I have a 1979 corvette with a 420 hp crate engine. When I start it it cranks slow like battery is dead then fires right up. It has a new battery and voltage regulator. Wonder if the starter is bad or not big enough to start this engine.

 

It could be that your compression ratio is too high, it could also be too much advanced timing.
do you know the motor’s CR and what timing you have it set to?

 

No I don't know either of those. I just bought it a few months ago and they didn't have any of the paperwork for the engine. I will check the timing

 

Is there a difference in starting speed between the motor being cold vice when it’s hot?
if it’s slow on both, it could also be the negative cable going from frame to battery has a higher resistance from age/corrosion

 

It seems to be worse when the motor is hot

 

when the motor is hot, the rings seal the cylinder/combustion chamber better making it harder on the starter.
it still could be the negative cable having high resistance, and the extra load when hot just makes it worse.
If you look under the car, under the battery box you can see where the negative cable attaches to the frame. Unbolt it and scrape/rough up the metal where the cable bolts too, make it shiny. Reattach and see if it’s improved.

I don’t think it’s compression ratio, just because your typical street built engine is not a ludicrous CR that a stock Chevy starter can’t handle.
if you have a timing gun you can check the timing, or
just try retarding it some and see how it goes.

 

Thanks I will try that

 

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I had this issue on my 427 equipped C3. After putting headers on the car it would really crank slowly when the engine was hot. It turned out the starter was getting heat soaked and that slowed it down. I replaced the starter and then installed a gear drive starter and the engine would immediately crank faster. Before the gear drive I had my local starter/alternator shop beef up my factory starter but that was not enough when the engine was hot so I then bought a Gear drive from Summit racing and that device is designed for engine with up to 15-1 compression. Gear drive starters are great and a very simple way of solving a weaker starter motor.

If the engine cranks slowly even while cold then you either have too much timing advance or you have a bad battery or power connection. The bad or dirty corroded connection is the more likely of the two in most cases. If the ground strap has any corrosion it can slow down the starter as would any bad corrosion on the battery Positive wire connection. You need to be absolutely sure that all the battery power is actually reaching the starter. This could be tested with a Multi-meter with the Min-Max Function built into it. You would attach the leads to the starter battery Positive connection and then the second lead on the body of the starter. When you crank the car with a meter in Min-Max it should show you the lowest voltage seen at the battery while cranking. I use this test but on the battery to check the condition of the battery in the vehicle. It is the best way to test a battery at home IF you have a multi-meter that does the Min-Max function. I personally like using Fluke Multi-meters as I used them at work for a long time and grew comfortable with them and their quality. I bought a Fluke 88 which is designed primarily for the automotive world and has a timing pickup and a temperature probe plug on it. Awesome multi-meters!

I have a MSD ignition system and one of the components allows me to retard (pull) the timing while cranking the engine to start. My 427 runs 12.25-1 compression and it makes the starter work extra hard. Pulling 10-15 degree of timing while cranking "unloads" the starter and allows it to crank faster. I now have a EFI system that has this feature built into it and it makes a big difference if you are running any kind of compression above the standard stuff. With both a gear drive starter and the timing pull back I am cranking my 427 very quickly which makes it start easier. My timing is returned to normal once the engine exceeds 400 rpm and this means the car acts normally once running.

Best regards,
Chris

 

Thanks for all the information. I am hoping to find some time to look at it this weekend.

 

I was having the same issue with my 73 when I bought it.
The negative battery cable looked new and I moved on the check other things like the timing, starter, etc.
After everything else check out I went back and double checked the battery and noticed a slight amount of corrosion on the negative cable.
I took a knife and stripped back a little bit of the insulation and found the copper cable was almost completely corroded through even though it looked new on the outside.
I replaced the cable and solved the issue.

 

Thanks. I will make sure and check that too

 

My guess is bad battery cables and/or starter heat soak. Good luck

 

do you have the stock style giant starter or a high torque mini starter. With high compression you will need a high torque starter.. Then get a insulating wrap to protect it from the headers

 

It's the stock starter. I was wondering if that was ok for this engine

 

nope. I had a similar issue and the starter was fine, it just didnt have the ***** for the higher compression. Go to a mini high torque starter. I have good luck with the East Coast Auto electric starter.
the full Summit selection
https://www.summitracing.com/search/...+D+-+L+(Search)

the starters
https://www.summitracing.com/search/...uto%20electric

 

A stock starter is good for what? Up to 11:1 CR if I remember right.
I personally would start with the checks that don’t cost money.
It is very possible that he needs a stronger starter, but even the highest torque stater out there cannot turn a motor if the negative cable is full of corrosion:

 

Ok thanks. I will look those up

 

This ^^^^^^

Not knowing comp ratio does not justify a mini starter, yet.

 

I got help for you possibly too much timing losing your distributor and moving in micro increments clockwise and counterclockwise until you get an easier crank it's better to have someone in the car while you twist the distributor then you will find The Sweet Spot once it's running get it get in hot then shut it off wait 10-15 minutes and then try starting again if labored starting appears again you have a bad hot start turn the distributor again until you find The Sweet Spot or warm the vehicle and set timing with the timing light I hope this fixes your problem good luck God bless you

 

Thanks. Will try this too .