As Previously posted , I have a set of Bare 990's and wonder if I should redo them, go aluminum , or make an even swap for bare 781's ?

Building a street driven 454 , 9.5-10.0 Compression , Lunati Hyd 280 / 288 ( 223 / 231 @ .50 ) 2,800 stall , 3.73 Gear :D

Found this Flowbench test of ALOT of different heads , but the 990's don't seem so bad after all !

LINK TO FLOW CHART (http://www.airflowresearch.com/performance/westech_figures.htm)


Need some longtime bigblock users help to answer my question at the top of this post graemlins/thumbsup.gif

Where they are a little weak is the .100, .200 .300 lift flow. If you already have them ready to go, use them.

I'd do the even swap for the 781's...I believe Chevy HP's website has a flow chart that includes the oval ports too.

http://www.chevyhiperformance.com/techarticles/41598/

http://www.chevyhiperformance.com/techarticles/41598/index8.html

http://www.chevyhiperformance.com/techarticles/41598/

It would be "more OK" if you were running more cam and compression. These heads will work best at 5000-7000. But as I've said before, unless you are stuck on minimizing ET, rect ports drive alright on the street. As long as they don't need lots of $$ machining. Not debating here, the ovals would definitely be preferred; if you can swap even, go for it. Also, bare 049s are cheap as can be. They need mucho milling to get compression right though.( still $500 all done/closer to $700 with big valves) )But you'd be fine with the 990s. Be sure to install your cam advanced. Helps on the intake velocity side.

Oval would be best for your application but I wouldn't trade even steven unless the ovals were already set up with the big valves. You could sell the 990's and buy a set of Canfields or Brodix. I'd sell'em for the price of 1-1.5 new aluminum head price then the out of pocket exspence is not so great! :D Or keep'em and use a short duration cam!! tongue.gif

Pay no attention to peak numbers..its the average across the board that matters IMHO..for what you plan on building,your 781's with 2.19/1.88 valves is all you'll ever need..I run the same cam with closed chamber ovals (215's) and run high 12's w/2.73's

Dave

I have a three 290 bare heads if you'd like to discuss a trade of some sorts. Email me if youd like to discuss this option.

Todd

Dave

I have a three 290 bare heads if you'd like to discuss a trade of some sorts. Email me if youd like to discuss this option.

Todd

Dave

I have a three 290 bare heads if you'd like to discuss a trade of some sorts. Email me if youd like to discuss this option.

Todd

290's Flow Chart (http://www.chevyhiperformance.com/chevyhighperformance/techarticles/p104867_image_large.jpg)

049's Flow Chart (http://www.chevyhiperformance.com/chevyhighperformance/techarticles/p104871_image_large.jpg)

Edelbrock RPM Aluminum Flow Chart (http://www.chevyhiperformance.com/chevyhighperformance/techarticles/p104891_image_large.jpg)

GM Aluminum Flow Chart (http://www.chevyhiperformance.com/chevyhighperformance/techarticles/p104893_image_large.jpg)


I've been told that the GM Aluminum head is really an edelbrock. These #'s don't seem to back that up as the flows are alot different.

RE : GM Performance Parts Aluminum

This head offers the highest average intake port flow and the highest peak flow numbers. The exhaust was very impressive creating an E/I ratio of 72%. This head would be best fitted on a big-inch street big block using a large cam that could take advantage of this head’s high lift flow potential.

:confused: graemlins/angry.gif :confused:

The GMPP ovals are made by Edelbrock ( same as RPM )but they have 2.25 intakes vs the Edelbrocks 2.19

Screw those flow charts..how about a timeslip :D
For someone to answer your question,they would have to run 990's vs. another casting # bb head and compare timeslips using the same 280/288 cam with no other changes..which I'm sure no one has done

Like I said, if you're hungup on timeslips, ya better do the swap. If not, they be fine.

65, I've had good results with 990s, but for a "street only" it doesn't matter which head you run. Money wise you would be best off selling the 990s and putting on a set of peanut ovals that bring about $25 to $40 at a swap meet for a "street only" engine. Do a standard valve job and ensure you have the correct valve springs with proper retainer to guide clearance. The above advice is if you plan on obeying all traffic laws and are only interested in cruising. Street battles are a lot more expensive if you get caught than what they used to be.

how are peanut ports good for the street if they won't turn past 4000?

If you re read my post you will see that I said "if you plan on obeying all traffic laws and are only interested in cruising." Driving 100 mph down a city street in a street race can be very expensive. If one were to street race I would recommend a different head, but street racing is a taboo subject on this site and I will respect the rules as Al has set forth.

last I checked 4.11 or 4.56 gears and 26-28" tires take 4000 just to keep up on the highway

Originally posted by knudsonm:
how are peanut ports good for the street if they won't turn past 4000? A peanut port will turn more than 4K..up to about 5000-5500..the runner in a peanut port is about 220 cc while a large oval is about 240-250-ish..and to put things in perspective,and Olds big block head is about 170-180 cc's..and they sure turn higher than 4000 rpm's..something to think about..

So why is it that I've been told by all of my local engine builders that my heads are junk. I have Vortec L29 heads. Most places have said I need to install larger valves, port the hell out of the intake ports(especially the short turn radius) and get a fairly large cam to make 350-375 hp@4500rpm from a 454. Most places are telling me if I only install a ZZ502 cam and don't touch the ports, I'll be luck to make 320hp. I know of a set of race ported iron Merlin heads for a reasonable price, but the chambers are too big(119cc) and I don't want to tear the engine down to get the compression back up. Oh what to do.

I found the flow numbers though for the L29's

.100 65 51
.200 135 99
.300 197 128
.400 238 153
.500 259 171
.600 272 179

it sure seems alot easier to make hp with a small block. my 350 made 400hp with very few big dollar parts.

Peanut port heads start down around 200 cc's!!

Large ovals start down around 230 and can go stock up to 262 or so.

Please cc the suckers first so you will know what you have!!!!

The best bang for the buck, (to me), is as stated many times is a set of large oval, closed chambered -215's, -063's or even -206's that are just cleaned up!!

AND I say this only b/c they can make a higher CR. motor vs the open chambered large ovals that do breath better!!

I went cast-iron Merlin ovals b/c I figured I would get hosed locally bringing my good large oval, open chambered -781's up to hi-po spec's but I also bought ROSS pistons to get me to the CR. I wanted for my particular combination!!

pdq67

I think either the 990 rectangle ports or 781 ovals would work... but each have their own trade offs. I think if you wanted to put bigger valves in the 781's and can get the right compression ratio with them go for it. They will be the best alternative IMO for a heavy street car.

You could probably clean up the 990's and they would work ok, but I think you would loose a bit of performance with em. Overall you would probably save the money for larger valves and possibly milling of the 781's and get decent performance if everything else is chosen well.

If it was my money... I would run the 781's.

Just an add on... I think the rectangle post heads get a bad rep these days. They work very well for lighter cars, cars that spend more time in the high rpm's, cars that run some form of forced induction/nitrous. I run aftermarket rectangle ports on my motor for that reason.

Another consideration is that you don't have to
run the larger valves to make good usable power
either, just to maximize the potential.I've run
everything from peanut port and 781's with stock
valves up to my current 840 rect. with 2.25 valves and they all made me quite happy in their applications.I have a 12.5-1 427 with stock valve
-781's that is 8 years old and sees regular 7000
rpm blasts and they work very well let me tell you.