Just like it says. Lets say you are building a motor from scratch. Is there a formula to figure out what your redline will be? What things must be taken into account for reliably at high rpm? A good rod/ stroke ratio is said to be 1.75/1. What about piston speed, is there a number that should not be crossed?

Hope i'm not confusing anybody. Just trying to build it right without expensive trail and error.

 

cams come in to play as well, where they stop making power....

 

Thats kinda why i'm asking. want to buy the ones(cams) for my planned rpm range.

 

well what is the RPM range you want?

 

Also the displacement will have an effect on the rpm range of a cam.

 

Alright here goes...intended setup is sleeved gsr block to 84.5 mm, b16a head w/ opened up chambers-ported, bigger IM, hytech header. Redline will dictate cam choice as well as valvetrain requirements. Don't want to run high valve spring pressures if i don't have to. (IMO it would be unecessary wear on t/belt, waterpump, idlers, etc.) Not to mention rob power.

 

The cam profile will pretty much dictate where your red line should be to make optimal power.
The rod ratio needs to be taken into consideration as well for reliability issues.

 

I don't think that you will be able to accurately determine your actual redline without some good dyno time...you will have to see where your power starts and stops depending on your cam and ignition and fuel profile...where your compression makes its power and torque. Looking at your rod to stroke ratio will give you some idea of what revs you are capable of...same with the valvetrain.

Obviously it needs to be somplace where you can rev to...then after shifting still be within your powerband...so you will need to dyno it....and, although this sucks...you might have to blow something up to really find out what your limit will be.

 

Redline as in no more power? Cams will dictate that. Redline as in component failure? Hard to say. There are lots of factors, like how much power it will make, how well oil can get to everything at full rpm, etc.

Reliability? Think about what components fail at high rpm. Rods, valvetrain. Make sure you have the right valve springs(should come with cam). Go overkill with the rods. Makes all parts that have enertia be light parts(pistons, valves, etc). Make sure the engine is balanced and blueprinted. Make sure oil can get to everything at the high rpms.

RPM that can't be crossed? F1 and CART cars rev to around 20,000 rpm right? Try to keep it under that.

 

Take it to the dyno. See where torque takes a dramatic drop. Shift before there.

 

True but just so that he doesnt get the wrong idea, you shouldnt set redline right where the torque begins to drop from a performance standpoint. The longer your in the lower gears, the better the torque multiplication.
USDM ITR gear ratios overall: 1st 14.212, 2nd 9.262, 3rd 6.415, 4th 4.871, and 5th 3.731...see especialy in the 1-2 shift and 2-3 shift, the torque multiplication difference between the two is dramatic. In fact, although I have no data to prove this, the ITR would be faster if it would rev to 8700 or more stock even with stock parts, because in 1-2 shift and the 2-3 shift, the torque drop after peak 7500 isnt enough to offset the torque multiplication advantage of being in gears 1 or 2. After that though, I think the stock 8400 would be ideal in gear 3, 4, and 5.

I think the B18C should not be reved past 9300-9500 for the street, even then I would replace all reciprocating parts as someone mentioned before, but that's just my opinion and I am by no means an expert on the matter.

 

Redline as in Kaboom! More concern with what the bottom end can handle. In other words, how do you determine max rpm allowed. At what rpm does the stress become excessive. Stock redline is 8400. Why not 9000. Would lighter rotating mass allow higher rpm range yet put the same or lower stress as stock components at lower redline?

So if someone put a shortblock in front of you and gave you all the specs. How would you determine its redline?

 

You look at the rod and stroke. What cams do you plan to use?

You are going about it the wrong way. First determine how much power you want to make and where. Then choose a cam that can accomplish it. The cam profile will tell you where it will make power up to, you then build up your valve train, bottom end, to accomodate the higher rev limit (if needed).

 

LOL

 

Reliablity is a perk.. but it's not the main reason.
The better the rod ratio is, the more torque you will make up top

Take my motor for example.. a B20 destroked to 1847cc(85mmx81.4mm), and take a normal B17A sleeved and bored to 85mm. Same dimensions.

My motor WILL make more torque up top and it will be a flatter line.