[Tony69]

Hi guys, this has been bugging me for some time, going round in circles here. I've narrowed it down to three cams but I want to here from you.

So I've got a 400ci, with #13 heads cc'd at 75cc after milling. I've built a solid bottom end with forged rods etc. but the rest is pretty much stock for now. Stock, intake, stock exhaust & stock quadrajet. Will upgrade later.

With 10.8cc flat top 0.040" pistons & 0.015" deck hieght, I will get a compression ratio of 9.5:1. If I zero deck it, my compression will be just on 9.8:1. I will need to be able to run 87 to 89 gas.

The rest of the car is pretty much stock, th350 with stock convertor & 2.73 rear.
I am at an altitude of around 5330 ft if that matters.


So here's the big question.... 9.5:1cr on 87 to 89 gas...What cam?

.........and 9.8:1cr on 87 to 89 gas...What cam?

Detonation gives me very bad nightmares

[72LuxuryLeMansLa.]

Originally Posted by Tony69

Hi guys, this has been bugging me for some time, going round in circles here. I've narrowed it down to three cams but I want to here from you.

So I've got a 400ci, with #13 heads cc'd at 75cc after milling. I've built a solid bottom end with forged rods etc. but the rest is pretty much stock for now. Stock, intake, stock exhaust & stock quadrajet. Will upgrade later.

With 10.8cc flat top 0.040" pistons & 0.015" deck hieght, I will get a compression ratio of 9.5:1. If I zero deck it, my compression will be just on 9.8:1. I will need to be able to run 87 to 89 gas.

The rest of the car is pretty much stock, th350 with stock convertor & 2.73 rear.
I am at an altitude of around 5330 ft if that matters.


So here's the big question.... 9.5:1cr on 87 to 89 gas...What cam?

.........and 9.8:1cr on 87 to 89 gas...What cam?

Detonation gives me very bad nightmares

Let me start off by saying that I am Not An Expert by any means, just a half-a$$ed intelligent man that has spent the last three years reading everything I can get my hands on regarding building Pontiac Engines for the street.
Maybe it is because of your location or budget but I personally would order some Dished (D-Shape) forged pistons to allow me to zero that deck and get the compression into a usable range for the fuel that you guys have available to you in S.Africa. According to Jim Hand zero decking "...allows more compression to be used with the same quality of gas due to superior air/fuel mixing during compression." this along with the proper cam, cooling system, and ignition timing should help you to avoid detonation.

Karl

[Tony69]

Karl, thanks for your input
I agree fully, buts its a bit too late for that as I have already purchased the flat tops with 10.8cc.

There's gotta be a few cams I can run on 89 with 9.8:1cr for street use?

[68 Firebird]

In my 68 Firebird I went with the old reliable Melling SPC-7 which is an
exact 068 cam.(wanted a wide LSA) I looked at it as a part of the complete drivetrain recipe. I was looking for a cam that was compatible with my existing motor.

I am running the original 16 heads, trw forged pistons and a Cliff setup Q-jet on a
68 factory iron intake. This is going thru a T400 with stock stall and original 3:08 rear gears. The HEI was a great addition as well.

Some may say it's too docile but I like the great street manners(great idle) and the performance.(she will move nicely!!!!!)

I run 93 octane and have zero pinging and detonation.

Actually got home from work early today and took it for a LONG afternoon ride!!!!!

Choose the cam to fit what you want and works best with compression level.

Good Luck

Gerry C.

[Tony69]

Thanks Gerry, the 068 cam is one of the three cams that made my list. Your comments are reassuring that the 068 is a good choice. I'm just not sure about the compression & octane levels I have. Youre running 93... I'll be running 89 at best.
What is your static compression?

thanks for the info

[68 Firebird]

Well according to the books it's 10.75 but I would bet it is closer to
10.25. When I had the lower end redone I did not have block decked as
it was very close as it was. But are below deck, the trw L2262F slugs were not dished.

IIRC cranking pressure is 175 to 180 cold. I have run 89 octane and just felt
that 92-93 was good insurance. Getting the correct ignition and fuel curve
are what made it all work together. the carb is spot on and I love the elec
choke. and after trying different HEI springs I found the Heavy ones from
the recurve kit along with factory center cam and weights worked best.

I am running 12 initial and 20 mechanical all in by around 3200rpm.
also hace 12 degrees in vac can from ported source. 17" of vacuum at idle.
dead stable idle in and out of gear with a 150 rpm drop in gear.(650 rpm)


I think there was a cam from crower i was also considering. I think it was
a high lift version of the 068.

Gerry C

[Tony69]

Thanks Gerry, very informative!
The cam from Crower you mention...if its the 60918, also one of my 3 choices...but I think I'd be more likely to detonate with that cam, i dont know....

here are the specs for the crower 60918

214/224 @ 0.050"...288/298 adv...& 112 LSA.
0.444"/0.464" Lift

[tekheavy]

I just installed the Melling SPC-7 in my GTO last week. The car is completely stock. Was toying with going with the Summit 2801, but decided on the Melling because the lift was equal to the stock cam lift and I was still using most of my stock valve train. Car has 16 heads which I believe to be untouched giving me close to 10.75 compression. I use 93 pump gas with no detonation with an initial timing as high as 16btdc.

[68 Firebird]

yeah i agree on not wanting any detonation. That's partly why I went with the

068. nice wide LSA to reduce dynamic compression and detonation.

Pontiac engineers knew a thing or two!!!!

[Tony69]

ok...so I'm settled on the 068!!

Now, there are 3 manufacturers to choose from: Crane, Melling & Howards.


Howards-----> .408/.408 lift ----288/302 adv---- 212/225 @0.050"----115 lsa $110
Melling-------> .408/.406 lift----285/298 adv-----212/225 @0.050"----115.5 lsa $144
Crane-------> .408/.407 lift-----unknown--------212/225 @0.050"----115.5 lsa $157

I dont know why Crane doesnt give the advertised duration. These are the specs direct from the respective website. I know Melling made the original factory cam, but the factory specs known to me are:

.408/.407--------288/302------212/225-----115.5

At a glance, the Howards cam looks good enough & considering the price difference, I think the Howards is a good choice. Also, I havent heard anything bad about Howards cams.

Any thoughts?

[Tony69]

Just to confirm...

will the crower 68404 valve springs work well with the 068 cam?

How about the comp magnum 1.5 roller tip rockers with 7/16 studs & poly-locks?

I know these wont fit under stock valve covers... so what can I use that will?

[salem1912]

I also went with the Melling SPC-7. I haven't had time to fine tune the car as it's held hostage in the body shop since the stock rebuild. I do like the idle,but I have low vacuum to run the new power brake booster. I hope to get this fixed once the car comes back.

[74Grandville]

I would go the next step up on cam, like a 2802. 224/234. Zero deck the block and remove any sharp edges in the chamber/piston.

Make sure to tune the carb and distributor correctly for the combo.

Detonation is not fun.

[74Grandville]

Originally Posted by 74Grandville

I would go the next step up on cam, like a 2802. 224/234. Zero deck the block and remove any sharp edges in the chamber/piston.

Make sure to tune the carb and distributor correctly for the combo.

Detonation is not fun.

just re-read your post of stock converter and 2.73 rear. I chose this cam on your compression. you would probably want to give it a little gear and converter if you went with the 2802.

[77 TRASHCAN]

I asked similar question some time back. Crower 60243 is close to Summit 2802

[Tony69]

2802 looks like a really good cam, especially the price tag

I've decided that I dont want to jump the gun & go for a faster ramp, higher lift cam just yet, but I want to set up my valve train etc. to accept such a cam later on but still run the 068 just fine for now.

I've never ran a 068 cam before so I want to experience it, so later on I can compare other cams to it.

[77Y82W72]

Originally Posted by Tony69

ok...so I'm settled on the 068!!

Now, there are 3 manufacturers to choose from: Crane, Melling & Howards.


Howards-----> .408/.408 lift ----288/302 adv---- 212/225 @0.050"----115 lsa $110
Melling-------> .408/.406 lift----285/298 adv-----212/225 @0.050"----115.5 lsa $144
Crane-------> .408/.407 lift-----unknown--------212/225 @0.050"----115.5 lsa $157

I dont know why Crane doesnt give the advertised duration. These are the specs direct from the respective website. I know Melling made the original factory cam, but the factory specs known to me are:

.408/.407--------288/302------212/225-----115.5


Any thoughts?

Tony, not sure if you've purchased a cam yet, but I picked up a Melling SPC-7 (the actual 068) from Autozone for $106 USD last week. Cheapest I've seen, including all the big box internet retailers.

[72blackbird]

Tony,
You're in the 9.5-10:1 SCR range- I don't think a cam alone is going to let you run 89, let alone 87 octane, with your current set up. I have a 406 with ported no. 48's and a Crane 284H (284 adv. dur., 228 dur.@ .050, .480" lift, 112LSA) in my Bird- my chambers and valve reliefs are smoothed out and have no sharp edges. I have to run 91 octane or my engine will ping. I chose this cam years ago when I built this engine, but if I had to pick another cam I would be running either a Summit 2802 or Crane 283952.

The 068 will help reduce your dynamic compression, but will it work on 89? Once you start detonating your bearings will get hammered and your oil pressure will be gone in no time. You'll need to reduce compression to run 87-89 octane, and that means you'll need to swap heads.

Geno

[mechanic17]

The 041 straight up or retarded just might get you to where you want to be, engine-wise, but as someone else said, anything that gets you there will require a lot more gear and some converter.

I believe Karl is right about the pistons--however, as an alternative you could get some careful chamber work done on the heads, unshrouding both the intake and exhaust valves, and taking out several ccs in the process. You might contact Dave at SD to see if he thinks this is workable.