I've recently picked up a complete V8 conversion out of an ef, I removed it all so I got everything needed for the conversion but I'm wanting to know what the power difference is between the 6 and 8 other than a better note. The v8 needs a fair bit of money spent to get decent gains where its cheaper to do with a 6.

What are the power differences between the 6 and 8, and can any one rattle off some mods and prices for the v8?

This might help, just my experience.
I had an Nc 5L, sounded tough and being dual fuel it was cheap to run. It had some power Na but I found second hand mods like extractors etc were hard to come by. Yes the Nc weighs allot more than an Ef, but it still had some balls.
I now drive an Ef i6, parts are cheap to come by for the i6 and she goes like the clappers with minimal amount of money spent.
Looking back on both cars, I miss the note of the 8 but dont regret owning an i6. Just my experience.
The general mods for the 5.0L is extractors, gt40p heads, better air induction etc. Check out the prices and availability of 5L performance stuff on ebay compared the the i6, heaps more i6 stuff and s**t loads cheaper.
I miss the 8 and would have loved to see what I could have done with it performance wise, but I am sure that it would have cost me 3 times more than what I have spent on my 6 for the same output.
Redbook reckon 165kw at the fly for the 8 with 388nm. The 6 ( non tickford) is 157kw at the fly and 357nm. Tickford i6 is 164kw/366nm at the fly. Xr8 is 165kw/398mn.
Your choice.

Ive done a few now.
XD : EFI 6 to 351. LPG both ways. Impco on the I6, and GRA on the 351.
The EFI 6 (Alloy Head) was much lighter - I noticed a complete change of handling of the car and regretted throwing the 351 in. It was like the car just wanted to go through corners, instead of around them.

XF GHIA : I have a 5.0 EFI /4 Speed Auto in the toy car. Running gear came from an NC. This car is just awesome to drive - starts easy, and its on LPG with an Airod Variable mixer. Its fun to drive. Its way more responsive than the EFI 250. I do beleive that *decent* extractors made a big difference in this car too.

EL Fairmont : My Daily is an EL Fairmont : Was a 4.0, and is now an EL XR8 185kw. Came with EL GT extractors, and the Exploder Manifold. This car too is on LPG but uses a LPG Injection kit. Lots of fun, and drives from Brisbane to the Goldy Every day. This car is also a lot more fun.

The Fuel Usage on the 5.0's around town is significantly different. up to 100km a tank depending on how you drive. The Highway difference is there as well.

Driveability wise, I really do like the 5.0 over the i6. Theyre strong down low, and dont need to be driven hard to get anywhere. Theyre really good for towing stupid loads to the tip as well (2.5 tonne = easy) - just cruising

The 5.0 can also be driven without a stereo. They just sound nice. The 4.0 really needs one.

One comment I would make is if you do the conversion, make sure you get (decent) extractors - Genies work, Pacemakers are good, but apparently the best are... er.. made in Sydney. Cant remember who makes them. I want a set when I have a spare couple o hundred. It completely changes the 5.0 to be able to breathe

There's a sticky at the top of the page about mods for the 5.0. They don't require lots of money to go good is just that mostly people do the wrong things to them or in the wrong order. A classic is too big a t-body or change the camshaft with the rest of the engine standard.

If you check out ebay for gt40p heads and then do a search for tickford i6 head, thats what I mean. Also second hand 5L extractors on ebay compared to i6 extractors. When I had my 5L I searched for ages for extractors for her for under $100 on ebay, sold the Nc and got the Ef i6, within a few weeks got mint extractors for the i6 for $37 off ebay.

There are Genie's on Ebay for $250 with Cat's at the moment, and GT40's for 300 (not P's)

Put a 351 in it.

That's what I'm thinking 79raven between the 6 an 8s there's not a great increase in power. I just put a reco T head onto my bottom end and done the T5 conversion and was going to sell the v8 to pay for bigger cam than it'd have more grunt than the v8 and for far less coin.
Though now my bottom end is failing I'm not sure which way to go, its a stock ef 5L so just paying for heads and manifold is going to hurt the wallet (which had moths ATM due to no work) I have a set of genie headers I picked up awhile ago for $50 so that's one thing I won't need to buy but paying for the rest I could easily build a strong 6 for half the costs.

How do the gt40's compare to the p's?

Its hard mate. You speak to a 8 lover and they will swear all day against a 6 and a 6 bloke would do the same. That sound the 8 produces though, sheer bliss. My i6 sounds tough but you cant beat that 8 grumble.
Im not too sure about the difference in heads, never got that far with the NC.

The GT40's are a good upgrade over the E7's, and Dont change the spark plug location.

Pete will advice, rightly though, that a set of AFR185's (alloy) are much better

Nigel

Until you've done all the bolt ons to the 5.0 don't even think about changing heads or intake. You simply don't need to. Have you read the sticky about V8 mods?

I've read the sticky and a few other posts about the V8 to get info, I'm just not sure what I want to do either to sell the v8 and build the 6 up or keep it and build it.

The other thing to put into account is the cost of the conversion and the engineers cert you will need. I dont know mate, I miss the 8 but it sounds like either keep the 6 or buy another E series thats already an 8 thats got engine problems ( so on the cheap) and swap engines over.
Really at the end of the day its up to you. Like I said an 8 man will swear by an 8, the 6 man will swear by the 6, they are that close. Just comes down to personal preference really, and not an easy question to answer

I'm not sure if an engineers cert is required. It isn't in qld as these are factory engines

If the engine ou're dumping in was a factory option for that model, then an engineers cert isnt required, at least in victoria. Had to ask vicroads about switching my LTD's buggered 8 to an I6