[Gusto80]

I have recently rebuilt the 1968 428 engine in my 64 GP as it was a bit tired. .030 over bore, I believe XE274H cam from memory, new valves etc. It's the 16 heads (72cc) with large valves. 3:08 open diff, T10 4 speed, Msd.

It runs really good, and from memory 370hp and 490tq on the dyno.

I have however picked up a heap of parts for it including the following which I'm contemplating trying to get a bit more power out of it.

*set of hooker headers (will pair with new 2.5" exhaust too)
*Tri-power
*New Edelbrock 61599 heads (for flat tappet cam)
*Posi (9.3") 3:73 I believe
*Super T-10 4 speed

What if any (or probably all) of these parts should I switch out? And will I get significant power gains? The alloy heads I'm assuming will yield the best results, although I already had the factory 72cc ones. Do I port the alloy ones? And what sort of gains should I expect? Do I port the tri-power manifold?

Also, I'm running 8-lugs with associated drum brakes and factory master cylinder and power brakes.. what would you suggest i do to make it stop a bit better? And should I go to a dual master cylinder? Has anyone widened the rear wheels but retained the 8-lug?

Any advice greatly appreciated.

Many thanks.

[tom s]

If you going to street drive it ,nix the headers and get Longbranch exhaust.A 5 speed OD would be my choice IF you think you need a new trans.Posi won’t show any HP gain on the street but will help in inclement weather condition.better flowing heads with a better cam will gain you some HP.If you want a dual master deal with someone that has done them and will give you a unconditional guarantee they will work correctly.Had a friend do a 62 Grand Prix and virtually almost went too the windshield on first use.Don’t waste money on the porting.If me I would use the KRE Dports.Good luck with your project.Tom

[Cliff R]

I've built several street 428 engines here, one of them used KRE aluminum "D" port heads with 74cc chambers and flat top pistons. I did not port the heads other than a simple gasket match to a stock Felpro intake gasket.

I had a custom ground HR cam done for it with 236/242 @ @.050, .361" lobes and added Crower 1.6 ratio Enduro roller rocker arms". Topped with my 1971 cast iron intake and 1977 Pontiac q-jet it made 497hp/540tq on the dyno. 12" vacuum at 750rpms with 10 degrees initial timing. That engine has been out there close to 20 years now and I still talk to the owner on occasion and he loves it. It's in a 64 GTO backed by a manual transmission and 3.73 gears.

I really see no need to port the heads or intake unless you plan on putting a lot of cam in it and trying to make well over 500hp..........

[Gusto80]

Will swapping the 16 cast heads for the alloy edelbrock (both 72cc) and the Holly 750 DP for the Tri-power and then swapping my long branch for the new headers give me any noticeable HP gains? I'm around 370 at the moment. I've only just put this new Cam in it recently, will that suffice? I was told it was the cam to go for by several people.

Thank you

[Gusto80]

Current intake is a edelbrock p4p with the Holly 750 DP manual secondaries

[Cliff R]

The heads bring the most to the table, not so much for the other items. Even with that said adding a little power in quite a few places adds up quickly to a LOT more power.

370HP seems pretty low to me with #16 heads and a cam with 230 @ .050" specs. As much as I dislike that line of cams it still should have made over 400hp with the current combination of parts. 428's are excellent engines, and will make great power, rivaling the power of the 455's with about the same parts used. They do however like to rev and favor larger camshafts.

Even the one I built here with unported KRE heads was pretty much done at 5600rpm's using a LOT more cam than a Comp XE274 grind........

[Gusto80]

Thanks, should I put a bigger cam in it while I have the heads off? Do you have one you recommend?

Thanks again

[Cliff R]

Are you doing all this with the engine still in the car?.....

[Gusto80]

Ideally yeah. Just totally rebuilt the whole engine only 500miles ago. And had no plans to change anything untill this bundle of parts was offered to me really cheap. I note the edelbrock head (61599) is setup for flat tappet cam

[61-63]

If you really want to upgrade the power forget the tripower and put a pair of AFBs on an offy medium rise dual quad intake on it. The afbs are more reliable, better engineered than the rochester 2 bbls were, and will give you more power.

[Keith Seymore]

Originally Posted by Gusto80

And should I go to a dual master cylinder?

Yes!

Originally Posted by Gusto80

Has anyone widened the rear wheels but retained the 8-lug?

Not 8 lug rims specifically, but I have widened a number of steel wheels myself and don't see any problem in doing so.

Are you thinking to keep the offset the same (adding material to both front and back) or add all to one side (back)?

What size tire?

Originally Posted by Gusto80

and then swapping my long branch for the new headers

If you ditch those long branch manifolds I would be interested in them and the associated hardware.

K

[25stevem]

In your 3rd paragraph you state that you would like a bit more power, so what to you is a bit more power, 25, 45?

What connecting rods are in the motor now?
If they are stock have the been up graded with aftermarket bolts and then resized as needed?

The factory power numbers of 390 hp for the top of the line 428s was a bit glorified!

These motors came with no more then a 068 Cam and even the RA4 motor with bigger better flowing heads and a bigger Cam where only rated at 370 hp.

That 370 hp rating has been proven to be correct in subsequent times.

[Cliff R]

Doing that much work over the fenders isn't much fun. Far better to pull the engine if you plan on going that far into it.....IMHO.

In either case I'm not sure what's out there these days with COVID and the fact I got out of the engine building business 4 years ago. Most of the cams I used in the last 10 years doing them were custom ground and most of those were Hydraulic Roller grinds.......

[64gp4spd]

I have a 64 GP with 455, 310cfm Kauffman Heads, 11:1 compression Hydraulic Roller 236/245 with 1.65 Rockers.
It is a 4 speed manual with 4:10 gears. For a big car it runs like a beast.
Have 12-13 inches of vacuum with this cam with an almost smooth idle.
in the process of installing a Tremec TKX 5 Speed. You will need to do a
bit of work on the tunnel to clear the shifter mount on top of the TKX transmission
if you decide to go that way. Just my 2 cents

[64gp4spd]

Hi, regarding the 8 lug Wheels I did buy a set of 15X8 from BOP Racing.
They have 4.25 backspacing and I use 275/60/15 Drag Radials.
15X7 on the front with same back spacing and 225/70/15 tires
Also, i have manual brakes and switched to a 1967-68 Full Size
Pontiac Dual Master Cylinder. Worked out great.