Author Topic: HP ?? stock 7 heads on stock 403  (Read 620 times)

via3d

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HP ?? stock 7 heads on stock 403
« on: December 23, 2018, 01:20:02 PM »
What would the expected/guesstimate power gains both hp and torque) for putting STOCK #7 heads on a STOCK .403. ???
« Last Edit: December 23, 2018, 02:05:22 PM by via3d »
~ J

kingwil

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Re: HP ?? stock 7 heads on stock 403
« Reply #1 on: December 26, 2018, 03:46:25 PM »
#7 Heads came on a 1971 350 Olds engine and are around 64cc's.  The 4A heads on a Factory 403 have 83cc's.  So, with the #7 heads, you are probably going to increase compression from the factory 8:1 to somewhere between 9 to 9.5:1 compression, which is a very good start.  Hard to tell you what the HP and Torque gains will be, because we don't have the valve size and the cfm flow numbers of your #7 heads @ .500 lift.  A factory 403 was rated at 185 Net HP and around 320 ft-lbs of Torque.

Let's say you go ahead and have the #7 heads flowed to see where they are at.  And, then decide to have them worked on to increase flow (assuming the #7 heads flow in the 190 to 220 cfm range) to somewhere in the 235 to 250 cfm range.  Then, you decide to put in bigger 2.000" intake valves and 1.625" exhaust valves.  You can probably expect to increase your horsepower by 100-150, depending on all you do with these heads, camshaft, and other engine mods.  A lot goes into increasing horsepower.  For instance, what valve springs do you plan to put in the heads?  Some factory valve springs had a seat pressure in the 90-110 lb. range.  And, many people may recommend putting in valve springs with 120 to 135 lbs. of seat pressure. 

Your HP and Torque can also be affected by the Camshaft being used in your 403 (sorry for stating the obvious).  Are you keeping the current camshaft?  Is it factory or has it been changed to an aftermarket cam?  If your 403 has the factory cam, the engine could also benefit from an aftermarket cam with 10 or more degrees of duration and higher lift, with those #7 Heads that will increase the engine's compression.   

Depending on where you want to go with this, you can take a 403 from that 185 Net HP rating to an engine with 300-350 horsepower, or horsepower in the 450 range like what is being described in the Olds 424 Stroker thread.     
79 Nocturne Blue 403 Firebird TA
72 Viking Blue 455 Cutlass Convertible

kingwil

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Re: HP ?? stock 7 heads on stock 403
« Reply #2 on: December 26, 2018, 04:00:34 PM »
Okay, I jumped ahead with mods and so forth in my answer above.  If you just want to put the #7 heads with 64cc combustion chambers on the 403 (which comes with 83cc combustion chambers on the 4A heads), you will increase the compression from 8:1 to over 9:1.  If everything else remains the same (aka factory 403 engine), you could feasibly increase horsepower 50-75.  Now, we do not know the flow of these #7 heads and if they have the smaller regular valves or the larger W-31 valves.     
79 Nocturne Blue 403 Firebird TA
72 Viking Blue 455 Cutlass Convertible

via3d

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Re: HP ?? stock 7 heads on stock 403
« Reply #3 on: December 29, 2018, 06:25:25 PM »
Thanks Kingwill for your input, what you think expectation of the slight mods will be for the following:

Car will have dual exhaust, x-pipe, long headers, 3.23 gear

at the moment the 403 will look like this  (32k original miles)

-refresh and hone (no bore needed)
-maybe flat top pistons or lower dished pistons (all else staying same)
-rebuilt '79 800cfm Qjet (with Ruggles kit metering rods increase primary rods 44)
-#7 heads stock (smaller valves, same springs)
-new cam (have yet to spec)





~ J

Grand73Am

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Re: HP ?? stock 7 heads on stock 403
« Reply #4 on: January 07, 2019, 08:57:37 PM »
I'm wondering if the #7 heads with 64 cc chambers will produce much higher compression than was estimated. I know that on a Chevy 350, 64 cc heads create 10:1 CR. So, it seems to me that 64 cc's on a 403 cubic inch engine would be well over 10:1, so too much compression for pump gas.

So, that's something to investigate further. I know the early 70's Olds 350 heads can be used, but don't know what is commonly done to reduce the compression to make it usable. Maybe dished pistons or opening up the chambers?

Of course, the head bolt holes on the #7 heads have to be drilled to 1/2" to be able to use them on a 403 too.
Steve F.

Re: HP ?? stock 7 heads on stock 403
« Reply #4 on: January 07, 2019, 08:57:37 PM »

kingwil

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Re: HP ?? stock 7 heads on stock 403
« Reply #5 on: January 08, 2019, 04:00:56 PM »
The 403 in my 79 TA has #5 W-31 Olds small block heads with 2" intake valves that were milled from 64 cc to 62 cc.  Blocked was decked to .20, as the block varied from end to end from .27 to .33.  Pistons are Power Forged TRW with 20cc Dishes.  This produces a tad above 9.5:1 compression taking into account the thickness of the head gaskets, compared to the 83cc 4A factory 403 heads that produced around 8:1 compression.   

If you use dished pistons (as I did), you will not be above 10:1 compression.  However, if you use flat top pistons, you probably will.  On these #7 heads, you haven't mentioned whether or not they come with the larger 2" valves or have the smaller valves (probably more common) which may be 1.875" in size.  And, my guess is that unless you had the heads flowed by a shop, you probably do not know the flow of these #7 heads.  I've heard, depending on whether they are the performance (W-31) or regular #7 heads that they can flow somewhere between 190 cfm to 210 cfm or so at .500 lift.  For example, the 1969 #5 W-31 Heads on my 403 were worked a bit and flow 238cfm @ .500 lift.  Not super great (like 280), but better than stock. 

You asked about dual exhaust, x-pipe, and long headers.  My 79 TA has these.  The 403 has ceramic-coated headers that connect up to a 2 1/2" Pypes Exhaust System with X-Pipe flowing thru some Dynomax Super Turbo Mufflers and out to 2 1/2" tailpipes that have the dual-chrome exhaust tips to make it look factory.  Hard to say what type of HP gains can be made with Headers, true dual exhaust, and X-Pipe, as I didn't have the car put on a Chassis Dyno before the exhaust upgrades were made for a "before" and "after" comparison.  Most people have claimed you can get 15 to 30 more HP with a free flowing exhaust system, so I'd be a bit conservative and assume you may achieve 15 HP. 

On the 3.23 rear gear ratio, that is a pretty good ratio to have.  It'll give you better performance and also allow you to drive the car on the highway, without the RPMs getting too high.  I have talked to a few TA owners over the years and learned that quite a few cars have a 2.73 and some as low as 2.41 for highway cruising with a 403/TH350 auto in late 70's TAs.  Pontiac 400s with 4-speeds appear to have the 3.23 gears in them, from what I have seen and heard.  In my case, my 79 TA has a 4.11 8.5" Posi Rear End (factory was 2.73) with a TH700R4 Overdrive Transmission in place of the Factory TH350.  This gives the best of both worlds - performance from a stop and then locking overdrive for a final drive ratio of 2.89 for the Highway. 
             
79 Nocturne Blue 403 Firebird TA
72 Viking Blue 455 Cutlass Convertible

via3d

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Re: HP ?? stock 7 heads on stock 403
« Reply #6 on: January 08, 2019, 09:32:11 PM »
great info, thanks !

I am in a quandry now, but looks like my plans have changed.   
Last week discovered build sheet was in place & mine is a WS7, and since it is almost entirely stock @ 32k original miles....

I may just do a near complete restore.

Regardless, I am pulling the 403 to freshen up & paint. At which time I will get most other areas in front cleaned & painted.
I will temporarily put in a '67 .330 stock high compression motor for when I take to get painted... meanwhile work on engine.

May still do dual exhaust at minimum as the back half sections show its age...

At this point, I need to determine, if I want to do some hidden improvements. I wonder how much this may add or deduct from value.

Of course gear, cam, and compression, pistons or hidden upgrades.
-  Does this further deduct from value? I am welcome for opinions.
-  Unfortunately, for maintain stock look, this may mean staying with 4A and work them as best as possible (mill, port, & larger valves)

UGH!!! But a good dilemma to have. ;)

~ J

kingwil

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Re: HP ?? stock 7 heads on stock 403
« Reply #7 on: January 09, 2019, 04:21:21 PM »
When you mention WS7, do you mean the WS6 Handling Package with the 4-wheel disc brakes and upgraded front and rear sway bars, heavier duty springs, and so forth?  I do not know what extra value a WS6 car has, as I do not pay close attention to resale value for WS6 vs non-WS6 Cars.  It's got more value, but hard to say how much.  My 79 TA came with the WS6 Handling Package and I've been in some non-WS6 78 and 79 TAs, and there is a difference in the ride (aka harsher and corners/handles much better). 

Keeping a 32K almost stock is a good option to keep originality.  But, if you are going to rebuild the motor, you can do some work on the heads to improve flow and perhaps go with flat-top pistons to increase the compression, and also look into upgrading the Cam a bit above stock.  Some internal engine improvements can be made while keeping a stock appearance, since a 79 403 Olds has around 8:1 compression.  You could look into trying to get the compression up to 9:1 (flat-top pistons in place of dished pistons) or perhaps as high as 9.5:1 and still run on pump gas, around 91 octane.  The timing is fairly lazy on late 70's GM V8's so you could also look into advancing the timing some to wake up engine response (aka power tune).             
79 Nocturne Blue 403 Firebird TA
72 Viking Blue 455 Cutlass Convertible

Grand73Am

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Re: HP ?? stock 7 heads on stock 403
« Reply #8 on: January 11, 2019, 08:22:53 AM »
When you mention WS7, do you mean the WS6 Handling Package with the 4-wheel disc brakes and upgraded front and rear sway bars, heavier duty springs, and so forth?           

WS7 is the same as WS6, but without the rear disc brakes. In 79, when the rear discs were first offered, there were times when the supply of rear discs could not keep up with the demand. So to help alleviate the problem, they came out with the WS7 option, so people could still get the other WS6 benefits, but with rear drums.
Steve F.

1979 Black and Tan

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Re: HP ?? stock 7 heads on stock 403
« Reply #9 on: January 11, 2019, 02:49:28 PM »
couldn't you just use flat Top Pistons and clean up the factory #4's ..if you are rebuilding your engine you are going to need new pistons anyway ..might as well use flat tops
1979 Trans Am
100% California Car, originally Atlantis Blue/ Black...All Original Unmolested 403, TH350, 2.41
63,300 orig. miles
1971 Chevy K20 4x4

via3d

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Re: HP ?? stock 7 heads on stock 403
« Reply #10 on: January 11, 2019, 09:25:03 PM »
Kingwill,
I was thinking same perhaps cam and pistons.

...and Grandam73 tunred me on to this WS7 option... all suspension upgrades sames as WS6 except rear disc.

Aus78formula, contemplating now keeping stock, including 4A heads.   I am not sure I agree, putting #7 heads would be obvious in sight to true enthusiast & is not so much bone stock.


4A heads
I read up quite in depth on Olds forums what can be down to 4A heads and why they are so frowned upon.  For right amount of $$$ seems they can be just as good
J&S has good flow data on his various Staged 4A head builds.
Seems to me you can go larger valves, port job, mill .010 or .020 and they would be pretty decent contending heads. This is not a racing car nor drag monster....  so more than adequate.
Heck that is the same thing that is suggested to do to 350 or BBO heads... for optimizing them - so seems same to be the same machine work and $$ to me.
Going BBO heads are often preferred option with some folks because larger valves are already there, the larger CC;s in mid 70 range for the chambers doesnt seem of concern....  so with $A 80CC just mill and get it down right ?

What am I missing or not understanding here??

Pistons
at 32k I would think there is good chance pistons are fine to refresh and all that will be needed is hone (not bore).
~ J

via3d

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Re: HP ?? stock 7 heads on stock 403
« Reply #11 on: January 11, 2019, 11:14:25 PM »
LOL...  my 330  has "4" heads.., maybe I let that slide... ;)
~ J

olds403

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Re: HP ?? stock 7 heads on stock 403
« Reply #12 on: January 12, 2019, 10:39:14 PM »
4A heads leave a lot to be desired.  Not sure where this thread is going...
To do a full motor is a lot lot $$ unless you know the machist and he / she works for free.
Our short block was $4000 plus parts on the 424.  We spent $2000 on the heads. 

Re: HP ?? stock 7 heads on stock 403
« Reply #12 on: January 12, 2019, 10:39:14 PM »
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