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-   -   do bigger cams have harder cold starts ? (http://www.hotrodders.com/forum/do-bigger-cams-have-harder-cold-starts-223512.html)

xzero117 08-29-2012 05:11 PM

do bigger cams have harder cold starts ?
 
I just did a new engine build with 274h comp cam

230/236 duration at .50lift

I've never had a cam this big before and i was wondering, do bigger cams have a tougher time with cold weather

I tried starting it today in my garage and it felt almost as if it were 20 below outside instead of 78 degrees

is my tune out of whack ? any tips to improve cold starts

I have a carbureted 350 chevy with electric choke

RWENUTS 08-29-2012 07:30 PM

Depends what carb!
I had an eddy with a cam like that. Wouldn't start without a lot of fussing. Pumping gas and choking it.
Put a holley 750 vac secondary on and it would start after a couple pumps with no choke no matter how cold it was outside. Even down to 20 below.

xzero117 08-29-2012 11:23 PM

that makes sense because i'm definately under carbing my engine with a 600 cfm edelbrock on my setup

it's the 274 cam, 10.3 compression, 2.02 1.60 valves

i added a 1 inch spacer a s half assed band-aid, when warm the engine feels amazing though

cdminter59 08-30-2012 07:11 AM

bigger cams
 
How do you have your timing setup? Initial___ mechanical___ total___. Read this article it explains everything in detail. http://www.crankshaftcoalition.com/w...EI_distributor

ap72 08-30-2012 08:25 AM

In my experience Edelbrocks are much easier to tune for cold starts, and do a much better job than holleys, BUT I have a bias towards those on any basic street engine anyway.

My 2.3L Bobcat has a edelbrock 600 (1406) with a single plane intake, header, and locked timing, that I've retuned and you just give it one little squirt with the accelerator pump and turn the key. The idle starts at about 800 and when its warm will climb to about 1000. Absolutely no start issues at all.

It is a little fussy on off idle tip in when its cold, but after a few minutes of driving it performs flawlessly.

F-BIRD'88 08-30-2012 09:15 AM

The key is correct ignition timing curve for the cam.
And not allowing the motor to idle at a low rpm while first cold.
Get it started and get the rpm to 2000+ rpm and hold it till some heat gets into
the manifold. if you think you can idle it low like a EFI motor when cold
you are going to go thru a lot of spark plugs.
Give it plenty of idle rpm when cold. Give it time to "warm up"

Correct the timing curve with plenty of initial base timing.

20-24deg base ,,34-36 at max mech advance
10-15deg of vacuum advance for part throttle cruise
the stock out of the box timing curve is never right.

Cammed up motors want a lot more initial base idle timing than stock.
Get a 750 eddy or 750 holley.

68NovaSS 08-30-2012 09:25 AM

My experience with big cams is easier starting, and less flooding, partly due to higher lift and longer duration on the exhaust side, JMO. In my blower motor flooding isn't a problem, I've only flooded it once. In the tunnel ram BBC bucket, same thing, easy to clear it out but it starts with a roar. I never crank the blower motor with the throttle open, and try not to in the bucket, but that is how you clear it.

xzero117 08-30-2012 09:43 AM

thanks guys

i'll try advancing the timing a bit, my previous engine with a few sizes smaller cam started up fairly easily in the cold with a choke and my foot slight on the accelerator

I probably just have to finish tuning the engine, if it's still kinda hard i'll step up to a 750

prostreet6t9 08-30-2012 05:16 PM

Mine starts right up.. 715 lift with a 1050 carb.One quick pump and it lights right off.

ap72 08-30-2012 07:29 PM

Quote:

Originally Posted by xzero117 (Post 1587128)
thanks guys

i'll try advancing the timing a bit, my previous engine with a few sizes smaller cam started up fairly easily in the cold with a choke and my foot slight on the accelerator

I probably just have to finish tuning the engine, if it's still kinda hard i'll step up to a 750

going with a bigger carb won't cure it, but a cleaner carb, or perhaps better tuned carb can make a difference.

xzero117 08-30-2012 09:03 PM

Quote:

Originally Posted by ap72 (Post 1587271)
going with a bigger carb won't cure it, but a cleaner carb, or perhaps better tuned carb can make a difference.


so tweak with my idle mixture screws ? I though i had those pretty much set

the carb is supposed to be tuned for performance right out of the box (1405 model edelbrock)

i played around with my choke today and advanced the timing slightly, guess i'll just have to start it up tomorrow and see what happens

spinn 08-30-2012 11:06 PM

Bigger cams use heavy springs, high compression, and require more initial timing. Heavy springs increase seat pressure adding rotating resistance at start up. Turn a stock engine by hand and then a big cam engine. The high base timing required will also be a load at crank and increases for hot starts. The warm up time will depend on many factors. The choke when tuned can work well. Starter timing retards can increase the life of your starter and make things easier. A high torque starter will crank the higher compression builds nicely.

The timing is probably the critical variable for asuring easy cold starts. A proper vacuum advance is needed for a driven vehicle.

Yes a big cam will cause harder engine cold starts. There is more load. Is that what you are really asking, I do not know.

xzero117 08-31-2012 07:18 PM

Quote:

Originally Posted by spinn (Post 1587317)
Bigger cams use heavy springs, high compression, and require more initial timing. Heavy springs increase seat pressure adding rotating resistance at start up. Turn a stock engine by hand and then a big cam engine. The high base timing required will also be a load at crank and increases for hot starts. The warm up time will depend on many factors. The choke when tuned can work well. Starter timing retards can increase the life of your starter and make things easier. A high torque starter will crank the higher compression builds nicely.

The timing is probably the critical variable for asuring easy cold starts. A proper vacuum advance is needed for a driven vehicle.

Yes a big cam will cause harder engine cold starts. There is more load. Is that what you are really asking, I do not know.


Well that was my big question, yes. For the most part I wanted some tuning tips on how to better start it cold, someone said advance the timing a bit, I did, it worked wonders.


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