Ok , need to step back

zigs said

Thats my point Dell 354 to 470 Ive replaced rear ends. Im like a little kid in a candy store
another project isnt going to help. Look in your own back yards . How many of you have projects that are on the back burner. Your waiting for time,money,health, kids to move out. Two cars in my garage ,one will be favored more while one sets.
Dell 400HP VS 500 + their would be a difference and I think more user friendly.
I guess my point is . when I was young I needed thinks and could justify it. Now that Im older I dont really need thing. I have plenty to keep me buisy . Kids ,grandkids
Part time job etc. Its time to come to grips

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A detuned 470 will be more streetable than a hot 340, 1 hp per cid is kind of the dividing line depending on ones idea of what driveablity is. The 470 can always be made to 130hp more than the 340 at the same streetablity. A certain amount of performance is gonna have a similar fuel mileage. Less you start taking turbos. I wouldn't overly let mpg decided your decision can take decades to recoup money spent to gain mpg, now if you taking driveablity / performance with an eye to decent fuel mileage then that's a different story cause your not expecting to get a monetary return on your investment other than fun.
But it's up to you what you want.