bad high RPM's

[Navy Lalor]

so i recently swapped out my junk 305 in my 84 c10 and replaced it with a mild 350 bored .30 over with a 650 holley carb,troubles are going on right now..when i am at high rpm's i dont feel a acceleration so i have to let off the pedal like a little bit to feel the pull yet still not getting the full horsepower out of it. also i am running long tube headers with some flex pipe becuase i cant fit flanges it will hit the trans crossmember. so i have 6'long flex to two cherry bombs..am i not getting enough back pressure ???.... one more thing...i no my oil pan gasket is leaking so i need to replace it tommorow would the mild amount of white smoke coming out of the engine bay when i drive caused by the oil splashing back on the headers??? and for the carb do you think i need to rejet it ??


langston

[68Timber]

If it falls flat at higher rpms I'd wonder about fuel starvation first, not back pressure. As far as the white smoke from under the hood goes, can you check it at idle?

[Wild83C10]

Go Navy!

You should post this in the engine section. Please define high rpms? 4000, 5000, 6000 rpms? Is it breaking up or you just don't feel any power? The cam/heads have a lot to do with the power range of the motor. What heads do you have and what are the cam specs?

Back presure is a bad thing, you don't want it. Ditch the flex pipes and either put an S-bend in there (if you have your own welder) or take it to a local muffler shop to have them fix it up.

If the oil pan is leaking so bad that the oil is spraying on the headers replace it ASAP. Make sure you use some black stuff gasket maker by loctite.
Almost impossible to diagnose carb troubles over the internet.

[nekkidhillbilly]

no back pressure will make your tq turn to nothing

[Wild83C10]

Originally Posted by nekkidhillbilly

no back pressure will make your tq turn to nothing

Please explain.

[68Timber]

Yeah, I'm ruling out backpressure. An overrated topic and I don't think it applies here at all.

[68 TT]

The first thing you need to do is fix the oil leak. It can cause a fire and that is the last thing you want to deal with.

The guys running the auto hobby shop on base are your friends. Get to know them and learn from them. They are car guys and will help you out. I learned a lot from mine when I was just starting out and learning about cars.

Have the headers connected to the mufflers by an exhaust shop. That flex pipe is horribly restrictive and could be causing some or all of your problems. If the motor can't breathe it will fall on its face at higher RPM's

Next get yourself a fuel pressure gauge and monitor what your fuel pressure is doing at the trouble RPM's. It sounds a little like you are running out of fuel in the carburetor.

After the fuel pressure is verified get a wide band air / fuel meter and install it. With this you can tune your carburetor properly. Narrow band gauges have a very narrow range of being able to tell you what you need to know and EGT sensors are at best just a guess as they can't tell you if you are too rich or too lean as both can give you the same EGT reading. Once you are done tuning the truck you can remove the wide band gauge and rent it out to your friends to get some of your money back. I have one I have been using for several years and have used it to tune at least a dozen vehicles. It has more than paid for itself.

[jchav62]

I agree with the guys...

Fix the leak, lose the flex pipe and check your fuel pressure. Also, make sure your vacuum advance in the dist. is working properly. Lack of advance at higher RPM's will result in power loss.

[Navy Lalor]

thank you all for the posts,i just replaced the gasket so no more leak and white smoke....i need to wait till my buddy gets back from deployment in two days to have a garage and welder and fabricate some sort of pipes so the headers wont hit the crossmember. ill look into that fuel pressure guage...ALSO i dont have a tachometer but i am talking just pedal to the floor on the highway if i do that the engine just doesnt pull. ill keeps you updated

[staggerd86c-10]

i would check the needles in the carb if its a used carb it might have some dirty needles and when the carbs starts pulling alot of fuel its not flowing. while your at it have someone adjust your carb really good that might just be the problem. 650cfm carb seams to be enough for a street 355.

[68 TT]

You could also have some ignition issues. Check the condition of the cap, rotor, rotor button, ignition coil and your plug wires & spark plugs.

With it running that rich you might have some pretty fouled out spark plugs.

Take a look at this:

http://67-72chevytrucks.com/vboard/s...d.php?t=362601

From the outside the cap looked perfectly fine and the truck idled and ran pretty well. I never pushed it past about 3000 rpm before I found this so you never know what is hiding under that distributor cap.

It looks like the rotor button disintegrated and the coil arced across the gap on its own and melted everything in the process.

[68Timber]

Originally Posted by 68 TT

The first thing you need to do is fix the oil leak. It can cause a fire and that is the last thing you want to deal with.

The guys running the auto hobby shop on base are your friends. Get to know them and learn from them. They are car guys and will help you out. I learned a lot from mine when I was just starting out and learning about cars.

Have the headers connected to the mufflers by an exhaust shop. That flex pipe is horribly restrictive and could be causing some or all of your problems. If the motor can't breathe it will fall on its face at higher RPM's

Next get yourself a fuel pressure gauge and monitor what your fuel pressure is doing at the trouble RPM's. It sounds a little like you are running out of fuel in the carburetor.

After the fuel pressure is verified get a wide band air / fuel meter and install it. With this you can tune your carburetor properly. Narrow band gauges have a very narrow range of being able to tell you what you need to know and EGT sensors are at best just a guess as they can't tell you if you are too rich or too lean as both can give you the same EGT reading. Once you are done tuning the truck you can remove the wide band gauge and rent it out to your friends to get some of your money back. I have one I have been using for several years and have used it to tune at least a dozen vehicles. It has more than paid for itself.

Learned something new - I've never used flex pipe but I did not know it is restrictive.

[68 TT]

Originally Posted by BRUISER

Learned something new - I've never used flex pipe but I did not know it is restrictive.

All those corrugations cause unwanted turbulence in the exhaust flow.

[68Timber]

Originally Posted by 68 TT

All those corrugations cause unwanted turbulence in the exhaust flow.

I can see that now that it's come up, I figured that's what it was - like one continous glass pack. I appreciate the time you spend here, it's not the first thing I've learned from you.

[68 TT]

Originally Posted by BRUISER

I can see that now that it's come up, I figured that's what it was - like one continous glass pack. I appreciate the time you spend here, it's not the first thing I've learned from you.

Glad to help.

[Navy Lalor]

well that is fun....through a push rod through my oil pan...crazy how it can go from where it is down there....i ripped apart the whole engine and saw howthe person who rebuilt the engine didnt put in the rods and pistons right......but i got a deal....a 400 small block with th400 ...cheap..and rebuilt by a real hot rod mechanic

[Hoods69BadBowTie]

Wow say that again so you blew your motor or you tore into it and figured out what was wrong with it? That sucks though man! Keep us posted.

[68 TT]

Did you put a connecting rod through the pan or a push rod?

That would take one heck of an engine failure to put a push rod through the oil pan.

I had a camshaft break into three pieces once at 7000 rpm going through the traps at the end of the 1/4-mile. One part ended up getting jammed through the bottom of the intake manifold. It shoved some pushrods through the valve covers. Needless to say that whole engine was toast.

Sorry to hear about the engine. Good luck with the replacement / repair job.