Hello,
A while ago, a friend and I accidentally built a 1904 stroker engine... I say "accidentally" 'cuz when I ordered the parts for the 1776, they shipped a 74mm crank... So we stuck it together (After a little clearancing). That engine worked so well, I want to build another Stroker. (Love the torque!!). So, I ordered a 76mm Crank, a set of Mahle A 90.5 Pistons & cyls., and some stroker rods. (Less, if any, clearancing). The rods I ordered are 5.4 long.... I "did the math" a few years ago, and now am wondering if I did the right thing.
I am beginning to think I should have gotten B Pistons and 5.5 Rods....
It is said that the 5.4 rods will work with the 76mm crank and A pistons, but I'm concerned about deck height...
Anyone already build this engine and have anything they can offer me? I just want to know if the A Pistons, the 76mm crank, and the 5.4 rods are a way to go, or should I go with the B Pistons and the 5.5 rods?.....
I think with the A Pistons and 5.4 rods, I'll have to use some good sized cylinder spacers to get the right deck height...I'd like to avoid any spacers that are "too" thick...
Oh, and I'm looking for around a 7.5 to 1 CR.
Thanks!
Stroker stuff
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ManxManiac
- Posts: 200
- Joined: Tue Mar 30, 2010 5:00 am
- Location: Ventura, CA
Re: Stroker stuff
Hey Richard, I've built a number of 1904cc stroker engines & all of them performed great!!! A few friends built the 1955cc (76mm stroke X 90.5mm bore) engines & one used stock length rods & the others used 5.7" aftermarket rods!!! All ran great, however the short rod engine produced all of its torque at the lower rpms!!! Those that used the 5.7" rods used the stroker pistons/cylinders & yes they ended up using barrel shims too, just don't remember how much for their application!!! The longer stroke was unbelievable in the lower & mid-range rpms!!! Stroker engines usually do not need the lower gear ratios either!!! Good Luck!!!
Michael Cates
ManxManiac
#958
Ventura, CA
Original Meyers Manx "Xena"
M1609C8S22
ManxManiac
#958
Ventura, CA
Original Meyers Manx "Xena"
M1609C8S22
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croakintowd
- Posts: 78
- Joined: Tue Jan 17, 2012 6:00 am
- Location: Frogbutt. CA.
Re: Stroker stuff
It gets confusing, 'cuz one website will say the 76mm crank works with A Pistons and 5.4 rods(5.4 is just a gnats eyelash from stock,,,, about .08 difference, if I remember right). Another site says, nope ya gotta have 5.5 rods and B pistons..... Well, when I figured it out a while ago, I thought I had it figured out. Now I guess I gotta redo my thinking process to see what I did. I don't have the heads, (the machinist misplaced them), so I don't know the volume of them... Guess I ought to wait and do the math again when I get the heads...... sigh....Ain't nuthin' easy? ........ LOL.....
Re: Stroker stuff
I am interested in what you find out. I to am building a motor that is said to use 5.4's but others say use 5.5's to keep piston at top? I'm going to test fit and if I need to deck block with 5.4 then I will buy 5.5 rods are less then machine work... Great post
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croakintowd
- Posts: 78
- Joined: Tue Jan 17, 2012 6:00 am
- Location: Frogbutt. CA.
Re: Stroker stuff
Hello JJ,
A friend in the Manx Club sent my questions to a guy who has experience with such things.... Here is his response. I'm not going to post his name and such, as I don't have permission to do so. But, here's the info he sent me......:
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First, let me say that there are only theoretical answers to your question, and that you should make a trial assembly of any stroked engine to make sure the basic dimensions are close to stock. The most obvious one is that the cylinder deck surfaces haven't been changed in height due to the cutting for big bore cylinders. Most machine shops do cut them down quite a bit, and this will substantially alter the figures I'm giving you.
To figure the theoretical spacers needed under the cylinders (with stock length rods, your 5.4 are almost stock) you would do as follows:
Take half of the stroke increase, and convert from mm to inches.
76 minus 69 equals 7mm/2 = 3.5mm
3.5mm * .040" = .140" cylinder spacers
Since the machine shop probably shaved off around .020" from the deck, my guess would you would need about .160" cylinder spacers.
Going the other way with stroker pistons and longer rods:
The piston deck heights are about .178" shorter (optimized for 78mm strokes) so you would gain that much deck height.
You'll lose about .100" with your longer rod, so the gain in deck height would be about .078". Lets say you started with .060" deck, adding the .078" would give you too much! (about .238" theoretically.)
You would then have to do some tricky machining, like shortening the tops of the cylinders this amount to get back to "normal" compression.
I personally think that the shorter rod will run better, even though it will require the motor to be a little wider physically. Going with stroker pistons and longer rods will result in a motor more like the width of a stocker, but with the trickier machining and loss of torque with the long rod.
To get your exact compression ratio, you simply have to measure the cc's in the head and calculate. Don't rely on the theoretical educated guesswork I've outlined here!
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So, that makes sense to me. I think what I have stands a decent chance of working... But I need to measure to be sure..... Hope this helps.
A friend in the Manx Club sent my questions to a guy who has experience with such things.... Here is his response. I'm not going to post his name and such, as I don't have permission to do so. But, here's the info he sent me......:
------------------------------------------------------------------------------------------------------
First, let me say that there are only theoretical answers to your question, and that you should make a trial assembly of any stroked engine to make sure the basic dimensions are close to stock. The most obvious one is that the cylinder deck surfaces haven't been changed in height due to the cutting for big bore cylinders. Most machine shops do cut them down quite a bit, and this will substantially alter the figures I'm giving you.
To figure the theoretical spacers needed under the cylinders (with stock length rods, your 5.4 are almost stock) you would do as follows:
Take half of the stroke increase, and convert from mm to inches.
76 minus 69 equals 7mm/2 = 3.5mm
3.5mm * .040" = .140" cylinder spacers
Since the machine shop probably shaved off around .020" from the deck, my guess would you would need about .160" cylinder spacers.
Going the other way with stroker pistons and longer rods:
The piston deck heights are about .178" shorter (optimized for 78mm strokes) so you would gain that much deck height.
You'll lose about .100" with your longer rod, so the gain in deck height would be about .078". Lets say you started with .060" deck, adding the .078" would give you too much! (about .238" theoretically.)
You would then have to do some tricky machining, like shortening the tops of the cylinders this amount to get back to "normal" compression.
I personally think that the shorter rod will run better, even though it will require the motor to be a little wider physically. Going with stroker pistons and longer rods will result in a motor more like the width of a stocker, but with the trickier machining and loss of torque with the long rod.
To get your exact compression ratio, you simply have to measure the cc's in the head and calculate. Don't rely on the theoretical educated guesswork I've outlined here!
-----------------------------------------------------------------------------------------------
So, that makes sense to me. I think what I have stands a decent chance of working... But I need to measure to be sure..... Hope this helps.
Re: Stroker stuff
I think it helps I will do math. But interesting short rod equals wide motor? I hope mine works because my block is not decked. Thanks
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croakintowd
- Posts: 78
- Joined: Tue Jan 17, 2012 6:00 am
- Location: Frogbutt. CA.
Re: Stroker stuff
I think the answer on the width of the motor has to do with the "A" or "B" Pistons... The "B" Pistons move the wrist pin toward the center of the crankcase. That facilitates the longer rods...
The 5.4" Rods are essentially stock. The "A" Pistons are essentially stock..So, I guess the throw of the crank is what pushes the "stuff" outwardly, toward the heads. That's 3.5mm (Each side) On a 76 Crank... I remember reading that the crank doesn't really move the piston further out, but that the longer throw keeps the piston at TDC and BDC longer, and that the Piston then moves faster between those two destinations...( I don't know about that.....I could be way off)....
I apologize if it seems I know what I'm talking about. I don't... I'm running off memory and poor judgement...LOL.
So, I can see where with the parts I have, I will probably need spacers, thereby making the engine wider. (A tiny bit). No biggy on a buggy, but I guess it might matter, if you put the engine in a car.....
Anyway, now I gotta go ice down my head...... LOL.
The 5.4" Rods are essentially stock. The "A" Pistons are essentially stock..So, I guess the throw of the crank is what pushes the "stuff" outwardly, toward the heads. That's 3.5mm (Each side) On a 76 Crank... I remember reading that the crank doesn't really move the piston further out, but that the longer throw keeps the piston at TDC and BDC longer, and that the Piston then moves faster between those two destinations...( I don't know about that.....I could be way off)....
I apologize if it seems I know what I'm talking about. I don't... I'm running off memory and poor judgement...LOL.
So, I can see where with the parts I have, I will probably need spacers, thereby making the engine wider. (A tiny bit). No biggy on a buggy, but I guess it might matter, if you put the engine in a car.....
Anyway, now I gotta go ice down my head...... LOL.