Engine firing conundrumNovember 19 2017 at 9:49 AM
|Pierre (Login cayuco)|
I am taking delivery of a rebuilt 350Q engine from a highly reputable mechanic with solid marine engine experience. We started from a raw block and put in all new components, crank, pistons, rods, heads, etc.. and used the Q intake from my old 327Q.
We're having a back and forth as we wire the distributor. I know, and he knows as he has the Chris Craft engine manual, that Q engines fire 1 8 7 2 4 3 6 5 (LH), with the peculiar 2 and 4 firing next to each other. He is telling me that the firing order of the engine he is delivering is 1 8 4 3 6 5 7 2. This is the same firing order CC had on the "F" engines, and the usual Chevy SB order.
My question is: What does the different Q engine order does and what are the implications of going with the "non-Q" firing order as the engine builder is telling me. Do I run the risk of destroying the engine one way or another with the wrong order (besides loss of power, etc...?) Is it a question of the camshaft being closely associated to the firing order?
I cannot question his expertise and dont want to change what he is telling me unless I can prove him a different setup is necessary.
I hope the engine experts in this forum can shed a light on this pretty crucial subject.
Also, the 350Q that CC offered had only 5HP more than the 327Q and less torque at same rpm. What was the value then of the increased displacement and should I not expect any significant power uptick from my new engine compared to the old 327Q?
Thanks much for your input.
|November 19 2017, 9:25 PM |
I really have no idea why Chris Craft would use a different firing order. The cam could definately dictate the firing order - both valves need to be closed on the compression stroke. If your builder put a standard SBC cam in then I believe it would need to be a standard SBC firing order.
From what I can find 18724365 is a firing order for a counter clockwise rotation engine and 18436572 is for a clockwise (normal) rotation. not sure but guessing the cams have to be different. SBC has paired cylinders 1 and 6, 2 and 3, 4 and 7, 5 and 8. When one is on compression the other is on exhaust.can't see how the reverse CCW firing order could work with a normal cam
|This message has been edited by jossar on Nov 19, 2017 9:48 PM|
|November 20 2017, 9:17 AM |
The cams do dictate the firing order.
There are two specific design items in a cam that determine rotation.
First is the cam lobe profiles and their relationship to the crankshaft. Reversing the engine rotation requires a mirror image of the lobe relationships since you are reversing lead and lag relationships.
Second which is the real biggy is that the distributor drive gear on the camshaft needs to have a reverse pitch since it is a helical cut gear. The oil pump is only driven one direction as there are no reverse rotation oil pumps. There is also the issue that the distributor needs the cam to drive the distributor shaft up as that is how the distributor shaft bearings are designed.
There are some oddball 180deg flat cranks out there that also require an oddball cam to match. These really are racing engine parts and I would hope is not what your new engine has.
|Paul A Mathias|
Re: Engine firing conundrum
|November 20 2017, 12:52 PM |
The Firing order on a Q motor is the same a a standard small block Chevy. The Difference is CC renumbered the Cylinders when they turned the motor around. Look at the page prior to the one posted in the manual it will show you.
Paul A Mathias
Paul A Mathias is right
|November 20 2017, 1:34 PM |
Paul you beat me to it. Last night I drew a photo of the block and the eight cylinders, inside the cylinders I wrote down the firing order of a F motor, and then I rotated a Q motor to the same orientation with the flywheel back instead of front, and wrote down the firing order of the Q alongside each cylinder, which as you noted is backwards starting with the numbers 8 and 2 forward instead of 1 and 2 for the F.
Then when I followed the firing order of a Q, guess what? It was the same as the F only backwards due to the way I did it.
The thing a lot of people should be aware of, is the fact that Chris-Craft took a STANDARD ROTATION Q motor which uses the standard automotive firing order, and when they turned it around backwards Chris-Craft declared it a RH motor simply due to the fact that it was oriented in the boat that way with flywheel forward. For any mechanic in the shop, they don't know or care about the orientation in the boat, they just go by which way the flywheel is spinning. So if the motor being delivered runs, just record the firing order and be done with it
As a point of information, looking at the power ratings for the 327Q and the 350Q, and wondering why the larger motor didn't have a power advantage, it's because the 327Q has higher compression ratio. Therefore the 350 should run better on fuel we have today and in theory should be understressed and last longer.
Regarding the cam gears, unles the motor is 1986 or newer, the cams all are cut the same way, the distributors all spin the same way due to the fact that a gear is used to control the direction the cam is spinning. The cam spins the same way on the standard or reverse motor, and the distributors are able to be interchanged. I ran into this when I ordered up a reverse gear on my 350 repower for the 327F, because it's a RH motor and much to my suprise it would not fit, and thats when I discovered there are NO reverse distributors for the F series (and I suspect the Q is the same but stand to be corrected on that if its not the case, since I have not personally been into a Q myself)
|This message has been edited by FEfinaticP on Nov 22, 2017 1:19 PM|
Paul and Paul agree but I can't see how Q and SBC the same
|November 20 2017, 7:25 PM |
Disregarding engine rotation, orientation, cam type or cylinder numbering:
Picture the cylinder layout as:
The SBC pattern (or CC "F") is 1 8 4 3 6 5 7 2
The first pair of cylinders fire in their opposite diagonal 1-8, then the cycle fires the middle cylinders 4-3, 6-5, and finally the cycle ends with the last two in their opposite diagonal 7-2
In the Q engine, the firing is 1 8 7 2 4 3 6 5
The cycle starts with the first pair in opposite diagonal 1-8, but then immediately goes to the other opposite diagonal 7-2, and then finishes with the middle cylinders 4-3 and 6-5
I cannot see those two firing patterns as being the same. Sorry if I'm missing something totally obvious.
|November 20 2017, 9:39 PM |
Is it possible your missing what Paul Mathias mentioned - that Chris Craft renumbered the cylinders when they turned it around?
8F=1Q, 6F=3Q, 4F=5Q, 2F=7Q, 7F=2Q, 5F=4Q, 3F=6Q and 1F=8Q
|This message has been edited by jossar on Nov 21, 2017 11:16 AM|
|Paul A Mathias|
Re: firing order
|November 21 2017, 12:51 PM |
Think About it. Do you really thing CC custom ground camshafts to change the firing order? No they did not.
|November 21 2017, 2:05 PM |
The deepest CC got into motors was to add the Q intake to the GM long block, and I think that was done at Galipolis Ohio. I guess they could have shipped those intakes to GM for installation there. Of course they could have specified a special cam if they wanted to. Ford provided reverse rotation cams for the 430, 431, and 427, along with other FE variants sold to INTERCEPTOR, but the SBC motors got the reverse capability by using a gear to spin the cam the same way, this the ability to interchange distributors. The Ford motors listed required a special reverse rotation gear on the distributor to work with the reverse rotation industrial marine products they were selling to the boating industry back then.
Timing, firing order, and valve adjustment specs for the Q motors
|November 22 2017, 1:15 PM |
|November 22 2017, 3:21 PM |
Thank you Paul, I have seen this as I have the manual. That is where I noticed that the Q firing does not seem like the standard SBC 1 8 4 3 6 5 7 2.
I'm going with what my mechanic says, if the engine runs "forget it" as it was suggested earlier