Why are some engines cold blooded? I have had engines that would start up and be ready to drive without any warm up, and some require a few minutes warm up to even idle. Now obviously I am talking about carbureted engines only. I recently rebuilt my 350 SBC. Before the rebuild the engine was not cold blooded. It had stock iron heads and manifold. I threw everything away except the block, crank, and the QFT SL-600-VS carburetor. New aluminum heads and dual plane aluminum manifold and with about a point and a half more compression ratio. Now the engine is cold blooded as hell. It takes several minutes for it to even idle. Probably the most cold blooded SBC I have ever had. About 3 pumps and it starts right up, but you have to play with it to keep it running. It runs and idles great after warming up though. When it is warm it fires on the first lick. Just reach in the window and turn the key. The new aluminum heads and manifold do not have the exhaust crossover passages. Is this the whole reason for the cold bloodedness that I have now, or are there other contributing factors? It has an electric choke. I have played with it from one end of the range to the other with no effect. It's like the choke comes off too early even at the richest setting. I've thought about putting a manual choke on it. I have an AFR meter in it and have tuned the carb to be running good in all modes. It is leaner now than when it was on the engine before rebuild. It took a lot of trial and error tuning to get it to cruise with 14-15.5 to 1 AFRs and still transition through the different circuits well. It was pig rich everywhere when I started tuning. I'm wondering if the lean tune is a contributing factor? I hate to richen it up just for the cold bloodedness at the expense of mileage or performance. The car runs the best it ever has..... after it is completely warmed up. It'll boil the tires at will. It makes me wonder because I would think the aluminum heads and manifold ought to warm up quicker than the cast iron stuff, but maybe not without the exhaust crossover. Anyway, how many of you guys have had cold blooded engines and were you able to cure it?
My tunnel ram takes 10 -15 minutes to " warm up" completely , dependent on weather , choke is in use up to 10 min. ( manual choke on 1 carb) . all the carbureted vehicles I've owned , I've set up a lean choke , I'd rather have to pump a bit than flood .
Your comment about it being a "rich pig" before tuning, pretty much covers why the previous setup wasn't cold blooded but the lean version is. In the mid 70's the car manufacturers introduced EGR and pretty lean mixtures. The complaints of stalling and/or poor running cold were the norm. I remember a service letter from Ford stating that if a customer's car only died twice when cold, it wasn't likely that you could make it much better. I agree that most electric choke setups cause the choke to come off too soon. I wonder what a resistor in the choke circuit would do to slowing down the heating coil. To keep it from being cold blooded you need the mixture towards the fat side while warming up. A 180/190 thermostat helps quicken the warm up period.
Have several, and all of them have different start up, and warm up issues. One is a dual carbed SBC with a tunnel ram, and it takes a good several minutes before it idles properly. But it doesn't even have choke plates, so not expected to idle well when cold. The other two both have electric chokes, and the typical Holley fast idle step ups when the choke is on. They both idle up when cold and no issues to taking right off. They work great, and idle down within minutes of driving, and start at just a touch of the key hot or cold.
I had a 396 that was cold blooded because of no exhaust cross over in the manifold. Its in another car now with an intake that has exhaust cross over passages and runs good now.
Is there really such a thing as a "cold blooded" engine?...or are they just engines with carb, choke or timing issues?
I would expect this to make it take a bit longer before it runs well, but it should not be the lone cause. Have you tried blocking the choke manually to see how the engine reacts to full choke longer time? Assuming it can be done without damaging something of course. If you KNOW it runs better with more choke, that's a point in favor of modification. No improvement? Keep looking for the solution elsewhere. Oh, yes. Running it permanently rich is like choking it all the time. It used to run well cold because you gave it enough fuel to run well, now you don't. Can you richen it up just at idle, with no or very little change in fuel ratio when driving down the street? Idling is a small part of normal driving (unless it's bumper to bumper city driving) and shouldn't affect the total fuel economy very much. Might not take much to make it idle good enough, and that seems worth it, as an engine that won't idle for minutes would be very annoying to me.
Dual plane good...no heat bad. No heat and air gap manifolds are really not your friend on a mild or stock street engine. Yes they do help in fuel percolating with today’s gasoline but there are other things you can do to help that. It sounds like your fast idle of the carb choke is too quickly to fall off and you’ve tried different settings to no avail. There are ways of going back to the stove type of choke and perhaps that’s what you’ll need to look into and do. Good luck
The electric choke opening a lot quicker than the engine that doesn't have a heat cross over in the intake needs it to is the big issue. That puts it pretty much in line with those of us running without a choke plate and blocked heat risers in the warm up battle when it is a bit cool. I'd say if it does pretty good after sitting out in the sun at a show and tell all day on a hot day you pretty well have your answer. That may be a small price to pay for great performance after it warms up to running temp.
Yeah, that's just the thing. I have low speed and high speed cruise at 14-15.5 AFR. WOT is about 12.5 AFR. All right where they need to be. Except the idle. It is at 12.4. Already way rich. I can lean it out with the idle mix screws but idle quality suffers or I start developing an off idle stumble. This cam is only 215/224 @ .050 with .470/.490 lift. So not a wild cam at all. Smooth idle, no lope, stock converter. I came to the conclusion that the cam must like a rich idle and gave up on trying to lean the idle out. And yes, it is a pain in the ass.
throw away the AFR meter, tune it so it runs good, but does not put out black smoke... Yeah, hot rod motors need a rich idle, and rich off idle, to be driveable. Don't try to use EFI AFR numbers with a carb, you'll end up with no hair after pulling it all out.
LOL! Just the opposite! One pretty warm day about 70 degrees about a month ago, I was playing with the carb and had the idle circuits and the mains leaned out to 15-17:1 AFRs. It ran pretty good there. I decided to drive it to the races about 3 miles from the house. It got down into the 30's before the race was over. That thing would barely run and pegged the AFR meter all the way home. Scared me to death. I richened it up the next morning. We are coming in to some 80 degree weather next week. We'll see what happens. I drive this car pretty much all year long. I'm afraid it is only going to get worse in the winter, so I hate to give up and just accept it.
I have a Holley 700 and opted to put a manual choke on it, which is really touchy so I rarely use it. I have a Dart air-gap intake too, aluminum heads so I just give it a few minutes, get it up to 150 on the water gauge and drive off. This is when it is 35 and under. Summer, I can drive it within a minute of starting. I drive it as cold as 3 degrees out and it does cool off real fast if I stop somewhere.
Lots of good points made about the choke intake and other potential factors. I can't help wonder if alumininm heads and intake may also be a contributing factor as alumininm dissipates heat faster than cast iron, so it physically takes longer to get warmer. I'm no engineer but have worked on cast iron and aluminum engines so it's just an observation I've made.
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