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Discussion Starter #1 (Edited)
I posted this in another thread here, but someone who also peruses these forums suggested I should post this in its own thread. Hopefully someone will find the info useful or helpful.

I just wrapped up the 3rd dyno session on the 496 out of my Chevelle.

To get everyone up to speed--

I originally built this 496 back in 2006 (I stated 2008 elsewhere in error). The original build can be seen here.

The engine consisted of a 2 bolt block, Eagle 4130 external balance crank, SCAT H beam rods, Probe pistons, a Crane flat tappet cam & matching valve train, stock stamped steel rockers, and a 163 intake. The cylinder heads are 100% stock 291 castings (rectangle port closed chamber) with 2.19 and 1.72 valves. The oiling system consisted of an M77HV pump (mistake #1) and a factory A body oil pan (mistake #2).

The first dyno session was done @ George Montgomery's shop where we recorded 6 pulls. The first pull was using the un-cut 163 intake, a LIST 3910 780 vacuum secondary carb, and open 2 1/4" headers.

RPM------CBT-----CBP-----BSFC
3000------522------298------.507
3500------520------343------.491
4000------504------384------.513
4500------479------411------.532
5000------459------438------.541
5500------428------449------.564
6000------414------474------.580

Over the next series of pulls, the headers were swapped out for a set of 2" Hedmans, a 3' long 3" exhaust was added with the actual mufflers that would be used on the car, the 3910 was replaced with a 3418 carb, and finally the plenum divider was removed which resulted in the following figures (the gains from the previous pull are in parenthesis highlighting the change solely from the cut plenum):

RPM------CBT---------CBP----------BSFC
4000------546 (+12)---417 (+10)---.483
4500------544 (+20)---467 (+17)---.454
5000------531 (+27)---505 (+25)---.493
5500------488 (+34)---512 (+36)---.507
6000------467 (+30)---534 (+34)---.536
6500------417 (+32)---517 (+40)---.580

The engine exhibited unmistakable oil control issues on the dyno, so the oil pan was swapped out for a 6 quart Stef's before the engine went in the car.

There was also a nagging ring seal issue which I finally found the time to address last month, which led to this series of dyno tests. The engine came down, the block was re-honed and I replaced the Probe pistons with a custom set of Autotec units which dropped the compression from 11.2 down to 10.5.

Fast-forward to 7/1/14: George's schedule prohibited re-testing there, so I made arrangements to dyno at Kammer Racing in Huber Heights, Ohio. The engine was put back to the same basic configuration as it was during the initial series of testing on George's dyno (as close as I could get it).

Here's one of the baseline pulls:



As you can see the numbers are very comparable, so I consider this a valid baseline comparison.

Pull #4 was a water/oil temp test. Pull #5 saw a swap from the 3418 carb to a 4781, but the pull was aborted due to the choke slipping closed during the pull.

Pull #6 with the 4781:



There was a significant increase in power at higher rpm with the 4781, but note the brake specific numbers between it and the 3418--the 3418 is going very rich up top. I'll be recalibrating the 3418 further and re-testing it again somewhere down the road.

Pull #7 was an oil level test.

Pull #8 was a 2° bump in timing.

Pull #9 was a swap from the OEM points distributor to an MSD unit. The curves were similar and the total was the same.



Pull #10 was very surprising. The 3" collectors were removed from the headers and 3 1/2" collectors were installed. Both pairs of collectors were the same length, and both tests used respective 18" collector extensions.



The 3 1/2" collectors hurt power everywhere. The 3 1/2" collectors remained for all subsequent dyno pulls for the remainder of this session (to pull #25), but for pulls #26 through 30, the collectors were changed back to 3".

Pull #11 was another water/oil temp test.

Pull #12 saw another drop in water/oil temps, and power went up again.



Pull #13 saw the 163 intake swapped for a heavily ported Holley Strip Dominator intake.



Pull #15 saw a lash change on the exhaust valves only.



Pull #17 was the addition of a 1" open carb spacer.



Pull #18 saw the addition of a 14X3 air cleaner. I tried to install the OEM air cleaner but I forgot that the base won't clear the secondary pump lever on a double pumper carb, so I had to use a "generic" aftermarket base.



Pull #19 was a spark plug test between non-projected tips and projected tips, both of the same heat range.



NOTE: Despite the oil pan swap, there were still oil control issues present during this round of testing. Varying oil levels were tried, but pressure still began to drop above 5000 rpm.

Continued.....
 

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Discussion Starter #2
Re: 496 Project V2: 600+ HP & TQ with 100% stock heads

Pull #20 was the removal of the choke blade.



Pull #21 was another ignition timing change.



Pull #22 put the timing back where it was and saw a change from the 2X 3 1/2" headers to a pair of 1 3/4 X 3" headers to see if they would recover the low end torque that was lost when the collectors were changed. They didn't.



Pull #23 was a swap to a pair of equal length race headers with 2 1/8" primaries and 4" collectors. Surprisingly these headers provided the best peak torque of the session.



Pull #24 went back to the 2" headers and a change in intake valve lash.



Pull #25 was the final pull for this session (2 days on the dyno) and saw an intake lash change in the opposite direction.



A few pics--

2" headers:



1 3/4" headers:



2 1/8" headers:



I had planned to call it quits here, but knowing the engine was still showing oil control issues, I couldn't bring myself to call it a wrap. I had a Milodon 31188 pan slated for another project, so I pulled it (and a standard volume pump) from the other project and installed them on the 496 for one more day of testing.

Continued...
 

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Discussion Starter #3
Re: 496 Project V2: 600+ HP & TQ with 100% stock heads

Here's the final results.

Pull # 26 was the first pull made after the oil pan & pump swap. Note that all the previous pulls were made at 300 rpm/second and dyno guy forgot to switch it from 600 rpm/second for this pull. (I've tested 300 vs. 600 back-to-back on several other builds and found roughly a 5-7 HP/TQ difference favoring 300 rpm/second)



596 lb.ft and 601 HP. I was shocked at the gains, I was expecting maybe 10 HP at best.


Pull # 27 was after swapping the 4781 carb main body for an HP main body I built & calibrated. Note that this was at 300 rpm/second:



616 lb.ft and 616 HP.

Pull # 28 was a swap from the Holley Strip Dominator intake and 1" open spacer back to the 163 intake with no spacer:



612 HP and 610 lb.ft torque.

Pull # 29 was an oil and water temp test. As noted on the sheets, all testing had been done with water around 110° and oil around 140°. This pull we bumped the water up to 159° and the oil up to 170°:



Didn't care for that at all.

For the 30th and final pull, I just happened to remember at the last minute that I'd neglected to re-set the intake lash back to spec after the 25th pull, which was the conclusion of that session. I had them set at .030" and the card called for .026", so the lash was tightened back up. The engine was cooled back down to 110°/140°.



Back to 614.5 HP and 601 lb.ft torque. The tighter lash gave up some mid-range while gaining very little on top (compared to pull # 28).

There is still more to be had, but I'm more than happy with the results at this point. Again, this is all with bone stock cylinder heads with nothing more than a good 3 angle valve job. Considerations are being made for cylinder head upgrades perhaps next year. I'm confident 650+ HP is well within reach with only relatively minor refinements.

Now I just need to get everything tidied back up and get it back in the car. I do plan to have the headers coated in the very near future, but that may have to wait until winter.

BTW...the oil pressure is now stable within 2 lbs from 3500 to 6500 rpm. :thumbsup:

To say I'm anxious to get this back together would be an enormous understatement. <grin>

Thanks for reading along. :)
 

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Re: 496 Project V2: 600+ HP & TQ with 100% stock heads

Lot of dyno time and information there. A lot was gained... Have fun driving it!
 

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2000 Trans Am WS6
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Re: 496 Project V2: 600+ HP & TQ with 100% stock heads

Very nice. Thanks for sharing! :thumbsup:
 

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Re: 496 Project V2: 600+ HP & TQ with 100% stock heads

glad you broke free of the intake tread! Again, thanks for posting all this!

If someone could SPREADSHEET this, compare...awesome!
 

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Re: 496 Project V2: 600+ HP & TQ with 100% stock heads

Wow, 25+ HP gain from oil control. That's a lot of parasitic losses.
 

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Discussion Starter #10
Re: 496 Project V2: 600+ HP & TQ with 100% stock heads

What do the heads flow?
I haven't flowed these particular heads, but for comparison's sake here's some figures posted elsewhere on here:

Eric Weingartner posted these #;s:

GM 291 BBC Rectangle port closed chamber stock 2.19/1.88
INT EX
.2-141---------112
.3-207---------139
.4-251---------163
.5-288---------180
.6-289---------194
.7-291---------197

840 Rectangle port closed chamber 2.19/1.72
INT EX
.1-65 60
.2-137 107
.3-195 137
.4-244 159
.5-283 176
.6-307 185
.7-312 192
 

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Discussion Starter #11
Re: 496 Project V2: 600+ HP & TQ with 100% stock heads

Wow, 25+ HP gain from oil control. That's a lot of parasitic losses.
I was surprised as well.

I do want to reiterate something here;

I am in no way, shape or form "bashing" the Stef's pan that was on before the Milodon pan. The Stef's pan is probably the best I have ever dealt with in regards to build quality and engine fitment, but it just wasn't the right pan for this build. On a <4" stroke engine I'd bet this pan would be just fine.
 

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Discussion Starter #12
Re: 496 Project V2: 600+ HP & TQ with 100% stock heads

I failed to mention in the first post, when I said "cylinder head upgrades", I meant to either the existing heads, or to another pair of rectangle port closed chamber units--the latter being my preference. I would very much like to have another set of heads done & ready to go so I could put the engine back on the dyno as-is, re-establish the baseline and do the head swap for a true "A-B" comparison.

I love taking parts that everyone says won't work and making them work. :D
 

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Re: 496 Project V2: 600+ HP & TQ with 100% stock heads

Amazing thread, hugely informative for newbies like me. The gains with the oil pan are very impressive. And offcourse, getting 600+ hp and torque with just about stock heads and a flat tappet cam.... again, amazing. Thank you for sharing this information :)
 

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Re: 496 Project V2: 600+ HP & TQ with 100% stock heads

Excellent post. Thanks for taking the time to post all this data.
Its amazing that a quarter inch additional stroke can cause so much power loss and oil control issues as the rpm rises.
 

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Re: 496 Project V2: 600+ HP & TQ with 100% stock heads

Can you state the cam and compression again, thanks
 

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66 El Camino 57 Chevy pickup 2004 Tahoe
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Re: 496 Project V2: 600+ HP & TQ with 100% stock heads & intake

that's a pretty healthy cam. What's the idle speed? any idea on vacuum @ idle?

That's pretty much kicking butt all over the place for a lot of stock parts.
 

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Re: 496 Project V2: 600+ HP & TQ with 100% stock heads & intake

292/300, Lift .618/.638, 256/264 @ .050, 108°LSA

Still got the stock rockers on it? They holding up ok?
 

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Re: 496 Project V2: 600+ HP & TQ with 100% stock heads & intake

I posted this in another thread here, but someone who also peruses these forums suggested I should post this in its own thread.
Was going to post a similar suggestion when you asked if you should start a new thread but I didn't want to disrupt the flow in the other thread. Glad you decided to make a separate thread which will allow an easier database search for it in the future. Good job and thanks for sharing.
 

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Discussion Starter #20 (Edited)
Re: 496 Project V2: 600+ HP & TQ with 100% stock heads & intake

Idle isn't bad at all, choppy but totally do-able at 900-1000 rpm. 500" calms the cam right down.

Once I had the part throttle operation of the 3418 carb sorted out, I could cruise through town in 4th gear (4 speed car) @ 1500-1600 rpm with only the slightest occasional hiccup.

I don't think I've ever bothered to check idle vacuum to be honest. I'll do that once it's back in the car & running.

The rockers are Crane Nitro-carb 1.7 stamped steel units, and they're holding up just fine. The springs aren't all that stout, just 99893's which were the recommended spring when I built this, but Crane now advises the 99890 spring for this cam so I may make the switch.

Stock parts rock. :thumbsup:
 
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