So I have had the car out a few times this season so far, usually on cool days in the 55-65* range. Car runs great when the gauge is reading about 160 degrees. I also have not run a thermostat as everytime I put one in the car overheats. Also I had the car out the other day when it was warmer out (like 75*) and the car was running at about 180* (Mind you I run an autometer temp guage) and everytime I got on it when she was this warm she did not have the power she has when she's cooler.... Any ideas on that? It was quite a noticeable difference in power between 160* and 180*... I never noticed it last year but I also never drove her in the cooler air last year either. Could it be timing issues? Mods are in signature... Also I'm aware I need to be running a 650cfm carb at least. haha. Any ideas? It's a little annoying as she really looses power....

 

Bump

 

First thoughts are hot air and hot fuel.

 

I'd look at timing - what the base timing set at?

180 is cetainly not too hot - autometer or not are we sure the gauge/sender is working properly? Have you ever had the car shot with a laser temp reader and compared to the gauge?

Maybe, since there's no thermostat, the car is never getting warm enough? At 160 temp maybe your still getting choke assistance, but at 180 your not getting enough chaoke assistance, yet the car isn't warmed up enough to run better? I know, weird thought, but it's something to debate/ponder.

My car runs right at 200 most days, regardless of outside ambient temps. Your car should maintain a relatively consistent temp regardless of how hot/cold it is outside. I run a 180 stat BTW. If it were me, I'd actually want my car to run warmer than 180 after 5 minutes or so - sure cooler running temps usually means better performance, but you can only go so low before you get a negative response instead.

Fans working properly? Air dam in place? Why are you avoiding temps above 180 (ie why are you not running a stat)? You do realize that actual overheating doesn't occur until well past 220 right?

 

Figure out and fix the cooling problem first of all. Heat energy is power. The more that saps into the heads means there's less pushing the pistons.

What are you gaining from overcooling the engine? More carbon buildup (and detonation,) less power, and less fuel economy. In other words, nothing. When it's 120degrees here, I have zero problems and I run a 195 stat.

The third-gen stock radiator and fans cool a properly running engine just fine when they're working and everything else is in order.

As for power, you need to read an O2 sensor readout to see which way the carb needs tuned. And timing curve is something to establish and tune. Base and total advance as well as what rpm all advance comes in by are minimum information you need.

You've got some good parts going for you. Now to best enjoy them, fix the cooling system and tune it up.

 

I have messed around with the timing a lot last year and decided it got it pretty good. I guess not... I always did it around 34* total advance in by like 3200-3400 rpms... That's what I've read the vortec heads like... If I'm cruising and drop a gear and say i'm at 4500 rpms and If I punch it or even push the pedal down quickly the car hesitates and the car jerks before catching itself and accelerating normally... I don't know a whole lot about carbs and I used to have tons of drivability problems with idling and stalling, etc. but now it is pretty drivable but still have more issues... It never ran all that well when it's hot, hence why I like to keep her cool.. and I have had cooling problems since I installed this engine... Which leads back to timing I'm sure... The old 305 never overheated...

 

Also I'm running a standalone fan controller. Has a little probe that pushes into the radiator fins then the unit has a dial on it to turn on and off the fans at a certain temp... Seems to work pretty good...

 

Have you checked the carb for proper powervalve sizing? What kind of dizzy are you running? The whole cooling thing sounds all wrong, should be able to run good at180-190 all day long???? Where is your base timing set at?

 

Its been awhile I don't remember my base timing, I'll have to look sometime. She doesn't like to idle low so I have to turn the idle speed up otherwise when the fans kick on she will stall out.. She idles a little over 1000rpms now... She will idle lower but like I said an accessory like the fan and sometimes the lights can stall her out. Using an accel aftermarket HEI dizzy. (Style with the coil on the cap) I know nothing of carbs, it was a Holley 600 bought and thrown on right out of the box...

 

I would size up the powervalve for starters, go to Holley's website and down load instructions, base timing should be right around 12-14*. Check your plugs, make sure they are burning tan, if not adjust the air idle mixture. While tuning w/ an 02 sensor is optimal, a vacuum gauge will get you in the ballpark, again download the instructions.
I know my carbed 385 needs to be right around 180* for it to have crisp throttle response. Carb tuning isn't hard if you follow the instructions on the website. If the plugs are not tan, you may need to re-jet? But I'd get the base timing where it should be and check the powervalve first....

 

I'm 99% sure my timing is around 12 degrees base timing.... The power valve I have no idea, haha.

 

Well I know this much a wrong sized powervalve will cause a hesitation, sounds like your timing is good....

 

Yea, It's pretty much no matter what rpm I am at if I floor it she will act like she gets very little fuel then picks back up... Not to mention if I'm cruising at 60 and give little blurps of the throttle she will do it then to. Doesn't have to be wide open...

 

Check the powervalve sizing, you'll need a vacuum gauge, go to the website and look it up. It's not that hard at all, the instructions are good...

 

I'm thinking of going back to TBI and trying that again. If I can get the TBI tuned right I would better drivability and make more power. Not downing on carbs but this stuff gets quite annoying after messing with it for a year and not getting anywhere.... I just don't like the drivability of the carbs....

 

Go ahead, carbs are simple,but it's your car...

 

Again I wasn't downing on carbs. (I love the look of carbs) I wish someone who knew what they were doing would come out here and get her running right! haha This is a pain in the ***! I can never seem to be able to get it right....

 

Im going to figure out the vacuum at idle to see if I have the right power valve in a few minutes.

 

Just curious, is this a electric fuel pump car
or mechanical pump?

I had similar issues last summer and the problem
was vapor lock. I upgraded my mech. fuel pump
with a holey mech. pump and those do not have
vapor return outlets. Once i figured that out i found
RobbMc pump with enough flow AND vapor return
option. Put that on there and problem solved.
http://www.robbmcperformance.com/products/chevy550.html

 

good question, if electric, how's it setup?

 

Its an electric fuel pump. (TPI pump) The lines run to the engine bay then where the washer fluid reservoir used to be is a return style regulator then that runs into a filter then into the carb... I believe the reg is set at like 5.5 lbs. or something.

 

O and Vacuum at idle is just under 13 idling around 1000 rpms...

 

Turn the regulator up to 6.5-7 psi, Should be pulling 14.5-15 vacuum, I have a hell of alot more lift and duration 584/584 .297.308 and have 14-15 on vacuum, can't remeber if you need a larger or smaller powervalve, but it sounds like it needs to be changed....

 

Normal engine should produce approx. 18-22 ins Hg, steady at idle. If there are any Intake manifold leaks between the manifold and the head, the indicator will drop anywhere from 3-9 ins. Hg, and remain steady. A low, steady reading at idle can also indicate late (retarded) timing.

 

While all this is true, it's not a normal motor, it's bored, has different heads, pistons, and most importantly has a CompCams XE274 camshaft. You'll never see those kind of vacuum #'s w/ that setup....

 

I don't know why, but your sig is not always coming up, I couldn't see what you had at the bottom. This entire forum always shows "Done, but with errors on page."

I still think under 13 is a little bit too low, does the vac reading change significantly from heat changes?

 

Holley recommended fuel pressure is 5-7 psi. If it's set at 5.5, moving it up to 6.5 isn't going to do anything. But, "believing" it is set at 5.5 psi isn't "knowing" it is set at 5.5 psi, nor is it "knowing" what the pressure is when your problems show up.

The power valve isn't going to change how the car runs between 160 and 180 degrees.

I have never seen a car run properly without a thermostat. If it's running 180 degrees in 75 degree weather without a thermostat, you have a cooling system problem that needs to be addressed.

Pusher fuel pumps don't "vapor lock". However, you might be boiling the fuel in the carb.

While all the tips you've received so far are fine when it comes to properly setting up and tuning a carb, none of them relate directly to the fact that it runs differently at 160 vs. 180 degrees engine temp. So, you either need to understand what is changing between 160 and 180 degrees engine temp, or you need to make absolutely certain that the problem is actually showing up at 180 degrees engine temp. It could have nothing at all to do with being 180 degrees.

By the way, you don't start diagnosing carb problems until you are absolutely certain the ignition is up to snuff. That includes the timing. Where is it set, and how did you set it? What distributor are you running?