animuL

iTrader: (3)

I am looking at a new TSP 408 longblock for my 98 Vette and trying to figure out what heads to go with. Car will be N/A daily driver. I look at the best flowing heads and they are the LS3 / L92 design. This would require a new intake, tb, maybe new rails, new maf, new intake bellow, etc. And I don't know if all that will be plug and play and be a good fit physically. Starting to look like a can of worms there so I started researching cathedral vs rectangular port as far as performance goes. Flow numbers all look better on rectangular but in a gmperformance article they dyno tested the two designs and actually only got a few more avg and overall hp and tq with the rectangular port design. So I figure thats good assurance that I can stick with the cathedral design, all my old parts work and I can make just about as much power.

So the next thing I start looking at is the various cathedral designs. I made a spread sheet here, the ones not highlighted are cathedral: https://docs.google.com/spreadsheet/...LT2d5c3c#gid=0

Some of those flow better than others but one thing I have to look at is chamber volume to keep my compression ratio in check. This is where I am having issues now. I have heard that the smaller the head gasket, the better the quench and safer against detonation so say I go to the thinnest .040 MLS gaskets. Then I have heard that flat top pistons should be used whenever possible over dished because it creates a better mixture (no turbulent dish rim) and also that dish rim can cause hot spots. So I figure it with the flat (-3cc) pistons. If I type all of that into a compression ratio calculator: http://www.csgnetwork.com/compcalc.html I get 10.9:1. That seems like it might be a little much for 91 octane and 30 degrees of timing. Thoughts?

If I look at it another way and decide to go with the best flowing cathedral option its a 68cc chamber. That would push my compression ratio to 11.3:1 with the "ideal" .040 head gasket. To get that back down I have to run a dished piston and they offer a -10cc which would get me down to 10.5 and thats where I feel safe. So I guess in the end, what is a better setup, the best heads and best gasket with dished piston and 10.5:1 compression. Or head that flows 7% less average, .045 (one step from "ideal") gasket, and "ideal" piston netting 10.7:1 compression?

I should add that I am not sure of the piston deck clearance but I was using .007" under deck based on some searches I have done (TSP wasn't answering their phone yesterday for me to confirm).

Thanks!

jlrz28

iTrader: (7)

Why not just use a TEA/TFS head (215, 225, 235) that will accept standard stuff, ie Fast intake, oem rockers?

RezinTexas

I wouldn't plan on finalizing your head gasket thickness until you measure the deck height of the pistons in the block. If you're 0.010" out of the hole, I would do a 0.045" gasket minimum.

animuL

iTrader: (3)

I guess the main reason for my head selection is because I'm looking at a Texas-Speed assembled long-block and the PRC are their options.

PREDATOR-Z

I would not put a 408 iron in a Vette. I would keep the motor Alum. for weight distribution purpose. Do not ruin what you have, this is obviously not drag setup so why not keep the Vette in its class, a light cornering machine.
IMO if you want big cubes, go LS2 based.

JakeFusion

iTrader: (7)

Or LS3 since the price difference is pretty minimal. LS3 to me offers to best balance of price/perf/weight. Certainly more performance than LS2 based solutions while being considerably cheaper than LS7 options.

And with the LS3 block, LS3 heads become a viable option. On a 4-4.03" bore, I like Cathedral heads. 4.07" bore and above LS3. And 4.130" and above, LS7.

animuL

iTrader: (3)

Not worried about the weight distribution, once you sit my azz in the seat its all over with anyway. Besides, I don't do a lot of cornering or really spirited driving. Its putt to work 5 miles and back home 5 miles then take to the track once a year for fun.

animuL

iTrader: (3)

I'm not against LS3, but if I go that route I have to change all sorts of stuff and its really getting out of my price range. The LQ9 is going to be around the $7-8k all said and done. LS3 is over $8k for just the long block so figure $10k ish by the time I get new top end stuff and everything else.