im about to start putting my short block together. i was wondering what i should gap the piston rings to. car is an 89 coupe, 306, might spray about 100 shot after breakin motor in.

Also, what kind of thread lock and all should i use to seal everything up???


also do you guys use motor oil on the bolts or assembly lube????

should i get pre-gapped rings or file fit???


Thanks

 

For a 306 with just a 100 shot pre gapped rings will do you fine.

Use ARP assembly lubricant.

Usually dont use thread locker on any engine bolts. Except for some RTV on the bolts that go into the water jackets.

 

i have a book that someone was building a motor. used pregapped rings and say they made 300 hp at 5500rpm. after changing the rings to file fit and closing the end gap they had like almost 100 hp difference at like 5500-6000. just from closing up the end gap. so i think it might pay off to take the time to file fit the rings

 

Ok let me go back and rephrase my first post....

File fit rings will always out preform pregapped rings if done properly!

While there is some hp to be had with the ring gaps I find 100 hp a little hard to chew. You serioulsy have to ask yourself though: How correct was the ring gap with the pre gapped rings?

For a modified street engine IIRC the rule of thumb to determine the ring gap is:

The top ring should be .0045 to .005 inches times the bore size (which on a 306 should roughly be about 4.030 give or take a little)

And for the second ring it should be .0055 inches times the bore size.

Oil ring gap is usually a constant at .015 inchs.

Whats the differance if you find a pre gapped ring at those specs or you file them yourself?

 

if i can find rings with a top end gap of .018-.020 and 2nd ring of .022 then i would buy them and then check to make sure. im going to look for the book, like i said im not sure it was exactly 100 but it was a big difference

 

You also have to ask what type of motor it was.

If it was a race motor where your stuffing 30+ psi down it, or a 3 stage nitrous set up puttin out a 600 shot, or a huge ci motor then yes ring gap comes into play in those situations. You have to accomodate of stuff like ring flutter, the rings butting up against the ends, ect.

But you a 306 with a 100 shot you will be know where close to having these types of problems.

 

this is the combo im workin with
tfs stage 2 cam
306 forged pistons
rods and crank have been balanced and turned .010
longtube hooker supercomps
straight pipes to 40 series flows
want to get some afr 185s
not sure which rockers, lifters to get

 

I thought the rule of thumb on n NA motor is was .001" X bore for the top ring and .0025" for the bottom ring?

And for a boost motor it was .0055" x bore for the top ring and .0065" x bore for the bottom?

My father inlaw gave me these number and its how he's been building motors since the 60's. I know times are different and he hasnt built a motor in the last 10 yrs or so but he's built 327 motors making 475hp NA, 455 Pontiac motors making 600hp,.. so I hold his 'old school' skills with a very high regard.

But are those numbers correct for todays motor builds or have things changed?

Hurst

 

^^^^

Those NA specs are pretty tight gaps, even lower than what most stock ring gaps are.

On an NA motor those will fly but I dont think I would run them on a nitrous motor where your jacking the cylinder pressure up.....too close IMO.