how much is too much?

I am rebuilding a 5.0 for my miata challenge car, and have a couple questions about boring it over. I want to get the most power as I can within budget. Someone told me I could go .060 over and I would gain a ton of torque, which is good. But I do play to spray some nitrous and am unsure if the cylinder walls would not handle it. Should I do less of a bore? Or go all out and hope it doesn't blow up?

They call the "thin wall henrys" for a reason. I went .030" over on my 347, and that's as much as I feel comfortable with on these engines. YMMV

are you just trying to keep it together for one days autocross and a few passes at the drag for the challenge, or do you want to have it be running afterwards?

boring an engine will gain you very little noticable power, you get a few extra cubic inches but thats about it, i would only do enough to get the bores straight and fresh and call it good

There is something like 8 cubic inches between a stock bore and a 0.060" over bore 302. At a "typical" 1 hp/cube, we're talking about 8 hp and nearly as many ft-lbs of torque. Definitely not worth it.

I would like it to run afterwards, ok so i would be better off just doing .030 over with say explorer heads and intake

yea thats a good place to start, that were you will get some noticable power increase

Don't worry as much about the over bore as you do cam/head/intake selection. That is where the real power is made.

Bobzilla wrote: Don't worry as much about the TURBO as you do cam/head/intake selection. That is where the real power is made.

I fixed that for you.

increasing the bore size makes a lot of sense ......displacement is cheap HP....... that is why it is done all of the time especially when you may have scored cylinder walls and need to open them up and buy new pistons. so if u need to go up in size by all means do it. I would go .030 over ........... leaving yourself room later in case you rebuild a second time to go 040

on the other hand if u can get away with just a hone and some new rings i would likely spend the money elsewhere.

I'm trying to wrap my head around a challenge car with a fresh built motor! Closes I've come to a fresh motor in a challenge car was a ring and bearing job I did on my Z31 after tanking the "fresh" ish motor I bought used.

Spray is only used on the drags, if you need that little extra and got a cheap kit go for it otherwise spend your money on making it hookup and turn.

Best HP/$ is going to be a junkyard turbo you fab up yourself. You can split the block for a grand. Can't imagine a much worse way to spend money to get HP than boring the cylinders out.