Ok... so I had my engine rebuilt, 030 over, cast steel crank, EngineQuest ch350h heads, Comp cams 270HR hydraulic retro roller cam. By all means, this should be putting out 350 horse and gobs of down low torque. Although I haven't had it on a dyno, it just doesn't feel like 350 horse. I rebuilt a spare carb, rejetted with 76 jets and 42 rods, reworked the idle circuit per Cliff's book, sent the distributor out for recurving/rebuilding, and acceleration is just flat.

Onto the issues:
The car starts easily and idles fine, but at full throttle acceleration just isn't where it should be. I borrowed an A/F meter and it shows crazy lean at idle, like 30. I didn't think a car could run that high. At WOT the A/F dived down to 10 at the lowest point. Adjusting the mixture screws had no affect on the A/F ratio. I'm questioning the accuracy of this device. I put back on my stock carb rejetted with 76 jets and 44 rods, and the numbers didn't change. Performance did not improve either.

I pulled the valve covers and noticed the third from left valve on both heads (both were intake valves) only had the rocker tip about 50% on the valve stem. I called the builder and he suggested trying an offset rocker to correct the alignment. I ordered a pair for now and will install when they arrive. I don't think this is contributing to my performance issue, but it is an issue none the less.

I pulled the plugs and ohm checked all the wires. Most plugs were tan, none were white like I would have expected from the 'lean' reading. Cylinder 4's plug was black. I cleaned all plugs and replaced. No change to A/F or performance.

At this point I'm just looking for suggestions before tearing into the engine. Eventually I'll pull the heads and correct the crooked rockers by clearancing the valve guide hole and installing guide plates for the two offending rockers, but I'd like to get the performance issues figured out first. It doesn't smoke (that I've seen) and I'd guess its running rich based on the soot accumulating on my brand new exhaust tips.



Most looked like this



This one wasn't so happy



new exhaust tips... 50 miles later

 

The plug that is covered with black soot is probably not firing so that would account for a lot of your power loss. I'd sandblast (or glass bead) all of the spark plugs and start over again. Are you running the stock QuadraJet? You need to verify your choke is coming completely off and your secondaries are opening. The choke linkage operates a little thing called a "secondary lockout" (on the right side and attached to the secondary throttle shaft) and if your choke isn't opening all the way your secondaries won't be opening at all.

 

I am still running the stock carb (with the bigger jets), the choke is working correctly, I wire wheeled and regapped the plugs (035), but still no improvement. I moved the o2 sensor to the driver side and the numbers didn't change there either. Running out of ideas.

 

Where to start? It could be a myriad of things. With your combo, should be a strong motor. First, is your throttle hooked up so that it is coming completely open when you mash the pedal? On my new rebuild, even after dynoing it, it was flat in the car. I had the throttle linkage in the wrong hole on the carb when I put it back in the car. Moved it forward and PRESTO. The secondaries had not been opening.

Is it running on all cylinders and what is your timing? If you have a dial light, set it at 36 degrees total and see how it runs. Do some research and look for a good guesstimated tune on the Quadrajet. I am also running a Quadrajet on my 1970 and it was pretty close coming right out of the carb shop. What tranny and gears are you running? That will have a lot to do with seat of the pants feel. Is it winding up and has solid ignition or missing at higher rpm? I.e. Is your ignition system solid enough?

Last, After a couple builds I took some advice and now dyno test all of my motors before they go in the car, and now I honestly believe that's the cheapest horsepower you can ring out of a motor, as you can see things that you have a hard time sorting on the street. Yours is obviously back in the car already, so mute point, but if you have a reputable chassis dyno in town, might be worth a try. You may throw hundreds at the car in parts you don't need, or drop a few hundred in a 1/2 day at the dyno and determine its just tuning. Plus, you'll know your optimum timing, carb tune and real world numbers when you're done. I think it's invaluable.

Just my opinion... and like they say, everyone has one. Good luck! We have all had our challenges sorting out a new combo. Anyone who says otherwise... well.

OH - in my case, also 350 based roller with aftermarket heads, I also ended up with offset rockers.

 

You had the engine rebuilt and have rockers hanging off the edges of valves? Really? Post up some photos please.

I wonder what else he screwed up?

 

Thanks for the replies! My throttle is correctly set up and I made a little indicator to ensure the secondary air flap was opening while driving. Here's a simulated test:


homemade secondary air flap opening indicator

I'm suspect of the running on all cylinders, thus why I pulled the plugs. I agree that #4 doesn't look like it was doing anything. Cleaning them did nothing, I'll move the plug around and see if the problem changes cylinders.

I don't recall the timing off the top of my head, but I'll double check that. The distributor was rebuilt and recurved and I believe i'm at about 36 degrees at 2500 RPM (without vac advance). I swapped the coil out with a spare I've had hanging around, but no change.

Here's a pic of the rockers. Sorry its out of focus but you can still see the 3rd valve is crooked and the shiny ring worn on the retainer. Glad to know someone else had luck with offset rockers in this case.

3rd rocker crooked

I have a 4 speed and the stock rear gear, believe it to be 3.36. I counted driveshaft turns and it was 3 and a bit of change, so I know its not a 'performance' ratio, but I've had the car 10 years and know what to expect. With the 10 year old hard tires, I should be able to break them loose pretty easily with this combo.

The A/F ratio is really bugging me because its telling me lean when I think its rich. I pulled a vacuum line off and the engine jumped up in RPM and 'sounded' better. That said, I don't want to melt any pistons.

 

Have you checked that the timing chain is installed correctly? If it's off a tooth or two it can mess up performance? Also did you do an accurate determi9nation of your compression ratio with the new heads?

 

Please take a new picture looking at the valve straight on and with the camera held steady so the picture isn't blurred. It only takes a TINY bit of wear on the side of the slot in the cylinder head to allow a rocker arm to run cockeyed so let's see a close up picture of the slot with the rocker arm and push rod removed.

 

Ditto on both counts, get a degree wheel and check cam, and compression. I've had new head gaskets not seal on SBC's before with poor performance after a rebuild.

that non-firing plug bothers me as well, something going on there for sure. damaged valve seal possibly.

 

No guide plates?!?!?

 

The holes in the head for the push rods are slotted. You can't use guide plates on them unless those slots are drilled out.

 

I have no idea what this is supposed to mean.

 

AFTERMARKET heads with SLOTS???????

 

I stand corrected. After digging out my old photos of my alum heads, there is no slot. Could have sworn . . . . . .

 

Okay you have several issues here so slow down and take your time to correct them before something gets broken.

Start with the rocker geometry. Commonly when the block is rebuilt it gets shaved or even decked enough to change the stock valve geometry and even the intake fit too. First get the p-rods to line up the rockers straight on the valve stem tips. You most likely need to grind out the head slots for this but what you want is the p-rod to move smoothly in the slot without friction or binding. Next get a p-rod checking tool from ProForm or Moroso ($15). Easy tool to use and let's you know if you need different length p-rods. Last check your rocker arm tip pattern on the valve stem tip- should be centered and nothing close to the edge.

Now that black plug kinda explains your 10:1 A/F ratio. That's carb jetting and the idle jet screws have very little to do with power above idle. They write books on carbs and I can't try to compete in a single post here - read up bud.

Now mechanical timing is something you can check with a timing light. Disconnect the vacuum advance and plug that hole towards the manifold or carb. Now you can write down what the advance is every 500 RPM while you slowly rev it higher in the driveway. No need to go over 3000 for this test and higher RPM will be bad for the engine unloaded ! Now you can graph your timing advance curve for yourself.

Whew! That's enough for now and let us know when you get these issues fixed or if you need more information.

Good luck.

 

Thanks everyone for your replies. The 10 A/F ratio at WOT doesn't concern me as much as the high 20's to 30 at idle, and doesn't explain how a only a single plug would be fouled. I've read up on these carbs enough to know I'll have to move the jets down a size to change my WOT enrichment in the primary circuit. I'm hesitant to do anything to lean it out since the A/F is so out of wack on the idle.

My block was not decked, as I didn't want to loose my VIN off the block, so I shouldn't have issues due to that. I've done some searching for the rocker alignment issue and it doesn't seem all that unheard of with aftermarket heads and having the pushrod slot shift in casting or just be poorly designed. JoeMinnesota mentions his did something similar on his heads. Although I'm not happy with it, I'm going to try an offset rocker first. If the geometry still seems off, I'll reconsider my choice in heads.

Although I verified the secondary air flap was opening all the way, I took another look at my throttle cable and verified I wasn't getting full travel. Thanks for pointing out the simple things Joe! I've made adjustments to correct this issue. I'm still leery of running it much with the A/F's being what they are at idle though.

 

One more thought about that ****-eyed rocker. Of all the rocker locknuts showing, it appears that the #6 INT has more rocker stud threads showing than the other seven. Could that rocker stud be the wrong length?
I had to order some rocker studs last year. What they sent me were the correct diameter, the correct thread pitch for the cyl head side, correct pitch for the rocker nut side and the correct length under the stud. But the distance of the upper stud and where the rocker would sit was off by a 1/4". H-m-m-m-m-m.

 

Just want to add something that maybe helpful here and not trying to flame anyone. BTW I like the OP's build as it is sensible performance effort for any C3 w/o spending the retirement fund.
In my small dyno experience if I lean the motor to 22:1 A/F it will try to stop running. I don't see how it could run at 30:1 A/F. I have expect a air leak and most likely it would be in the exhaust manifolds (both in your case) or exhaust system.

And I hate to mention this but new heads may not cure the p-rod alignment. Fastest fix would be drill out the head slots and install guide plates - but you still have align the guide plate slots.. If you remove the intake you could drill out the slots if you cover up the lifter valley well enough and most of the head to. Then clean with vacuum and alcohol wipes. But there's still a risk in leaving metal flakes so the choice is truly yours. Myself I would inpect the slots and see if there is enough metal in the slots to achieve a smooth gliding fit for all the p-rods and then use a grinding tool to fit things up.

Good luck and please post what works for you - it helps us all.

 

I know myself the Comp Magnum rocks come with locking nuts rather than the poly locks shown. . I truly don't know if Poly locks are compatible with the Comp Magnum rockers - there could be a miss fit. Poly locks will easily work/turn loose if not locked up correctly.

 

Agreed. Some of the aftermarket heads with more significant port sizes cause misalignment issues. In my case, DART SHP aluminum 180cc and I was very unhappy to find that I had to run offsets on the exhaust and std intake rockers. The alternative is to machine the openings for pushrod clearance, but there's not much meat there. No way I would attempt with an air grinder on $900+ heads.

Anyhow, you can make what you have work. And THEN, I actually split my one-pc guideplates into individuals for each pushrod (Cut them with a cutoff wheel and finishedvthevedges on a grinder) and pulled the studs to reinstall individual guide plates. Us a hardened washer (grade 8) between each plate and the base of the stud before torquing - the washer will allow you to hold the plate in position without spinning when you tighten them down. Easier as a 2-man job. This way your pushrods won't be 'ganged' on each set of valves and you can individually adjust for best vertical geometry and add a little clearance at some ports as you need to. complete BS on brand new heads, I know, but glad I went to that trouble. Evidently your builder didn't bother. I called 2 shops to ask, and both admitted they go in with a mill on certain heads to make clearance.