[Skip Fix]

Depends on if you are wanting a hydraulic roller or flat tappet. My 78s pump gas motor has KREs 320 cfm CNC on them and I have T2 I blended a LOT and had to weld the top of top fit their 2.400 port and it does well with hydraulic flat tappet Ultradyne lobes 296/304 239/247.

[92GTA]

I don't mind going to a hydraulic roller setup from my hydraulic flat tappet so I can run the best cam profile to get the most out of 461. Long as I don't have to pull the block and make any modification to do so.

I just want to be able to swap the cam, heads, intake, and carb all in my friends driveway in a day, or 2 with some beer We are old hats at this stuff but this will be the first Pontiac engine for both of us.

I'll send Dave at SD perf an email and see what he recommends since I'll be buying the ported intake and heads from him. I'm sure he can make a great cam suggestion.

[Cliff R]

"So let me ask your opinion; if I get the SD Performance 325cfm heads, have my Torker II ported to match, what cam would you suggest?"

That is a LOT of head flow for one of these engines, so the cam should be matched to it.

We typically run 260cfm to about 295cfm for 455 street engines and 10 to about 10.5 to 1 compression.

SD's Old Faithful HR cam is a very good choice for them. They typically make around 550hp/and 580-600tq.

The last one we helped with and got dyno numbers on it made 552hp/604tq. The compression ratio was just over 10 to 1 and 295cfm head flow using SD's ported KRE aluminum "D" port heads. It used a port match RPM intake (no spacer) from them and one of my 850cfm q-jets.

I really see no need for the 325cfm version, but Dave at SD would be the one to ask about what cam to use with them........Cliff

[92GTA]

Gotcha.

OK I sent an email to Dave, I'll see what head and cam he recommends.

Thanks everyone for your helpful suggestions and info!

[i82much]

Just to play devil's advocate, there aren't a whole lot of guys running around with 850's on built 450+ CID Pontiacs going, damn, this thing just doesn't have any throttle response ...

[KEN CROCIE]

I'm surprised no one has called you on an effective 100 cc head yielding 9.9:1 C/R.
BTW, 750 cc is more than enough. Perf RPM will make more power & tq. up to about 4600 RTM on that combo.

[92GTA]

Originally Posted by KEN CROCIE

I'm surprised no one has called you on an effective 100 cc head yielding 9.9:1 C/R.

All I know is that in the paperwork from BP, the say that those dished pistons with the 72cc 670 heads I have will yield 9.9cr with their .045 head gasket. I see nothing in my paperwork mentioning deck height tho. I do know the engine was dyno'd using 110 Sunoco at 32 degrees of timing.

But have I done a compression test to know what my cylinder psi is yet, nope. I will though so I know for sure.

What would you guess my real cr is?

[KEN CROCIE]

Not as low as I thought. I get 9.4-9.6 with zero deck. With 110 oct., more timing was available-IF it was needed. I've been fooled before on timing requirements on a given head at the Dyno. IOW I say it should take X deg. total timing for max power, but the Dyno says Y deg.

[92GTA]

Good to know!

Once I get all this stuff lined up and installed, I'll for sure be trying to find someone who is a master at chassis dyno tuning these things and trust them to get it sorted properly.

[ta man]

Originally Posted by 92GTA

Gotcha.

OK I sent an email to Dave, I'll see what head and cam he recommends.

Thanks everyone for your helpful suggestions and info!

Dave won't steer you wrong..just be honest with yourself with what power you need or et you wish to run and be prepared to make the changes..

[NeighborsComplaint]

Many moons ago, I had the pleasure of corresponding with Pete McCarthy over my first 455 Pontiac build. At that time he was the Pontiac Guru and I requested his input on the motor I was planning.

We discussed 6X-8 heads, various camshafts and carburetors. A few of the things he told me were counter to the current trends at that time.

He advised that he favored the Engle grind now called EP22HYD for the street 455's he was building/ The cam was a straight duration 230/230 with just .483" lift with 1.50 rockers, no split duration magic. I asked why no split duration and his reply was "Stock heads go into turbulence over .500" lift and it's game over and that cam lobe favors the heads' low lift sweet spot. More exhaust duration is not needed. Enlarging the exhaust valve to 1.77" would enhance flow and benefit from a split duration cam like a RAIV grind and again, lift over .500" was unnecessary.

Obviously, camshaft technology has changed since those conversations but the principles remain the same.

On the subject of carburetion, I advised I had an 850 Holley double pumper and asked if would be workable. His advice was "a 750 Holley w. vac secondaries is all you need with stock heads and an automatic trans. The 850 will work but won't make any more power than a 750 and will just use more fuel."

[Cliff R]

I've had 455 street/strip engines on the dyno in the 500-550hp range and swapped carbs out on them back to back.

To about 4500rpm's a 750cfm carb will make the same power, from there up to about 5500-5800rpms you will make a few more HP with an 850cfm carb. It's not a butt-load of difference, usually less than 10hp, but they big 455's at that power level will like the bigger carburetor.

Down around 375-400hp I doubt if you'd see any difference at all, since the engine isn't going to be making power past 5000rpms' anyhow......Cliff

[pontibeast]

Cliff, that's good to hear as I chose an 800 Q-Jet for my new 455. Sounds like an 800 would give you the best of both as far as an average. Thanks for posting dyno results, it really helps make decisions easier.

[Cliff R]

The larger q-jets actually flow a bit more cfm than that, so you woln't loose any power at all vs an 850 Holley style carburetor in the same application.

I've had my 1977 Pontiac q-jet on the dyno, and back to back track runs scores of times against "850" cfm aftermarket carburetors. My q-jet is typically 1-2hp better on the dyno and a few hundreths quicker at the track every time I've tested it.

The only time it's taken a back seat to large CFM square flange carburetors is on single plane intakes w/o a spacer, and really high HP stuff where we swapped to a Dominator intake/carb.

Ya, not typically what folks like hearing when it comes to these things, but it is what it is........Cliff

[Tom Vaught]

The truth is not always as fun as advertising.

The Carb people knew their jobs, be it Rochester, Carter, or Holley guys.

Tom V.

10 HP on a 500 HP engine is about 2% and sometimes the weather change can be more than that (unless testing one carb immediately after the other, as Cliff has done many times).

[OCMDGTO]

Great info as usual Cliff, thanks for posting.

[torqjunki]

FWIW....I backed to back a Q850 carb and a Holley 750. Both with no choke. This was on pretty rowdy 467 with ported Eddy round ports. Ran identical times. The 750 was better for cruising.

[TCSGTO]

I had my 464 dynoed with a my 750 and the shops' 950 and the 950 made 10-15 more HP and torque all the way through the pull. The motor had out of the box E-heads,247/252 flat solid cam and RPM intake. Made a little over 500HP and would run mid to high 11's.

Never ran anything other than my 750 on that setup so I don't have any in car comparisons against a bigger carb. Probably wouldn't have made much difference.

[Blued and Painted]

This is America, where bigger is better.

[Tom Vaught]

Originally Posted by TCSGTO

I had my 464 dynoed with a my 750 and the shops' 950 and the 950 made 10-15 more HP and torque all the way through the pull. The motor had out of the box E-heads,247/252 flat solid cam and RPM intake. Made a little over 500HP and would run mid to high 11's.

Never ran anything other than my 750 on that setup so I don't have any in car comparisons against a bigger carb. Probably wouldn't have made much difference.

I can believe that with a back to back against a dyno shop's carb that most likely has seen a lot of dyno pulls and is really dialed in to the fuel curve/BSFC.

When I sent the dual Holleys to Tony B to be tested on the RA-V engine years ago, my calibration was the best one tested on the dyno but I had a lot of research into those two carbs and what they wanted. Tony, was at a disadvantage, in that he was just trying to "better" an already good calibration. Those carbs were old style 750 double pumpers.

So your 10-15 HP difference is logical.

Tom V.