duh

iTrader: (16)

So I'm doing some math trying to figure what I can build. The car is burning oil (ring seal sucks). What I'm thinking is doing a 355 with a long rod. Instead of doing the typical 6" rod, why not go with a 6.125" or even a 6.250" rod. The compression height would be 1.125" and 1" respectively. Since the car is 95% street driven, and I really don't plan on a power adder at this point, aside from maybe a small 100 hp shot, what issues can I run into? The 1" compression height pushes the oil rings into the pin, but with the support rail it shouldn't be too much of an issue. Is there anything to be gained by making the rod longer aside from keeping the piston at TDC a little bit longer? If you go off what I put in at eagle's site (just compression and dynamic numbers)

Deck height 9"
Stroke 3.48"
Rod 6.250"
bore 4.030"
Compression height 1"
Chamber 52cc
Gasket .029"
Piston dome -4cc

Compression comes to 12.34:1
1.8:1 rod ratio
with it whole set .010" in the hole

That puts the squish right at .039"

Personally I think it's a good combo. and if I knock it down to a 6.125" rod it only changes the rod/stroke ratio to 1.76:1.

Everywhere I've read says they shoot for 1.75-1.8 for a rod/stroke ratio.

Can anyone give me anymore insight as to why I should or shouldn't go with the longer rod?

duh

iTrader: (16)

Bump, still curious to hear your opinions.

WS Sick

I know the pistons for that combo will be pretty pricey. A good flowing set of heads and a computer that lets you take it to 7500 and that thing should make some power!

1961ba427

iTrader: (26)

I honestly don't think it will be worth anything recognizable in a typical LT1 engine to use such a high rod to stroke ratio. If you're buying new pistons and rods anyway, go with a 6" and call it good. Or better yet, for about what your long(er) rod combo would cost, build a 383 with 6" rods. I've checked into this stuff a good bit, and for the money it's hard to beat a 383 in a HP/$ invested standpoint.
I'm going to be building a 5.7" rod 385". Not because I think the short rods are better, but because I got a deal on the parts by buying a used balanced forged rotating assembly for $750.00
I'd prefer to have 6" rods, but I still feel the difference is negligable in my application.

F0x Slaughter

Um can you even fit a 6.25" rod into a LTx block?

WS Sick

yep but the rings are tight togeter and the oil ring usually uses an insert in the pin hole to help support it. Like I said they are pricey. Also the top land or crown of the piston is thinner than most.

93 LT1 Vette

Because of the lack of material is nitrous out of the question? Sounds like a lot of cash for something that seems weaker than a common 6 or 5.7 inch rod motor. Exactly what are the benefits of a longer rod other than less wall wear. TDC and BDC are the same place are they not? Wrist pin location is different.

duh

iTrader: (16)

Believe it or not, 1" compression height pistons forged can be had for under $500. I can also get 6.250/6.125" rods for under $600. It really won't cost that much more than doing a 6" rod 355. That's why the question is "Is it worth it to go with a longer rod?". In theory it makes a more efficient engine. My goal isn't to spin it much more than 7K rpm since I don't want to spend the money to go with the valve train to go that high.

duh

iTrader: (16)

It allows the piston to sit "near" TDC longer which should allow the engine to make more power for a given amount of fuel. In theory.

WS Sick

I personally have never run one, Ive run a couple of 6 inch rod 355s, and truthfully the head and valvetrain combo I had on it them were not optimum for that, but they were still respectable. I think unless you were going to spin the pee out of it it wouldnt be too noticeable of a difference.

1961ba427

iTrader: (26)

Don't forget that if your piston dwells longer at TDC, that your PTV clearance will be effected since your minimal PTV clearance isn't exactly at TDC.
There is also a very valid arguement for short rods that "snap" the piston down from TDC quicker, but it's not a common practice. I've heard some knowledgeable builders say to pic a stroke, then a piston design that suits your builds needs, and let rod length fall where it may to connect the two.
The tests I've seen didn't change power by more than a small percentage either way.

93 LT1 Vette

Yeah I always thought short rods, shorter stroke for big RPM's. 3.25 stroke 5.7 inch rods forged pistons. Not knocking the long rod motors but I'm sure with 6 inch and longer rod, a good balance and blue printing becomes much more critical. Internal harmonics must be greater with the longer rods and may kill the bearing quicker. Maybe??????

duh

iTrader: (16)

Well seeing as I'm planning n/a why not go with the smallest/ lightest piston I can find? The long rod should keep the walls nice longer, and allow for the most compression time, therefore maximizing efficiency. Everywhere I've ever read including Reher-Morrison says that rod ratios of 1.75-1.8 are ideal, so I'll be there with either setup. I'm more curious if anyone has tried it yet, or what feed back is available. Otherwise I have two blocks so if I grenade one engine I always have another to build, plus the current one.

OutlawZ

iTrader: (4)

well the increase in power or efficiency would be probably negated by a heavier rod. the longer the rod the heavier it will be.... I think that you're MOST efficient rod/piston ratio is the 6" rod 355. well according to john lingenfelter that is....

at some point the ring pack and piston crown will be compromised. So you're trading piston strength at the top which sees combustion events like 9 billion times in it's lifetime. and for what? maybe a few hp. 3-5??? maybe slightly lower oil temps by like 4-5 degrees.... Also i'm not sure what the length will have on the rod contacting the bottom portion of the cylinder when you get that long. I might be trippin but if you could put whatever rod you wanted in there ppl would be building 7" rod 355's...

I say keep the rod strong and as light as possible. a 6" rod is as long as you should go and still maintain an engine you can rev to the moon. you said you wanna rev the **** out of it but you're going to make your rod heavier by making it longer... which costs power to spin the added weight...

duh

iTrader: (16)

I don't plan on spinning it high in my opinion. I'm talking 7K tops. To me high is 10K. I suppose I should be looking at what weight penalties I would be getting. The piston will be lighter but the rod heavier. I guess it's really just a matter of if I should build to handle spray. I could save even more by going with a hyper piston.

1961ba427

iTrader: (26)

I think you should go for it or you will always wonder "what if"......I honestly don't think it will make much difference either way, but that's only my opinion and I've been wrong before a few times. LOL

1961ba427

iTrader: (26)

On a side note: (but still related to this topic)

I am constantly amazed at the amount of threads saying that over 6,000 rpm is really bad for a stock internal 350" LT1. I guess I'm a lot older than alot of you guys because I have known of MANY stock internal 350's that survived being twisted to 7,000+ on a regular basis and lasting for years. These weren't LT1's, but were normal SBC with plain old cast pistons (not hypereutectic) and standard rods (not pink or powdered metal) and they were on the factory balance job. Don't get me wrong, I'm all for going with good parts when you rebuild, but am I the only one who remembers stock stuff being alot stronger than everyone is giving credit for?

duh

iTrader: (16)

I think the old adage of "they don't make things the way they used to" applies here. Back when there was a lot more pride in what people did for a living. From castings to assembly. I think that I might just do a hyper piston since this will be a build meant for n/a, with nitrous being a possibility. Besides hyper pistons are well known and proven for handling 100-150 shot. Heck stock lt1's handle it all the time. Besides if I don't like it, I can always build another engine (as much as the wife won't like it).

OutlawZ

iTrader: (4)

well you can't spin an LT1 to anywhere near that cause the PCM won't let you and you won't make any power cause you'll float the valves....

Things were made better bakc in the day cause it was made here and it was better quality steel. now companies are farming **** out to china (IE Eagle) and they are making inferior castings....

yes you are right the piston will be lighter but i think you're sacrificing strength in the wrong area which is the top of the piston...

duh

iTrader: (16)

Fwiw I just saw that KB makes a hyper piston with coated skirts and a 1.130 comp height that summit sells for $300 for the set of 8. this piston is actually made for a 383 with a 6" rod. Therefore I'm not sacrificing anything in strength since we all know 383's with 6" rods can handle tons of abuse. I could go with a forged slug and spray the world at it. For the extra $200-300 it would be worth the extra strength. That would let me use the 6.125" rod and give me a 1.76 rod ratio which is still way better than the 1.5x of a 383. To me that says better durability and longevity in the design. Again just thinking out loud.