Roller Rockers

Hi guys,  so I started a thread over at FTE on the inline six section and I'm looking for more answers and AB did a good job on schooling me but I would like to get your take on this topic.

https://www.summitracing.com/parts/scc-scp1059 

Thoughts? They're for pedestal mount head so to mount them would you just do like the stock rockers torque to spec. Also they're 1.7 vs stock ratio of 1.6


my engine is Ford 300 six with overbore of .20, port and polished head with a 3 angle valve job,  crower 19212 cam, crower spring kit,  the head is milled but only a clean up mill decked the block, offy c series intake manifold, efi manifolds edelbrock 500 cfm,  and DUI distributor.

Would the 1.7 be more stress on my valvetrain? I did use stock pushrods and the original rocker arms with no issues.

 Would it make my exhaust sound more like a choppy?

I have run 1.7 rockers on several SBF engines I have built. It's simple power. Even though you are only effecting lift . . you actually change the effective duration. You increase it. What that means is . . many consider .050 as the amount of lift where flow really starts to happen. That si why cams will be spec'ed at .050 lift. Well since you now have more lift from the 1.7 rocker ( it is multiplying the lift by 1.7 now, rathwer than 1.6 for example ) you will get to the .050 lift sooner. So even though your cams duration does not change, the effective duration is increased . . more power  :)

Sounds lik a neat build, please keep us updated...

I am certainly no guru on rocker ratios, but the little bit of info I learned about them from my IDI build is that you are going to want to talk to the cam manufacturer and see if the 1.7 ratio will work with that cam as far as clearances. The ratio increases the lift and thus reduces the piston to valve clearance. They should be able to tell you if that rocker ratio will still clear.

As far as duration, that does not change. I get what Pete is saying. Since it amplifies the lift, you will achieve .050 earlier on the lobe, and maintain it later on the lobe, so technically the duration at .050+ is in fact longer. But the timing from open to closed remains the same. It will breathe more, with more power potential, but it will slightly change the characteristics of the cam. Again, I am not a guru and I am not familiar with the cam you bought. I would call the manufacturer and ask.

A higher ratio will put more strain on the valve train. You bought upgraded springs which is good to prevent valve float at high rpm, but will also increase the stress on the rockers, studs and push rods. It is not a crazy ratio, but since you have this much in the engine you might want to look into some upgraded push rods (I think I was looking at Smith bros.) and stronger rocker studs if such a thing is available. I am a 300 fan myself but I don't know anything about performance building them.

Best of luck, and oh yeah... welcome to the forum!

Thank you guys for the replies. I will look up the brand of pushrods you recommended also 85 to 96 used pedestal mount rocker which is basically a bolt in the head to hold down the rocker arm and there no adjustment to the its just a torque down to spec deal with this cylinder head.

I'll also have to get into contact with crower to see if it would be okay to use that ratio with that Camshaft.

 

Please post what you find out. I would like to follow you build either here or elsewhere if you have an active thread going. At some point when my diesel is finished I may want to do some "things" to my straight six 😉

I have built a few engines using the 1.7 ratio and the extra breathing is noticeable. The slight increase in lift is usually well within the tolerance that a street cams gives you. I'm not saying it isn't something to check. That can be done during the engine build, without involving any heads at the cam shop. For example, a cam with a 3.00 base circle will increase lift .030 , going from a 1.6 to a 1.7 rocker.That's not  a lot when it comes to piston/valve clearance with many typical street cams. If you are going very radical, all bets are off. Again, my experience is with Ford V8, not the 300 six when it comes to performance builds.

I may offering irrelevant advice then... since my research was on the IDI. That engine has completely flat heads, and piston protrusion out of the block is about .010" new with .031" being max spec. Compressed gaskets measure about .065" so that does not leave much. There was a guy on OBN who ran an engine with the pistons .054" out and had valve marks on all 8 but just visible marks. Not enough contact to remove any metal. This suggests the piston to valve clearance is only about .044" when new, and .023" at max spec. 😬Needless to say the discussion about rocker arm ratios for an IDI was a short one... especially since the Stage 1 cam that I bought already has more lift than stock.

Most engines do not have pistons sticking out of the bores. Typically .100 exhaust valve clearance is considered a safe minimum. You can get closer, thats that's a safe bet. S simple clay mock up will tell you what you have during building time. But like I said, unless the cam is aggreesive, you aren't near those limits.

Hi guys just wanted to give you guys an updated.  I finally got into contact with someone from Crower Cams.  This is what he said.

"When you go up on your rocker ratio… you are basically making the cam a lil bigger… all you do is bump up the power band… if you are looking for a lil more mid to top end… this is the way to go…"

Basically what Pete said.  

Now i wait till I do my taxes and get sokme extra cash I most likely will end doing this and hope for the best I'm very sceptical about doing a mod like this.

Thanks for the followup.  Let us know how it goes.  

Thanks for the update. Like the guy said it will help the mid and top end. The farther the valves open and the sooner they open the more gasses can flow in and out of the cylinder and the better it will breathe at higher rpm. The cost, of course, is that valves closing is what builds cylinder pressure and torque, so there is a price to pay. At low rpm you are still paying the price without any benefit so that isn't what you want for a crawler or low rpm puller. Most modern engines sweeten the compromise with some form of dynamic variable valve timing, but we have to choose what we think is best for the intended use.

And then we get into proper gearing . . . .

Yes proper gearing is key.  That what is next for my truck before I do this mod but its back to the drawing board I was set in 3.55 gears for my truck because I still do the occasional towing not heavy loads but medium size and not often either.  I've also thought maybe 3.73 for a bit more acceleration that's the 16 year old me saying that.   I'm still leaning towards more of the 3.55 over 3.73 I have a 3.08 open differential right now.