Chevy350 problems

[Chevy 350 Fan]

Hey guys I'm a senior in high school and have a 72 GMC truck I'm restoring after it burned up. Anyways I scored a sweet 500 HP Corvette Motor for it. It was built in a race shop in Texas. Obviously I didn't buy it new. I bough it from a buddy I have done business with before he had it in a mudding jeep. he said he hasn't put many miles on it. Anyways I went to start it for the first time and its really trying to run but only header tubes 2 and 4 are getting hot. It has a dual plane intake so I don't think its fuel as its sucking gas and air from both sides of the carb for 2 and 4 to run. Another important detail is he told me to follow the firing order on the distributor cap. Its not the typical Chevy firing order.
1 8 4 3 6 5 7 2 is the good ol typical Chevy firing order.
1 8 6 2 7 3 4 5 is what the cap said and he told me to use
now if its supposed to use the traditional firing order one would think 2 and 4 would line up but as you can see they don't. I'm running a MSD 6AL rev limiter/spark controller. I'm really lost here any advice would be much appreciated.
Thanks!

[summitflier]

Hmmm... pretty familiar with the first firing order you have listed there.
The second one I haven't seen. Later model LS engines are different from
small blocks. But the second firing order doesn't match that either.
Cadillac northstar engines were different also but they weren't really chevy small blocks.
GM small block V8 engines are 1-8-4-3-6-5-7-2.
GM LS V8 engines are 1-8-7-2-6-5-4-3

I suppose it's possible, but I haven't seen any other firing orders. To change the
firing order you would have to change the crank and the cam (and a few other things).

[Taibo]

Originally Posted by Chevy 350 Fan

Hey guys I'm a senior in high school and have a 72 GMC truck I'm restoring after it burned up. Anyways I scored a sweet 500 HP Corvette Motor for it. It was built in a race shop in Texas. Obviously I didn't buy it new. I bough it from a buddy I have done business with before he had it in a mudding jeep. he said he hasn't put many miles on it. Anyways I went to start it for the first time and its really trying to run but only header tubes 2 and 4 are getting hot. It has a dual plane intake so I don't think its fuel as its sucking gas and air from both sides of the carb for 2 and 4 to run. Another important detail is he told me to follow the firing order on the distributor cap. Its not the typical Chevy firing order.
1 8 4 3 6 5 7 2 is the good ol typical Chevy firing order.
1 8 6 2 7 3 4 5 is what the cap said and he told me to use
now if its supposed to use the traditional firing order one would think 2 and 4 would line up but as you can see they don't. I'm running a MSD 6AL rev limiter/spark controller. I'm really lost here any advice would be much appreciated.
Thanks!

Since you are using MSD ignition here is what they say about firing order. I think your buddy was just a bit confused. From the chart I believe it obvious that the order you have is incorrect. Wire it up for 1-8-4-3-6-5-7-2 and see if it starts!

[Chevy 350 Fan]

its not an LS motor. its from a 80-90's vette probably LT1. Sorry, I probably should have specified.

[Chevy 350 Fan]

Originally Posted by Taibo

Since you are using MSD ignition here is what they say about firing order. I think your buddy was just a bit confused. From the chart I believe it obvious that the order you have is incorrect. Wire it up for 1-8-4-3-6-5-7-2 and see if it starts!

they make special cams to eliminate cylinders 5and 7 from firing next to each other. its supposed to be easer on the bearings. Its rare to find an engine with one of those cams though. but yea I was going to try it with the traditional firing order. Thanks for the reply!

[hugger6933]

Now if it is an LT motor you would notice the water pump is Not driven by a belt. Normally where the w/p pulley is you would have a flat plate. No the firing order change type cams it is just two that are swapped or so I thought.
I would try to wire it in a traditional fashion and crank the timing up a bit it sounds low.
Good luck keep at it you can get it running. Jim

[hugger6933]

Also those firing order change cams use to be real expensive and at one time only super serious guys had them. Like pro stock guys and such

[Chevy 350 Fan]

Originally Posted by hugger6933

Now if it is an LT motor you would notice the water pump is Not driven by a belt. Normally where the w/p pulley is you would have a flat plate. No the firing order change type cams it is just two that are swapped or so I thought.
I would try to wire it in a traditional fashion and crank the timing up a bit it sounds low.
Good luck keep at it you can get it running. Jim

any idea what the firing order is supposed to be for those cams?

[MARKDTN]

Do you have a photo of this engine? The LT1 is going to look different than anything else.

[Chevy 350 Fan]

ill post a more recent pic after school with everything on it. But yea its pretty much what came out of the truck. I though earlier LT1's looked like this? like the 80's and early 90's.

[Taibo]

Originally Posted by Chevy 350 Fan

ill post a more recent pic after school with everything on it. But yea its pretty much what came out of the truck. I though earlier LT1's looked like this? like the 80's and early 90's.

Early 80's corvettes used the L98 engine. GM didn't start building the LT1's until 1992-1997. The LT1 engine used a shaft driven water pump, nor a belt driven one as illustrated in the attached pictures and those do not, in any way, resemble the pics of the engine you posted.


Only way to be sure just what you have is locate the casting numbers on the block you have and post them!

[geezer#99]

Easy to check your firing order using the compression test.
Pull all the spark plugs and the dizzy cap.
Put your thumb over the plug hole on #1. When you feel compression then you know #1 is just about ready to fire. The rotor should be pointing at #1 on the cap.
Then follow the firing order, checking each cylinder in turn. Watch the rotor while you do each one.

[Taibo]

Originally Posted by geezer#99

Easy to check your firing order using the compression test.
Pull all the spark plugs and the dizzy cap.
Put your thumb over the plug hole on #1. When you feel compression then you know #1 is just about ready to fire. The rotor should be pointing at #1 on the cap.
Then follow the firing order, checking each cylinder in turn. Watch the rotor while you do each one.

Wanna bet that it's 1 8 4 3 6 5 7 2?

[bad68nomad]

Originally Posted by Chevy 350 Fan

any idea what the firing order is supposed to be for those cams?

You are referring to a 4-7 swap cam. 18736542

[Chevy 350 Fan]

I fixed it! firing order was 180 out and one plug off. She Runs great now! thanks to all who commented. And yes it was the traditional 1-8-4-3-6-5-7-2 firing order. The guy I got it from is just not the brightest bulb I guess.

[Taibo]

Originally Posted by Chevy 350 Fan

I fixed it! firing order was 180 out and one plug off. She Runs great now! thanks to all who commented. And yes it was the traditional 1-8-4-3-6-5-7-2 firing order. The guy I got it from is just not the brightest bulb I guess.

Winner, Winner, Chicken Dinner! Good Job! Glad you got it running.

[67 chevelle]

Your firing order is wrong , imposable for the engine to fire 3 times on the same bank 8-6-2 will not fire in that order