Good Article on the Optimizer


Well-known member
just to add the info here in this thread just in case it makes the stickies.

I have posted in:

The optimizer was being cast by Navistar for GEP up to appox. 2013. They have switched and now use Dalton Forge in Indiana and Dalton machining in Ohio.

I just purchased a new GEP Optimizer, not a p400.

Attached is the cast markings for an Optimizer from Dalton. They use a backwards D with an F made into one symbol with a circle around it.

The Navistar logo is two triangles back to back to resemble a diamond. Any block pre optimizer these days is considered junk and there are Chinese knock off blocks and heads that have the Navistar logo's. I don't know if there are Dalton knock off's yet, probably not since the change was not announced and it just happened in the last couple of years.

You can no longer purchase a new Navistar optimizer. they used all the castings. If you have someone selling you a new Navistar optimizer it is a knock off.
There will be approx. 2000 Navistar P400's available but they are not going to start machining the remaining cores until next year. They will be machined by Dalton.
Once the inventory is depleted all P400's will be Dalton cast and machined also.

Dalton is made in the U.S.A., and has a good reputation. Dalton cast a lot of things for a lot of other people so the optimizer strength should continue.

if you are getting a used block, make sure it has Navistar logo. There is still a chance it is a knock off and not original but very small chance. Knowing where it came from helps in determine if it is legit.

I just found this out because I received my new GEP about 5 days ago and it did not have the correct markings. Thus since then all of the above info has become available through GEP.

I am supposed to get the new date code information on the Dalton blocks and I will post that info when I receive it.


to add to this, the heads are marked by dimples on the front side of the head I believe the Navistar had two dimples and the Dalton will have 3. still trying to confirm this info.


Last edited:


Well-known member
Steel Soldiers Supporter
Amersfoort, The Netherlands
I am supposed to get the new date code information on the Dalton blocks and I will post that info when I receive it.
I don't like bringing up an old thread, but I have to ask. Hope you are still reading these forums. Did you get the date code information? There is not a lot of information about blocks cast by Dalton to be found and I just won one at an auction. I'd like to know more about it.

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