with their header for the 94 4.0. What head could possibly have ports that large, or be ported that large. You say that the earlier ports were lower, but were they larger? I've emailed Borla on this and am waiting for a response as well. According to the website, the 17039 header is only for the 93-97 4.0 cherokees, so either they know of a 93-97 head that can be ported to accept it, an aftermarket head for the 4.0 made during that era with larger ports, or it is a gasket for an earlier 4.? head with larger ports(in which case it shouldn't have been included with a 17039 header).

[Shark]

why would that header be only for the 93-97 4.0 cherokees? that overlaps 2 head castings. it doesnt include the beginning of the 7120 head or the end on the 0630 head.

[gradon]

So I just read that someone polished their head out to 61cc. Is that an extreme or can 60cc come with some effort? What numbers have some of you got? I also have a question about the valves. Some valves are tulipped--does this increase the volume in the head? I think I've read that the shape helps promote good flow.

[dwg86]

Well I opened up the combustion chambers and polished the. With the stock valve in the heads i got 61.4 to 61.8cc's. I haven't had the head milled flat yet, but hopefully it will only take a couple of thousands to make sure its flat. It didn't take much grinding, but alot of time getting the cc's to match. ( .4 was close enough for me. Thats about 3 to 4 drops). I have SBC 1.94/1.50 undercut stainless valves that I am going to use($64.00 shipped to my door). I have to ream the guides bigger, from 5/16 to 11/32, but that will save some money on installing new guides. Also have to have the intake seats opened up from the stock jeep valves 1.92 to the SBC 1.94 valves. The SBC valves are a little shorter than the stock valves...maybe .030, so I am concidering having them installed a little deeper in the heads. This would add a few cc,s. I need to talk to my machine shop about that. After the new valves are installed, I will cc the heads again to find out where I'm at. I wll try to post some pics of what I have so far...if you want?
Oh, tulip valves should increase the cc's a bit.

[Flash]

Well I opened up the combustion chambers and polished the. With the stock valve in the heads i got 61.4 to 61.8cc's. I haven't had the head milled flat yet, but hopefully it will only take a couple of thousands to make sure its flat. It didn't take much grinding, but alot of time getting the cc's to match. ( .4 was close enough for me. Thats about 3 to 4 drops). I have SBC 1.94/1.50 undercut stainless valves that I am going to use($64.00 shipped to my door). I have to ream the guides bigger, from 5/16 to 11/32, but that will save some money on installing new guides. Also have to have the intake seats opened up from the stock jeep valves 1.92 to the SBC 1.94 valves. The SBC valves are a little shorter than the stock valves...maybe .030, so I am concidering having them installed a little deeper in the heads. This would add a few cc,s. I need to talk to my machine shop about that. After the new valves are installed, I will cc the heads again to find out where I'm at. I wll try to post some pics of what I have so far...if you want?
Oh, tulip valves should increase the cc's a bit.

Just a thought here, and i don't know if it apply to the jeep head but.........chry claims that the best you head will flow is when its new and every valve job that you do will decrease the the flow and is why larger valves will flow better.......because the seat is raise back up to the top.....

Maybe there is enough material under the seat to lower the spring seat surface..............Lisson to you machinist before Me

[gradon]

Another thing, from what I've gathered, going to 1.97" intake valves and 1.625" on exhaust valves is about the best the head can flow based on the flow of the intake runners? I would rather ream than install valve guides, but I believe the mopar valves are all 8mm. They cost $17.50 a piece at Mopartsracing.com/Jeepconnection.com so they're about 3xs more than the Chevy's(I still prefer to use a Mopar part, though). I'm going to be using a 256* .45 lift cam so I think it would benefit from a lil larger valves.

[jeepinwi]

Another thing, from what I've gathered, going to 1.97" intake valves and 1.625" on exhaust valves is about the best the head can flow based on the flow of the intake runners? I would rather ream than install valve guides, but I believe the mopar valves are all 8mm. They cost $17.50 a piece at Mopartsracing.com/Jeepconnection.com so they're about 3xs more than the Chevy's(I still prefer to use a Mopar part, though). I'm going to be using a 256* .45 lift cam so I think it would benefit from a lil larger valves.

You didn't happen to win that cam off eBay, did you?

[gradon]

Nope, I've had it since Oct/Nov. and knew when I ordered it(from Mopartsracing.com) there were only 2-3 left in the US. It was manufactured on my B-day(6 months prior to me ordering it), so I know it's a meant-to-be thing.

[gradon]

So I took the head off the 94 block today. Removed the rocker arms. Pops doesn't have a valve spring compressor so I went to Advanced and rented one. I follow the picture instructions on removing the springs and it takes me 20 min to get one valve out. The retainers are not compressing the spring when I follow directions and have one end of the compressor on the face of the valve and the fork end on the retainer. Supposedly with enough pressure, the retainer will move down, the valve will stay in place and you can pull out the keepers/locks--but not so. What am I doing wrong? I can compress the spring and move the valve when the fork end is on the retainer and the rod end is in that dimple b/t the valves. I thought the keepers/locks just hold the retainer to the valve so that it won't fall out. Is there something preventing the retainer from pushing in (besides the force of the spring)?

[cherokee]

On a very high milage head with huge amounts of carbon buildup I found I needed to loosen the keepers a bit first. I took a socket that hit only the retainer and gave each valve a good hit to loosen up the carbon gluing the keepers in place. This was done with the head still on the block and I made sure to rotate the crankshaft to keep the pistons from possibly being hit by a valve. If you've taken the head off already I suggest tipping it on it's side first. Put the valve spring compressor on and if it opens the valve tap the valve face with a soft faced hammer. Make sure you do this in an area you'll be able to find the keepers if they pop off when hitting the valve face.

[gradon]

Basically the spring compressor I rented is a POS--probably good for the install but horrible for the removal(at least in my case). I ended up resting the valve face on a big socket and using the rubber mallet to whack a socket a little smaller in diameter than the retainer(Dad's old school trick). Got them all out in 10 min and a couple of the keepers went flying somewhere. Tomorrow(today) I'll get crazy with the die grinder.

[Flash]

What i do is tap the end of the retainer until the tone or sound changes.............At that point you valve spring compressor should work just fine

When you go back together you should smack the valve stem to seat the keeper back into the retainer


Flash