ArcticZ28

iTrader: (14)

Just thought I'd share some quotes from Darin Morgan of Reher-Morrison in the August issue of Chevy Hi Perf. The first one is on Rod Length...

"Most people tend to overgeneralize this issue. It would be more accurate to compare different rod-to-stroke ratios, and from a mathematical stand-point, a couple thousandths of an inch of rod doesn't really change things a lot in an engine. We've conducted tests for GM on NASCAR engines where we varied rod ratio from 1.48- to 1.85:1. In the test, mean piston speeds were in the 4,500-4,800 feet-per-second range, and we took painstaking measures to minimize variables. The result was zero difference in average power and a zero difference in the shape of the horsepower curves. However, I'm not going to say there's absolutely nothing to rod ratio, and there are some pitfalls going above and below a certain point. At anything below a 1.55:1 ratio, rod angularity is such that it will increase the side loading of the piston, increase piston rock, and increase skirt load. So while you can cave in skirts on a high-end engine and shorten its life, it won't change the actual power it makes. Above 1.80- or 1.85:1, you can run into an induction lag situation where there's so little piston movement at TDC that you have to advance the cam or decrease the cross-sectional area of your induction package to increase velocity. Where people get into trouble is when they get a magical rod ratio in their head and screw up the entire engine design trying to achieve it. The rod ratio is pretty simple. Take whatever stroke you have, then put the wrist pin as high as you can on the piston without getting into the oil ring. Whatever connects the two is your rod length."

This next one talks about Coatings...

"In all the testing we've done on our Pro Stock and Comp Eliminator engines, coating the piston crowns and combustion chambers has not proven to be worth lots of power, maybe 6-8 hp at most. However, on an inefficient engine where thermal efficiency is lacking due to poor chamber design, cam selection, or poor inlet charge mixture motion, coatings can help quite a bit and give you 12-15 hp. In other words, a poorly designed motor - one with too much cam or too much port cross-sectional area - stands to benefit more from coatings than a properly built motor. There is a big difference between thermal coatings and lubricity coatings. The Casidium coatings we use on our bearing and wrist pins have really saved us, and we put that stuff on everything. They let you get away with running half the oil that you ran before and allow tightening up the ring package as well."

I thought those were two pretty interesting/informative quotes considering the controversies that go on here pretty regularly concerning both of these topics.

DavidNJ

This would seem to be at odds with Erik's comment on another thread that supporting the ring over the pin wasn't a problem and had become standard practice.

$500 for eight otherwise unavailable HP may be a good deal. It seems to be around the cost people spend for more power: $60/hp.

Old SStroker

I suspect Darin and Erik might disagree on a few things.

Google "Darin Morgan" "Reher" for some interesting reading.

racer7088

Darin is not talking about all engines when he says that! For one in the previous paragraph he was talking about NASCAR engines and like I said they can't run the pin as high there for a 500 mile race or it will die from the heat. I think you will find that I agree with the the guys at R&M 99 times out of a 100.

You should know that Reher and Morrison sells engines everyday that come with the pins in the oil rings. You guys simply need to understand that there are no black and white rules on these things. I think almost every engine I've seen from them had the oil rings in the pin. You need to see more and do more of this stuff and not take these magazine articles and internet articles as the gospel.

There's a lot of difference in a 622 with NOS than a 358 that is forced to run a huge deck height. One is very cramped for ring lands and one has tons of room, maybe too much but can't cut the deck down. If you're building a small engine or one with a tall deck height there would be no reason to put the oil ring in the pin now would there? I've never said it's a PLUS to put the oil rings in the pin on all pistons but rather it's no big deal and one that causes no big problems and is done everyday.

I would say I agree with 99 percent of what Darin says but you'd have to talk with Brad there too as no one at any one of these shops agrees on everything plus the fact that these guys will tell you something different a year from now as will all guys at this level. The only thing I disagree on with Reher and Morrison as a whole is their exhaust port thing but I am sure on their stuff they have seen that. I don't know anyone else that has ever had that experience but they weren't working with the same engine of course. Many other guys that have won several NHA PS championships tend to like exhaust ports that "flow too much" even if R&M don't!

Old SStroker

Darin Morgan recently discussed "hyper-square" engines or engines with a Bore/Stroke ratio 2.0 or greater. He sorta liked them...a lot. I agree with most of his thoughts there.

Is that concept in the 99% you mentioned, Racer?

racer7088

Yes it is. I am extremely well versed in hyper-square engines OldSStroker. They are my first love as they are SUPER hard to make work. Everything matters in these engines and the chamber and piston tops must work very well together along with the cam or all compression is lost.

These engine's can have valve lift that's a fair percentage of their stroke! For strictly HP/liter though it's the only way to go in a piston and poppet valve engine. You must have airflow to make big power and that's the way to get the most possible airflow per liter of displacement.

Now back in reality land I still wouldn't ever build one as a street engine and there's a damn good reason no OEMs do either. I think it's pretty self-explanatory. Another thing to note is that these engines will pick up a ton of power when stroked as well but when displacement is limited big bore and short stroke is the ticket.

Ed Wright

iTrader: (1)

You need to see more and do more of this stuff and not take these magazine articles and internet articles as the gospel.


AMEN!!!