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Cam choice for Pontiac 400 build

14K views 24 replies 5 participants last post by  LATECH 
#1 ·
Hi all. I'm in the process of rebuilding the Pontiac 400 out of my '78 Trans Am, and I'm kinda wondering which cam I should go with? This is/was a budget build, so I would like to use one of the cams that I have on hand already if possible. Specs are listed below, but I've got a Summit K2801, a Summit K2802, and a Crane Energizer 105082 (284 H12) available. As far as what my goal would be performance wise, well I don't feel the need for excessive power. Previously the engine dyno'd at 230 hp/300-ish tq at the wheels and had a best 1/4 of 14.25 (I'm not the best off-the-line). I'd like to do better than that, but I don't want to sacrifice streetability with an excessively high idle to keep vacuum levels up (I had idle set at 750-ish RPM with a Holley 650 before). If it's got a lope then great, but I'm not gonna choose on lope alone.

Car specs:
1978 W72 Trans Am. Original 400 engine, ST-10 4spd manual, 3.42 posi rear. I am in the process of swapping in a t56 6spd manual trans as well.

Engine specs:
W72 400 block (not the weaker 557 block), bored 60-over. Stock crank (turned 30/30) and rods, cast pistons, stock-style cast iron rings. Stock 6x-4 heads that I am in the process of cleaning up the ports/runners/bowls and will get a 3-angle valve job when finished. Screw-in BBC 7/16" studs with locks to replace stock non-adjustable studs. Stock springs, pushrods, and rockers. Stock 8.1-ish compression I believe.

Bolt-on's: Performer Pontiac aluminum intake with rebuild Q-jet. Tri-Y longtube headers into true dual 2.5" exhaust dumping after the axle.

Camshafts that I already have:
Summit K2801:
Int dur @ 0.050: 214, Ext dur @ 0.050: 224
Int lift w/1.5 rockers: 0.444", Ext lift w/1.5 rockers: 0.466
LSA: 112 deg. RPM range: 1,800 - 5,000

Summit K2802:
Int dur @ 0.050: 224, Ext dur @ 0.050: 234
Int lift w/1.5 rockers: 0.466", Ext lift w/1.5 rockers: 0.488"
LSA: 114 deg. RPM range: 2,200 - 5,500

Crane Cams Energizer 105082:
Int dur @ 0.050: 228, Ext dur @ 0.050: 228
Int lift w/1.5 rockers: 0.480", Ext lift w/1.5 rockers: 0.480"
LSA: 112. RPM range: 3,000 - 6,000

Thanks for any guidance you can offer!
 
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#2 ·
Of those three, I think the K2802.

if those three are all used cams, and they aren't going back in the same block they were originally used in, and with the lifters back on the exact same cam lobe they were on original....then trash can the whole batch.

Used cams in another block and/or mixed up lifters is begging for early catastrophic lifter or cam lobe failure, and a mess to clean out inside the engine.
 
#3 ·
Nope, they're all new. Or at least never even been installed/out of the box. I had picked up the Summit cams a couple years ago (scope creep), and a friend gave me the Crane cam after his project went south. Also a couple years ago.

I do know that the low CR is probably the limiting factor here. I had been considering the Crane cam, until I read that it likes a higher CR than what I've currently got (hence the question here).
 
#4 ·
From what I have done with these Pontiac's with either an OEM head or the Eddy head a reverse split cam works the best; more duration on the intake then exhaust.

I'm doing a 400 for a customer in NC with a 78' TA. Cam is as follows with his ported heads:
.608/.590
236/228 .050
108 LSA

I've done about 30 of these now. All the customers are very happy.
 
#5 · (Edited)
Stock 8.1-ish compression I believe.
Is there ANY way you can do yourself an enormous favor and bring that compression ratio (prolly actually in the 7's) up around at least 9.5:1 ?!?!?

Those cams are all going to be ranging from mushy to horrible with that stock compression ratio !!! You want a snappy engine... and better MPG...

I'm talking getting you from the low 14's into the mid 13's or even high 12's where you belong... 20 MPG...
 
#6 ·
Unfortunately not easily. I've finally got the short block assembled, so decking the block would be a real pain, and I can't afford aftermarket heads either (taken too long just to get to this point). Best I can do is have the heads milled some, although I'm not sure how much could be taken off.

It ran well before I tore it apart for a rod knock. Seasoned racers said it was a 13 second car, but obviously I wasn't/am not a 13 second driver.

I've seen people suggest Comp's XE268H cam too (224/230 @ 0.050, 110 LSA, 1,600 - 5,800 RPM), which I could justify a lot easier than new heads.
 
#11 ·
Unfortunately no. I might have something buried in my notes somewhere, but this rebuild started maybe 7 years ago, so that info might be lost to time. I remember trying to look up the part number on the back of the cam, but don't recall anything specific. It probably wasn't too wild since it used the stock non-adjust valvetrain.

I'll check and see if I have any notes or pics from the teardown later tonight.
 
#12 · (Edited)
Well, looks like I do still have the rebuild info - found a pic of the cam that was previously in this 400. Unfortunately I haven't had much more luck finding any information as when I first tore into it (pic was dated Sept 2010, so almost a full 7 years since teardown).

Anyway, looks like it was a Reed cam. Two numbers stamped on it are "G8024" and "TM280HDP". Maybe one of you might have better luck deciphering it.

Edit: and here's the dyno sheet of said Reed cam. The blue lines (223hp/310tq) were through a full exhaust, while the red lines (239hp/323tq) were through the muffler cutouts.
 

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#14 ·
First, you should deck the block to zero.Period.Take out the slugs and crank and do it.
If you have the 8 valve relief pistons, dump those.They suck.

You will need to mill.065 of the 6X-4 heads to get the Static CR close to 8.8 to one,(as the advertised chamber size is 101 CC ) which you will need for either one of your cams , and the Static CR still comes up a tad short, IMHO.

I had.040 milled off mine and I am sure there was .010 milled before I got them .You should CC them to be sure where they are (size wise ( CC's))
They are pretty beefy , so mill away. Just remember the margin at the sides where the valley pan is mated to the heads disappears when you mill , and you need to mill the intake side of the heads so you can run any intake you want whenever you want.

Having what you have, if it were mine ,I would get some aluminum heads for it and do the math for your compression ratio / chamber size so you can get it up high enough to run the cams you have.
 
#15 ·
Thanks, StraubTech! I always wondered what specs that cam had.

As far as zero decking and new pistons, I've got a budget to keep in mind and can't justify that with everything else that still needs to be done. Obviously aluminum heads are not possible, either. I can deck the heads at least, and get a different cam if I sell the ones I've got, but the CR is what it is. I know it's a crappy combo and won't be as effecient/ideal as possible, but it's what I've got to work with. If I wanted to wait longer then maybe, but it has taken this long already and I actually have the desire to work on it. Something which has been seriously lacking in the past.

I guess I can always take advantage of the low compression and go forced induction somewhere down the line if I feel like it, but that's not in the cards right now, either.
 
#16 · (Edited)
I wouldn't spend a $1,000 doing all that butchering/milling on a getting rare genuine Pontiac block and heads... I'd go custom pistons for less or use the new mini-dome pistons for Pontiacs that KB came out with a year or two ago...

As expected of a 227/227 cam, the dyno chart shows the engine doesn't want to start pulling hard until 2800 RPMs...

And it's also obvious from the dyno chart that the low compression ratio causes the engine's HP curve to go FLAT at a mere 4100 RPMs... yet that fine 227/227 Reed cam wanted the HP curve to continue rising until 5500 - 6000 RPMs... shifting at 6200 - 6400 RPMs...

Need a high rise Performer RPM or other brand of higher performance aluminum intake if have the hood clearance... the standard Performers die at about the same RPMs as a base level stock intake...
 
#17 ·
1978 400s arent Rare.421 SD engines are RARE.

Any performance build requires machine work.
Reffering to it as "butchering " is misguided at the very least.

Take a look at my build in my photo journal.

1965 389 punched to 400.Balanced.forged pistons ,rods.
pontiac heads milled .040 = thou

Crane cam 218/226 @ .050

Its a beast.

I have a spare 400 block and heads and I know where there are plenty more.
 
#22 · (Edited)
1978 400s aren't Rare. I have a spare 400 block and heads and I know where there are plenty more.
LATech will prolly sell you a Pontiac short block for $50 and a pair of heads for $50 since they're a dime a dozen...

Your current intake manifold may be a bit of a raised design...

I recall the '64 GTO 348 HP tripower intake was a low flat integrated design and then my '65 360 HP tripower intake was a higher rise airgap design... but I don't recall just what they did with the 4 bbl. intakes... I think my '65 also had like a central 'power bulge' ridge in the hood with a scoop that could be opened up to make a ramair... and to clear the higher air cleaners...

I think my '65 also had a stock 214/214 'S' cam... I bought it used a couple years old and we thought maybe the engine was junk because of the rough, lurchy idle in 1st with the 4 speed manual... until i floored it... and the engine tripower with 3 unsilenced air cleaners squalled, the rear tires went up in a cloud of smoke, and the car started spinning in a circle... my brother and I never forgot that... before those days, cars just didn't do that...
 
#18 ·
I'm looking into things a bit more right now. Yea, I want to get the build done and on the road, but I also know it's better to build it correctly the first time instead of redoing it all over again.

I wasn't planning on decking the block because it's the original numbers-matching engine, and decking it would remove those numbers. Probably gonna go ahead and get it done though. What I should have done is stick this engine on the shelf and build a different one, but c'est la vie. Little late for that now.

I'm gonna stick with this intake for now because it fits under the shaker scoop. Going to the RPM intake will also require a drop base air cleaner, but at least the intake is an easy replacement.
 
#20 ·
I could've sworn that there was a 5 or 6-digit number stamped into a small boss on the front of the passenger side deck surface, in front of the head which matched the VIN. I just checked and that spot exists, but no more numbers... I do remember it was there when I first bought the car...

Nevermind. I see it now on the front passenger side by the timing cover. Don't mind me, I'm apparently going insane over here :drunk:
 
#23 ·
Well........ They aint that cheap, but what is?

I am not looking to sell anything, but there are places where one can source them. There are a few laying around here.Not a rare item by any means.

BTW....first year for a GTO with tri power was 65. If you had a tri power 64 gto, the setup probably came off of a 64 or earlier B body
 
#25 ·
Local guy has a whole car that had the engine replace many years ago. Has been setting in his field for years.It should have a 350 in it, but he said that the engine went bad years ago and someone put a 455 in it.
He offered it to me for scrapping a few cars for him

I dont need the engine or the extra work
 
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