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" )


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