Chevy350 sounds congested; down on pwr. & overheats...?

Question

I've replaced: All new MSD ignition/plugs/set timing. I've ck'd installation config...all OK Replaced radiator/thermostat/H2Opump and the gauge sensor. I've 'burped' the coolant sys. This is a new motor/install. I have a new exhaust sys. also.
The motor is down on pwr; idles great. Exhaust sounds "airy"The overheat condition is slow...takes about 30 minutes of stop and go driving in 75-80 degree heat, to get motor to 212 degrees...turned on heater to control it.
Since it's in a 4wd vehicle; the exhaust coming off the pass. side goes forward to join the drivers side tube coming across the front of motor. It joins at a 90 degree ...could THIS be causing backpressure??

OK, the consensus seems to be to ck the timing. I WILL when I get home tonight from work..; although it was JUST set by a pro shop!
The exhaust is a staight through; no catalytic. {Take THAT; Mr. "Communist!"} I AM now wondering how large a hole the exhaust installer burned into the main pipe from the pass. side...What if it's too small? ...knock 4 of the eight cylinders out? It sure FEELS like a pathetic 4 cylinder! I know I'm harping on the exhaust...I'll start with the timing and re-ck the plug gaps. I really appreciate the responses. I've been struggling with this build for 3 years. I'm somewhat disabled; {spinal cages/bone graphs/rods/screws holding my Lumbar region together}, so this is a big accomplishment for me. But only if I can get it to run well! :)

To answer some questions:
The model year is inconsequential because this is a transplanted motor into my JEEP. This is the 3rd motor I have purchased over the years from this builder.
I'm running a CARB [Holley Truck Avenger series] Which is also [like everything else] BRAND NEW.
I'm using the stock fuel pump with a fuel regulator to control pressure. I have an in-line guage to verify pressure.
I plan on ck'g the timing [again]; removing the muffler; ck'g the spark plug gaps; as a start. I've already added new/more grounds to the system just to be certain THAT was not the issue.

Is there a way to ck the cam without disassembling the whole motor? The motor was build by a shop that I have used twice before. It is a 'brand-new' rebuilt motor from the ground up...EVERTHING 'inside' is new...and most of what's 'outside' is too...I have a LOT of $ tied up in this. As I mentioned, I've been working on this for THREE and a HALF years...I'm ready to go play in the woods! But I'm reaching the end of my rope...I' getting SICK of the whole project; it dominates my thinking...trying to fix it. the timing has been ck'd and re-ck'd. The idea of a bad cam has me scared. sigh... :(

EVEN MORE DETAILS:

The timing is OK; it's not 180 out...I know because I STARTED off being 180 out! :(
The radiator is a high dollar Alum Radiator from Novak Converstions; specifically made for my application.
Although I'm the one that brought it up {the exhaust question}, I realized later that the motor had the SAME problem BEFORE I even put an exhaust system on it!
****
I decided to give the original repair shop a second chance at fixing it. My schedule is awful; {an "extra" full-time job + school} However, the suggestions here {and from other sites} have given me over 20 things to ck! I'll let everyone know what happens with the shop; keep your fingers crossed...know any bankers? I may need a loan to get it out of the shop this time! :(

Answer 1

if it is restricting the exhaust from moving like it should yes it could be cause to much back pressure..the ones that I have worked on with that exhaust config. have U shape crossover pipe to take it to the driver side and then it is Y into the other pipe they way yours is configured you are blocking both at T

Answer 2

I think you might have an internal engine problem causing the down on power part... the airy exhaust sounds like the camshaft is off a few degrees from the crankshaft. You did not mention about what camshaft your are running. Even a mild camshaft is bigger than the stock cam that comes in most engines. The higher lift and longer duration is great, but it makes the camshaft timing (relative to the crankshaft) even more critical. If the cam has been changed (not the cam that came in the motor, even if it is a stock replacement cam) It must be degreed in. I know that most will just trust the manufacture to make accurate parts, but that doesnt happen. Some of the variables are the crankshaft"s key way that that drives the camshaft gears, the camshaft gears and/or chain, the camshaft itself. Somewhere in replacing parts, the timing is easily off and it causes many major engine problems... one of them is the airy exhaust sound you said it had. If you did not build the motor found out who did and make sure it was degreed in. This is probably the most common cause of poor performance in an engine that has the cam and/or the timing gears changed. The timing is very important and it needs to be checked, not just hope it will be ok. I have had engines that drove me nuts either not wanting to start or were down on power. I have always bought the best parts and the cam was still out of time. I think the factory choos a more mild cam to make being accurate not as important. If you are sure the cam is degreed properly, what else can you tell us to help with your problem?

Answer 3

You don't say what year and if it's Carb or FI... If it's carb, make sure the manifold heat flapper valve at the junction of the exhaust manifold and head pipe is not stuck closed.

If you're SURE the timing is set corrrectly...

Also, even though the exhaust system is new, it may have an obstruction. I've seen brand new mufflers that had baffles that weren't welded in and partially plugged up the system. It can cause symptoms like you describe including the slow overheating problem. Take the pipes loose at the manifold and see if it runs like it should.

I bought 2 year old car once for $500 because the owner said the engine was shot. A $25 muffler was all it turned out to need.

Answer 4

If you are using the same radiator that is stock in the jeep, it won't provide enough cooling for the Chevy. You'll need to add a seperate cooling line or a larger radiator (especially if turning on the heater worked to draw down the temp). If, except for the manifolds, you are routing the exhaust the same way as the stock jeep, and using the same diameter pipes, you are creating a back pressure issue on top of the 90 degree bend issue. Your engine can't breathe, because it's not exhausting fast enough. You also don't mention whether you're using the O2 sensor off of the jeep, the computer off of the jeep, whether you've swapped out the ecm, or if it even has an ecm. That would help, and knowing the year of the engine and the vehicle will tell us what you need for conversion to the jeep. Combine the suffocation of the exhaust, with the lack of cooling ability and that Mouse motor is just suffering. (If you want to put it out of it's misery, you can send it to me....I'll even pay shipping on the engine....lol)

Answer 5

Ok first there is only 2 ways the cam could be causing that. First is the special grind cam that swaps cylinders 4 and 7 in the firing order and it is wired wrong which you should now about. The second is a lobe of the cam wore not likely on a new cam. The only other way possible is a lifter not holding pressure(unless you are using solid lifters). Pull the valve covers and make sure all of the valves are moving as they should. As far as the over heating 212 degrees is not hot for small block chevy I consider that ideal temp. I build alot of race motors for me and myself and like I said that is the ideal temp for them. You could get into the more difficult stuff like not enough heads for the cam. I don't know all of your specs but if you would like to post them I would be glad to try to diagnose if that is the problem. You could email them to me directly if you would like. [e-mail]

Answer 6

The exhaust issue shouldn't be the problem unless it's LITERALLY 90*. I mean, if it's something you ordered, then it's fine...I know the Y-Pipe in my Bronco is like that.

Your issue is most likely in the timing. Did you get this as a crate motor or is this something you built? Did you replace the cam yourself or did someone do that? This is almost definitely a timing issue. Have you called the manufacturer of your block too to get the proper timing? And next time you go for an engine, go bigger...preferably 572 just to get that communist's panties in a bunch.

Answer 7

I would do a careful check on timing. This is a big cause of power loss. I would double check distributor installation, one tooth off could cause your problems. I doubt tje exhaust connection is at fault unless something is in the pipe to restrict it. If this is a custom exhaust the installer may have cut the hole too small at the 90 connection. You also have symptoms of a restricted catalytic converter, if you have one.

Answer 8

you'll need self belief it if it says that. the files comes from a equipped-in thermal sensor designed to keep the electronics from burning up. maximum probable causes are that your fan isn't turning or that it really is jammed up with lint or dirt. close off your computing device. turn it round so that you will see what's doing with the fan. attempt utilizing a pencil to expose it by skill of hand. seek for crud blocking off the air openings. Vacuum it away in case you be conscious that. turn the computing device on and be conscious if the fan spins properly and is shifting extremely some air. pay interest to no matter if it makes screechy sounds from its bearings. If the fan is the mission you would prefer to purchase a clean potential furnish because the followers have a tendency to be interior them. There would also be a fan on the proper of the CPU it really is seen in case you open the computing device. that could want to turn properly at the same time as the computing device is on. If no longer some thing obtrusive is misguided convey it to Circuit city which has a loose computing device checkup furnish.

Answer 9

I had a newly rebuilt 283 in a truck once that did the same and to find out there was not enough clearance in the bearings and eventually took the crank out
never knocked or anything til about 5000 miles

Answer 10

I'm wondering if the motor isn't starving for fuel? Maybe you should look into a higher volume fuel pump & I wonder if your radiator hose isn't sucking shut to help overheat condition or a flex fan or cowling around the fan to promote air thru the radiator