1971 455 Upgrade recommendations - Pontiac GTO Forum
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post #1 of 5 (permalink) Old 04-06-2018, 08:25 AM Thread Starter
 
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1971 455 Upgrade recommendations

I have a completely stock 1971 455 (325 hp) that I am putting into my 71 Lemans Sport. The setup is the 71 engine (has #66 heads), built 200r4, 3:23 10 bolt rear, power disk front drum rear. I do a lot of highway driving so good street manners is a must to me. I am looking for recommendations for a good camshaft/lifter/carb combination to go along with a performer intake and rare ram air exhaust manifolds. I am not looking to get crazy power but would like a little lope to it and retain some fuel economy if possible.

TIA
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post #2 of 5 (permalink) Old 04-06-2018, 08:33 AM
 
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Lunati Cams are a good starting point : Voodoo - Hydraulic Flat Tappet - Lunati Power

I would recommend you call them and discuss your current setup and goals.
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1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #3 of 5 (permalink) Old 04-06-2018, 09:25 AM
 
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Originally Posted by cij911 View Post
Lunati Cams are a good starting point : Voodoo - Hydraulic Flat Tappet - Lunati Power

I would recommend you call them and discuss your current setup and goals.
I second that. Am using Voodoo in my GTO. Those Voodoo cams were designed by famed cam designer Harold Brookshire. Although he had some fast ramps in his lobes, he always used the GM closing ramp so the valve would not "slam" into the seat like many other brand cams do. Good recommendation cij.
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post #4 of 5 (permalink) Old 04-06-2018, 01:39 PM
 
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"...completely stock 1971 455 (325 hp)...looking for recommendations for a good camshaft/lifter/carb combination to go along with a performer intake..."


If the engine is "completely stock", I assume that means that it is about 47 years old, pistons, rings, bearings, an all. If this is the case, it may not be a good idea to go with a Voodoo cam. A Voodoo will increase cylinder pressure, which is good for low CR engines, provided they have & will maintain a good ring seal. BUT, if the bottom end can't handle any more pressure, a Voodoo might not be a good idea.

But, IF the shortblock has been recently rebuilt & will maintain a good ring seal, I agree with the Voodoo cam. A 268 might give you what you're lookin for. But, those cams have more lift, a steeper ramp, & require stronger springs. Bigger cam/stronger springs will put more stress on the entire valve train. Some have experienced valve failure, with the factory 2-piece valves. Most now recommend SS 1-piece valves, for bigger cams with stronger spring pressures.

But hey, you might be lucky & get by without all the upgrades many recommend. The 068 is the biggest cam Pontiac ever put in a non-SD 455. The SD455 had a cam with the same specs as a 744 cam. Both the 068 & 744 had less than .410 lift. The 068 will have a dead smooth idle in a 455. The 744, not quite as smooth. These cams are still available as a Melling SPC-7 & SPC-3 respectively.

Next up from the 068, I assume would be a Summit 2801, which is similar but with more lift. The Summit 2802 is similar to the 744, but has more lift.

Between the Summit 2801 & 2802 might be something like the Lunati 10510312.

Street Master Hydraulic Flat Tappet Cam - Pontiac V8 276/286 - Lunati Power

I'd run an iron Q-jet intake & a properly rebuilt Q-jet carb.
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Last edited by bigD; 04-07-2018 at 11:45 AM.
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post #5 of 5 (permalink) Old 04-06-2018, 08:23 PM
 
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The 325HP 455 with the #66 heads, big valves, are shown to have 8.2 compression with a nominal chamber specification of 111 cc's. Most are slightly larger and you will see 114 cc's as a general rule.

As pointed out, you really don't want to go higher on the lift than factory unless you add matching valve springs and make sure no interference between valve and piston top. Adding more pressure could accelerate wear on parts that may already be worn - without knowing the condition of the engine. I suppose a compression test or leak down test would give you a much better idea of how well the rings/valves are sealing which would indicate the engine's condition if you don't know. BUT, with everything else you stated, your engine may already be rebuilt?

You also did not state if you were looking for a flat tappet cam or roller cam? So assuming flat tappet cam is your choice.

If the engine has been rebuilt, then I would take advantage of the low compression and install a cam that will build additional cylinder pressure. The Competition Cams with their 110 Lobe Separation Angle (LSA) will typically build additional cylinder pressure (or most any cam with a 110 LSA). The mention of fast closing ramps and valves slamming seems to be a relationship with higher lift cams as the nose of the cam lobe has to be taller which can sacrifice a less radical closing ramp contour. I used a Competition Cams XE274H kit, matching springs/retainers, and stainless steel valves in my former low compression 1972 400CI (manual drums, 3-speed manual trans, 2 1/2 duals with stock manifolds) and was very pleased with its performance. Pulled real well and plenty of pep. Power peaked at about 5500 RPM's and dropped off sharply - which is just fine for a stock built engine and more RPM's than would be used if going by factory specs. It would be tamer in a 455CI, so might be a good choice as long as it'll pull enough vacuum for power brakes. Can't say as I heard any valve noise from the valves slamming closed, but never listened for it either. After about 25,000 miles of hard running, the SS valves and valve seats still looked pretty good to me, but I don't know what I would be looking for as a result of slamming the valves shut.

VooDoo cams are also recommended here, but have never used one. I went with a Crower solid cam/lifters this time around on my 455CI build, but can't give any reviews until I get the car put together and back on the street.

The Summit cams are also well recommended by many. Just want to match the valve springs with the lift and I don't think valve clearance between the top of the piston and valve should be a problem, but it is something to inquire/check into as you begin to go higher than stock lifts.

So cam recommendations on this forum will generate a lot of suggestions. You can also contact a cam supplier as to their recommendation and they will steer you to something they feel will work best.

Assume you have the Performer intake already? Go with a good quality remanufactured Q-jet. Should give you good response and decent fuel mileage.

Just my suggestions thrown into the lot.
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, LeMans & GTO Engine Tuning and High Performance

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