Newbie Gen IV questions

[efnfast]

Just purchased an 08 roadster with a bunch of bolt-on mods (headers, exhaust, race pcm and intake as far as I can tell).

1 - Can a "race pcm" (it supposedly comes from Hennessey *ducks for cover* but maybe is just an upsold mopar unit, I'm not certain) be tuned just like if you were going to tune a corvette? I.e., throw it on the dyno, watch the a/f, tweak it with HP Tuners until happy, or is it more hardcoded? According to the last owner (if I understand his description properly) the shop that did the work bolted-on a bunch of stuff, returned the car, check engine light for a/f came on and was only resolved by putting in the race pcm. I don't have prior experience with Vipers so I'm not certain why it would need a "race pcm" as opposed to just dyno tune the stock pcm?

2 - What visocity of oil is recommended in a climate where driving temperatures range from 30 to 70*F (and in the winter drops down to -50*F)? I've read everything from 10w30 to 0w40 and in between, although havn't seen anything about 5w30. Any chance 5w30 would work (I have crates of Mobil 1 5W30 since that's all I use in my other cars)?

[Steve M]

Hennessey didn't do shit with the Gen 4s other than overcharge for slapping on the standard bolt-ons, so consider the "race PCM" an upsold Mopar unit just as you suspected.

Tuning is a bit more complicated, but it's a function of the available options. You can overwrite the Mopar PCM with HPTuners, but you'll be replacing that tune with a "stock" tune, and you can never recover it. HPTuners overwrites whatever is on the Venom PCM on the first write with a custom operating system that enables some key features. I'd recommend shelving the Mopar PCM as a backup, and sourcing the stock PCM that you can adjust with HPTuners until you are happy with it. The Gen 4 Vipers tune just like any other car, with a few quirks here and there that are pretty well documented on this board. The Mopar PCM ("race PCM") is nothing more than a canned tune optimized for cars running headers along with turning off the typical emissions related trouble codes that usually accompany exhaust work on these cars.

The factory fill was 0w40, and I'd stick with that. If you are set on driving during -50°F weather, you might want to think about thinner just for those occasions, but I'd probably just leave it parked if it were me. I run in a bit hotter conditions, and also tend to attend a handful of test and tune events at my local quarter mile drag strip, so I run 10w40. If you are tracking in the heat, those in the know highly recommend 15w50. I would not recommend running thinner oil than the factory fill, so keep your 5w30 for the rest of your fleet.

[efnfast]

Good to know about the pcm. Is the canned tune halfway decent? When i've used canned tunes (GM crate engines) I've picked up good power, but i can see why GM would provide them with a conservative tune.

[Steve M]

Good to know about the pcm. Is the canned tune halfway decent? When i've used canned tunes (GM crate engines) I've picked up good power, but i can see why GM would provide them with a conservative tune.

You can always get more with a custom tune, but it of course depends on the person doing the tuning, and your tolerance for risk.

As canned tunes go, the Mopar PCM (to include the Mopar PCM with the Arrow Racing calibration) appears to be decent - I've never run one on my own car, so I can't really comment on the quality vs. what I've done with HPTuners. It is the only other option for "tuning" a Gen 4 Viper. Most Viper owners seem to prefer the plug and play approach, and the Mopar PCM fits that bill nicely.

[efnfast]

Thanks - at some point I'll throw it on the dyno and see what it does. So many projects so little time.