corvette_maniac

I know it's not a Vette question, but I value the knowledge on this board. Actually my c3 can't get out of the garage until I get the Firebird out of it's way!

Here's the deal, I have had this 400 for a couple of years with a mystery cam in it. It's very lopey and runs strong....and it only pulls 6hg of vaccum. I pulled the heads off of it because the valve seals were getting hammered. I had the guides ground down and vitons installed to resolve that problem, and while at it my machine guy milled the heads so that I'm at 85cc instead of 98.

That brings me to the present...I am ready to put everything back together, but....after degreeing the mystery cam and getting a 106* ICL, I dialed it to see what's in it...and it's big..probably too bid. It's at 242/246 @ .050 and the lift is .500/.528.

The car is a `79 Firebird and it's got a 3.08 rear with a Borg Warner Super T-10 4 speed. I have headers as well.

Should I go smaller to gain some more low end torque?....something like a 220/230 @ .050 / .455/.470 on a 112 LSA? Keep in mind that I gained a point on the static compression to probably 9.2:1.

What do you guys think?

Thanks

tsw71

I'm not even sure where to start. The gears have to go. The 3.08's will not work well with that cam. Are the heads stock pontiac? The Pontiac heads flow very poorly on the intake side unless you go aftermarket (E-heads, KRE, ect..). What has been done to the shortblock? Pontiac connecting rods are a weak point and will grenade with high RPM, so I would lean towards smaller cam fo that alone. Check out the PY forums. http://216.178.81.108/forums/ This is the pontiac equivilent of the corvette forum. Very helpful folks.

lars

You don't have enough compression to use that cam. Your 85 cc heads are not even getting you into the 9's (you have about 8.9:1 compression with the 85cc chambers). Combine that with the gears you're running, and you do not have a good combo.

The stock Pontiac bottom end will rev reliably through 6000 rpm, but the exhaust ports on the stock heads peeter out at about 5200. If you run a cam that shifts your torque curve to better match that rpm range, you will actually end up with more average horsepower across the usable rpm range, and the car will be quicker overall.

Wrencher

I agree completely with the previous post. I drag-raced Indians for years and you need at least a 3.70 gear to take advantage of the torque they produce, yet still not run out of breath at the top end. I like your idea on the cam, but don't go any less. For some reason, I had great success with Sig Erson cams in my Pontiacs. I ran a '64 GTO into the 12's through stock iron intake and exhaust manifolds with some port work and the afor-mentioned 3.70's..

Hans

corvette_maniac

The heads are stock heads.....6x-4s. They also have been ported.
The CR should be closer to 9.2:1 as the block as been 0 decked.

I am a member of the PY forums and have gotten advice there as well.

Would the summit 2801 be to small for that combo?

ajrothm

Hey bro...I have a lot of experience with old school pontiac 400s. The absolute best cam for a stock type head(ported ofcourse) with a CR or 10-1 or so is something ground to this spec. I used to always run Ultradyne cams in my pontiacs but they went out of business. I am sure comp will grind it for you though.

It was a hyd flat tappet, 288/296 adv, 231/239 dur @.050, .485/.507 lift on a 110 LSA. The cam sounds great, makes good power starting at 3500 and pulls good to 6200rpms(at least with the lightly worked heads I had)

I had this cam in a .030 400 with TRW L2262F pistons, 1969 #16 heads with 72cc and light pocket port and bowl work. Torquer II intakes work awesome on pontiacs, especially with a 1" 4 hole space(that combo is MUCH stronger all the way through the powerband then a Performer RPM). Holley 750Dp, hooker small tube 1 5/8" headers and a curved distributor and we estimated it at 450 crank HP. Never dynoed, only ran at the strip a lot.

In a 3700lb 78' TA, this combo would run 12.00-12.10s with a 2800-3200 stall speed converter and a 3.42 gear. It would leave hard, 60' LOW 1.60s. Would only run about 108-109mph on the back half but...I think the converter was slipping too much on the back half.

Pontiacs do not work well with big cams with a lot of duration unless you have some seriously worked heads, stock type or edelbrocks. Then the problem is the cast rods don't like anything over 6k rpms so you have to becareful there or put Eagles in it. I would not run that 240+ duration cam unless you are doing some serious headwork.

On my 400, we tried a SOLID FLAT Ultradyne that one of the big pontiac gurus recommended. We did some more headwork, went to a 3.90 gear and freshed the motor. The cam was 255/260*@.050 and .540/.556 lift. I could not ever get the car to match what it would run with the small hyd flat cam and taller gears. Never got it under 12.40s@106 with the new hardware. It just wasn't setup right.

ajrothm

Wrencher, I too had decent luck with Sig Erson cams in pontiacs.
Corvette Maniac, I too had that same Ultradyne flat tappet (288/296) in my 400 with 6X heads for a while. It was the same shortblock from up above but I lower stuck the 6x heads on it to sell the car. They were lightly ported and milled .030. I don't even think the compression was 9-1, prolly more like 8.75 or so. A stock 77-79 pontiac 400 is only 7.7-1 compression unless it was a WS6 car with the TA 6.6 motor, those had 8.1-1. Mine was the base motor so I had to change the pistons to get anything in the high 8s-1 with 86 cc heads(milled .030)

Even running that same cam with the crappy flowing 6x heads and 8.75-1 CR, the car still ran 12.80s NA and I put a 175hp shot on it. It HAULED A$$ on the juice but with the 3.90s I put in the rear, it ran out of gear quick.

If you stay 3.08s, stay with the cam you thought about, if you change gears, got to a 3.42-3.73 MAX... Pontiacs don't like a lot of gear. You gotta use that torque.

1971 #96 heads are good street heads. They flow well and are like 84cc I think. They will get you around 9.5-1 on a .030 400 with the felpro head gasket(perma-torque). I used these heads on another mild street build that ran 12.40s in another 78 TA.

corvette_maniac

Hey...thanks a lot guys! I guess I know what I'll be doing next weekend.

corvette_maniac

What do you guys think about this cam for my combo...the CompCam XE268H?

The specs are :
224/230 @ .050
.477/.480 / 110

I'm about to order it.

redc3

i dont know, i kinda agree with lars here ( for once haha ). for some reason, we always put ponts in our chevys growing up, my step father loved the combo. we always gouged the hell out of the exhaust side and the stock heads worked fine. as long as you can find the forged stuff, the bottom end would always take anything we would throw at it. we had more problems with yanking pinions out of rear end housings. stick with the cam, and port or change the heads.

ajrothm

That cam you posted will work well in a stock head, low compression motor with highway gears and a 4spd. Definetly don't go any larger then that. You may shop around and see if you can find some thin, MLS headgaskets for it to help raise the compression. You really want at least 9.5-1.

The original Pontiac 068 was a good cam also. It was tiny in comparision to the new style cams but I am telling you they work. I did a 455 for a GTO, it had #96 heads on it,(around 10-1 comp) stock unported, pontiac 068 cam w 1.65 roller rockers, Torquer II intake and no spacer, 750 DP and it ran 12.30s in a heavy 67 GTO with a 2500 stall and a 3.31 gear.

myblackC5

go with a 212 218 cam, 400 have lots of torq. the valves are real close to the pistons. the one you mentioned would be the biggest i would go with your gears for street use. or you cam and 355's.........what T10..some have the 288 first which would help. good luck pontiacs rock, sometimes i think GM stoped building the wrong engine.

redc3

ill tell you a true story.
my step brother had the same 69 gto my step father drove, while we were growing up. when i turned 19, i got a loan for 4 grand and bought it from him. we had installed a 455, and the only thing done to it was a massive cam, bored out, and headers. it was a four speed car. on the day i bought it, my step brother was showing my how to drive it.
to make my long story short, when the front wheels came back down and he shifted into second, the rear pinion shot out of the car and we all just set there, not knowing what to say! in true fashion i said, " ill take it! " just a nice story i thought some would appreciate

corvette_maniac

That's a great story, redc3.

Hey....I replaced that cam today this is what was in it!! :

HIT-302-2-NC
246/254 @ .050
302/310 adv. dur.
116 lobe centerline
.512/530 valve lift 1.5 rockers
Cam Part Number 284571
3500-7000 Basic RPM Range

"HYDRAULIC - Rough idle, Performance Usage, Good Upper RPM HP. Increased Compression Ratio Required"


Well that explains a lot. I only had 6 hg of vaccum at idle. My initial timing was 20 + degrees for it to idle right. The 6x heads were stock and CCed at 98 so I would have been lucky to have had 8.2:1. The car was surgy as all get out at part throttle. The valve seals were hammered to heck and back....as there had been no machining for retainer to guide clearance and the springs were stock.....no doubt coil binding. grrrrrr......the guy who build the engine apparantley missed some things....such as OVER-CAMMING IT!!! The 116 * LSA would have been the last thing that engine needed as it had low compression.

I have mixed emotions. Very glad to know this info, because it explains so much now. On the other hand, unhappy with the carelessness of the engine builder in choosing the cam.

At least know that I'm doing it myself and doing it right. I pulled the heads and had them totally redone. My compression with also be a point higher. The 224/230 110 cam ought to be sweet.

Jamie

cerino2000

The XE 268 that you thought of is exactly what I was going to suggest. With the 6x-4's, your pretty good on the compression and should be fine. I gotta tell ya, those XE series cams are impressive. I had the next one up from what you are using in my 455 and it was the strongest 455 I ever put together. Lots of fun.

corvette_maniac

What did you have, the XE 274? I bet that was a stump puller.

I'm anxious to see what the smaller cam is going to do with the higher compression that I now have; 9.2:1...and the 110 LSA building cylinder pressure. The other cam was bleeding it away which was the last thing that I needed in an 8.2:1 engine. I had .065" shaved off of those heads to reduce the ccs to 85 and the block is 0 decked. It's gonna be great to hopefully see all of those above mentioned problems go away.

cerino2000

Yes, I had the 274 and with a 455, 6x-4's, and the 274 cam I was burning the tires in the TA from a dead stop with 2.41 differential! You should have seen the grin on my face the first time i tried it.

corvette_maniac

I broke the cam in yesterday. All went well. I still need to tune it. That's gonna be the fun part!!

Here's what it sounds like: http://heathpenguin.homelinux.net/firebird/XE268.wav

What do you think?

cerino2000

Wow! Very comparable to what mine sounded like. Here's a vid of mine:

Right Click and then Save Target As

corvette_maniac

Cerino2000,

That's just wicked sounding!

I tuned mine yesterday only to find that it had pre-detonation problems. I backed the timing down.....at work...so I didn't have my light with me. It still pre-detonated a little driving home last night. I believe that the distributor springs that I have in there are a little light - in the order of total timing at 2200. Gonna put some stonger springs in there. It ran strong though.