Question for maxrace and everyone else about 990 heads

[Josh W]

I have a set of 990 heads on my new motor. My complete combo is listed in another post a little further down. I saw some other post that you made with some very detailed info on other GM big block heads. Do you have that type of info for these heads that you are willing to share? Can you give an opinion on my heads? Do the numbers look OK or high/low? Thanks for any info you are willing to share.

990 heads with 2.25/1.88 11/32" valves
bowls blended, short side radius reworked,valves back cut, and chamber unshrouded
flow numbers are for #6 port(bad port?) & no pipe on exhaust
.100 72/59
.200 143/113
.300 215/139
.400 261/165
.500 290/186
.600 306/204
.700 323/213
.800 333/216

[maxracesoftware]

The Howards Roller Cam (278/287-110 CL .790/.731) is pretty close to the baseline CamMotion cam we usually run in 468 +cid engine
we mostly run 1.80 ratio across

your Headers ( 2 x 30" , 3.5 x 10" ) are on the small side, especially with 250+ HP Nitrous plate

for 481 cid at 7000 RPM => 2 1/8 x 31" to 35" Collector= 4" x 18" to 19"

overall, everything you Posted about your combo looks OK
the only other thing that might be weak is the Weiand Team-G on just engine power....i usually use the Edelbrock 454-R instead

990 heads with 2.25/1.88 11/32" valves
bowls blended, short side radius reworked,valves back cut, and chamber unshrouded
flow numbers are for #6 port(bad port?) & no pipe on exhaust
.100 72/59
.200 143/113
.300 215/139
.400 261/165
.500 290/186
.600 306/204
.700 323/213
.800 333/216

some FlowBenches read High, and others Low
so at 600 Rpm/Sec Dyno test, you should make approx
635 to 650 Peak TQ and 660 to 760 Peak HP (conservative Dyno)

your 4000-4500 stall rpm is too low for only Engine HP
but with Nitrous it should be good, and stall higher
same with 4.30 gear ratio


on just Engine HP 660 to 760 HP
you should run 9.70's to 9.90's at 136 to 142 MPH

with 250 HP NOS , usually make at least 200 HP gain
so 860 HP to 960 HP
should run 9.20's to 9.40's at 149 to 153 mph

the 4.30 rear gear ratio looks perfect with NOS

On just Engine HP/TQ, a rectangle-port #990 casting 2.250-1.880
naturally likes 5500 to 7500 RPM range

its very hard to make #990 casting make a great power curve
from 4000 to 6000 ...usually if you cut back on Cam in an attempt to shift the power curve lower, you just loose too much HP 4500 RPM upwards

the cross-sectional area of #990 likes 5500 to 7500+

Stock out-of-box Port volume CC's (NHRA) = 323 CC
that gives you an average cross-sectional area = 3.359 sq.inches

3.359 sq.inches likes 7631 rpm ...so approx 5600 to 7600 RPM power curve

7631 RPM = ( 614 * 3.359 ) / ( 4.375 * 4.375 * 4.000 * .00353 )

using a stock FelPro gasket port match area 1.775-1.800W x 2.525 H
= 4.482 sq.inch area....you can see why #990 casting likes 5500 RPM and upwards power curve

#990 Port CenterLine Lengths=
GPD Roof=6.885" Floor=4.850 CL=5.868" Length
BPD Roof= 6.810" Floor=4.710 CL= 5.760" Length

Exhaust
Roof=4.715 Floor=1.890 CL= 3.303" (NHRA=127 CC) = 2.346 sq.inch


your Numbers =>
Lift---Flow---Velocity fps at Gasket(4.482 ") port match dimension
.100 72------38.6
.200 143 ----76.6
.300 215-----115.1
.400 261-----139.8
.500 290----155.3
.600 306----163.9
.700 323----173.0
.800 333----178.3 fps

Lift-----Curtain ----Curtain Area FPS
.100----0.707------244.4 fps
.200----1.414------242.7
.300----2.121------243.3
.400----2.827------221.6
.500----3.534------196.9
.600----4.241------173.2
.700----4.948------156.7
.800----5.655------141.3

around .650" Valve Lift your Curtain Area = Port match gasket area
you can see its important to keep Lift above .600" as long as possible to pickup Port velocity fps, especially around peak piston velocity , including lag-time.

[maxracesoftware]

on my FlowBench with 4.280 Flow Fixture Bore size
with 1.000 thick radius entry and with a Pipe on exhaust ports
a stock -out-of-box #990 casting flows=
(2.190-1.880 factory OEM valves and valve job)

Intake Flow at 28"
Lift-----GPD Flow-----BPD Flow
.200---130.7---------129.04
.300---201.8---------201.0
.400---234.3---------228.0
.500---271.7---------249.7
.600---303.0---------275.4
.700---322.1---------288.6

Exhaust with Pipe
Lift-----Flow at 28"
.200---105.8
.300---138.0
.400---162.3
.500---181.5
.600---194.0
.700---197.4

Have a Merry CHRISTmas !!!

[maxracesoftware]

a little more Info you might be interested in ???

Stock OEM #990 castings
Intake Flow at 28"
Lift-----BPD Flow--Gasket port match velocity FPS
.200---129.04--- 69.1
.300---201.0 ---107.6
.400---228.0 ---122.1
.500---249.7 ---133.7
.600---275.4 ---147.5
.700---288.6 ---154.5 fps

BPD - your #990's Bowl-worked with 2.250-1.880
Lift---Flow---Velocity fps at Gasket(4.482 ") port match dimension
.200 143 ----76.6
.300 215-----115.1
.400 261-----139.8
.500 290----155.3
.600 306----163.9
.700 323----173.0

most Racers don't realize that Porting or Bowl-Porting
a pair of Cylinder Heads actually picks up the Port Velocity

you went from OEM 147.5 fps at .600" Lift (at port match area/entry)
to your Bowl-ported 163.9 fps at .600" Lift (at port match area/entry)

Have a Merry CHRISTmas !!!

[Josh W]

Thanks alot. That's exactly the kind of info I was looking for. The reason the headers are so small is b/c there's only 2 off the shelf headers available for a G-body. This was the largest set. What is the problem with the Team G vs 454-R? Again thanks and Merry Christmas.

[maxracesoftware]

What is the problem with the Team G vs 454-R?

not much a problem, but as you get heads to flow more later on,
the cross-sectional area at the int runner entry inside the plenum
is smaller than Edelbrock Victor 454-R ...usually the Victor 454-R will make more top end HP

and if you build a 540 cid or larger the Edelbrock Super Victor works pretty good