490 SBC pumpgas 23* dyno results, need expert "power" advise

[67RS502]

I posted this on YB, but really got little help.
I would like some input from engine builders on what to improve with this combo.
I'm just a dummy doing this in his garage, so...
I need more rpm to make more power, heres the 2 specifics I'm looking at, as I don't want to totally change this combo.
1. the cam was to peak at 6500+/-, it peaked at 6000, retarding it 3 degrees got peak up to 6300.
2. is the induction holding it back, and what can be done to improve it, is there a CSA problem considering the stroke and piston cfm demand?

COMBO:
Dart Iron Eagle tall deck
about 11:1 comp.
Wiseco 14 cc dish piston .985” CH 1.2 1.2 3mm
4.200” bore
4.420” stroke
6.2” rod small journal
Piston is .015” out the hole, with a Felpro #1036 head gasket .051” thick, yea pretty tight, but I’ve done others around 35 before.
Brodix 10X 23 degree raised runner heads, with 2.14”/1.60”, Jesel 1.7s
Chambers ended up at 73cc
CSA is around 2.9”, no P-rod pinch.
I’m happy with the intake ports, as they were ported and I only did some csa, minor short turn and chamber work to them.
That’s as comfortable as I felt with the exhaust ports, since I don’t have a sonic checker, but they don’t sound as clean as I’d like on the bench.
Flowed on a 4.155” bore:
200 142/107
300 202/154
400 263/190
500 308/222
600 345/240
700 361/248
800 370/252
900 376/252
1.0 380
Old Pontiac 3374 Intake I hogged out to 3.8” at plenum.
HR cam, 252/257 on a 109, .670”
Johnson HR lifters.
2” headers
---------------

DYNO:
Had some issues
But the final #s are 691hp @ 6300, 640tq @ 4800 retarding the cam 3 degrees just to get a bit of rpm, as it would only go 6000 before.
The goal was 700, so I’m happy, didn’t do any jetting, it was close, but I know there may be a bit more in it, just ran out of time.
This was with 1st gen Camaro 2” chassis headers on it.
It really liked retarding the cam 3 degrees, as peak power went from 5900 to 6200/6300, so what does that tell us?
Would it really like more cam? I believe so, but would like to hear from cam pros on this.
I also believe I could utilize the heads better more duration and lift.
Also makes plenty tq, I would gladly trade some tq for more hp up top.
I’d like to open up the intake manifold up a bit, but theres not much more meat in it.
I’d like to find a mopar intake, or just swap to the Victor Ram I have, along with more cam, I believe more rpm and hp would come.
What would you guys change??? Not that I’m really disappointed, but always looking for more down the road…

I feel like more cam, around 10-20 degrees, would let it rev and make some more power, and that may be what happens
once it goes down the track with this cam.

Thanks
Rafel

[CGT]

Really cool and interesting engine build. I think it ran real nice. OF COURSE....more cam, more area, more lift would make more power, your power from retarding the cam is telling you that I believe. But...I know from experience that its easy to lose site of originally stated goals and purposes .

Everyone is likely going to have a different idea on things to do with this cam or that cam that would do everything better...blah blah. But cool deal. Good job.

Curious when you retarded the cam, it went from what ICL to what ICL?

[PRH]

Not really any “advice” at this point, more of an observation.......

The fuel flow curve has a huge dip in it in the middle(with corresponding bsfc curve).

Were any other carbs tried?(Demon 1000 listed on dyno sheet).

Bsfc numbers are climbing kind of quickly at the end of the pull, along with the fuel flow and dropping a/f ratio.

The question for me then is, is that because of the carb calibration, or is the calibration a/f being influenced by something going on in the manifold?

[67RS502]

LSA is 110
Cam grinder wanted it at 109
retarded it to 112
So does that tell me it wants more cam? I've never played with cam timing on the dyno.

I don't want to loose sight of the original purpose... street strip ride, I want the lobes to be streetable.
As for more area, the head is at 2.9" right now, set up by bore/stroke for 6500rpm.
The intake is around 3.8" csa at the plenum, does that sound right?
Does it actually need more because of the huge stroke?

I built this thing like pumpgas 496 oval port BBCs I've done before, while shooting for 700hp.

[67RS502]

That's the only carb we tried.
It seams like it always goes a bit rich up top, I didn't mess with it.
Would this be an air bleed or emulsion bleed fix?

[mag2555]

Your knife edged runner dividers in the Plenum is a problem.

[Carnut1]

Did you get to flow the heads with the manifold, carb and air cleaner? More than once I had the manifold choke a nice intake port. If it is the manifold the tunnel ram will really wake it up if it has the area. Thanks, Charlie

[n2omike]

I built this thing like pumpgas 496 oval port BBCs I've done before, while shooting for 700hp.

Love it!

A 496 has much larger heads, intake, etc... so it won't need as much cam to rev on up.
With the small block architecture, you'll need more cam to get the same RPM range as the big block.
I seriously doubt it's hurting for low end power, so I wouldn't hesitate to throw a little more cam at it!

Good Luck!

[67RS502]

Theyre just that ways about 1" at the top, rest of the way theyre rounded with a big radius.
Also that picture wasn't quite finished, work in progress, they top was shortened a bit and rounded off.
Pic just shows the general size of the runner.
Ive heard 2 theories on the knife edge/radiused.
I do a sharper edge on top of the divider, as a well respected head porter told me this works.
Yes I rather have things radiused anyway.

[67RS502]

I built this thing like pumpgas 496 oval port BBCs I've done before, while shooting for 700hp.

Love it!

A 496 has much larger heads, intake, etc... so it won't need as much cam to rev on up.
With the small block architecture, you'll need more cam to get the same RPM range as the big block.
I seriously doubt it's hurting for low end power, so I wouldn't hesitate to throw a little more cam at it!

Good Luck!

Actually both are sized the same... csa
BBC ovalport = 2.9" csa for a 6500rpm 496, a ovalport Victor jr. is around 3.8" csa at the plenum (if I remember right)
These are the same sizes as these SBC parts, but I am limited to a 2.14" valve.
I even used a 2" header, which is whats used on most 496 BBC builds.

[n2omike]

In the meantime, can you run a carb spacer? This engine should be a great candidate for a 2" open spacer.

[67RS502]

Yes, I don't think I've ever done anything without spacers... easy power.
I start with a 1" open phenolic.
then I have a home ported 2" tapered I stick on top of it.
End up with 3" worth of spacers.
Always makes more power, this spacer combo usually make 5-8 on most engines.
Even the dyno guy was surprised, as he said they usually don't see hardly anything with spacers,
I'm guessing they just try 1" spacers compared to none.

[67RS502]

So cam wise what do you'll think?
The intake / exhaust ratio is poor.
The cam only has a 5 degree split, now I cant argue with the cam guy,
but peak tq was to be at 5000, it was at 4800, 4900 after retarding cam... close
Peak hp was to be at 6500, and carry to 7000.
was at 6000, and is at 6300 after retarding cam, should shift at about 6500.

How would you cam this thing?
Would the long stroke and piston cfm demand play a big role?

[paulzig]

You are driving all the events later with the retard.

"LSA is 110
Cam grinder wanted it at 109
retarded it to 112"

252/257 on 109icl 112icl

IVO 17 14 BTDC
IVC 55 58 ABDC
EVO 59.5 56.5 BBDC
EVC 17.5 20.5 ATDC

It revved up with later IVC, but you have also made the EVO open later..

Keep the IVC where it is, return the EVO to original or earlier and the cam is going to look a bit different, 100s of ways to get there too...

[CGT]

I would want an earlier EVO for sure, I just can't see another 10° earlier EVO doing anything but helping.