Originally Posted by Catmaigne

You're over-thinking this build way too much. Pouring all of this money into a mild build will get you nowhere, especially in a featherweight car that will roast tires and go like stink no matter what turd you throw in it. The difference between some gaudy tri-y headers and rusty pacesetters won't even be discernible and the same goes with the rest of grandpa's SBC mumbo jumbo. I suggest you go drive a lightly modified LT1 car so you will realize that it doesn't take that much to build a stout gen 2 motor.

Originally Posted by moehorsepower

Listen to what Caprice and buf says, But if you don't want a computer controlled setup and this is your first build and do not want to shell out cash for no significant gains, why don't you just get a good ole small block 350, Believe me, an old school 350 with say vortec heads, cam, intake ect will be more than enough to move that little Z. I knew of a guy that went the same route you are going and at then end just was a smoke show at every light.

Originally Posted by DavidBoren

First off, I am wanting to drop a LT4 into a 1970 240z. That is my intent.

My question(s) is, since the main difference between the two (the LT1/LT4) is valve size and minor head design improvements, would porting and polishing the heads of an LT1 give me the same (if not better) results? Lt1 engines are much easier to find than Corvette LT4 engines, and I would want to P&P the heads no matter which one I find.

And can larger valves be put into LT1 heads (with the proper milling, etc)? People put larger valves into engines all the time, I do not see why it wouldnt be possible here.

My plan is to stay with the 350ci displacement, and just port/polish/blueprint/balance everything to make it as good as it should be. MSD ignition, LT4 "hotcam", Edelbrock intake/58mm TB's, Clear Image Tri-Y Impala SS headers (if they will fit in the Z-car). Chevy 350 engine, Chevy 350 transmission, 3.50 rear diff gears... with 350rwhp being my goal.

The Tri-Y headers help with lower RPM torque. And I have read about a good deal of milling that can be done to the heads/valves for low-valve-lift/low-RPM torque. This is not going to be a high-revving engine, so I want as much torque available as quickly as possible. And I want a nice smooth power curve for nice street manners. I want the car to drive smooth, I dont need anything fancy... its a 5.7L V8 going into a 2,000 pound car.

Originally Posted by 96capricemgr

LT1 is hands down the better choice here.

To get 2.02/1.6 valves in LT1 aluminum heads you need new seats which is pissing money in the wind.

Edelbrock offerings for the LT1 are not worthwhile.

MSD ignition is at best a waste of money and if any result atall it will be to degrade the reliability of the stock system.

Clear Image's Tri-Ys are much talked about but don't buy into the hype, they are fine nothing more and in no way shape or form with the coin he charges. I have done business with him and so have friends and I would recommend you just find a SBC header that fits your chassis rather than worrying about the grossly over hyped Clear Image stuff.

With such a modest goal I would not even begin looking at a valve size change, stock valves are pretty good and will serve you just fine.

Some bowl work and a cam fitting your rpm range requirements and you should have no problem atall with that goal for cheap.

I would echo the comments about a stock TB opened up to 52mm or even one vendor I have seen offer 54mm if you really want big as possible and hassle free.

The LT4 manifold is NOT AN UPGRADE over the LT1 intake it just has more metal above the port, the internal ports are actually the same as the SMALL LT1 trapezoidal ports, the early LT1 rectangle ports are actually larger.

If done well torque is no issue in an LT1, worrying about making maximum lowend for a 2000lbs car is at best wildly ignorant, remember this engine came in the b-bodies with a base curb weight of TWICE what you say your car weighs. and a best ratio of 3.08 with most cars being 2.93 and the 4500lbs wagons often got 2.56 with a best of 2.93 with the 5000lbs tow package.

I know I just said you were wrong about a LOT but stop and think about the fact I have a over 4000lbs street car that can pull 1.5 short times and is still making good HP at the 7000 rpm pcm limits, peak HP being around 6400rpm so it is a high rpm motor AND makes more torque than your car could ever begin to use.

FWIW I have the Advancecd Induction 200cc package with a 228degree intake duration cam. Times in my sig are NA 150miles from home, valves in these heads are only 2.00/1.56 and this head has gone 9s NA in a bracket race 3400lbs f-body with a solid roller 383 putting down over 500rwhp. Does that make your questions about bigger valves seem kind of silly?

You are trying to spend a lot of money for a very modest goal.

If I were you and were making the shortblock rpm reliable I would sooner look at making broad power all the way to the pcm's limits than worrying about lownend. Unless the cam is almost deliberately screwedup an NA LT1 held below 7000rpm should have more lowend than you can use.