455 street cam choice
 

I am building a 73 2 bolt main street duty 455 motor. Block will be bored .30 over. Heads will be 7F6 and factory HO aluminum intake from 72 455. I believe the general factory cam is a 068? The car will be a 4 speed muncie m20 with 12 bolt posi with 3.55 gears and stock G60x15 tires. The car is a 72 GTO WW5 car. Car will be mainly for car shows and a few drag races. I would like a lumpy idle but able to sit at a stop light. Any suggestions for a cam and lifters?

Are you staying with the factory Hi Po exh manifolds, or will you run headers?

With 3.55 rear gears and a cam that will make peak power at a higher rpm you should ditch the factory connecting rods during the rebuild process and also and while your at it get the compression up to 9.2 if not 9.5 depending on the fuel you have access to.

Manifolds
 

I will use reproduction factory round port manifolds for the heads and factory exhaust

Neat engine.

A couple years ago I did a 72 455HO with the same 7F6 heads, HO aluminum intake, but the heads were ported and compression bumped to 9.98:1.
Paul C did a nice custom hydraulic roller for it 239/243 @ .050 on a 112 LSA that made good power with the RA manifolds in place. 507/571 and peaked at 5600rpm. It idled nice and ran the AC and power brakes.

I'd probably tame that down a bit for what you're doing. I imagine your compression will be lower as well since those heads have pretty big chambers. Being a 4 speed will be nice, no converter to worry about. The really common 230/236 Comp cam chosen for many builds like this would work well enough from what I've seen and make decent power. Cliff has used that cam quite a bit as well as several others, and is something that Butler sells a lot of.

In fact Cliff and others have dyno numbers they have shared on builds almost exactly like that.

Sounds similar to the 464 I’m building. Are you looking for a roller cam or a flat tappet?

I went roller with my build and originally had a 230/236 picked out, but the crew here urged me to go bigger so I’ve got a 236/242 .521/.540 114 going in now. I chose a 114 because I have A/C, power brakes and an auto. You could probably go tighter with a manual to get more lump.

Just planning a flat Tappet cam

Here is a more 'stock' 455HO engine rebuild that we ran a Summit 2802 cam in it (224/234/114 duration @ .466"/.488" lift). It is .030" over with forged Eagle H-beam rods and TRW/Sealed Power forged (heavy) pistons. The heads, intake and RA manifolds are all untouched factory pieces. The short block was from an older build (2000 miles) and we just added the 455HO heads, intake and exhaust manifolds (2.0625"/2.125" outlets!). The first pull made 410 hp @ 4800 rpm and 515 lb-ft @ 3600 rpm. After richening the Q-jet as far as we could go with the jets and metering rods we brought, it eventually made 431 hp @ 5000 rpm and 535 lb-ft @ 3500 rpm.

Dennis

Thanks for the engine build dyno info. How did the engine idle, was it streetable? The 2802 is a cam that I have seen recommended for the 455 motor since it seems to provide more horsepower and torque then the milder summit cam,I think 2801 version. All comments welcome. Thanks.

Nice numbers!
It’s good that test started at 2500 to show just how low massive torque is already being made.

The Tq never drops below 460 from 2500 all the way up to 4600.

Did that total timing of 38 turn out to be the best?

Yes, it is totally streetable, nice idle with a burble. It ended up with 8.6 to 1 compression ratio and the 197 HO heads measured 108.0 cc's across all 8 chambers(!). A 2801 is very similar to the factory 068 cam, so very docile. I think the 2802 is leaving power on the table, as are the factory RA manifolds with their tiny outlets. Hopefully you have the repro RA Restoration 'enhanced' versions with the 2.5" outlets. Definitely run the Pypes 2.5" mandrel headpipes on either manifold as that first bend to the back robs a ton of horsepower if it's not mandrel bent and at least 2.5"!

Dennis

Steve, we started with 38 degrees initially (used 93 octane E10 gas), but then bumped it up to 41 degrees and got half of the hp/tq gain (10/10). I wish I made a last pull form 2500 to 5500 rpm.

Dennis

This is the car ('71 GT-37) the 455HO now resides which is waiting for new canyon copper paint and eyebrow stripes (R/W). It's taking the place of the original 455HO engine that is all apart and in storage.

Dennis

Wow,,,41 total. Out of the mild to race engines ive had built from Eheads to ported iron ive never had a engine like even close to 41 degrees. Maybe 35 at the most.

These old chamber heads seem to like timing on some engines. My buddy would occasionally take his 69 COPO 427 camaro to the race track for fun back in the 80's and early 90's, and that thing always ran best with 42 degrees of timing in it.

I used to run the Nomad here back in that time frame with it's 327, with hump heads, and I always kept the timing at 41 on that thing where it ran best, and daily drove it that way.

My 454 Chevelle, even with more modern AFR heads with heart shaped chambers makes best power at 38 degrees, which I didn't expect at all.

Then take dad's 571 Pontiac for instance, with it's old style Edelbrock bathtub style chamber heads that everyone says likes more timing, didn't like anything more than 34 degrees when that was on the dyno.

Go figure. That's why I prefer to dyno and test these things, they seem to be all over the place for what they like on timing. No set number.

To add what FJ posted, when we dyno'd 455HO's back in the days before we understood what tight quench did and the actual static compression was lower 8's (8.0 to 8.3 range) the best power was in the 42 - 44 degree range all in by 2500 rpm. But that was probably with 93 octane 100% gasoline (no ethanol). The RAIV's liked 36-38 degrees all in by 3000 rpm with a minimum of 100 octane blends of real gas.

Dennis

Here are dyno numbers from a 1973 455 Super Duty engine done here. Cam card attached. Nothing special about the engine and I didn't flow test the heads. It was recently "rebuilt" shortly before I go it but only lasted about 180 miles.

Pretty "basic" build, steel rods, Icon pistons, zero decked, didn't compute the compression ratio but probably about 8.8 to 1.

Idled smooth with a "deep/heavy" sound, made 14" vacuum at 750rpm's with only 10 degrees timing in it. I wouldn't use a cam with less than 230 @ .050" if you want to make good power with the round port heads. Even this Super Duty 455 was pretty much done by 5200rpm's. The problem with "low" compression 455's and big flowing heads is that cams to take advantage of that much head flow really start to get "soggy" at idle and in the "normal" driving range. So pulling the LSA down for your "lumpy idle" is going to hurt idle quality, throttle response and power in the "normal" driving range.

In contrast I'd go bigger with the cam and push it out on a 114LSA. We've done very well with that deal on the big 455 HO and Super Duty builds without putting domed pistons in them or cutting the heads really hard........
https://forums.maxperformanceinc.com...1&d=1663152248https://forums.maxperformanceinc.com...1&d=1663152248

You just can’t make any type of blanket statement about what a given type chamber wants in terms of timing.

Many folks engine combo’s that are similar just have too many important factors that are different.

The propagation of the flame front across the chamber ( assuming no detonation) is influenced by many factors, of which two of the biggest are cylinder pressure rise as the piston gets close to TDC and the different jetting needs for a specific gravity of the fuel used, and not to leave out the chamber suface temperature difference between a iron and Aluminum head.

Also to stuff a third factor in there the wet flow characteristics of the intake runner and port are part of the picture too.

Big droplets of balled up fuel don’t light off if at all until the piston is already moving down the bore.

This. Creates a power loss, and sometimes a big one if the motor detonates as is the case many times when that balled up fuel goes off at a sonic expansion rate.

Even if there is no detonation the dyno guy will wrongly see a need lean out the jetting to get some of the power back that the motor should be making, but then since your putting less fuel into the motor your also in turn making less power then what could be made if all was well, and since your now lean the motor is on the razors edge of detonation once again.

It’s a very hard wall to be backed up into!!

See 12.2 ET Sig for the largest HFT cam to use 9.0:1 compr. and get WOT on 87 Octane, 89 for 1/4 mile duty.

Cliff, does the "HR112" mean it's a hydraulic roller camshaft? If so, that would be a big difference comparing to a flat tappet hydraulic.

Related to the above....

Hydraulic roller vs hydraulic flat tappet
https://forums.maxperformanceinc.com...d.php?t=659923

( Within that thread I incorrectly stated the Comp XE 3315 lobe had 181 degrees at .006" tappet lift. That is incorrect, in their catalog it is rated at 282 at .006", and with Cliff's "B" lobe it has 281 degrees at .006" )


.

Interesting my RAIVs like 34.

all this total timing talk assumes everyones timing marks were 100% accurate with a piston at TDC.

Most people dont check this unless they suspect a problem and just because parts are new is no guarantee of accuracy

Thanks for the comments. My engine builder is recommending the summit 2802 or comp xe278 cams for the motor. He said the 2802 will be milder and the xe 278 will have more lope at idle but will still produce vacuum. My 7F6 heads were still factory so they need new valves and springs. Thoughts?

Sorry I meant the comp cam xe 274h not 278.

im looking for something as well for a 1966 4dr bonneville, i have a 72 455 with 7m5 heads looks like a stock rebuild was done to it before i got it, im putting headers with 3" exhaust, street dominator manifold with either a 750 or 800 carb, th400 with 2.75/1.78 gear change in the transmission not sure yet about the rear end id like a solid flat tappet cam any suggestions.....

Xe cams don't get any love around here. You're better off with 2802 based on everything I've read.

Drewsgto, You're going to need new valve springs with either cam, but my vote is for the 2802 as it's easier on the valve springs from the slower opening and closing ramps. I had an XE274 (with the default 110 LSA) in the stock '71 455HO (only 8.2 to 1 static compression ratio) and it sucked, sounded like the lifters were clacking all the time, made very little vacuum for the power brakes, no low end torque (lots of feathering the clutch from a stop), etc., etc., etc. We swapped in a Summit 2801 which ran sooo much better and it comparable to the factory 068 cam, but admittedly, a little too tame for that big 455. I think the 2802 is a good choice for a lower compression 455, but certainly no smaller....some views will vary.

Dennis

It’s kind of difficult if you’re wanting both good street manners and a lumpy idle.

Pick one or the other.

The 2802 is a proven performer and would be my choice.

im more of a lumpy but i want a solid

camshaft
 

what about this one im not sure about the compression with 7M5 Heads on a 455

I have the XE268 in my 461. Its very similar to the XE274 on paper. My engine idles smooth and quiet. Pulls hard and is all done at 4800. Def too small for a 455/461. If I were doing another HFT prob. just use the 2802.

"Lumpy" idle means less effficiency as you have to increase overlap to a point where you are bleeding off a good amount of cylinder pressure at idle and pulling some intake charge over into the exhaust.

Cam companies cater to that deal but for sure it does NOT make more power, improve idle quality, or engine efficiency in the "normal" driving range,. I actually LOVE the fact that folks buy into that deal because more times than not it requires advancing the timing at idle speed clear off the scale at idle speed and bringing in a lot more fuel from the carburetors idle circuit, plus additional idle bypass air to keep the throttle angle low enough to avoid "nozzle drip".

7M5 heads have HUGE combustion chambers, some of the biggest out there. On a 455 with flat top pistons you are probably going to end up around 7.5 to 7.7 to 1 compression without really tightenig things up with decking/squaring and shaving the heads down a bit. 7M5 heads are also very prone to cracking across the exhaust valve seats. I can't ever remember finding a pair where one, the other or both weren't cracked. They also have really short valves in them. Pretty much "boat anchors" or door- stops in this deal.......IMHO...........

Cliff, I shake my head in vein to try a see the logic in guys like this who state that I want a real Hot Rod sound to my built/ car, but then don’t seem to mind that it can’t live up to its sound.
It’s a flat out total waste of time, money and effort to me , especially when folks like this want help from others in achieving this goal of substandard performance!

I'll put this out there as a "general rule of thumb" for a street engine build.

If you find your new build wanting, needing, liking or responding well to having to run much more than about 10-14 degrees initial timing you missed the cam choice vs the CID/compression ratio a bit.

With about 10 degrees initial timing your engine should make at least 12-13" vacuum at 700-750rpms. Take a gander at a hand held vacuum gauge and note where the "green", "yellow" and "red" zones are at if you think I'm off base here.

Of course it doesn't mean that the engine woln't run OK, nor does it maean that you can't start "crutching" it with a LOT more timing and pig-rich carburetor. That's been going on for decades and how a LOT of us make a living with custom tuning carbs and distributors. This industry caters to "bling" and just about everyone associates "menacing" idle quality with improved engine power and performance, when in many cases nothing could be further from the truth.

Attached is an overlapping dyno sheet I've put up here many times. The 455 at 9.3 to 1 compression had a "rougher" idle with the smaller XR276HR cam than it did with the custom ground HR cam I recommended to the owner to replace it. It also made MORE power at every RPM and quite a bit more upper mid-range and top end power. Even the very experienced engine "builder"/dyno operator was amazed at how much better the big 455 ran everyplace with a much larger cam in it on a wider LSA.

Just some food for thought when it comes to choosing cams for the big 455 engines..........
https://forums.maxperformanceinc.com...1&d=1664967796

That’s a very huge difference even if you just want to compare both motors at 4800 rpm.

The other big difference as to how both motors would perform in a car is how much faster the motor with the custom cam would rev up!

I'd rather have a 455 iron headed "street" build that idles well, and pulls hard to well past 5000rpms making nearly 90 MORE HP at the shift point. Not so mention torque production in the upper mid-range and top end is up nearly 60-100ft lbs at every point. The naysayers usually come back with "all I want is good low end torque" and not concerned with top end power. That's complete horsechit....IMHO. Why not make more power at every RPM with better idle quality and street manners? A 455 is also going to make more "low end" power than you can handle anyhow in just about any configuration. Things done to spread that power out and push some of it to higher RPM's only results in the vehicle being a LOT faster the day you decide to take it to the track and get some numbers on it.......FWIW......

You touch on a point that I have tried to get across before, and it’s a very important one that you have kindly present.

If you have for example been running a well tuned 9 to 1 compression D port iron headed 400 which should be able to roast your street tires at will in first gear, provided you have at least a 3.08 rear gear., then stepping up to a well built 455 with the same heads as the 400, but pistons used to also have a 9 to 1 comp, then we find this.

This 455 even when fitted with a lowly 068 cam will be making 13% more torque but also at a 13% lower rpm then the 400.

This then opens the door to running at least a 8% bigger cam, yet still maintaining the same drivability that the 400 cid motor had.

Both motors you would find would still be making the exact same peak hp numbers since the factory iron heads are inadequate for any 400 cid motor , no less a 455 above 5400 rpm.

Also a way to go now with the 455 is to step up to a aftermarket head with a 13% greater minimum port area .
The added minimum port area ( bigger choke point) along with even just 30 more intake cfm and a good cam pick produces the numbers as you posted in your dyno sheets .

This assumes the motor is fitted with a intake manifold that can pass the added cfm we are talking about here.

I'd put in an 041 spec cam and Rhoades Lifters. Very streetable and you get the assurance of a proven flat tappet combination and a high quality lifter. As you know, Pontiac originally intended to use the 041 cam in the 455SD with low compression heads like yours but could not meet emissions standards with it. The Rhodes Lifters will clean up the idle a touch. With a stick car, it should be a solid performer with plenty of rump in the idle and no bad habits on the street by nature of the 114 LC. It's an old combo, but a proven one if sticking with a flat tappet cam.

I run a Crane 234/242 very similar to a RAIV in a 9:1 iron headed 455 with standard flat tappet lifters a 2500 stall convertor and 355 gears and it gets around town like a normal car and idles just fine so it's easy in stop and go, etc.

I'm less concerned with how fast my car is relative to other cars of its type than I am the actual driving experience. I am in the "make it sound and perform like a muscle car and cruise it" frame of mind these days and just enjoy the torque and the rumble.

i understand that these heads suck on this motor, i purchased this rebuilt motor as is, im not sure what cam is in it i am putting the motor in a 66 bonneville and wanted some power and found this cam listed, just wondering if it would work, im changing the transmission gears to 2.75/1.76 with the factory stock 3:08 rear gears with headers and a 2200 converter

Not sure why you would say that. Compression ratio aside, they are one of the better flowing heads Pontiac made. You can mill them and the intake .060" and get the compression back up and they will out-perform the typical 6x, 4x, 5c and 96 heads.

i just wanted to know if this cam would work rather than leave it a mystery

Sorry, had you confused with the OP with the 7F6 and missed the thread drift. You won't be able to mount headers unless the end holes have been drilled and tapped. Not sure if they will accept Dport RA manifolds without the end holes.

It'll be a small cam in a 455, especially with the 8-10 degrees you loose with a solid cam's lash, so more like 204-206 degrees actual at .050 lift. You'll need good valve springs with the .500" lift which will help add some power back. The 110 lsa is pretty tight for a 455 as well. If you want a solid cam, get something bigger (230/236) to offset the loss of duration from the lash clearance and 112-114 lsa. I would swap to 6X-8 heads (easy to find and cheap) to rebuild. That'll get you a solid 9.0 to 1 compression...or more with minor resurfacing to true the surfaces.

Dennis

Buy the NIB Summit 2802 w lifters @ $100 in the classifieds if it hasn't sold already.