853's To 243's
 

What kind of power difference will I see if I change out my 853's with 243's ? Will it mainly be peek or will it be "use able" across the entire rpm range? What would I have to change? Will they bolt right in and use the springs I already have? I'm wanting to make a change "more power & quicker e.t.'s" and this is one I was thinking about and wanted to learn more about it. Thanks.

Are we talking stock to stock heads here?

Yes and I have the same questions about changing my ls1 intake to a ls6.

Stock ls1 heads to stock 243/799s is a small increase. 15-20rwhp is the optimistic average, and that's typically with a light milling. Cost of the heads, head gaskets, head bolts, fluids, likely need a tune, and the severe pain in the ass time consuming process that is cleaning out the head bolt threads of the block prevent this from being a good bang for buck mod IMO. If you have a killer deal on the heads and/or already have some of the other parts it's not as bad.

The ls6 intake has picked up between 8-15rwhp depending on the mods done to the car. Cammed cars gain more than stock or bolt on cars. It's an easy swap and the number of lsx style truck motors getting swapped into older cars has driven up the price of ls1 intakes so you can recoup a nice chunk of the cost of the ls6 intake. Last I looked ls6 intakes cost around $350-400.

i was told by TSP their stage 1 243's would be about 20 rwhp over my stock heads (heads only) . i just liked how well they flowed for the money. stock flow cfm is like 235 & stock 243's is like 265 cfm; ported stockers like 290 with my 243's ported 320 (thats only stage 1). get good springs , i wish i chose better than the ls6 springs. hope that helps! if you've got the cash get the TSP 2.5's. just my one cent.

What cam is in the motor?

It has a custom grind.

It all how the parts work together. Yes they may only give 15-20 RWHP but I'd mill them down to a 61 cc chambers and get a couple more ponies there. Later if you get a better manifold, bigger cam and with LT headers those heads will widen the gap over the stock heads.