[Steve C.]

Good luck. I know there is always a bit of apprehension on the first few dyno pulls.

.

[Cliff R]

Yep, I'm never comfortable with running these engines this hard right off the engine stand, but they don't grumble much. Running them in before they go into the vehicle is a good plan. My main concerns are coolant and oil leaks, no matter how good you are or what you know these rear seals can give you some grief, it's just not that good of a set-up back there.......Cliff

[Half-Inch Stud]

CLIFF,

Please summarize the profiles ; the bad cam that pinged & couldn't idle, and the reco'd (good) cam power, ping?, idle with Q-JET.


Because my cam in the 12.2 ET signature will NOT idle nor start with a known-proper Q-JET, nor rebuild Q-JET, but will start and idle (when warmed) with a hyper rich 1050. Yet my combo makes good cruisecresponse and WOT behavior. Still my cam is wrong.

[Cliff R]

The Q-jet actually has an EXCELLENT idle bypass air system and well laid out idle fuel delivery. If you can get the correct parts and settings in place it will idle fine with a big cam in it. I've set these carbs up for engines over 700hp with HUGE cams in them in cars running into the 9's and they are fine. The owners actually comment on how well they idle, stage, and drive back down the return road compared to the "big" Holley style carburetors.

Anyhow, I put the cam specs for those two cams up several times.

The first cam that pinged the 455 was a "shelf" Comp HR, the XR276HR, 276/284, 224/230/110LSA. It has pretty small lobes, around .520/.540" lift nearly as I can remember. That cam has a "quirky" idle in a 455 with 9 to 1 or so compression, I've tuned several of them and very octane sensitive as well.

The replacement cam was a much larger .381" lobe HR, 289/308, 236/245/114LSA. It idles better than the smaller cam on the tighter LSA, and smoother off idle, no noticeable "reversion" in the 1500-2000rpm range, and more power at every rpm......Cliff

[Cliff R]

A few more engine pics......Cliff

[77 TRASHCAN]

Does the SD intake have the huge dump on the bottom of a it, like the stock heavy 73 and 74's do?
Do these intakes look any much different from other stockers?
Thanks!

[Cliff R]

I'll post a pic of it tomorrow.....Cliff

[taalltheway]

….i have to admit to run the XR274 in my SD455…first with the stock heads, now with E-heads…no pinging and it runs incredibly strong in the low and midrange…i will eventually change it for a 230/236/112 HR cam but i can not really say something bad about this cam…i plan to reuse it on my stock 73 455 T/A…maybe add some 6x-heads…i bought this "small" cam to work with the low compression of the SD…i am also thinking about putting the stock head back on so i am very interested in the results you get from this build...

[Cliff R]

Those cams are designed to increase cylinder pressure at lower rpms, and narrow up the power curve on low compression engines. In a 455 build they are pretty much done by 4800-5000rpms, so wouldn't take any advantage at all of the superior head flow of the Super Duty 455 engine. A 455 with a set of 6X heads will make as much as, and probably more power using that cam than the Super Duty due to the higher compression ratio provided by the smaller chambers.......IMHO......Cliff

[Half-Inch Stud]

Originally Posted by taalltheway

….i have to admit to run the XR274 in my SD455…first with the stock heads, now with E-heads…no pinging and it runs incredibly strong in the low and midrange…i will eventually change it for a 230/236/112 HR cam but i can not really say something bad about this cam…i plan to reuse it on my stock 73 455 T/A…maybe add some 6x-heads…i bought this "small" cam to work with the low compression of the SD…i am also thinking about putting the stock head back on so i am very interested in the results you get from this build...

CLIFF, Read this ,and respond to my note here: According to Davd Vizard's 128 rule, my cam ought to be a 104 LSA, and due to being 9.0:1 it should REALLY be a 103 LSA. My present cam in Signature ran 12.2 ET but sucks gas and won't cold idle with the 1050, with no Q-JET ability. No ability to ping, so bragging on 89 Octane, but no MPG ability. Soooooooooo, seems Vizard could cause me to install an old UD 104 LC cam (LSA happens to be 104) to effect a positive result.
With Duration beng chosen based on max RPM.

[blykins]

Changing to a 103-104 LSA most certainly won't help you in that respect. Don't get me started on David Vizard.

I think your gas sucking problem is related to the carburetor only....but would need more information. The camshaft is mild enough that it's not sucking gas because of overlap. Going to a 103-104 LSA and adding duration would make your overlap go from around 68 degrees to over 90.....

[Half-Inch Stud]

...as if ANY cam above 106 LSA is crap in any Pontias combo. This being due to the awesome 2.11" intake valve, and 30degree seats.

[Half-Inch Stud]

Originally Posted by blykins

Changing to a 103-104 LSA most certainly won't help you in that respect. Don't get me started on David Vizard.

I think your gas sucking problem is related to the carburetor only....but would need more information.

Please please please get started on David Vizard. we all need to know. HIS

[blykins]

Originally Posted by Half-Inch Stud

Please please please get started on David Vizard. we all need to know. HIS

Nah, there are guys on here who think he's a master genius, and I don't have time to argue....LOL

A tighter LSA on the camshaft would help with drag racing, but I'd be thinking something around the 108 number, and then making the duration match the rpm goals.

I do think your fuel sucking issue is with the carburetor. It may be too large for the combination.

[pastry_chef]

Originally Posted by Half-Inch Stud

Please please please get started on David Vizard. we all need to know. HIS

This lengthy thread has many replies by Vizard himself.

http://speedtalk.com/forum/viewforum.php?f=1

Look at the "Vizard's secret '128' cam spec # revealed"

Another fantastic cam specialist I know very rarely ends up with anything wider than 107 or 108 LSA
Most all of his stuff has been backed by dyno tests.

Vizard created "COS-CAM" software that he claims will precisely give your required cam specs. These guys offer the service - twperformanceparts.com
Apparently this even takes your valve seat angles into consideration.

It would be neat to see a few Pontiac guys with nice engines use it!

[Cliff R]

CLIFF, Read this ,and respond to my note here: According to Davd Vizard's 128 rule, my cam ought to be a 104 LSA, and due to being 9.0:1 it should REALLY be a 103 LSA

I don't read anything from Dave Vizard, so can't comment.

What I do know is that if you look at the dyno chart below, it clearly shows what happens in a 455 engine build when you put in a small cam on a tight LSA with good cylinder filling abilities.

As far as moving your current cam down to a 103 or 104LSA that would be a disaster, IMHO. You'd be much better moving it out to 112 to 114, where it will have the engine idling better, and broad/flat power curve........Cliff

[blykins]

Cliff, I may send you a bump stick to try....

[Half-Inch Stud]

Originally Posted by Cliff R

......I don't read anything from Dave Vizard, so can't comment.....You'd be much better moving it out to 112 to 114, where it will have the engine idling better, and broad/flat power curve........Cliff

12.2 Signature shows a 112 LSA already.


Did the SD-455 get run yet?

[Cliff R]

"Cliff, I may send you a bump stick to try...."

What application?

HIS, if you move the cam to a tighter LSA it will INCREASE overlap and decrease cranking pressure. You might offset this some by advancing it, but I've tried all that stuff and the 455 engines absolutely LOVE the ICL in the 108-110 range and LSA out in the 112-114 range.

Doesn't mean they woln't run OK with tighter LSA and advanced intake positions. Even with that said my past experience with these things has shown that until you get into pretty "big" cams, moving the LSA tighter than 112 degrees doesn't work as well.

For our full "race" stuff, we usually have them on 110LSA's, and .050" numbers 260 @ .050" or greater. Since we're over here in the street section, most of our street engines use 112 LSA, and on occasion will move them out to 114. Lots of variables in the equation and decision making matrix for that deal, we just do what works well based on the testing we've done.

I think I posted this dyno sheet earlier on another thread, but here's what happens when you let the customer supply their own custom ground cam highly recommended for their 455 engine build from another vendor.

We built a 455 like many others we've done using the 290cfm KRE heads from Dave at SD. In this instance the owner supplied the cam, 244/252 on a 110LSA. We usually see around 550hp/600tq with the exact same engine using the Old Faithful cam from Dave at SD. Look at the dyno run below and see how much power we left on the table and the engine quit much earlier in the rpm range..........Cliff

[pastry_chef]

http://www.hotrod.com/how-to/engine/...-engine-build/

Engine Displacement 473.5 ci
Peak Horsepower 578 at 5,500 rpm
Peak Torque 588 lb-ft at 4,700 rpm

Compression Ratio 9.95:1

Comp Cams Hydraulic roller

Duration at 0.050 242/248-deg
Lift 0.540/0.562-in with 1.5:1 rockers
Intake Centerline Installed at 106.5 deg
Lobe Separation Angle 110 deg

He continues, "We knew the engine would operate on 89-octane at times, so we limited its compression ratio to just under 10:1. Wisely, 92-octane was used during the dyno session, and this is likely why it peaked with 42 degrees of total timing instead of the normal 36-38 we see when combining Edelbrock heads with 92-octane fuel. I'm confident it will produce similar peak power numbers with less timing when running on 89-octane; I suggest that timing be set to 38 degrees in those conditions."