Well I know it's kind of a dead issue to build or modify a set of J heads because of the low cost of more desirable castings, but I decided to find out for myself. I have a set of c, ga, and J castings at the shop. Visual inspection the J ports are very different. They are much smaller and they have a very high short side. I hope to answer many questions about the job heads. I have some good numbers but unfortunately it takes a bit of skilled porting to get there. I will post pics and numbers soon.

 

If the heads are going to be ported and modified,it makes no difference what you start with.
I know a guy running in the 10's with wheels up launches on J heads.

 

I think you might change your opinion when you see the numbers ; )

 

They can flow great with porting but are horrible to start with, same goes for 4A or any later "#A" heads. Heads like 8's can be improved greatly on the exhaust side with a bowl hog, J heads and 4A heads need hours of port work, not an easy fix. It will interesting to see before and after numbers and include the time spent on them.

 

I just priced having the local NAPA do a basic valve job and surfacing on a set of heads, no porting, etc. $460 a set, plus any springs, parts, or guides. It makes aluminum heads start to look very tempting.

 

They are overpriced in my opinion. Not to take away from your point. I charge 225.00 to do a " valve job "and mill up to .005.

 

Or maybe I am underpriced

 

I have some numbers on the J heads.
Stock
.50 36
.100 63
.150 91
.200 121
.250 149
.300 169
.350 174
.400 180
.450 187
.500 189
.550 190

 

Here are the flow numbers for the ported J heads.
.50 37
.100 71
.150 106
.200 137
.250 167
.300 190
.350 208
.400 216
.450 219
.500 221
.550 224

 

 

From what I can tell so far it looks like the J intake port is a copy or the small block olds head intake port. The port work that I have done is all in the bowl area with some guide boss reshaping. I will try to post the flow numbers from a set of C castings for reference soon.

 

 

 

In my opinion, the NAPA Shop is to high. There's a fine line in charging, too much and they go Aluminum heads, too less and you won't be able to keep the lights on. Around where I live, we had lots of machine shops, not anymore. My main shop I used, the owner that I've known from school (1956) passed away. One nearby shop is closing before the end of the year. 2 others have closed in the last 5 years. The two I still use aren't getting any younger, both mid 50s. Nobody rebuilds Chevrolet heads anymore and that was the shops bread and butter. If I had other cores (C, E, G) I'd choose one of those. Jmo.

 

Thank You!

 

Engine machine shops are a dying art. It makes me sad too. There are many reasons for the decline. I do have a set of Cs and a set of Ga heads at the shop. But I really wanted to explore the potential of the J heads, mostly because of the countless internet forum post with people asking about the J heads and getting the same answers.

 

Also I would like to say that there were at least five separate flow test between the before numbers and the finished numbers that I posted. The J head Intake port is very sensitive to where you remove material.

 

Makes you wonder how many J heads that had considerable machine work done to them were discarded by folks who saw the J casting and tossed them without looking to see if they'd been worked.

about 18 years ago I had a set of J's worked over by a machine shop, all new guts & ported. About $800 worth- simply because I already had them and was too lazy to try and find better castings at the time. Put them on the stock 455 with plans to build a better bottom end eventually, but sold the car.
about 3 years later the car came up for sale again, I saw it and contemplated buying it back- spoke to the new owner (not the guy i sold it to) he said the 455 had spun a bearing and he had found and installed a 403 in a wrecking yard to replace it..

I asked what happened to the heads that had been on the 455 and he told me he junked em with the engine because they were J's... and everyone knows J is for junk.

Doh!

 

Well maybe if we all work together we can change that

 

 

interesting read - I just this weekend picked up a complete '73 455 with J heads, appearing thus far unmolested. I'd be very interested to see how a properly modified set of J heads would perform against other more popular option factory heads but I guess I'm part of that hesitant group that wouldn't readily spend retail money to take a chance on them, based on everything I've read to date.

 

What about the even worse side, the exhaust side? Now there is some serious grind time. My 4A and 5A heads were bloody awful even compared to 8 heads on the exhaust side. Aren't the 8 heads a better starting point and also have BBO sized chambers?

 

One thing to remember is that most NA engines only need around 65% to 75% intake to exhaust flow ratio. So with my math at 220 cfm intake we would need around 165 cfm max on the exhaust side. I haven't tested them yet but I think that shouldn't be a problem. I am not saying that the J heads are great and everyone should use them. I am simply trying to see if the J heads have any potential and what they might work well on. I port many different cylinder head castings. There is always a favorite but some times the favorite is not the best for the application. Think about Chevrolet Big Block. There are three intake ports to choose from. Peanut port, big oval, and rectangular port. If we used a cylinder head based on flow numbers alone than every Rat engine would have Rectangular ports on it. I don't want to get ahead of myself but I think that a nice ported set of J heads in some applications might out perform the C castings. Thats not a negative statement against C heads, just making the point for careful selection of parts . In a street engine, if you have a choice of two heads that flow close to the same numbers than the one with the smaller volume is the better performer. Now thats my opinion.

 

 

 

 

 

J head exhaust port
.50 NA
.100 59
.150 84
.200 102
.250 112
.300 117
.350 121
.400 123
.450 125
.500 126
.550 127

 

J head Valve job

.100 52
.150 77
.200 98
.250 118
.300 126
.350 131
.400 136
.450 140
.500 142
.550 143

 

J head valve job bowl blend

.100 53
.150 76
.200 97
.250 119
.300 132
.350 138
.400 145
.450 153
.500 158
.550 160

 

Funny the intake stock was crappier than I thought and the exhaust is better stock than I thought, go figure. I didn't realize J heads had the stupid lip under the exhaust valve like #8 heads. They end up around what stock big valve castings flow, not bad.

 

If I have time tonight I am going to flow test one of the stock C castings that I have to give us a good reference point. My bench is very stingy. 220 on my bench is 245 on others.

 

Does anyone know the factory port volume on the Olds castings?

 

 

Thank you

 

Stock C heads with back-cut 2.00 valve 1.678 exhaust valve

.50 29 na
.100 66 59
.150 101 83
.200 133 105
.250 156 121
.300 171 131
.350 187 141
.400 199 150
.450 208 157
.500 215 161
.550 222 165

 

 

You should have used the right seat, small Inner diameter.

 

This is a stock G head tested on a 4.155 bore @ 28 inches, small valve.

200/122 .300/172 .400/196 .500/209 .550/215 .600/220 .700/226.

 

Dead horse won't really be beat until we see a dyno shootout for who can build the most powerful J headed 455 with stock stroke . Maybe make it worth the time with a $500 - $1,000 buy in.

That would be entertainment.