[General Z]

Freshly rebuilt and broken in. Specs are below. Back when I was still using 6H heads, I could easily use 87 octane. Just wondering any opinions on what grade I need to use now that the performance level of the engine has been increased and the compression ration increased as well.

Thank you.

My specs are below:

Engine: 1970 455 Block, bored .060
Bore: 4.2109, Stroke: 4.21

Crank: Pontiac factory crank, ground .010 on rods and mains

Pistons: Sealed Power forged pistons

Rods: RPM International forged rods

Heads: 1971 400 Heads, Code 96
Mildly Ported, Stainless Steel Valves, Dual Springs
96cc, Valves 2.11/1.77
Comp Cams roller rockers, Ratio: 1.52

Compression Ratio: 9.53:1

Intake: Edelbrock Performer, dual plane, port matched

Lifters: Comp Cams Hydraulic

Cam: Comp Cams XE262H

Carb: Holley 0-3310S 750cfm 4-bbl with manual choke. Using ½” carb spacer.

Rear End: 3.73 Gear ratio

Rear Tires: 216-65-15

Accessories: Power Steering, Power Brakes

Ignition: Unknown brand HEI

Radiator: Aluminum 4 core, big block with electric fan

Transmission: 700R4

Torque Converter: Unknown

Exhaust: Hedman Headers, Dual 3” exhaust with H pipe

Oil: Rotella T 15W-40 + a bottle of Comp Cams 159 additive.

[PunchT37]

That thing`s gonna need 93 octane. And rear tires.

[General Z]

Thanks. Do you mean rear tires because I'm going to burn them up or some other reason?

[torqjunki]

With the 3.73 gear and 3.06 first gear in the 700r trans, it will be a tire fryer. Small cam, iron heads.....tire fryer. I would ditch the performer and run an RPM intake with no spacer if it will fit. If not, I think the crosswind intake made about same power as a tricked out factory 4bbl intake which works real well. The performer is pretty restrictive on the big motors from what is reported here. I had a non pontiac street car that worked real well with 4.30 gear and the 700r4 with loose converter. Wheel speed in first was so slow that it would hook and go with no wheel spin like a tractor. Always wondered how it would work with a big pontiac mtr.

[General Z]

My budget is beyond shot on this build. The car is a cruiser / driver, not a racer or show car.

I'm just worried about the 700R4 holding the torque I'm putting out. If I blow the trans, I'll probably do the Bowtie Overdrives Level 3 kit. http://www.bowtieoverdrives.com/cata...hp?ITEMID=7013

[leeklm]

Pretty similar to my build and definitely need 93 octane. I run about 34-35 deg of mechanical advance, but would still have pinging under load at part throttle low rpm. I installed an adjustable vacuum advance that allows the vacuum to come on slower and stiffer advance springs which helped.

I tried a tank or two of 91 octane non-oxygenated fuel, but the pinging came back, needed the extra 2 points... I could probably back the timing down a couple of degrees, but so far all is good with 93 octane.

[General Z]

Thanks leeklm. I'm running about 35 total timing, with the vacuum disconnected. I didn't check it with the vacuum connected.

I guess 93 it is.

[General Z]

So, there would be a big difference in taking off the Performer intake and switching to a cast iron one? I don't have hood clearance for a Performer RPM.

[Cliff R]

I guess that I'll have to be the bearer of bad news here, WRONG cam choice. Not sure who or how you got that little cam combo'd up with a 455 engine at a SCR of 9.5 to 1, but it is not only the wrong choice for pump fuel, but you left a TON of power on the table at every rpm.

How does Cliff know this?

I got DIRECTLY involved with two almost identical builds in the past couple of years, as the owners of them contacted me to do carbs for them, AFTER they had considerable "issues" with their fresh 455's. The issues were down on power, and pinging at heavy to moderate rpm's on any grade of pump fuel, and neither one could add any vacuum advance or they "rattled" when driving them gently. Their engines seemed to do OK in cool/cold weather as far as detonation, but in the summer heat they POUNDED like sledgehammers when going down hard on the throttle when the engines were heat soaked.

Both of those folks ended up removing that cam. One went with the Crower 60243, pretty sure the other went to the Summit 2802 (haven't heard the outcome there). The customer who went to the 60243 absolutely LOVED the cam change, as his engine now enjoys a BUTT-LOAD more power with a TON more in the upper mid-range and top end, and is not octane sensitive anyplace with normal timing/fuel curves.

As a coincidence, got a call a few days ago from another Pontiac enthusiast who was told (by a shop who does this for a living) to install the XE256 cam in his 455 with 9.3 to 1 compression. We had the same discussion.

I hate to come across these threads as a Comp XE cam "basher", that's not really the deal, but I'll take the heat. Those little cams do OK in a 400 engine at 8 to 1 or so compression, tuned a few here, not overly impressive, but they do OK. I wouldn't even consider for one second installing the XE256 or XE262 in any 455 build unless it was 7.7 to 1 compression or less. They simply are WAY too good at cylinder filling/building cylinder pressure at low rpms/mid-range, right where the engine reaches peak volumetric efficiency, and will POUND like sledgehammers even with close control of timing, fuel, and engine temps in higher compression engines.

While I'm on a roll, I'll also mention that I've got involved with several 455's to date around 9.5 to 1 compression that move up to the 224/230/110 Comp HR cam. Same deal, POUNDED like sledgehammers on pump fuel, a DIRECT result of superior cylinder filling abilities of the little HR, tight LSA, and early intake closing.

Folks, we've got to be smarter than that here. Cliff certainly doesn't know everything about this deal, but I do know what does NOT work well, what works OK, and what parts will literally tear your head slam off across the entire load speed range (on pump gas), after several decades of building and tuning Pontiac engines, and building carburetors/distributors full time to help folks out with their new engine builds......Cliff

[torqjunki]

wait for it....wait for it....saw that coming Thanks for the info Cliff. I did'nt want to go there because I have no experience with those cams.

[Cliff R]

You are welcome. I would say here, before the "heat" is on, that I get no pleasure whatsoever, or any sort of self-satisfaction from posting this sort of information. Matter of fact, makes me a little sick at my stomach when I read threads like this, because I know how much effort, time and expense, goes into these projects, and it quickly all goes sour when you have issues, or come up short of your expectations, etc.

At this point in my deal, I really don't have a dog in any of these fights, so to speak. We're backlogged well over a year in the shop, and turn down 10 jobs to every one that do take in, and only want the best for folks when it comes to these things. So basically I could never put up a single post and it effects nothing as far as my work load goes.

I certainly hope in this particular case that you can make it work, but ALL the odds are pretty heavily stacked against it.....FWIW.....Cliff

[CROCIE JR]

93 octane will be a challenge. If you want all the power, 36 total by 1500 with 100 octane. I feel you would have to run 36 total by about 4000 to avoid ping on your engine. Max cylinder fill will be at about 3600 with that cam. So going a little past that with the advance rate should supress the detonation. By running such a slow curve, you just turned your 455 into a 389 for torque production. My advice, 36 total by 2500 and 1 can of NOS "off road" formula octane booster with every fill up. I've tested it. Will net you about 96 octane depending on tank size. Try to get a vac. advance can that drops timing fast. Theres a vac unit out there for 454 HD Truck apps. that has no advance bellow 7-8 inches of vac. This should soften up the ping as you get into the throttle for daily driving.

[CROCIE JR]

Secondly, I would get a 10.5 or 9.5 power valve in that carb. You will be cruising at 13-15 inches in OD, so economy will stay in tact. As you go deeper into the throttle the power valve will open for some extra fueling, and shortly after the 454 HD vac. can will drop timing. Stock, out of the box Holley jetting is about perfect for your set up. If you are 10-15% alcohol like we are here, I would go up 2-3 sizes in the primary to start. Get it on a chassis dyno. Look for about 13.6-14.0 AFR at cruise. On the intake manifold note. Anything you do from here to increase volumetric effecientcy will be a bad move. Like adding headers or a better intake or a free flowing exhaust.

[Skip Fix]

I used an XE 262 on a 112 in a low compression 400,Performer, 3310(then a Q jet) and it was pretty mild even in it and I was not impressed with power. I'd look at a different cam even for a cruiser. Even the cheap Summit 2802 cam in a 455 would be pretty mild and give you more power and I bet run on pump gas better. I used the 2801 in another low compression 400 and it was a better choice.

[The Champ]

FWIW...

My 462 build from last winter had many of the same/similar parts to the OP's with the exception of the cam and intake and carb.

I have the Crower 60243 cam that Cliff recommended, factory intake and quadrajet.

I have the same #96 heads and 9.5 to 1 compression. My car still retains it's original Muncie with a 12 bolt rear end with 3.42 gears. I have 255/60/15's on the back.

I run 91 octane because it's readily available - and have never had a single "ping".

This combo works, and works well. It's possible I could get buy with lower octane, just haven't tried to push it.

I can't imagine this car with tiny 215/65/15's, a set of 3.73's and a 3.06 1st gear...

[General Z]

Well dang guys. Way to crap in my wheaties.

The cam was purchased from and recommended by Jim Butler.

The car is a convertible and will NEVER see a race track. I was going for smooth idle, driveability, low/no exhaust smell, quiet and fuel economy. I knew I wasn't getting max power, but that wasn't my goal at all.

At this point, with all the trouble I've had with this car, I'm just happy that it's running and I can get in it and drive it.

[Cliff R]

Sorry, that certainly was NOT my intent.

Even in a smaller 400 engine at 9.5 to 1 that cam is BARELY manageable. When those cams first came out, I built a 400 and used the larger XE268 grind in it, with high ratio rockers. The danged thing idled dead smooth, not the first hint of "lope", just a deep/heavy sound. It ran OK, but WAY down on power from the 60916 and 60243 cams we typically use in the 400 builds. The XE cammed 400 ran into a brick wall about 4800rpm's, instead of pulling up to 5500-5600rpm's like the larger (seat to seat timing) Crower cams. Got singed hard enough we never did that deal again.

Anyhow, I've tuned worse combo's, and the owners ended up relatively happy. The key to success right to start with will be engine temps, followed closely by very close control of timing/fuel curves. If you can keep the engine cool, it will help ward of detonation. If it climbs up past 190 degrees on hot days, it's NOT going to be happy.

If the pushrod guide holes were modified, a set of high ratio rockers will really help it. I did this "crutch" fix on a 455 at 9.5 to 1 compression using the XR276HR cam that was having detonation issues on pump fuel. That move didn't completely fix it at "normal" timing/fuel curves, but really helped a LOT.

The Summit 2802 cam or Crower 60243 would be a "home-run" for your build. They turn those mid 9 to 1 455's into big "tractor" engines, nice idle, responsive right off idle, smooth in the "normal" driving range, and TONS of mid-range power. Even those cams give up about 5000rpm's or so. You need even more cam to make big top end power, but doesn't sound like that's a goal here.

Another thing I would mention is that we ALWAYS use vacuum advance for street driven applications. It needs to be there so you can run a for efficient fuel curve in the "normal" driving range, and keep the engine cleaner and using less fuel, etc. Most medium to high compression builds will take at least 10 degrees from the vacuum unit, we typically try to use 12-15 degrees for most of them. A lower compression or slightly over-cammed engine will tolerate considerably more, so it is on a case by case basis.....Cliff

[General Z]

If I pull the engine again and start buying more parts, I think my wife will leave me. LOL.

I do run the vacuum advance connected, I was just saying what my total timing was with it disconnected. I run it to full manifold vacuum, not the ported port.

So, you're saying, I want to check my total timing with the vacuum advance connected?

Right now, I'm at 36 degrees with it disconnected and plugged.

Thanks

[Sun Tuned]

Well there are certainly better cam choices that could have been used, but then there are a couple worse too.

That combo can be worked around to be suitable as it sits.

I really don't care for the intake, at all.

I'd also take a real hard look at the distributor.
2500 is too soon, 4000 is too late.
36 total is too much.
I can set that up without need for octane booster.

Work it yourself, or if not have someone pretty well skilled take care of it.

Just remember lots of ways to reach a certain total timing number such as 36, but take it from me smoother is better. So get that dist looked at.

For what you're trying to get done that's a workable setup, not the best, but very workable if you don't get greedy.

[The Champ]

Originally Posted by General Z

Well dang guys. Way to crap in my wheaties.

The cam was purchased from and recommended by Jim Butler.

The car is a convertible and will NEVER see a race track. I was going for smooth idle, driveability, low/no exhaust smell, quiet and fuel economy. I knew I wasn't getting max power, but that wasn't my goal at all.

At this point, with all the trouble I've had with this car, I'm just happy that it's running and I can get in it and drive it.

I had a similar recommendation from Jim on the 262. I'm glad I didn't follow it.

My car is a convertible too. It's been on the track one day - back in 2001 for the Jim Wangers all Pontiac drags for the GTOAA meet.

My goals for my build was to have a nice idle, be able to drive the car in any kind of traffic and run on readily available pump gas (91 octane). I wasn't really concerned about fuel mileage.

Mine does all that, and I haven't noticed any drastic change (good or bad) in fuel mileage. It's got a ton of power - but is actually more streetable than the original #'s matching 389 that is now in storage.