Heads

[GIT-R-DONE]

1. Are all the heads on these trucks the same from 1989 to 1998. 5 12 valves?



2. Any years that are better than others for flow or perfomance, or are they all the same?

 

[dodgenstein]

The 2nd gen 12V head is said to flow slightly better in stock form and also has more clearance for the P-pump. Early heads (89-91) had larger injector diameter (9mm vs 7mm). They were prone to cracking.

 

[bgilbert]

What he said.

 

[Sri Ram]

Early heads (89-91) had larger injector diameter (9mm vs 7mm). They were prone to cracking.

So, the 91. 5-93 engines had the new injector diameter?

 

[HRDROKN]

Yes

Yes... that is my understanding also.

 

[Moab4x4]

Head Crack Question

I called a machine shop this week and was told that almost every 12V head that had been to that shop was cracked and needed replaced. :--)

I am between having mine checked and rebuilt or just ordering a new head.

I have heard of the cracking problem with the 9mm injector holes (on TDR where else? ) , but do the 7mm heads have the same problem? Is that shop just trying to sell me what I probably don't need?

What are your experiences?

TIA

Ken

 

[GIT-R-DONE]

So, the 91. 5-93 engines had the new injector diameter?

Which makes me wonder if my 91 is either a 91 or 91. 5. What is the difference or how do you tell the difference between them? Is there anything in the VIN code that specifies that?

 

[Greenleaf]

To the best of my knowledge, it was the 91. 5 model year that the new emissions equipment was employed such as IC/smaller injectors /different pump timing.



The local machine shop told me that all the 12 valve heads are cracked when they get them in and have to be replaced. I took one in and came out with a new one. They showed me the cracks. It was the old style/9mm injectors.

 

[bgilbert]

Which makes me wonder if my 91 is either a 91 or 91. 5. What is the difference or how do you tell the difference between them? Is there anything in the VIN code that specifies that?

Yes, but easier than the VIN, if you have an intercooler you have a 91. 5. No intercooler you have a 91.

 

[CumminsKid]

Also if you have the A518 (46rh) Overdrive transmision ( if auto ) you have a 91. 5. Look for the overdrive lock-out button on the dash. You should also be able to see the day of production inside the drivers door jamb.

 

[CumminsKid]

Also the only heads I have heard of cracking are the 9mm injector hole heads, pre-91. 5. I've been told that is why they went to the 7mm, to keep them from cracking between the injector bores. They also started to put in a new and better head gasket in 91. 5.