990 vs 781

[grayson]

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&rd=1&item=280250743532&ssPageName=STRK:MEWA:IT&ih=018

I know i've asked a few questions lately,so i apologise for all the questions. but i was looking at these heads, if i can get them at a decent price, would they be better than my 990 rectangular heads?the cam is only a hydrolic 556" lift.

The valves in these heads are smaller than my 990 heads, they have the 2.19 intake.

I just want the best power i can get for the money, its a pretty mild engine, Dual plane/850 vac sec/4 bolt 454.
i also want to bore it 60 thou, making it 468.

any advice is appreciated,

all the best
Grayson

[RiverRacer]

If it's for a ski boat running low rpm's the oval ports are the way to go, but for high rpm's and power the 990's are what you need!. But with the bigger valves and a clean up they will make good power to 6500. Something to consider though is the cost, with the original cost of the heads and parts, by the time you're done you could have as much in those as you would in a set of aftermarkets right out of the box and still have less!.. Just something to think about!..

[gfinishline]

The little secret that hasn't been mentioned is that when we use 'oval port heads' we install the BIG VALVES, to make power. The oval port heads without the big valves, are just "work truck heads". BB Chevy heads breath around the valve edges, so open up the chambers around the intake and exhaust valves, this will allow the valves to breath. Use the BIG HEADS, and control power curves with the camshaft/valve timing. NEVER RETARD a cam in a V-drive boat, infact I always ADVANCE the cam atleast 3 degrees when building a V-drive motor. (play or race) "If it doesn't PULL HARD, it's a lazy dog".

[grayson]

Thanks Art and George,
i was concerned the heads had the smaller valves, but i was thinking if the heads were good - considering they were mostly done i could save some money. I have the reasonably mild cam,good stainless valves,comp cams stainless roller rockers,decent dual plane manifold and the 850 vac secondary, i'm hoping that they should allow for some low end as well as being able to use the big heads once it gets going.
I will stick with my 990 heads, they sound cooler too ha ha.:D

really appreciate you guys taking the time to answer me