[J.p._Lane]

Hey all, I’m very active on FB and Instagram in some communities but figured I would bring it over to here to get some details during my rebuild. I have a 77’ GP. Beautiful car and had it about a year now. Since I’ve had it, I experienced low oil pressure and I pulled the engine and the bearings were shot. Decided to do a full rebuild. So here’s where I’m at.
406 cubic inch displacement
4.150 bore 3.75 stroke
Camshaft: (comparable summi 2802) 224/234 duration @ .050 114 lobe separation .466/.488 valve lift (actual cam .471/.486)
Keith Black Hypereutectic flat top pistons compression height 1.72” +6.00cc volume
Cylinder heads: #15 stamp
Valve size:1.96 intake/1.66 exhaust. 182@.450/ 190cfm@.500
Ram Air exhaust manifold 2.45 diameter feeding to 2.5 true dual flow master 40’s.
Carburetor: Quadrajet 7040263 800cfm
Edelbrock Performer RPM high rise intake
Deck height .023
Compressed head gasket thickness .040 FelPro 8518PT
2500 stall
I recently picked up the #15 heads to upgrade from my ‘73 heads. The cam is from the previous owner and I figured I’ll stay with it it’s in good shape. But with the new heads, I was wondering if u can simply swap the valve train over to the 15s from the 46s (those springs and valves were in great shape) or do I buy all new springs? They are being taken to the machine shop to get new seals and cleaned up. I was doing research and maybe the comp cam 988-16 springs would work? It ran great with the springs that were on it before I pulled it.

Also, I believe this cam may be a little too much even with all these upgrades. the summit 2801 would be ideal, but It ran so good with just the stock setup so I figured I’d keep it with this setup and see better gains maybe. I’ll be at about a 8:9 to a 9:1 compression.


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[steve25]

In no particular order here’s my 2 cents worth.

The performer rpm intake buys you nothing but a average loss of torque due to
1) a 3.750” stroke motor.
2) only 9 to 1 compression,
3) stock heads, no less small intake valve heads!

You will be far better off with a iron intake, or a standard performer.

Your Cam is a little big for neck snapping throttle response with only 9 to 1 compression, especially if your keeping the smog era gearing in the rear of the car!

You might think about adding Rhoads lifters if you do not mind the solid type lifter noise when hot?

Your valve springs should swap over to the number 15 heads just fine, but may need to be shimmed back up since they are used since you to have at least 120 psi on the seat with a 1.96” valve.

This shim process will hopefully still leave you with enough coil bind clearance and will have to be determined.

You did not state the connecting rods your running, but if they are stock and went thru a bearing failure session then it’s likely time for new one, forged new ones which are not only stronger, but lighter and add to performance by letting the motor rpm faster!

You may need a new oil pump which should be the 60 psi one, and a HD pump drive shaft will be needed also,

Piston wise I do not like those pistons you want to run, not so much because they have been known to crack, but because they are very very old school with there 5/64” compression rings that they use!

Pistons with 1/16” rings will make for less friction and in turn free up Hp and lower oil temps,

I would really like to see this build get to 9.5 compression and while the heads are off you could have a valve job done to install 2.11” valves and then mill the heads ,025” .

The big valve install will also pick you up some much needed intake air flow as a side benefit.

[694.1]

Sounds like a great car, let's see what it looks like.

[hurryinhoosier62]

Back in 1988, I built a new 400 for my ‘72 GP when the original 400 spun a rod bearing at 64,000 miles. The block was out of a ‘72 Catalina my dad had owned(200hp 2 barrel YZ block). I had it bored and honed .030 over, used TRW flat top forged pistons with a standard tension ring set (file fit). When the decks were machined the pistons were as close to “zero decked” as possible(.005 in the hole). I installed ARP rod bolts after the rods were magnafluxed and had them resized by a friend of mine(no aftermarket forged rods were available other than Carillo at $1,000 per set.)The heads were 6X-4s milled .040 to give an 86cc chamber (static c/r of around 9.2:1). I had 1.77 exhaust valves installed instead of the OE 1.66 exhaust valves. The intake was a Performer, since this engine was more about efficiency over brute power. In hind sight, I should have stayed with the OE iron manifold but I was young and impressionable. The cam was a Comp Hi-Energy 260( 212/212 at .050, .440 lift with OE rocker arm ratio of 1.5:1, 110 LSA) installed “straight out” with 1.6:1 Magnum roller tip rocker. The Q-jet was rebuilt and recalibrated using a kit from H-O Racing. The dizzy was recurved and a new vacuum advance installed. I probably left a few horsepower on the table, but I did have a 400 that could burn 89 octane and not “knock”, got reasonable fuel economy ( 16-18 miles per gallon when I kept my foot out of the Q-Jet), could idle in I-75 construction traffic in Cincy without overheating and “smoked” more than a few 5.0 Mustangs and Z28s.

[steve25]

I had a 72 GP with a 400 for about 2 years, and what a land Barge it was!
Looking out the front windshield was like looking out over the deck of a Aircraft carrier from the Stern!

That’s a hood you do not take off by yourself like you can a A body or F body car, lol!

Non the less it was pretty good once I added high lift rockers , recurved the Dizzy , rejetted the carb after adding RA exh manifolds and the accompanying bigger exh system.

I forget how much it tipped the scales at, but it was great highway car!

[hurryinhoosier62]

Originally Posted by steve25

I had a 72 GP with a 400 for about 2 years, and what a land Barge it was!
Looking out the front windshield was like looking out over the deck of a Aircraft carrier from the Stern!

That’s a hood you do not take off by yourself like you can a A body or F body car, lol!

Non the less it was pretty good once I added high lift rockers , recurved the Dizzy , rejetted the carb after adding RA exh manifolds and the accompanying bigger exh system.

I forget how much it tipped the scales at, but it was great highway car!

5200 lbs gross weight. Yes, they are great road cars. I put nearly 40,000 miles on mine before “tin worm” destroyed it. Back in ‘96 when I parted it out there were zero aftermarket replacement body or trunk panels. The worse rust in mine was the rear window area(vinyl top).

[J.p._Lane]

Originally Posted by steve25

In no particular order here’s my 2 cents worth.

The performer rpm intake buys you nothing but a average loss of torque due to
1) a 3.750” stroke motor.
2) only 9 to 1 compression,
3) stock heads, no less small intake valve heads!

You will be far better off with a iron intake, or a standard performer.

Your Cam is a little big for neck snapping throttle response with only 9 to 1 compression, especially if your keeping the smog era gearing in the rear of the car!

You might think about adding Rhoads lifters if you do not mind the solid type lifter noise when hot?

Your valve springs should swap over to the number 15 heads just fine, but may need to be shimmed back up since they are used since you to have at least 120 psi on the seat with a 1.96” valve.

This shim process will hopefully still leave you with enough coil bind clearance and will have to be determined.

You did not state the connecting rods your running, but if they are stock and went thru a bearing failure session then it’s likely time for new one, forged new ones which are not only stronger, but lighter and add to performance by letting the motor rpm faster!

You may need a new oil pump which should be the 60 psi one, and a HD pump drive shaft will be needed also,

Piston wise I do not like those pistons you want to run, not so much because they have been known to crack, but because they are very very old school with there 5/64” compression rings that they use!

Pistons with 1/16” rings will make for less friction and in turn free up Hp and lower oil temps,

I would really like to see this build get to 9.5 compression and while the heads are off you could have a valve job done to install 2.11” valves and then mill the heads ,025” .

The big valve install will also pick you up some much needed intake air flow as a side benefit.

Steve thanks for the reply. I’m very aware of the short comings on the build. Working on a budget and with what I got, I’ve learned a lot along the way. As soon as u find something better about newer parts there’s always a downfall somewhere to them as well (referencing pistons). Based on my research I felt at the time that was the best route, didn’t feel forged was worth it in this relatively low hp and non racing application. I agree about the cam. And it was funny someone else just threw this cam in when the motor was stock. It was way too big for it then and will slightly be too big still after all this work has been done but I’m hoping the 2500 stall makes up for it on the low end. It’s was a great performer before I pulled it and ran like a banshee. So I’m anxious to see it put back together. As far as the rpm intake I respectfully disagree. Everyone told me I would not see any gain from installing that and wow what a difference. The throttle response and acceleration improvise dramatically. I gained 2 seconds on my 0-60 time. A lot of these things are very relative and going off paper charts makes it sound like it won’t perform well, but at the end of the day the particular inner workings of each engine determine that individuals engines power. Being a 557 block I’m not going crazy and chasing massive power bc this block simply won’t handle it. I would work the heads like u say but imo it’s not worth putting the money into bc at that point, if I’m dropping a 1000 on cast heads I would drop another grand and just buy the aluminum ones. And in all honesty, I’m seriously contemplating doing just that at some point. I believe these will be temporary.

I did purchase a new Melling 60psi oil pump. I am reusing the stock connecting rods, they are currently being resized and checked at the machine shop.


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[steve25]

The way to do it is to build the short block( spend the most funds ) like your where planing on making 500 or more hp from the get go!
Down the road you can then always up grade the top end of the motor for more flow and to kick the compression up a tad.
If the valves in your new 15 heads lap in well then just swap over the springs, keepers and retainers from the other castings.

One thing I would do though with that lift your running is to get them set up for screw in rocker studs and get the guide tops cut for positive valve seals, both intake and exh.
I tried running only .450” lift on two different motors with pressed in studs with poly locks and at around 5400 rpm in one motor I broke off a stud and in the other I pulled a stud out some!
And yes, there was no coil bind taking place and the retainer was not pounding the top of the guide!

[Jay S]

Welcome to PY..

Only thing that sticks out to me is what Steve said on the heads if they are still pressed in bolt neck studs. . Using the 224/234 cam with those lifts is a roll of the dice, could push a stud out and leave you stranded sometime.

Since you had the short block apart, and I assume it is the original 77 bock, did you happen to notice whether there are dowel pins indexing the main caps or roll pins?

Does the car still have the 2.xx highway gears? Be nice to use something closer to a 3.08 or 3.23. More performance gains there than most of the stock type engine internals.

[padgett]

Sorry but the GP was just a few hundred pounds more than a GTO, My 70 (4 speed/AC) was just about 3950 lbs and 72 GP was the same chassis.
Probably had more GPs than anything else, mostly with manual transmissions, last one was a 93 GTP with DOHC 24 valve V6, 5 speed Getrag and AC (sold mainly because had a timing belt and was black).. Great sound.

Think there is a 77 400 (base, not 220 hp) buried in the back garage. Was something about motor mounts were changed but forget exactly what.

[U47]

Originally Posted by padgett

Sorry but the GP was just a few hundred pounds more than a GTO, My 70 (4 speed/AC) was just about 3950 lbs and 72 GP was the same chassis.
Probably had more GPs than anything else, mostly with manual transmissions, last one was a 93 GTP with DOHC 24 valve V6, 5 speed Getrag and AC (sold mainly because had a timing belt and was black).. Great sound.

Think there is a 77 400 (base, not 220 hp) buried in the back garage. Was something about motor mounts were changed but forget exactly what.

Is this about his build or all about you? Just like AACA?

[steve25]

You’ed be surprised what level of power the 557 block can handle if you keep the stroke to the stock 3.750” and lighten up rotational mass some with aftermarket rods!

[hurryinhoosier62]

Originally Posted by steve25

You’ed be surprised what level of power the 557 block can handle if you keep the stroke to the stock 3.750” and lighten up rotational mass some with aftermarket rods!

Tom S will vouch for this. He built one that developed 500+ hp.

[hurryinhoosier62]

Originally Posted by padgett

Sorry but the GP was just a few hundred pounds more than a GTO, My 70 (4 speed/AC) was just about 3950 lbs and 72 GP was the same chassis.
Probably had more GPs than anything else, mostly with manual transmissions, last one was a 93 GTP with DOHC 24 valve V6, 5 speed Getrag and AC (sold mainly because had a timing belt and was black).. Great sound.

Think there is a 77 400 (base, not 220 hp) buried in the back garage. Was something about motor mounts were changed but forget exactly what.

The 5200 lbs GROSS weight stat I quoted came right off the disclaimer tag in the driver’s side door jam. I remember being somewhat baffled as to WHY my GP had nearly the same GROSS weight as my dad’s ‘72 Catalina four door hardtop.

[PunchT37]

Originally Posted by hurryinhoosier62

The 5200 lbs GROSS weight stat I quoted came right off the disclaimer tag in the driver’s side door jam. I remember being somewhat baffled as to WHY my GP had nearly the same GROSS weight as my dad’s ‘72 Catalina four door hardtop.

That`s the GVWR rating. Not curb weight.

[padgett]

Because that is the Gross Vehicle Weight Rating (maximum load), not the curb weight. Here is the one for my 4400 lb Jeep.

[jerry455]

I had a 1977 Can Am, very similar size and weight to your GP. I weighed it at Milan Drag way along time ago and it weighed 4,270 lbs. It had power everything like most GP's of those years. I had a 3.08 axle, which helped it move a little better. The A/G bodies of that time were big and heavy cars.

[hurryinhoosier62]

Originally Posted by jerry455

I had a 1977 Can Am, very similar size and weight to your GP. I weighed it at Milan Drag way along time ago and it weighed 4,270 lbs. It had power everything like most GP's of those years. I had a 3.08 axle, which helped it move a little better. The A/G bodies of that time were big and heavy cars.

My '76 GP certainly was a land yacht. It had 2.21:1 rear gears as I recall. It couldn't accelerate off the line to save its life, but it could cruise at 70mph and still get 20-21 mpg(350P/2bbl/T-400).