DMM

I was thinking about an LS3 based 427, however I have a spare LQ4 and figured why not? The 421 kit has 4.125" stroke crank and 4.030" bore and would mainly be a non-boosted DD that might see a 150 shot at the most, if ever. Thoughts are to top it all off with ported LS3 heads and intake with 1 7/8" headers.

Would this combo be reliably capable of near 550 rwhp while maintaining very good drivability? This would go into a 4000 lb, M6, with either 3.55 or 3.73 gears and will primarily see DD type cruising. Emissions not being of any concern, of course.

I understand that over-square builds are not very popular, but what are the real world results?

wildcamaro

iTrader: (15)

You could get that kind of power out of a 408 if you get the big heads and intake for sure...if you notice all LS engines are the same stroke (other than 4.8) which makes me think GM didnt change strokes all this time because a shorter rod is better, however in your case i favor a 4" stroke 408 compared to a max effort 421, you are just asking for long term complications

DMM

Well, its the same 4.125" stroke that is used in the popular LS3 based 427. Also, not looking for an all out max effort race motor here.
Its the same price to get a forged 421 as a forged 408 from my perspective. What are the real world problems with a 4.125" stroke, if any?

zacht

iTrader: (18)

i was under the impression that the 421 combo doesnt do well with power adders at all...

i would vote for a 408 as said above. probably pretty close in power...then you can build it to take way more nitrous safer...

zracer323

iTrader: (12)

If you are planning to remain NA then go with the 421. It should be plenty reliable. If you want to spray it then I would probably do the 408.

wildcamaro

iTrader: (15)

Yea I guess if the same price I would go for more cubes for sure, but I agree if you try to spray or boost I would go 408, sounds cool though either way