This motor is a nightmare

[ben88]

Hey Yall,

My name is Ben and I currently attend Long Beach state studying mechanical engineering. I am the proud owner of a 68c10 Stepside. A couple of years ago my dad and I swapped the 6Cyl. to a SBC 350 and I was able to get a muncie at a steal, so really not a bad setup. However, ever since I swapped the engine, I have never had a good running motor. The engine was rebuild by a engine builder in Bakersfield, then I installed a comp cam extreme energy 274, Edelbrock performer eps manifold, headers, Edelbrock carb. Even after the rebuild the engine did not run properly, so therefore I purchased a new Carb (625 electric choke) and MSD distributor (HEI replacement). At this point the only part that is still the same as before the engine was rebuild is the intake, so I bought a old school performer (not eps) and plan on installing it soon. The truck runs fine at highway speeds, but in the low rpm's its sluggish and under load it misses and wants to fall on its face. I have worked in multiple shops and currently work in a motorcycle shop as a part time job but I can not figure this damn thing out. I know swapping the intake shouldn't really make a difference but thats how desperate I am.

[hugger6933]

The intake is not your problem but you will hurt the potential of the motor by putting the intake on, it is too small for the cam you have the intake you need is what you have already. The problem is in the fire,could be as simple as the spark plug wires or a spark plug but my guess is the spark plug wires. Jim

[hamjet]

As far as being sluggish, the cam is a higher RPM cam,( fat cam).. plus was the timing gear advanced or retarded? this can make a strong high RPM motor fall on its face at lower RPMs. Whats the comp. ratio of the motor. the cam can be too much for a low CR motor. Lower rpm missing can be a lot of things, burnt valve, ignition, etc....

[engineer_gregh]

I rotated your engine picture. I'm not an expert on MSD ignition but how are you vacuum lines routed, i.e., vacuum advance? What is the timing set at for initial and does it advance with rpm's?

[geezer#99]

You need a heat plate under your carb, a fuel regulator to limit pressure to 5 psi, a hard line for your fuel line (and not tied to your heater hose), and you need max initial timing!
What's your initial timing?

[leftybass209]

That cam isn't ideal for what you're looking for. Timing should cure most of the issues, and that manifold won't cure anything, and only has the potential to make things worse. You can't piece random parts together with fingers crossed. They have to work with each other.

[alsriv2]

Potential good motors can be turned into a mess by not getting reliable and accurate information for performance parts. Everything an engine is has to be tuned correctly and matched to the intended uses. Others above have given you some good pointers. Find someone in your local area who truly knows your engine, listen to their pointers and the information here and you will get some good results without throwing your wallet at it.

[no1udknow]

I agree with these guys ^^^^, i think you need to look at timing and possibly carburetor adjustment. Chaining your carb and manifold should really only affect your torque curve and top end performance. Most engines can be made to idle using a homemade carburetor. I would suggest the following steps.

Check timing, Check vacuum advance (ensure it is hooked up properly and advances under throttle), check power valve in the carburetor (make sure it squirts when you actuate the throttle) and check the carburetor adjustment.

Assuming you have all new plugs, wires etc, and the bushing is good in your distributor and it's not tearing up the inside of the cap, one of these things should correct your issue.

[GASoline71]

Also if you swapped in the HEI, you can't use the original "hot" coil wire with a resistor that was attached to the old canister style coil. You need a dedicated 12v wire with no resistor hooked to the HEI "Batt" side.

Gary

[Jonlopes]

I built my first motor in a 66 GTO when I was 19. I went through all of the catalogs and ordered all of the coolest performance parts. I also talked to all of my friends; one mentioned an intake manifold I should use, another told me about a cam he used before, another pointed me to a set of headers. When the motor was done it would beat all of my friends in a drag race but it sucked to drive. It ran hot, it hated to idle, it plain sucked for around town driving.

What I learned from that expensive mistake was think long and hard what you want to do with the vehicle before you build. The mechanical engineers in the 1960's were pretty darn good and for 90% of applications the parts they developed are a great choice. Besides (My opinion of course) these trucks are too heavy to have both a high performance small block AND nice road manners without a lot of thought and tuning.

[cooperhw]

It sounds like my Chevy brethren have just about covered all the bases of "where you should start" and go from there.

Just remember an internal combustion engine only needs a few things to run.

Suck, Compression, Bang, & Blow.

A little more complicated than that in that the suck needs to be sucking in the correct amount of fuel and air.

The compression goes next and it needs to keep that proper air/fuel in the cylinder until the bang happens.

When it bangs is as important or more than most of the others. (This is the root of a lot of problems)

Next comes the blow when the piston comes up and pushes out all the burn fuel/gas mixture.

That's all there is to it.

When you look at it with this type of an analytical approach you can ask yourself this question; which one of these is the likely culprit that is causing me headache? Work on that.
Sometimes we tend to think "that part is good so I need a new part here". When if we take the time to get back to basics and say "I am not sure any of this is good so I am going to check each and every one of them" we can get right to the heart of it.

Here's your truck flipped.

Nice looking truck by the way.

[wbc409]

That's a big cam for a small block if all your going to do is drive around town. I use my truck for pulling the occasional trailer and cruising. It has a 454 in it and that cam you put in your small block is to big for what I use my truck for. With a cam that big you should have checked the gear ratio in your axle and installed a higher stall torque converter. Figure out what you truly are going to use the truck for and adjust your plan to the actual use of the truck. My guess is after you get everything sorted out you will probably change the cam to a smaller one. The idle won't sound as cool but your driving experience and pleasure will be much greater.

[wbc409]

That cam needs a 3.73 or numerically higher rear gear ratio and a higher stall converter. If the engine wasn't rebuilt with around 10:1 compression it will add to the problem.
The 2 biggest and easiest traps to fall into for an inexperienced engine builder is to install a cam and or carb that are to big for the actual/intended use of the vehicle. A cam That big would make my low compression 454 sluggish at lower rpm's

[cdowns]

ii'd try changing the gas line now or wait till it burns to the ground and scrap the truck

[Davidf]

I tend to lean to the ignition timing part of the equation. Forget what the timing mark/pointer says and advance it a little at a time and see if things improve. Also, don't rule out camshaft damage during initial start-up. Have you check compression on all cylinders?

[tranz am]

there are a lot of variables which can cause an engine to run badly. the only way we will be able to help you figure out what the problem might be is if you run some tests yourself and let us know what the outcome is of each test. it's a process of elimination. You need to check air, fuel and spark, what the compression numbers are by running a compression test and a leak down test. You need to know what your ignition and valve timing is set at, spark plug gap, fuel presure at carb, etc. There are just a lot of things to check.

[ben88]

Hey all, Okay that was a lot of useful info. To address a couple of the suggestions, the muncie is a 4-spd manual so no torque converter is used. I purchased the cam because I originally had a 30/30 duntove and when I had the engine rebuild I was told to run the com cam 274 because it was a "mild street cam." I have played around with the distributor, advancing and retarting it. When I set the timing correctly at idle it runs like complete dog. If I advance it so it runs ok at idle it pings once it reaches full mechanical advance. I completely agree with having to get metal fuel lines, my issue is that I had multiple helpful connections in Bakersfield, since I moved to long beach I am sort of on my own as far as mechanic friends and I don't have the right tools to make the fuel line. I used to be stubborn and had my head set on certain performance parts, now I just want a drivable hotrod with a little Umpppfff. I am willing to change to different engine components I just need to figure out to exactly what. Also I checked the wires and plugs recently, all are fine.

Thank you for flipping my pics I didn't realize that they were upside down until posting.

If anyone is in the socal /oc area and feels like sharing some wisdom i would greatly appreciate it.

[ben88]

If anyone sees a major issue with my engine components not matching and has a helpful suggestion I would definitely be open to it, i should also mention that it seems like it runs better when the engine is cold. Maybe because of the choke.

[ben88]

I also contacted comp cams to see if this cam had to be degreed and they said that it did not and can just be aligned dot to dot.

[Fitz]

Originally Posted by cdowns

ii'd try changing the gas line now or wait till it burns to the ground and scrap the truck

That was helpful.

[Troy Sr]

ben88 have you verified that the outer ring on the balancer has not slipped? My Camaro had one that slipped and I couldn't get the thing to run when the timing was set, once I replaced it and the timing mark was correct it could be timed and ran great. Good luck.

[geezer#99]

Originally Posted by ben88

Hey all, Okay that was a lot of useful info. To address a couple of the suggestions, the muncie is a 4-spd manual so no torque converter is used. I purchased the cam because I originally had a 30/30 duntove and when I had the engine rebuild I was told to run the com cam 274 because it was a "mild street cam." I have played around with the distributor, advancing and retarting it. When I set the timing correctly at idle it runs like complete dog. If I advance it so it runs ok at idle it pings once it reaches full mechanical advance. I completely agree with having to get metal fuel lines, my issue is that I had multiple helpful connections in Bakersfield, since I moved to long beach I am sort of on my own as far as mechanic friends and I don't have the right tools to make the fuel line. I used to be stubborn and had my head set on certain performance parts, now I just want a drivable hotrod with a little Umpppfff. I am willing to change to different engine components I just need to figure out to exactly what. Also I checked the wires and plugs recently, all are fine.

Thank you for flipping my pics I didn't realize that they were upside down until posting.

If anyone is in the socal /oc area and feels like sharing some wisdom i would greatly appreciate it.

You're sorta on the right track with timing. Advance it until it pings or is hard to start then pull it back 2 degrees. That's your best initial. Then you need to adjust the mechanical in the dizzy so your total timing is 32 at 3000 rpm.
As an example if your initial is 18 then you want to adjust the mechanical at 14. Then add about 10 degrees with your vac advance.
Here's a link on adjusting your dizzy. You'll also need a digital timing light to set your timing curve.
http://www.crankshaftcoalition.com/w...EI_distributor
And here's a link on proving your timing tab/balancer marks.
http://www.crankshaftcoalition.com/w...op_dead_center

[GRX]

Just to reiterate what others said. That is a high rpm cam and you fell into the bigger is better trap. Which leads me to this:

The engine was rebuild by a engine builder in Bakersfield, then I installed a comp cam extreme energy 274 ....

"Then" being the main concern here. Stock springs would surely bind causing all sorts of issues. Did you install proper springs to go with that new cam? Or ... did the Bakersfield engine builder install ones which can handle the new lift? Do you have any info on the original build? Cam specs etc?

[edit]: here is the Comp cams page:

http://www.compcams.com/Company/CC/c...x?csid=87&sb=2

And here are the springs recommended on that page:

http://www.summitracing.com/parts/cca-981-16

[Shell]

I'm thinking the samme as GRX. I changed cams without the changing springs & it did all kinds of crazy stuff. Worth a check. Good luck!!

[no1udknow]

I wanted to touch on the fact that you said it runs better when it is cold?? what kind of choke is on this carb, and have the jets been replaced? possibly float level too high? I think you eliminated the timing issue by the fact that it ppings when advanced. Pinging occurs about 500 rpm before you actually even hear it, so if you are hearing it at all, you should back off the timing. As far as the cam, I have an elgin pro stock cam in mine, with .080 over-bore, 10:1 pistons and I run stock springs/rockers/pushrods, my lift is even greater than yours and my truck lopes at idle, but the second I touch the gas it breaks the tires loose. I think you have a carburetion/fuel issue.