rockyw

i got a 90 cyl head for the 9mm injectors would it be a good idea to use this head or would it bebetter to use the 7mm injector head i want to get this ported and get a good exhst manifold i want to be able to build 500hp easy i acctually have the complete spare 90 motor will my ve pump be able to supply the fuel for this much hp ?

rockjeep73

If you had the option then I would say go with a 7mm head, they are less prone to cracking as there is more material around the injector bores. I also believe that the newer heads flow slightly better due to some changes in the casting.

tboling

If I were u I'd go with a 24valve head, it dose not take much to make it work. The 24valve head will flow more cfm's and make lower egts for making more hp.

flashgordon

each inj line need to be the same langth.......How would you do that.

A-Poc

Pick the farthest injector from your injection pump, measure a line for it and then make five other lines identical to its length. Therefore you have 6 identical lines. All they need now is to be bent around to match up to their corresponding injectors.

Underpsi

You make it sound easy but to make up lines for it would be harder then just that they would also be expensive. Not to mention i think 24valves have different bowls in the pistons since the 24 valve injectors have different spray patterns so the 12valve injectors probably wouldn't hit inside that bowl correctly

flashgordon

sence you have the 90 head allready, i would us it...........if i was going to throw a lot of boost at it and lots of fuel mods then maybe you should look for the 7mm head.

How big a problem is the cracking 9mm head? when do thay crack?over heating them? to much fuel? pyro heat? casting flaws?

if you can ansore these ? you will have a much better idea witch one to use!

And I would love some one to ansor these ? for me two, haveing a 91 non intercooled(9mm inj) head allso

Underpsi

I just had my 9mm head sent out for a rebuilt and they magnafluxed it as well as pressure tested and there are no cracks. Im not the most gentle person to it either as my pyro as been pegged to the 1500deg many times

bgilbert

Well since he's looking for big HP, the old head/technology is not the way to go. Cummins upgraded the head for a reason. I would not spend money on the 90 head.

To answer your questions, I would say all of the above except for casting flaws on why they crack. Although the reason has been answered already.

When I had the choice of head work and fire rings I bought a new style cylinder head. I never considered doing work on the old 89 head. Less prone to cracking under intense use, slightly better swirl, option of using different size injector washers. This is so you can move the fuel spray closer or farther away to the piston bowl. Non-intercooled head with 7mm injectors you only get to use the thick adaptor bushings. Yes not a problem if you're using 9mm tipped injectors, but you're not gonna make big power with 9mm stock injectors.

Underpsi

True you can't make good power with 9mm stock injectors but I believe that the 9mm injectors have potential to edm them or hone them and that type of stuff.

Sorry to get off topic there but Bill is actually right. they changed the head for a reason so in the long run it is much better to go with the 7mm head. I on the other hand didn't have the cash for the new head so I got work done to my 9mm. Hopefully I didn't throw my money out the window (knock on wood) but i guess we will find out.

On the 24valve head idea it is much more cost effective to just extensively port your 12valve head for better flow then to get the flow qualities from the 24valve head

mhuppertz

I have heard the 24 valve head is MORE prone to cracking between valve seats under extreme use..... I would get the 12 valver extrude honed (intake and exhaust ports). If I could I would.

frostie

I would definitly go with the 7MM.
If anyone wants a 24 valve top end I have one, I was going to do that conversion till I saw how small the ports are on a 24 valve
anyway I used a 95 cylinder head, ported it and the ATS manifold, it made a huge performance difference.
I believe the ATS manifold needs porting where the exhaust enters the manifold. If you get one you will see a serious restriction right at the entrance of each port.