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Let's talk about Cranks!

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21K views 31 replies 14 participants last post by  Import Builders  
#1 · (Edited by Moderator)
I really couldn't find much on cranks after wasting 3 hours of my works money :rolleyes: So lets start with some basic info.

Someone double check these #'s for me :up:

Code -- Bore -- Stroke - rod length - crank throw - journals - weight
k20a - 86mm - 86mm --- 152mm ---- 43.18mm -------------- 38lbs
k24a - 87mm - 99mm --- 152mm ---- 49.53mm --- 22mm
RDX -----------------------------------------------------20mm
F22c -----------90.7mm

Edo thread on widening k20a journals lots of nice pictures
http://www.k20a.org/forum/showthread.php?t=2378

Firstly, thread on the S2k crank in a k20a with some machine work
http://www.k20a.org/forum/showthread.php?t=3775&highlight=s2000+crank

Secondly, are the k20 and k24 cranks interchangable with or without stock internals? I heard the k20 will fit the k24 but not the other way around, since the k24 has a taller block.

Thirdly, RDX = another 99mm crank to use with smaller journals, which means less rotating friction and more meat for the crank strength, i believe custom pisitons needed. Read on...still being researched.
http://www.k20a.org/forum/showthread.php?t=17989



I believe the reasoning behind this is... well i dont' really know actually. That's my question then. WHY?

Do any other H, B, F (D's :silly:) fit the K's?

K20a3 is unbalanced? I heard it just has 4 counter weights? where the k20a has 8? K24a?

well I'm wrecked, tired... i'll continue another day...

Fill in some answers for me!!
 
I
#4 ·
Many people have built K24's and at higher than 13.5:1 compression the average I would say is around 270 WHP. With good ported heads, I would say the average is around 285 WHP. If you get a $1300 custom header, ITB's, 89 MM bore at 13.5:1+ compression with real good head work, you could hit 300 WHP.

I think there is a growing falsehood around here that making 300 WHP is just real easy, just change the pistons and a couple parts and its done.

Its not that easy, some people with 15:1 compression dont even have 300 WHP in 89 MM bore. The Key is you have to have a really good Head port.

That is the key.

Jeff
 
R
#5 ·
K20A rod length is only 139mm. Another spec you will want to look at is the rod journal diameter. The K-series uses the H-series Honda big-end rod size of 51mm (48mm rod journal diameter).

Here's something of interest: the 4g63 rod is 1.140" wide (Crower lists 1.115" but I know that's not the official dimension of the stock 6-bolt rod) with a 45mm rod journal diameter (48mm big-end). Stock length is 150mm but Magnus Motorsports sells long rods in either 156mm or 162mm.

Idea? Offset bore a K24 crank to the smaller 4g63 size, while widening the journal. An offset of 3mm gives a reduction of 6mm of stroke. It also allows for 3mm more of rod length, meaning the wrist pin would have to move up only 1mm to fit the 156mm rod. Wrist pin diameter is 21mm (meaning the overall height of the wrist pin hole would only move up half a mm).

Another thing to think about is using a 7-bolt rod versus a 6-bolt rod. The 7-bolt uses a 22mm wrist pin but is .1" thinner than the 6-bolt rod. Just something to consider if you're thinking about using a DSM rod.

The rods Magnus sells are Pauter and are basically bullet-proof. I believe they are around $750 a set but they are made to withstand 800+ hp. They might not be the best choice in an N/A application but they will certainly work well in a boosted setup.

I like this idea because it uses a stock crank and shelf rods. For a relatively cheap combo, one could order custom Wiseco pistons to fit for around $550. At 89mm bore, you'd get 2314cc, 1.677 R/S ratio, and .957 B/S ratio.

I hope I'm not too off the aim of your topic here, but I thought I might offer some info that I found interesting.
 
I
#6 ·
I believe if you made the R/S ratio 1.667 you would lose power over 1.54.

You would not want to do that. Please, dont take my word for it, check every single all motor domestic application, they have about I would say 1.62 or so rod ratio max. I am talking about pro cars. Most of them run under 1.6 in the 1.54-1.58 range. A shorter rod has a dramatic effect on how the air is pulled from the head. Shorter rods prove to make more power naturally aspirated. Running a long rod all motor is absolutely unheard of.

They did a test even in one of the magazines, and the shorter rod motor with everything being equal killed the longer rod motor from 0 RPM to maximum RPM. From top to bottom it was better. Because it has a dramatic effect on how the air from the head is being pulled into the chamber.

Without bringing complexity into it, this is a nutshell understanding of why you want under 1.62 or so rod ratio for naturally aspirated.

Jeff
 
R
#7 ·
That magazine was Import Tuner, I believe. I read that article. I was a little unsatisfied with their testing.

The thing is, the B16 is a great N/A engine and has a R/S ratio of 1.7. So does the 4g63 (which I realize is typically a boosted engine, but still).

Another thing, regarding domestic engines, is the whole 2-valve thing. I understand the differences of cylinder filling between a long-rod engine and a short-rod engine, and the short-rod setup seems to match the characteristics of 2-valve heads better.

I'm not saying that a long-rod motor is necessary. But there is certainly significant advantages, both for longevity and rpm capabilities of a long-rod motor, and that's the whole reason Magnus sells these rods. Those two aspects are beneficial to ANY engine, N/A or not.
 
I
#8 · (Edited)
Sorry for messing up the thread its about cranks, not about rod theory.

As far as the cranks I think the best Crank you can put in a K is the 2000 S2000 Crank with the shorter stroke. It would be the most reliable option.

Jeff
 
I
#10 ·
rarson said:
I agree, but how much work does it take to fit it? It's not a drop in crank, or is it?
Click to expand...
Snout mod thats it. Drops right in
 
H
#11 ·
Import Builders said:
Many people have built K24's and at higher than 13.5:1 compression the average I would say is around 270 WHP. With good ported heads, I would say the average is around 285 WHP. If you get a $1300 custom header, ITB's, 89 MM bore at 13.5:1+ compression with real good head work, you could hit 300 WHP.

I think there is a growing falsehood around here that making 300 WHP is just real easy, just change the pistons and a couple parts and its done.

Its not that easy, some people with 15:1 compression dont even have 300 WHP in 89 MM bore. The Key is you have to have a really good Head port.

That is the key.

Jeff
Click to expand...
can you run pump gas (93) on 13.5:1
 
#13 ·
Import Builders said:
I believe if you made the R/S ratio 1.667 you would lose power over 1.54.

You would not want to do that. Please, dont take my word for it, check every single all motor domestic application, they have about I would say 1.62 or so rod ratio max. I am talking about pro cars. Most of them run under 1.6 in the 1.54-1.58 range. A shorter rod has a dramatic effect on how the air is pulled from the head. Shorter rods prove to make more power naturally aspirated. Running a long rod all motor is absolutely unheard of.

They did a test even in one of the magazines, and the shorter rod motor with everything being equal killed the longer rod motor from 0 RPM to maximum RPM. From top to bottom it was better. Because it has a dramatic effect on how the air from the head is being pulled into the chamber.

Without bringing complexity into it, this is a nutshell understanding of why you want under 1.62 or so rod ratio for naturally aspirated.

Jeff
Click to expand...

What about f1 engines? They run big r/s. Sometimes in excess of 2.0.

F1 is different from drag though. Their motors run for hours virtually non-stop. Drag is a totally different ballgame.
 
I
#14 ·
Next time we want to build a 20,000 RPM honda, sure I think 2.0 R/S would be better. Now watch some dude will want to put a 6.5" rod in a K24 and rev it to like 15k or something. lol.

Jeff
 
#15 ·
Import Builders said:
Next time we want to build a 20,000 RPM honda, sure I think 2.0 R/S would be better. Now watch some dude will want to put a 6.5" rod in a K24 and rev it to like 15k or something. lol.

Jeff
Click to expand...
I'm with you in that _most_ applications discussed on this board the obsession with r/s is not warranted. I do think that an engine that doesn't rev to 20,000rpm will have certain advantages when using a bigger r/s. There is a reason why the s2000 has the largest r/s of any stock honda inline four (that i'm aware of anyhow, not including motorcycles). It has to do with wear moreso than power production if I had to take a guess.

I think the stock 1.60 r/s is GREAT. I'd have no problems taking it to 10,000 and beyond in an all out n/a build.
 
I
#17 ·
As far as cranks, the general rule is you want the least amount of stroke possible that can achieve the compression that is maximully efficient with the ideal piston.

On a Honda, a lower displacement motor can make more power than a larger displacement motor BY RPM, thus be faster. This means that if we cant get the ideal compression for a GAS engine with a 86 MM stroke, we go up until we do, remaining as short as possible. 99 MM stroke is excessive and will not be ideal. I would say the range of perfection based on current technology would be between 86 MM and 96 MM at the most.

And again, to go the fastest down the track, the rod ratio would be under 1.65, which would be on the excessive end.

V8 blocks are very similar to honda blocks, just 2/3 bigger displacement in some cases. The principles in a V8 works in a Honda, etc. Building a Honda motor isnt a re-invention of engine building by any means. If you build a Honda Pro-stock motor to mirror a NHRA Pro-STock motor, it will be extremely dominant. No doubt about it.

The problem with the Honda community as a whole is they have this "bigger is better" mentality, bigger strokes, longer rods, bigger plenums, bigger ports, bigger headers, big big big big. Most people cannot even argue WHY the bigger is better, they don't even know.

Honda guys think of a V8 and always argue that the Honda is more effecient, it has a lighter rotating assembly, etc etc etc.

Professional built V8's with 8 rods and 8 pistons and a larger crank have a lighter rotating mass than a stock b16A by many pounds. V8's are way more effecient, and a Honda guy could do alot to learn from the V8 industry instead of trying to come out with all kinds of experimental things that are just guesses.

No need to guess, do what works on a V8. Shorter crank, shorter rod = fast fast car.

So thats my argument on cranks.

Jeff
 
T
#19 ·
Import Builders said:
As far as cranks, the general rule is you want the least amount of stroke possible that can achieve the compression that is maximully efficient with the ideal piston.

On a Honda, a lower displacement motor can make more power than a larger displacement motor BY RPM, thus be faster. This means that if we cant get the ideal compression for a GAS engine with a 86 MM stroke, we go up until we do, remaining as short as possible. 99 MM stroke is excessive and will not be ideal. I would say the range of perfection based on current technology would be between 86 MM and 96 MM at the most.

And again, to go the fastest down the track, the rod ratio would be under 1.65, which would be on the excessive end.

V8 blocks are very similar to honda blocks, just 2/3 bigger displacement in some cases. The principles in a V8 works in a Honda, etc. Building a Honda motor isnt a re-invention of engine building by any means. If you build a Honda Pro-stock motor to mirror a NHRA Pro-STock motor, it will be extremely dominant. No doubt about it.

The problem with the Honda community as a whole is they have this "bigger is better" mentality, bigger strokes, longer rods, bigger plenums, bigger ports, bigger headers, big big big big. Most people cannot even argue WHY the bigger is better, they don't even know.

Honda guys think of a V8 and always argue that the Honda is more effecient, it has a lighter rotating assembly, etc etc etc.

Professional built V8's with 8 rods and 8 pistons and a larger crank have a lighter rotating mass than a stock b16A by many pounds. V8's are way more effecient, and a Honda guy could do alot to learn from the V8 industry instead of trying to come out with all kinds of experimental things that are just guesses.

No need to guess, do what works on a V8. Shorter crank, shorter rod = fast fast car.

So thats my argument on cranks.

Jeff
Click to expand...
So k24 crank in my k20 block FTW??

Back to the subject of cranks, ave anyone try to use the 96+ H22 crank in the K block. Last time I put the 92-95 crank in the K24 block everything seem to line up except for the fact the the 92-95 H22 crank use 50mm journals. The 96+ H22 crank use 55mm journals.
 
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#20 ·
You could use a H crank in the K, snout modification, and use H rods and it would work. H rods are 5.630 long. The stroke is 90.7 MM. Like a new gen S2000. Which is why people want to use the new gen S2000 Crank in a K20, which would be a very fast combination on a track. On the street, I would use a 2000 Shorter S2000 crank, which is I think 84 MM. That would work better, and give you mroe MPH in each gear, with the added RPM. With the TQ taken away, and a taller tire, it would be the faster street car 0-60.

Jeff
 
T
#22 ·
Import Builders said:
You could use a H crank in the K, snout modification, and use H rods and it would work. H rods are 5.630 long. The stroke is 90.7 MM. Like a new gen S2000. Which is why people want to use the new gen S2000 Crank in a K20, which would be a very fast combination on a track. On the street, I would use a 2000 Shorter S2000 crank, which is I think 84 MM. That would work better, and give you mroe MPH in each gear, with the added RPM. With the TQ taken away, and a taller tire, it would be the faster street car 0-60.

Jeff
Click to expand...
So I can use the H22 crank and rods in my K20 to make it ~2.15L?? Will the H22 rods fit the K20 pistons?
 
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