head decisions??

BobW · Post by **BobW** » Sat Dec 10, 2005 10:30 am

I am currently running a 505 in a 4000lb 72 Malibu best performance to date is 11.0018@122.28 and looking to run 10's year around and keep it on the street. The combo goes like this 505 4.352x4.25, 10.53-1 per builder, 781 GM ovals 2.25/1.88 ported but not flowed, Performer RPM intake,HP950, hedman 2"x3" thru 3" exhaust w/H pipe, I'm using the XR286R solid roller,billet core 654/661-dur.248/254@.050-dur.286/292@.015 on a 107lsa installed on 106.5 icl,ATI 10" converter (35-3800 stall) th400 w/4.11 gears,best 60ft to date 1.507,best 1/8th mile-6.95@97.89, I shift at 6k and cross at 6300. Since I'm wanting to keep the relatively low shift point for longevity I was looking at Brodix RR ovals and RR rectangle port heads, ovals have a270cc intake runner,rectals 290cc but yet both flow almost identical down the chart, I've always heard velocity builds torque so that has me leaning towards the ovals if I'm getting the same flow thru smaller runners, the question is, at what point do you go to volume over velocity? if both flow the same numbers? The builder says the motor can handle 7k with the Scat LW profiled "cast crank" but I want to keep it under 6500rpms. MikeL aka Wolfplace told me this is where I need to come to find my answers,some of the best head porters around hang out here. Can you help me out guys? and What are the best numbers you've gotten out of GM781 ovals? I am picking up almost 25mph on the backhalf, but the front half seems to be down a little, an 8" converter is in the works also, not to mention losing 75lbs off the nose of the car. Thanks again.

edit: was looking at www.brodix.com and under the link to the RR ovals there is a pump gas 540 shown with dyno sheet putting out some pretty impressive numbers with the oval port heads.

Wolfplace · Post by **Wolfplace** » Sat Dec 10, 2005 1:40 pm

HI Bob,
And Welcome from the peanut gallery

You will find this one of the most well run "non ego" forums on the internet in my opinion.
Some very cool folks that are willing to share information you probably will not find anywhere else if you care to do a little searching & a lot of reading.
First as I told you, in my opinion the head you have is too small for a 500" engine at 6500 RPM.
I would prefer something along the lines of an AFR 305 w/ the CNC chamber options but the Brodix RR rectangle is a really nice "bolt-on" head at only 290cc's. I do not know the area of this head but am sure it is larger than the stock GM casting.
Here is a recent post to read:
http://www.speedtalk.com/forum/viewtopic.php?t=1964
Larry among the others here have over the years posted a number of excellent threads regarding the math involved in deciding minimum cross-sectional area & it has been discussed at length if you do some searching.

Also general discussions regarding port shapes, valve angles, chamber shapes,,, the list goes on.
Again, spend some time here reading past posts, I feel I have learned more in a couple of years here regarding heads from people like Larry Curtis & Darin than 30+ years of reading & playin but then again a head porter I am not,,,,

You might also visit Larry's site & check out some of his software too. Desktop Dyno it definitely aint

EDIT------
You might also contact Bill Jones about the books he has written regarding head porting,, I have had them for over 5 or 6 years at least & still find them excellent reading.
Very inexpensive for the information shared.
Just don't expect any 8x10 color glossy's,,, just great information
Thank you Bill

cboggs · Post by **cboggs** » Sat Dec 10, 2005 3:10 pm

Bob,

Even though you're a friend of Mike AKA "wolfplace", ..
I'll still discuss this with you, .. ( Joking Mike, .. just Joking )

Welcome, .. agree with Mike, .. the BEST group of guys on the net, ..

BTW, .. have you seen the awesome animals he has?

OK, .. Mike was right down the proper road as far as I'm concerned.
I think cross sectional area is the key and your 505 might be choked for air.

As you know air speed is important, .. but too much can be worse
then not enough. First thing to look at is the minimum cross sectional area, ..
or the "smallest window" the air sees in the port.
Cross sectional area should be looked at like a "slice" of the port showing
just how much "size" there is to flow through.

Your combination for a 6000 rpm max power needs a minimum of 2.8"
of minimum cross sectional area and my guess it'll "Like" 3".

Second is the amount of lift you are running and the valve size, ..
this also might be a choke point, .. but I'll need to run some math to
find out. The Curtain area is the area available to flow at the valve seat, ..
it's lift and valve size, ..

It's going to be hard to max the combo out and still keep it streetable, ..
but it looks like you're taking the proper steps, ..

I'm a fan of Brodix stuff, .. I like the castings as they have mostly been
thick enough for me to get good port shapes in, the heat treat is good
and holds seats well, .. I just like Brodix and am a Brodix dealer .. so of course I would
be in favor of the oval port Brodix head. With a little bowl porting and good
valve job they should easily out perform your 781's.

Curtis

BobW · Post by **BobW** » Sat Dec 10, 2005 10:51 pm

Hey Mike, thanks for recommending the site, I'll be spending quite a bit of time here doing some research. Thanks Curtis, thats why I'm here, I used to be great at math in High School but I'm afraid what I learned there won't help me much for figuring what my combo needs. The cross section in the oval ports is greater than the rectangle ports, right? and I'm guessing the shape of the port is why they can flow with the larger Brodix rectangle heads? The car is more strip than street right now, but want to keep it so I can cruise 15 miles to the local hang out when I get the opportunity, no more road trips as its set up now.

67RS502 · Post by **67RS502** » Mon Dec 12, 2005 2:44 pm

Couple of things I'd like to throw in. My 502 was pullin over 1.5" of vac. on the dyno.
Shop said it was because of the 049 heads, but the carb (Demon 1000) is a bit small
too, I'm sure a dominator would be worth 25hp or so. Your 950 is loosing some power too.
Have you considered going with a oval port single plane intake. I run the Dart, with some
plenum work, with a 1" open and a 1" tapered spacer on it. A oval port single plane will still
have a small cross section, and will make good mid range power -my 502 made 627tq at 4500.
What exhaust are you running on your chevelle, as there is usually power to be had there
on most street cars. Have you tried shifting higher? I'd go with a small rect. head that flws good #s and keeps the air speed up.

BobW · Post by **BobW** » Mon Dec 12, 2005 8:05 pm

I've tried a 1" open spacer on a Victor Jr intake gasket matched to the FP1210 gasket, I lost 60ft and gained a little mph, thats it. I've also tried a Holley 1000hp and it was only worth .02 over the HP950. I am using Hedman 2" x 3" headers, into 3" pipe,3" H pipe to Dynomax Ultraflo welded ovals with dumps. I've got my rev limiter set at 6500rpm, just don't want to get crazy since I'm using a SCAT LW profiled crank (cast) The builder said it will go to 7k, I just try and keep it under 6500, I shift at 6k and cross at 6300 w/4.11 gears and 30" tires.

edit: I've tried most everything to try and squeeze a little more out of this combo and I'm thinking the heads may have been screwed up when the 2.25 valves were installed? maybe disrupting flow at low speeds yet working fine on the back half, as I'm picking up 23.5-25mph. The cam should be fine for my rpm range. I know of several people running low 10's or quicker with GM oval ports, I just had mine done by the wrong person I guess?? I could pull them off and have them flowed or just bite the bullet and go with the RR ovals, something we know that works and lose about 75lbs off the front of the car. At Brodix' website they have the ovals mounted on a 540 and it made some pretty good numbers with them.

MadBill · Post by **MadBill** » Mon Dec 12, 2005 9:46 pm

Before you start tearing the engine apart, I think you could do more with the exhaust. How far is it from the end of the primaries to the H pipe? Since the H, especially if fairly large, 'sort of' acts like the termination of the collector length, it should likely be only ~ 18" away. Also, 3" is pretty small from a tuning standpoint for a stout BB. (although it's plenty for flow) Ideally, you should probably have 3 -1/2" collectors. A taper/megaphone up from the current 3" (or even a little smaller) throat to 4" over the 18" length would probably be better still, but if you need to run though mufflers, something like 3 -1/2" Flowmaster, Spintech or other 'empty box'-types can seem like open air to the engine, allowing an "open tuned length collector" effect if mounted say 18" -24" back of the end of the primaries.

Also, engine vacuum at WOT is not increased by poor head flow. Quite the contrary, since it is a measure of the pressure drop through only the carburetor, it is a product of the engine's V.E. and the carb's CFM rating. If you see a 1.5"Hg. vac., it means the engine is ingesting exactly the CFM (e.g. 950) of the carb's rating, since carb CFM is of course rated at 1.5". Typical race engines respond at high RPM to considerably lower pressure drops, as low as 0.6" or thereabouts, which would require at least a Dominator-range flow capacity in this case. (A big carb does of course make getting good low RPM response a bit of a challenge.)

Moving inside the engine, 10.5:1 CR is pretty low for a combination like yours. The intake valve closing point works out to about 70 ABDC, which means that the dynamic compression ratio (calculated from the displacement after the valve closes) is only ~ 8.2:1. It is widely felt that up to around 9:1 is safe with 93 octane, which would mean ~ 11.6:1 static CR and a cranking compression of ~200 -220 psi. (although big bore BBCs are a bit sensitive re detonation, so a little less CR might be a lot safer, if pump fuel is the plan) A simple way to gain DCR would be to advance the cam maybe 3 degrees. Although the resulting torque gain is often offset by a high RPM power drop, you aren't spinning it that high anyway, so this might be a good tradeoff.

scottm · Post by **scottm** » Tue Dec 13, 2005 12:29 am

Hi Bob, sounds like you want to get the RRs and are looking to confirm your choice with replies from here. I think they would be a good choice from results that Wolfy and others have posted on some other sites, but I have no personal experience with them.

But while the subject is open, if you dont mind me chiming in on your thread, I would like to pick the brains of the very knowledgable people on this board about your engine combination. My combo is nearly the exact same, only with a hyd roller.

I have been doing a little playing with engine calculators and have these numbers about the 781 oval heads and 505 ci BBs.

1..the minimum port CSA required for 6000 rpm @ 505 ci is 2.77"
2..the head flow required at 6000 rpm is 291 cfm
3.. a "good" set of 781s with 2.250 valves and pocket port flow around 295 cfm @ .650 lift
4.. Choke point cross section area @ 6000 in a 505 is 2.77"
5.. Cross section of a 781 head is 2.77" (by my rough measurements of the port with calipers)
6..mach index of the 505 is .56 (calculator made no reference to port size)

Isnt this info saying that the 781 heads are completely maxed out in all areas on a 505 at 6000rpm, even to the point of being a restriction?

I have figured the numbers for a 454 also, and the 781s appear to be a very good head for a 454ci up to 6000. But the long stroke and higher piston speeds are making me think the 496/505s are a completely different animal for head and cam selection than a 4" stroke BB.

Wouldnt the (too) high port velocity of .56 mach at 6000 make the flow get very turbulant and impossible for it to make the short side turn?

Sorry for all the questions, and please, add to, or correct me where I'm off base. I'm here to learn and help where I can. And hopefully Bob and I can end up with heads that are optimun for our 505s. I'm looking at the AFR 315s

Thank you,
Scott

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Post by **SchmidtMotorWorks** » Tue Dec 13, 2005 1:59 am

I am currently running a 505 in a 4000lb 72 Malibu best performance to date is 11.0018@122.28 and looking to run 10's year around and keep it on the street.

That reminds me of an interview of John Force I heard a few years ago, he needed to get some weight off the car and decided the easiest place to get the most weight was going on a diet. Coincidently I think he was advertizing slimfast at the time. Always promoting.

BobW · Post by **BobW** » Tue Dec 13, 2005 7:32 am

Very well said Scott, I never was a wizard with words. In my case I would very much like to keep the oval port design, if they'll get the job done.

67RS502 · Post by **67RS502** » Tue Dec 13, 2005 9:24 am

Bill
Thanks for the input on the carb, as I thought it was more of the culprit of the high
vac. reading then the heads, but the shop that I used for the dyno said they've seen
high vac. on most oval port BB motors - I'm guessin thats because these milder motors
usually have small carb

I think my Demon 1000 was pulling 2" at 6800, peak power was
at 6200.

Bob
You could try uncapping it with header extension, to see how much your exhaust
is hurting you. I've built a few exhaust systems and have noticed the motors around
500cubes (600+hp) really pick up with a 3 1/2" and 4" exhaust. 3" will usually slow them
down 2-3mph (sometimes more). I've run my car with a 4" (with a H-pipe) system and
uncapped (with hdr extensions) and it runs almost identical times. It picks up a about
1/2 mph, but the exhaust was around 55lbs, which accounts for that.
Now I have a 3 1/2" system with and X-pipe "box" (with some volume) and Magnaflow
mufflers, (trying to get it a bit quieter) havent ran it with this setup but it should do
just as well.
I hear what youre sayin about keeping the rpm low, but you should be fine shifting a bit
higher, it may go faster if it make power up there. I shift mine at 6800 with a cast crank
and 3/8 rods, gonna replace that next yr;)
I've researched what heads to stick on my motor and looks like a small rect port is
the way to go on a 500cube motor, as long as the increased cross section comes with
a good increase in flow. I've seen 10 sec cars pick up over 3mph, which is around 50hp.

SUPRSLO · Post by **SUPRSLO** » Tue Dec 13, 2005 2:04 pm

MadBill wrote:Before you start tearing the engine apart, I think you could do more with the exhaust. How far is it from the end of the primaries to the H pipe? Since the H, especially if fairly large, 'sort of' acts like the termination of the collector length, it should likely be only ~ 18" away. Also, 3" is pretty small from a tuning standpoint for a stout BB. (although it's plenty for flow) Ideally, you should probably have 3 -1/2" collectors. A taper/megaphone up from the current 3" (or even a little smaller) throat to 4" over the 18" length would probably be better still, but if you need to run though mufflers, something like 3 -1/2" Flowmaster, Spintech or other 'empty box'-types can seem like open air to the engine, allowing an "open tuned length collector" effect if mounted say 18" -24" back of the end of the primaries.

.

I've been attempting to find a muffler like you speak of but one that flows in the 800-900cfm range. Looking for two of them actually. I'm assuming the ideas you are speaking of regarding the "empty box" muffler are in line with Vizards ideas of pressure wave tuning. However, as he's indicated in his articles, one must also find a mufler which is able (or find a total muffler flow) to flow 2.2 cfm per open headered horsepower the motor produces to not exhibit anymore then 1% loss. Has anyone been able to identify a "empty box" muffler which infact does flow in this range. Sorry to steal away from the original posters question, but i'm looking for something for a motor in the 700-750 hp range and it seems as though a muffler like this does not exist. Thanks.

MadBill · Post by **MadBill** » Tue Dec 13, 2005 3:30 pm

Yes, Walker seems to be the only company that publishes flow numbers for (at least some of) their mufflers! I'm pretty sure my 4" 40 Series Flowmasters would (they are 12 x one cylinder's volume per Vizard's recommendation), but I haven't been able to flow them.

SStrokerAce · Post by **SStrokerAce** » Tue Dec 13, 2005 3:34 pm

SUPRSLO wrote:
MadBill wrote:Before you start tearing the engine apart, I think you could do more with the exhaust. How far is it from the end of the primaries to the H pipe? Since the H, especially if fairly large, 'sort of' acts like the termination of the collector length, it should likely be only ~ 18" away. Also, 3" is pretty small from a tuning standpoint for a stout BB. (although it's plenty for flow) Ideally, you should probably have 3 -1/2" collectors. A taper/megaphone up from the current 3" (or even a little smaller) throat to 4" over the 18" length would probably be better still, but if you need to run though mufflers, something like 3 -1/2" Flowmaster, Spintech or other 'empty box'-types can seem like open air to the engine, allowing an "open tuned length collector" effect if mounted say 18" -24" back of the end of the primaries.

.
I've been attempting to find a muffler like you speak of but one that flows in the 800-900cfm range. Looking for two of them actually. I'm assuming the ideas you are speaking of regarding the "empty box" muffler are in line with Vizards ideas of pressure wave tuning. However, as he's indicated in his articles, one must also find a mufler which is able (or find a total muffler flow) to flow 2.2 cfm per open headered horsepower the motor produces to not exhibit anymore then 1% loss. Has anyone been able to identify a "empty box" muffler which infact does flow in this range. Sorry to steal away from the original posters question, but i'm looking for something for a motor in the 700-750 hp range and it seems as though a muffler like this does not exist. Thanks.

Yeah the only way to get that "terminator box" is to build it.

As for mufflers that flow the CFM you need, look at a Dynomax, they have a few street mufflers that flow 2200cfm + in 3" size. As bill said they are made by Walker, which I believe also makes Magnaflow but I haven't proven that yet.

67RS502 and MadBill, I was going to comment on the intake vacuum but Bill beat me too it. If you are getting more vacuum at WOT it means the heads are working better not worse and the carb is the restriction. It's always a suprise to me how a dyno shop can screw something simple like that up.

Bret

SUPRSLO · Post by **SUPRSLO** » Tue Dec 13, 2005 3:50 pm

MadBill wrote:Yes, Walker seems to be the only company that publishes flow numbers for (at least some of) their mufflers! I'm pretty sure my 4" 40 Series Flowmasters would (they are 12 x one cylinder's volume per Vizard's recommendation), but I haven't been able to flow them.

Well you wouldn't happen to have access to a flow bench for them would you

. Every time i've ever tried to ask any of these muffler companies about flow they just told me about how it doesn't mean anything yadda yadda yadda. It would be nice to be able to get the benefits of the wave tuning and have the adequate flow in a muffled system without having to build one of these space consuming terminator box setups suggested by vizard.