Help needed with strange SBC drivability problem.

So since I put my 79 Malibu together a few months ago, it's had a weird power issue. Off idle, with barely any pedal, it pulls away fine. Give it any more gas, and it doesn't do a thing. Basically, it goes harder at 1/4 throttle than at half or full throttle. I had a thought that the cam was in a tooth off, but I just took it apart and it's dead on.

Here are the specs. It's a 260hp GM crate motor with the stock cam. Edelbrock EPS Performer intake. 600cfm Edelbrock carb. Stock pickup manifolds. Stock TH350 with stock converter. Highway gears.

The engine also gets HORRIBLE MPG. I've had 4 different carbs on it (3 600cfm Edelbrocks and one Demon 650) and no difference. It did it with the 2.5'' duals that were on the car when I first got it, and the stock Monte SS exhaust that I have on it now. Timing is set at 12 degrees initial, goes to about 44 total including vac advance. Fuel pressure checks out fine.

I'm about to put this cam in it, just to see if it solves anything.

http://www.summitracing.com/parts/CCA-CL12-205-2/

 

Forgot to mention, it also WILL NOT rev pas 4,000.

 

Sounds familiar, Ive been dealing with one doing some of what you have mentioned..

I'll be watching this one..
Have you checked the Vacuum?
if you have, tell me what you see.

 

Check the numbers on the block.Also change cam to 2102 and add 305 heads.I think you might of gotten the truck 350 with 8 and 1/2 compression.or it might be 8 to 1 .Truthfully I forget.Also could be a bad distributor shaft.

 

It does have 8.5:1 compression. I'm not looking for a lot of power, but right now my TBI 350 yukon would DESTROY this thing in a race, and hell my 85 C/10 with a 305 probably would too. It's really lacking power compared to what it should have.

 

Here is the engine that is in it;

These GM Performance Goodwrench 5.7L/350 c.i.d. engines have approximately 8.5:1 compression with 250 hp at 4,300 rpm and 350 ft.-lbs. of torque at 3,600 rpm. These crate engines have a 4.00 in. bore and a 3.47 in. stroke with 4-bolt mains and 2-piece rear main seals. Camshaft specifications are .383 in. intake lift and .401 in. exhaust lift. The open duration is 194 degrees intake and 202 degrees exhaust at .050 in. with a 112 degree lobe separation. The cylinder heads are cast iron with 1.94 in. intake valves and 1.50 in. exhaust valves, 76cc combustion chambers, and 7-bolt style exhaust flanges.

 

what balancer did you use...? i put one of those motors in a customers 35 ford 4 dr....it ran like a scalded dog...

 

I see you said it gets "horrible" gas mileage, any smoke?

You actually saw the 44 degrees at the timing mark? At what rpm?

 

44 including vacuum advance sounds low...HEI?


Try setting it to 36 total if you have a dial back light at 3000 rpm or hatever it takes to get your timing all in with the vac advance plugged.

check your advance weights to see if the are binding, also check to make sure your limiter bushing is in place...I can't rememebr if HEI had one or not.
Can you swap a known working dizzy to rule ignition out?

 

good info since there are too many combo balancer/timing tabs you may have one that is not matched to the tab...

 

im having the same issue with my 305

 

Not meaning to be disrespectful and really appreciate the attempt being made to correct this persons problem, however, the more we keep responding to O/T cars and issues the more I'm becoming concerned with this site. I really find it interesting that so many old HAMBers are responding to his thread. Does the HAMB need a special area for post '63 vehicles? I know I'm venting and maybe in the wrong thread. After all this person has a legitimate question and this site is better at giving him advice than any other site he'll find. God bless and I hope he gets the situation ironed out. -Mike

 

Way to be an asshole.

Who cares what year it is. What is all boils down to is that we're all car guys. Have you ever had someone ask you for help, and you refuse because " oh, im sorry, i only work on pre 64 cars"

A cars a car, when it breaks we fix em

No matter if its 1929 or 2009

 

The car might be OT but the engine problem isn't.

And the sooner Moloko gets it squared away the sooner he can get back on his hotrod or custom.

I'm With Dooley in that I would be making sure that the dampener timing mark and the timing mark on the timing cover do indeed match up at top dead center.

there are so many different combinations that it is pretty easy to be off.

Other than that, the advance weights in the distributor as Dooley said again ( ah hell, just go read what Dooley said)

The other thing is that the timing of the cam may be off a bit from it wants to be especially if you used a multi slot timing gear.

 

I don't think it really matters what body the engine is in. It is still an engine that sees alot of use in these cars either directly or as a derivative thereof.

With that said, I think 44 degrees may be too much for a street driven engine especially if running pump gas. I too think you should make sure you have the correct balancer for the timing tab/front cover as mismatching them will give crazy readings and very poor performance.
I worked on a car last year for a customer who had mismatched stuff and using a dialback timing light the car would only run fairlywell if the timing was at about 60 degrees or better. Obviously this is not correct and I was able to get the car running fairly well using a vacuum gauge to help set the timing. This will get you in the ballpark, but you really should get an accurate reading by finding true TDC and marking the balancer accordingly.

 

Jeez, I thought I wrote my post in a way that didn't step on any bodies toes. It's just that these type of posts seem to be the kind that are constantly called off topic on this site. Your point is well taken and I appreciate your candid answer. I can understand the question and feel your personal attack was a little hard to take, but I appreciate your view and give my best. God bless. -Mike

 

Now that I go back and read my previous post and the other posts of this thread I can see where this wasn't the correct thread to ask this question. It's an interesting point that at one time I had a '73 350 in my 56 Nomad and currently have a '69 327 in my '53 F100. Although I'm not a fan of SBC's both of these engines have given excellent service and I don't plan on changing them anytime soon. Currently I spend as much time on this site as I can and like to think I'm becoming more aware of other peoples feelings with what I write. Sometimes though I still have to mess with heads once in awhile and yes I can be an asshole but in this particular case I was simply asking a question. God bless -Mike

 

Next time I'll say the engine is in the 55 Chevy if that helps. I didn't think the car mattered, since it's a crate motor and I could put it in a Conastoga wagon if that made it old school enough.

 

I have a professional products 8'' balancer, same one I have on my Chevelle. It's a quality unit, so I'm sure the marks are right. I lined it up to TDC when I took the engine apart, and when I took the cover off the alignment marks on the timing gears were dead on. It's not a multi-position timing set, so there is only one option for alignment.

Here is a wacky theory I had. I'm using the OEM cam with this motor, but the timing chain is something I just had laying around. I'm wondering if this cam isn't for a newer SBC, if they are any different.

 

I'd run the timing back a little to about 38 degrees total with initial setting at 8 degrees BTDC. Also make sure that the distributor wasn't dropped in one tooth off. Is the vacuum advance or mechanical advance working? Put a vacuum gage on it and see what it shows. Another wild idea to explore is a resitiction in your exhaust.

Bob

 

something that hasnt been mentioned......maybe go thru and adjust your valves. ditto on the timing check and vac gauge.

 

so is it a crate motor or did you build it? you said its been apart, if it was a crate why has it come apart? older motor gettin freshened up? all info is important.

 

If your like me you want to throw alot of things at it at once.


If you can rule out the carb, and I think you said it happened with different ones, then check igntion, but first make sure you have good fuel pressure 4-7 psi.

Thios dizzy could be missing weights or something, can you swap a working one from another car?

Once you check that off, look at the valves, but if they were off you would have noise and other issues like a misifire.

Re-reading your post are you sure your carb linkage is correct, and could you have a rev limiter somewhere?


If it stops at 4000 I think it's timing or in the dizzy.

 

I was thinking the same thing. Sounds maybe they are run down a little tight.

 

I'd be looking at ignition. My experience is that a weak spark will give me these symtoms. maybe a weak coil?

 

when you say alignment marks on the gear set , you are referring to the dots and not the keyway ...correct? gotta ask.

 

Have you run a compression check?
this could rule out the tight valve idea..or late valve..(or early) valve timing issues

 

Are the valve springs matched to the cam? Rockers the right ratio?

If you can pull your cam card and check that as well..

 

What distributor are you running? This may be unrelated but I had similar performance problems with the 283 I put in my 5W. It came out of a "running" (so I'm told) 66 Impala so I had no idea how well it was going to ran. Under hard acceleration it fell flat on its face but otherwise it ran great. I ended up putting a Pertronix unit in the distributor and it cured the problem. So I wouldn't rule out your ignition.

 

Aren't there several different timing covers for SBCs and they have the timing pointer in different places?
Finding true top dead center is important.
It can be done on an assembled engine.
Once you know that, you'll know where your timing is for sure.


Disconnect the vacuum advance line at the distributor and plug it.
Shoot the timing and see what you get.

Keep in mind that mechanical advance responds to RPM and vacuum advance responds to load.


Put a vacuum gauge on the engine at idle - source it to manifold vacuum and not ported vacuum.
With your mild cam - and depending on altitude to an extent - you should see 17"-19" vacuum at idle.
(You'll lose 1" of vacuum for every 1000' of altitude gain.)

Assuming the engine is well sealed - valves, rings - and the vacuum gauge reads 10" or so and steady that's a good indicator the cam is retarded.

The engine - once it's in tune - will run cooler with the vacuum advance sourced to manifold vacuum and not to ported vacuum.