Hey Guys,
I'm looking for all setup's for a 454 with
990 head's. Please post what U got and what
U use the boat for (race,skiing,cruising etc...).
Please list as much info as possible, I'm not
looking to copy anybody, I'm just interested to
see what works best in all situations & what is
definately NOT a good idea to do. I've got a 74
18' Kona w/ a 454 Ls6 & "A" impeller & i'm just
searching for info before I start buying everything
& I don't want to make any mistakes. Thanks in
advance!
The Bahner in the pic does a solid 82+ mph. I say "+" because it was done with two people and a cooler sittin shotgun. It's a typical LS6, Isky Z-89 solid cam, TR2X tunnel ram with two 750's, 990's MSD. Pump has a droop with an A and an extreme loader. Nothing crazy just a good lake combo. People have gone slower with alot more.
http://www.hotboatpics.com/pics/data...1-0005-med.JPG
my boat is a 1997 youngblood tx-19 with 990 heads that were on it when i bought the boat in 1982, comp roller rockers, jomar stud girdle, venolia pistons, edelbrock intake, two 750 holleys no. 6109, lunati roller .680/700, b impeller. boat has full interior and turns 5850 rpm`s at wot. dont know the mph. its a lake boat. lots of fun.
There are 2 "ole" sayings:
#1 Speed costs---how fast do u want to go?
#2 If it ain't broke---don't F__K with it!
IMHO--#2 applies to u!...if it runs good now...leave it alone & go have fun
make some mods to the hull, add a loader, shoe, ride plate, droop, diverter & u might be pleasently surprized at what the results will be!
just my .02 cents
fastrat
make some mods to the hull, add a loader, shoe, ride plate, droop, diverter & u might be pleasently surprized at what the results will be!
The boats completely torn down now, I'm installing a shoe, ride plate
and loader & we're going to blueprint the bottom. The cam was a
smaller solid lifter cam and it was too tame, so I'm looking for
more power & just checking to see what people have done &
their experiences. I know there's potential in her, I just want
to make sure I do it right!
From what I have been able to find ......
Stock "LS-6" Heads: (Mortec)
3946074....69&71...rect...OPEN...'69 427 L88, ZL1, Aluminum, 118cc chamber
'71 454 LS6, "round exhaust port"
Port sizes:320-326/120cc
'990 heads:
6272990....70-up...rect...OPEN...454 service replacement, used on some MKIV crate engines, 118cc chamber
Port sizes: 318/125cc
Same stock valve sizes, 2.190"/1.880"
Basically, same spec heads. Why spend $$$$? You're not going to change much, if anything.
The only port flow Stan Weis site lists for both is .600" lift, here it is.
'990 - 292cc I/204cc E
'074 - 331cc I/201cc E
Just how tame is "too tame"?
I've seen quite a few engines, jet-boat engines, come in here OVER-cammed to where they can't spin the pump hard, sure lok good on a dyno, till you look at WHERE the HP & Tq numbers come in at.
Smoke...i agree...not much difference in the heads...why spend the $$$...maybe put in some 2.225 valves to breathe better...chng the manif to a Air-Gap & add a different carb...get a cam similar to urs & along with the other chngs IMO it would run great!
fastrat
I do have the 990 heads & everything else has casting
#'s of a Ls6. I can't ID the cam that was in it. It had
165r & 951812 stamped on the gear end. I tried looking
at all popular cam manufacturer's & came up empty. As
I remember it was pretty mild from when my buddy had
it. It is a solid cam though. What RPM range do you guys
like the torque at? Is 2500-5500 or so a good ballpark? I'm
a car guy and I'm new at this, so please bear with me. Do
these motors come up really quick to a certain RPM like a
torque converter? Thanks for all the info & recommendations,
I really appreciate it. Keep It Coming!!!
Take a Micrometer (or hell, a caliper for the purposes of this) and find out what the cam lift is/was. Personally, I would not go over 290* seat to seat duration, and for most of the time, I think closer to 280* is more useful.
That cam doesn't cross to any Chevy part numbers I have so it's a major question mark.
Find out it's lift and you have a reference to start with.
According to my data, a vactory LS-6 ran a solid, non-roller, .500" lift cam with 306* seat-seat duration, Number 3863143 or 3904362, depending on which manual I check. The newer manual says 307*/298*.
Personally, I'd go .560" to .600" lift, not over 290* seat to seat duration, I think that's somewhere arround 240* @.050" lift. or you're gonna hurt the torque curve and push it up high, perhaps so high that a missmatch occurs and your motor can't make enough mid-range power to stay ahead of the pump.
You're already gonna have some trouble with the large rectangle ports at moderate RPM (4 to 5-grand) cylinder filling, try to avoid making it worse and it should run good.
I'd put as much CR in it as possible, measure and calculate it, don't just take the catologue reference for what it says. Quite a few of us on here can figure out the calculated CR if you give us enough information.
Chamber cc
Piston style & dome size
piston depth below deck top @ TDC
gasket thickness
bore & stroke
Aim for a MAX RPM of 5500 on a lake motor for the cam, not a peak at 5500, or it may push you too high IMO.
I'm real happy with only 8.5:1 (so far) running a hydraulic .565" lift, 280* duration. There's a lot of breathing still left in her held back by the small-valve stock heads.
I'm also running the Performer RPM Air Gap and love the response, but I have large oval ports the whole way down.
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