990 Oliver GM

Richard, Take notice of the second picture (prior posting), the late model sleave opening is still smaller than the (large port) block opening. So far we have not seen any performance-difference's. Also as a quick reference from the outside (identification), early 371's had "GM" stamp on right side. The later 371's have the Detroit cymbal. Picture that I've posted shows the later Detroit engine (power unit). This engine would have to be reconfigured and you would use your bellhouseing,governer exaust-maifold,front motor mounts, front crank pulley, fan, possibly your starter and a few other odds & ends. Hope this helps.

The engine was just overhauled before I bought this tractor with new sleeves, pistons, and entire in-frame overhaul. I have no idea if the engine had N sleeves and pistons installed...but I doubt it. Therefore, I need to maximize what I have.

I may benefit from replacing the rebuilt injectors in it with N injectors but don't know if they can be installed in my head. The serial # on my head casting is 5183927. If any of you guys have an old reference book could you tell me? Also, the rebuilt injectors that are in the head have the following # B1206. Do any of you guys know what style and size these injectors are? My shop manual says they original engine came with 3 different sizes of injector tips for this engine, and of course they were not "needle valve" injectors. I would cerainly appreciate your advise. Please include your E-mail address with any responses. Thanks!

Picture of Large port on later released Detroit engines & small port opening on early GM engines.

It takes a little practice, I've posted the email site for downloads. I hope you have patience,it will be worth it.

N-series injectors have a better spray pattern and deliver at a higher pressure. It's impossible to say exactly how much HP you will gain just by putting in N-series injectors without knowing what your engine has or without knowing what size injectors you plan on putting in. As an example, if you have N-series pistons and sleeves then N-series injectors are going to help a little more than if you have the old HV pistons and sleeves. Also, if you are going to the trouble of replacing the injectors for the purpose of pulling you will probably put in bigger injectors too. With bigger N-series injectors you can expect to see a fairly significant HP increase. Incredible HP increase for the money actually. At a guess I would say up to 30% more HP. You won't have any problems with big injectors pulling because pulls are relatively short but you could have problems if you lugged your engine down doing something like plowing. I recommend installing an N-series cam if you are going to install N-series injectors but most guys don't.

Changing from HV-series injectors to N-series injectors does not require any new parts. Not even "injector lines". Just make sure you get the right injectors for your head.