Last fall I dropped a 396 into my 72 Chevelle, got the timing set up, drove it and everything seemed fine except that it just doesn't pull as hard as I would have expected. We set the timing at 14 deg. initial and I beleive about 36 deg. total at 3000 rpm. Off the line I don't expect much because of the motors power band but in first gear around 3000 I would expect it to scream.

The car only has 3.08 non posi rear, does need a higher stall converter, and well the exhaust is an old off the shelf system with stock mufflers.

My plan is to change the rear to 3.55 posi and likley this will be the only change I can afford to make this year.

My question is will gears make a big difference? I've read that guys like Mr. 4 Speed are running highway gears yet pulling times of 12.99 ?

I'be owned GTO's in the past that had tons of power with stock motors and exhaust, but they had 3.55 gears.

My combo is as follows:
396 - 30 over domed pistons
oval port - 112 cc heads
cam - 280 dur, 525 lift
edelbrock RPM, with edel 750

Is there something I'm missing or are the tall gears the problem ?

Thanks for any input.

I run 3.08's in my wagon and it halls a lot of lower lumbar. I know that changing exhaust system will gain you power. I also have a 454 bored 30 over in the wagon. It also depends on what else is in and on the motor.

Try bumping the base timing up to 18-20*
A friend of mine has a 69 SS396 Chevelle,has a mild cam,11" 2500 stall,3.08 12 bolt posi and has run a best so far of a 14.42/94 MPH with a 2.24 60 ft. But,it only has a Holley 600 vacuum secondary carb,and he's running a Performer intake.We're figuring with a 750 vacuum Holley and say, a 2.0X 60 ft. it'll get into the high 13's,may be 13.80's
Traction and a convertor are a must.
IMHO and experience,with a 4000# car,a mild 396 in its current state of tune/build w/3.08 gears high 13's is certainly and reasonably obtainable..And yes,I have run a best of a 12.99 with my mild 454 and 2.73's in street trim.I'm expecting high 12.8X's/low 12.9X next time out with traction graemlins/thumbsup.gif

Off the shelf stock exhaust??? Do you have headers on it??? Old stock exhaust systems are very restrictive,I'd opt for 3" pipe x or H pipe and straight thru mufflers,like Dynomax

FYI,my friends 69 SS has Dynomax headers,Summit mufflers,and the Flowmaster 2.5" exhaust kit.And,for what its worth,the seat of the pants dyno feels good in his car,even with the 600 cfm carb :D

I am running headers, but the pipes are likley 2 1/8" dia. with stock mufflers. Not great.

I'll try upping the timing, when the car comes out this week. Any other thoughts ?

Well, I know what a stock 396 feels like through a Muncie and 3.08s, and it isn't much, but its not bad. Low 14's kinda stuff if I was to guess.

Chris' car turns that 2,73 cog so nice due to obscene cylinder pressure. Well, pump gas friendly, but big cylinder pressure at a relatively low rpm = TORQUE. So, if it isnt a tuning issue,i.e not enough timing or jetting is off ( or both), then you might look deeper into that 280 cam and your compression.

With a 396 you have to have BIG domes to get compression, even with a relatively small 112 cc heads. EG, 427 domes are around .250-.275" high and only net out around 10.5:1 with 112.5cc. Now that's a big bigger bore, but you get my drift.

How domed are they? and what EXACTLY are the spec's on that cam? Again, issues only if simple tuning doesn't help. But for the record, a GOOD cam for a stock 396, 3.08 geared, small exhaust, assuming small valves and around 10:1, would be in the 210-215@.050 range on a tight 110 or smller LSA. Gives you maybe 5200 rpm capability, but quick peak torque at 2500 rpms or so falling off quickly at 4500 -5000.

Again, only relevant if you have 9.5:1 compression and a 280 hydraulic cam on a 114 LSA. Then, I believe, the issue is cylinder pressure. Again, using Chris's experience, quickest ETs with 3.08s mean the motor isnt really turing much above 5000 rpm, and crossing the stripe at 4000!

Also, in addiiton to checking your timing, you might also want to run through the valve lash setting once more to be sure.

I don't think the gear by itself is killing you, but when combined with a tight stall and restrictive exhaust . . .

Gears and stall would be my first move personally.

Thanks for all the replies.

427L88, You raise some good questions, the pistons are domed about 0.200" I'm guessing, looking at a pic of the motor before the heads went on. I have tried to get the exact specs on the cam but the gentlemen who built the motor no longer has that info. My mechanic friend felt that the cam's centerlines were close together based on the idle, vacuum, etc. for what thats worth. Also, the heads are ported with big valves installed. So you would recommend a possible cam change, if the tuning issues do not resolve ? Not sure what to do now, wondering whether I should resolve this cam issue before gears, stall etc. Can you recommend a good method to figure this out. I'm a novice at this but learning quickly.

Thanks again.

Gearing will make the most difference in how the
car "feels".Of course, the rpm range will increase
also.

you know i have to say this post looks real familiar to my first post here. any of you guys remember the post Torqueless????

i posted complaining of a lack of power, sure the car felt faster than my biscayne with its mild 350 but it still wasnt what i expected. i think the post went 4 or 5 pages and i received replies ranging from changing headers, cam, and changing heads to oval ports. i was 22 or 23 at the time and this being my first big block everything was new to me.

wouldnt you know it ended up one of my plug wires were bad, running on 7 cylinders. so i bought a new set of wires and the rest is history.

please check the basics before you go tearing things apart and changing things. verify the timing order, numbers 5 and 7 are real easy to get mixed up. test your plug wires and or swap with a set that you know is good, and check your timing to make sure it is acceptable.

Originally posted by Eric68:
I don't think the gear by itself is killing you, but when combined with a tight stall and restrictive exhaust . . .

Gears and stall would be my first move personally. Hey, i saw your picture! Nice!

BTW, the gear will help, and personally 3.55 isnt a real bear to deal with. My car now has 4.10 gears, and i've driven another car with 4.10 gears and really didnt mind it in ethier.

Its very much a personal preference, i dont mind driving slowly, especially around town, so it doesnt bother me much.

Plain and simple, if you drive mostly on the highway, then you want highway gears!

Chris' reason for sticking with 2.73 gears is simple, he does alot of highway driving, even his ride to Englishtown is over 3 hours.


Your exhuast is probably 2-1/4", it would be a big upgrade to have 3" pipes built, along with an x-pipe (or H-pipe) and Dynomax ultraflo mufflers.

have you done a compression test? what is the cranking compression?

badbob71,

No I have not, what type of pressure should I be looking for ? This would be in psi, correct ?

A compression test would indicate if the cam selected matches the static compression ratio, figure about 160psi minimum. 170-190 would be really good for premium pump gas. I'm no expert but cranking compression directly relates to low rpm torque output.

3B,

No offense to anyone suggesting an exhaust upgrade but a 396 with a mild cam and 3.08's just doesn't seem to warrent 3" pipes. The car has headers and most likely has at least 2.5" pipes into the mufflers and likely at least 2" tails. The headers, duals, and stock mufflers should be good to close to 5k I'd think. I'd look elsewhere.

Standard dome on a 30 over 396 forged piston is, I believe, in the range of .180, which nets to a displacement of about 21 CC's. I'm assuming the piston is down the usual .020.

I used the following numbers in Pat's DCR calculator: CYL = 8, bore = 4.125, Stroke = 3.76, Chamber volumn = 112, head gasket thickness = .041, head gasket bore = 4.3, piston to deck = .020, domed pistons @ 21cc's.

I'm obviously making some assumptions but, if the numbers above are close they indicate a static compression of 8.83. If the piston/deck is zero it comes in at 9.17. Further, since you mentioned that the heads were fitted with larger valves, if the head chambers were worked at all they likely come in over 112cc's.

With the 280 cam it would appear the 396 is over cammed for it's compression. However, since we don't know the real numbers the only way to be sure is to take it apart and verify what's in it.

Short of taking it apart, Bob's suggestion of a compression test is good. I'd get the compression/cam sorted out before diving into the rear gears.

Good luck!

Dan

Dan, thnx. That's what I'm thinking, there's a flaw in the design here, OR it was made to run on 87 octane ASSUMING there's nothing amiss with tuning.

Cranking compression would shed some light on the dynamic compression. AS said before, north of 175, you start making some decent torque regardless.

Pull the plugs while the engine is still somewhat warm and get to cranking!

Just looking at the specs, looks to be a 9-1 280H motor.
Your lack of compression is your big problem assuming it is a .180 piston.
My 383 pulls a 3.08 gear no problem with a similar cam but 10.8 CR. Since you can only afford one thing, I'd go with 2.5" exhaust or a smaller cam. A 270H would be a better match or even a HE268.

Originally posted by 427L88:
ASSUMING there's nothing amiss with tuning. you know what they say, when you assume it makes an ass out of you and me. id hate to see someone complain of a lack of power and go and spend money and change things just to find out that the wires were bad or it was out of tune.

but what do i know. :rolleyes:

Thanks all for your input. I will check the obvious things like timing/plug wires first. (However they are brand new MSD's)

My gut feel is that something is awry, although my knowledge is limited, I have driven plenty of powerful cars, and right now I would say the car feels like 275hp max. The guy that sold me the motor had hi-comp heads on it originally, but said that oval ports would be better for the street - sounded fine to me at the time. Likley he wanted to the other heads for something else.

Should the basic tuning efforts fail, I'm really wondering whether the cam change would be a good opportunity to select one that does not require a high stall, maybe add one later type of thing, when the bucks are there. I'm looking to build a nice street machine not run at the track.

Any guys out there running 396's without hi-stall converters ? Do you still get good power ? I saw the posts by SGAYLORD earlier in January and sounded like he was making tons of power, over 430 hp and similar torque.

Again thanks for the responses and pardon my ignorance.

BBB

just because parts are new doesnt mean they arent defective, ive seen new wires, plugs and cap/rotor defective out of the box.

i can also say this from experience, big blocks are hard on plug wires and are very sensitive to tuning problems, timing out of spec, sticking advance, etc. etc.

another thing, dont be too proud to think you did everything right, even the most experienced guys cross wires and etc.

edit: also dont forget the fuel system, being a malibu your car probably has the small fuel line.

what fuel pump are you running and what does your ignition system consist of?

BBB
I am running a 402 with a 274 adv.duration cam and low static compression(about 8.5:1),not the greatest combo for making power,but I found my engine likes lots of timing.Try cranking in as much initial advance as you can.listen and check plugs for detonation,but you will probably run into starting problems before the detonation monster strikes.

This is of course "assuming" that your cam is the one you think it is.

Ratonastick,

Yes the fuel line is the original 5/16", and the fuel pump is a OE replacement for 375hp aplication.

i would think about upgrading to a 3/8s line in the future. i cant really comment on the pump, i know that Gene aka 427L88 runs a stock replacement pump on his ride and she runs pretty good.

what about your ignition system? are you using an hei? points?

maybe the fuel sock is plugged in the tank?

without knowing more about the car/combo and how it drives and performs were all guessing. will it burn any tire? even with the fact it may have too little compression and too much cam its still a big block and should be able to roast that right rear tire.

Rat,

HEI, with MSD coil.

Yes if I punch it around 2800 rpm in first it will lay down about 5 feet or so.

For sure its all speculation, I really only got it running and drove it for a couple weeks before the weather turned cold and I put it away. This has been in the back of my mind all winter.

When it comes out this week, I plan to start going through everything, and will post anything I find of interest.

Thanks,

Really nothing wrong with low compression,you just need a stall and gear to make it perform,and it will have its limits.I bet with 3.73's and a 3000 flash stall with a 1.90 or so 60 ft. would get the car into the low 13's possibly.It would all depend ultimately on how well the car is tuned,traction,driver skill etc.Now the flip side would be my car with an 8.5 to 1 454 and a mild cam wouldn't run be able to 12.99 or a low 13 unless it has 3.55's-3.73's

Update

Checked cranking compression and its about 150psi... :(

Back to the drawing board. Assuming I were to go with a milder cam, what type of power could this combo make ?

Ahhh, so your compression is down a tad.
I still think a 3.73 might wake it up some
and you might think about a small Weiand 177
blower when you want to step it up.You might be
able to run it on pump gas and I'd bet 450 h.p.
would be easy.

Well if I may add something that I don't believe was already posted, what are your shift points set at? Maybe a governor recalibration is in order to place the shift points at a higher RPM more suited to the engines operating range for max power. Worked a miracle on the 454 we used to run. Is your kickdown linkage working also? I don't know about a turbo 350 but fixing the kickdown on the turbo 400 made it shift later also.

Don't mean to beat a dead horse, but assuming my motor is about 9:1 compression or thereabouts will a milder cam increase my cylinder pressure enough to make good power/TQ ? Or would going to a set of closed chamber heads be a better idea ? As I mention earlier, my cranking compresion is about 150 psi at this time.

By the way, I have a copy of the " How-To" book by Ed Staffel on order in case anyone was about to make that suggestion.

Happy Easter.

I guess it depends what you want out of your engine.I read your combo and right now it seems you have about 9 to 1 compression and i'm not sure on what cam you are running but it sounds like a mismatched combo.If you go to closed chamber heads and it could raise your compression to much for the cam you have and then you would have to change the cam anyway,so in the long run it would probably be cheaper on you and less time consuming to just change the cam for what you have now,if it were me I would go with a solid cam it will give you a little more low end torque and you can run a little more on the duration side and will give you a few more rpm's on the top end,but remember this is just my opinion and you have to build what you want and get the results you expect out of your own car.Here's a link for a little reading ! Post of some cams (http://www.chevelles.com/forum/ultimatebb.php?ubb=get_topic;f=4;t=019695#000000)

Your cranking compression is a little low at 150 IMO but should work well with 87 octane. The 5/16 fuel line is small-should be 3/8 if the car originally had a bigblock. But the fuel line shouldn't be an issue for the first two gears anyway. Let's look at some low dollar options. You could increase your low end by advancing the cam some. Also maybe look to different head gasket options to raise the compression some if the deck height clearance permits. Timing with low compression usually likes more initial somewhere between 12-18 BTDC. 3.73 gears would help the engine come on the cam sooner. What is the Lobe seperation angle of the cam? The tighter the seperation angle the more critical a freeflowing exhaust and also makes the engine less responsive just off idle. A 2 1/2" dual exhaust system with freeflowing mufflers would be just right IMO. Also if you're running vacume advance try disconnecting it, sometimes it will put too much timing in at part throttle with the large amount of initial and mechanical coming into play- I've seen as much as 60 degrees total with all three combined at part throttle! The timing curve usually takes some tuning to get it right. Even with 150psi cranking compression your car should smolder the tire through first and second without any problem even with 3.08's. Time for some tuning IMO. Bob

How about getting some 063 heads with 100.9 cc chambers? That would bump up the cylinder PSI which would help out your performance. I'm running them on a 402 +.060 with trw 2240 (.182 dome) pistons and an XE274 cam. Cranking PSI is running at 170.

Update.

Going to tear off the heads check the piston #'s, and check the cam number. I have acces to a set of fresh 702 98cc closed chambers for reasonable $$, I may swap these depending on what I find.