What should my spark plug gap be now and what is my compression ratio?

Ok, motor in, behind schedule but gonna try to fire it up tomorrow. Since this is no longer stock. What should my gap be and any idea of my compression ratio? And can i run 93 octane pump gas?

The major parts of the build are....

'72 350
TA Stage 1 intake
.030 over Buick V6 flat pistons
Crower level 3 cam, springs and lifters.
Stock heads .20 off
Holley 650.
TA headers 1 7/8
TA timing chain
2.5 dual exhaust with x pipe.
Points were converters to electronic replacement bolt in.

I can fill in more blanks if you need them

Thanks

 

How far are the pistons "in the hole"?
I'm going to guess on comp. ratio.... 9.5 to 1

 

Assuming.090 below deck with 1.805 height.
.043 fel pro gasket. About 53 cc chamber at .020 off head(estimated)
And .030 over with 3.0 flat tops.
Around 10.30 compression.
You may want to run some octane booster/race fuel mix.
.030 gap I'm gonna guess.
Did you polish combustion chamber at all?
You may want to set initial timing at 6 for startup and see what it tolerates

 

Thanks. What octane am I shooting for? and what do you mean polish combustion chamber? If I have to ask then probably not hahaha... Sorry I need 2nd grade explanations.

 

Polish as in grind surface smooth. . So you probably didn't. Average 95 octane should be ok. Just to have some protection from detontation. Should be very torquey. What did you set cam at? Stock , advanced or retarded? I would retard it at the compression. That would help drop dynamic compression a bit. Give alittle more top end rpm.

 

Ok, we didn't polish anything. My engine builder said he degreed the cam and set it "stock" at zero.

Does that mean I still set initial timing at 6 degrees?

I see lots of Octane boosters but not many of them say how much it boosts. Not sure there are any 95 Octane stations around here, wasn't expecting the higher octane.... what do people do to boost the octane from either 87 to 95 or 93 to 95?

 

Cam timing has no effect on ignition timing. Yes start out at 6 initial. Then advance 1 or 2 degrees to see what it likes without ping.
If you get racing fuel then it's an average. Say 2 gallons of 98 and 2 gallons of 87 . Add 98x2 and 87x2 . 370. Divide by 4 gallons equals 92.5

 

Here is a good thread all about how to increase octane for gasoline with formulas to mix your own race gas and more;

http://www.v8buick.com/index.php?threads/has-anyone-tried-this-octane-booster.323258/

 

If you try to start up and run in a healthy cammed engine with very little initial timing, it is going to run really hot and create other issues. Your exhaust will probably glow.
If it isn't under load, there's no need to back the timing down for compression and octane reasons, in fact...the opposite is what you want to do. More initial, less total.
Total timing needs to be conservative when it gets taken out on the road and run hard.
It's nerve wracking to see when someone is assembling their own engine and isn't aware of compression, tuning, fuel quality, etc., and just begins to ask those questions 'after' it's put in the car and getting ready to fire.
Plug gap? How about a cooler heat range.
Polished chambers? How about those sharp edges around the chamber after machining.
Those are more prevalent factors.

 

ok thanks Larry.


8ad-f85 .......... I realize I probably chose the wrong engine builder.... Plus TA's pistons were backordered for 4 months so we worked with what we could find..... Many folks have been very kind enough to offer their feedback on my build and the general feedback is that pump gas would be fine so that's why I was a little surprised that I needed higher than 93 octane. All I wanted was a little more horsepower out of my weak 72 350, something that had an upgraded cam, nice take-off from a stop sign, but safe enough to take the kids to cruise night or get ice cream... I apologize to all for always being a rookie or things needing to be explained to me like I was a second grader but I thought that's what these types of forums were for.... a place to talk Buick engines, offer advice, learn and share stories etc. Again, thanks to all that have been so kind to take time out of their day to help.... especially folks like Alec296, Jason Cook, SeanBuick, Larry The Wzard, Brian Trick and others not mentioned....

So, I will gap my plugs at 30, set total timing to 32 degrees with the yellow lighter springs, break in the cam, find a way to boost my octane to 95 unless anyone else wants to add anything else?

Thanks again

 

My comments were in no way meant to be a dig on you!
I should have made the following more clear, instead of assumed...
Criticism was intended towards the engine builder or shop for leaving you at a point in which little more could be done during that phase of the build, things that would have negated much of the concern over octane tolerance.
A tiny bit of communication solves so much.

My personal philosophy to this is to NOT build them on the edge of pump fuel, and simply add a touch of magic juice (good ol' high test) when you are going to race...
Either build them very much race gas (E85, whatever) intended...or absolutely pump gas safe.
Even the experienced are going to run into potentially damaging problems playing that game.
Stations have different refinery sources and contracts. the pump fuel can be very inconsistent, regardless of octane #.

 

Do a conpression test, that will tell you a lot about the octane requirement.

 

Thanks guys. Gapped the plugs at 37. I received the moroso mechanical advance kit and put the lightest springs in it.... it seems really light tension..

Engine builder didn't measure the chambers but i called him and he offered to come over tomorrow, do a compression test, help me fire it up, break in the cam and time it to about 32 degrees at around 2000 RPM (If I understand that should be correct?)

Any other tips? Will let you know how it goes....

Thank you all!

 

Is it possible I could have 180psi? I have an older compression tester and let it turn over about 3 or 4 times and it went up to 180 on cylinder 1 and cylinder 2. Seems high but I don't know. What does that mean for octane?

 

That is a good number for compression... That should run fine on a medium octane level as my educated guess. Always start out with higher octane fuel and then slowly reduce the octane level and listen closely for any ping noises. Also start pulling out out number 3 spark plug to inspect it for signs of detonation because you cannot always hear it unless it is severe. Number 3 plug tends to be theleanest burning and most likely to detonate.

 

You can read the plugs.
Search "4 seconds flat, plug reading" and other pertinent searches here.

How did this morph to an oil pump concern?
How is that going to solve what you don't know yet?
Even if the assembler has left you less than confident or unable to convey specs over the phone to the next guy, I wouldn't rush out to buy a $500 part hoping it would solve any perceived and unverified problems.
If you could somehow prove you need it, and could not easily solve whatever ails your current oil pump/timing cover.........then I would begin to consider it.
Please don't throw parts at this ahead of your concerns.

The best thing I can say if you are not feeling confident enough to run your $5000 engine and would possibly be prepared to tear it halfway down for a mystery and unverified oil pump "issue" that hasn't presented itself yet then I would:
Remove and partially tear down.
Simple measuring tools are adequate to assess a go/no-go situation.
A couple of rod and main caps removed would be a good way to gauge whether or not you go further.
I've had clients bring in fresh mystery builds to measure for a small fee, less than the cost of a new timing cover.
There's a number of ways you can set your mind at ease before going any unwanted direction.

All that said, the TA cover is a fine product.

 

This can be tricky. SBC engines with over 200 cranking PSI can burn 89 octane, but those are also running close to 9:1 DCR with perfect quench.

Static compression, your cam's timing events (and resulting DCR), VE, upper RPM scavenging, ambient engine temperatures, induction temperatures, head material, ignition timing, combustion chamber size and shape (including piston shape), hot spots, etc. will all play prominent roles in detonation resistance.