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Old 12-06-2006, 01:20 PM   #1
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Default Honda Internals? - question for markp

Figured that I'd put it on the forum rather than PM you as per your prior request.

I've been researching stronger internals and came across at rather interesting thread where you were discussing the possibility of using honda internals (which apparently are much cheaper) to actually destroke the BP motor via a longer rod and maybe recapture some of the lost displacement of the shorter stroke via an overbore. The major benefits being a desirable rod ratio, a shorter stroke that theoretically allow you to rev higher safely via lower piston acceleration, and the big one -> $$$$. So here come the questions:

1) Aside from the engine management to deal with the changes, would this require anything more than the longer honda rods, larger pistons, overbore for wider pistons, and a crank regrind to accomodate the new rods? Maybe some stronger valve springs for the higher rpm?

2) How much of an overbore could you realistically do and still use a stock head gasket?

3) How much much more of an rpm window do you think the shorter rod would allow?

4) If I decided to be a guinea pig, would you help me out in terms of knowledge (aka answer a million stupid questions since I know zero about internals)?

Thanks in advance for any answers.

Tom
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Old 12-06-2006, 02:18 PM   #2
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So you're saying to destroke the crank when regrinding it to the honda rod journal size? How much smaller is a honda journal than a miata journal? Just sticking longer rods in there doesn't change the stroke.

I heard you can't go much larger in bore. This is why FM increases the stroke to get their 2.0 instead of a larger bore. Maybe they just want to justify charging you what they do for 2.0 liters. I could be wrong.

It may be easier to just stick a honda motor in the car.
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Old 12-06-2006, 02:25 PM   #3
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So you're saying to destroke the crank when regrinding it to the honda rod journal size? How much smaller is a honda journal than a miata journal? Just sticking longer rods in there doesn't change the stroke.

I heard you can't go much larger in bore. This is why FM increases the stroke to get their 2.0 instead of a larger bore. Maybe they just want to justify charging you what they do for 2.0 liters. I could be wrong.

It may be easier to just stick a honda motor in the car.
Sorry I meant aftermarket honda internals. IIRC from the old thread, I think that the journal size difference is very minimal, around 0.002. Mark had discussed a suggested setup that would use stronger aftermarket honda sized internals with a longer rod and bigger bore piston to get close to stock displacement of 1.8L (for a 1.8L that is) that would have a shorter stroke length for rpm and a rod ratio of around 1.66 IIRC.

Just checking out the different options, and it might be fun to be different....we can't all have twin turbo setups ya know!
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Old 12-06-2006, 02:57 PM   #4
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Nonono I totally understand thinking of another way to do something different is a good thing. I'm just trying to understand the idea. Don't take my questions the wrong way.

To keep the same displacement with a larger piston, you have to shorten the stroke (which you understand). But lengthening the connecting rod doesn't do anything to the length of the stroke. You need a crankshaft with a shorter stroke. This could be done by regrinding a stock crankshaft to smaller journals and getting custom rods done (same thing with creating a "stroker" crank).

Again, my guess would be that the limiting factor to RPM would be mechanical valvetrain and cylinder head flow issues (maybe that's because I'm in the fancy valvetrain business???). Having a more over square engine would techincally rev easier/higher, but I would spend $ on fancy valvetrain.

I also think rod ratios or offset wrist pins or whatever are not worth much.

Last edited by TurboTim; 12-06-2006 at 05:12 PM.
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Old 12-06-2006, 02:57 PM   #5
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sounds interesting, would be very cool if it could be done.
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Old 12-06-2006, 07:26 PM   #6
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yeah, sounds uber interesting to me!
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Old 12-06-2006, 07:59 PM   #7
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Nonono I totally understand thinking of another way to do something different is a good thing. I'm just trying to understand the idea. Don't take my questions the wrong way.

To keep the same displacement with a larger piston, you have to shorten the stroke (which you understand). But lengthening the connecting rod doesn't do anything to the length of the stroke. You need a crankshaft with a shorter stroke. This could be done by regrinding a stock crankshaft to smaller journals and getting custom rods done (same thing with creating a "stroker" crank).

Again, my guess would be that the limiting factor to RPM would be mechanical valvetrain and cylinder head flow issues (maybe that's because I'm in the fancy valvetrain business???). Having a more over square engine would techincally rev easier/higher, but I would spend $ on fancy valvetrain.

I also think rod ratios or offset wrist pins or whatever are not worth much.
I hear ya, and I know you are not criticising.

I'm not totally clear on the whole idea myself, which is why I am asking for more info from markp. From my limited knowledge, I only mentioned the longer rod b/c I think the stock honda rods that mark was referring to are a bit longer than the miata rods which is why you have to destroke a bit so that you don't have issues with the piston rings coming down too low on the down-stroke? I also assumed that this would be accomplished when regrinding the crank to fit the rods as well. Also from what I gather, the shorter stroke (in combo with a fancy valvetrain ) allows for higher rpms via less strain on the piston in terms of velocities.

I am still thinking about building a 94 shortblock + 99 head engine for my next FI project. So $700 for stronger internals + a "unique" setup sounds like more fun than spending the same amount just for some stronger rods. Plus, if you can improve the flow with a 99 head/oversized valves/Begi intake manifold/etc, you would probably be able to take advantage of any added upper rpms.

p.s. I didn't know you were also in the fancy valvetrain business....if I do decide to go down this route, I may ask for your assistance, and by ask I do mean $.
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Old 12-06-2006, 09:06 PM   #8
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....we can't all have twin turbo setups ya know!
NOW you tell me . What the hell am I supposed to do with this now???
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Old 12-06-2006, 09:13 PM   #9
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What in the...
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Old 12-06-2006, 09:20 PM   #10
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Man's version IRTBs. Nice
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Old 12-06-2006, 09:41 PM   #11
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NOW you tell me . What the hell am I supposed to do with this now???

Evilbay it...They'll buy anything
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Old 12-06-2006, 09:51 PM   #12
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Originally Posted by brgracer View Post
Figured that I'd put it on the forum rather than PM you as per your prior request.

I've been researching stronger internals and came across at rather interesting thread where you were discussing the possibility of using honda internals (which apparently are much cheaper) to actually destroke the BP motor via a longer rod and maybe recapture some of the lost displacement of the shorter stroke via an overbore. The major benefits being a desirable rod ratio, a shorter stroke that theoretically allow you to rev higher safely via lower piston acceleration, and the big one -> $$$$. So here come the questions:

1) Aside from the engine management to deal with the changes, would this require anything more than the longer honda rods, larger pistons, overbore for wider pistons, and a crank regrind to accomodate the new rods? Maybe some stronger valve springs for the higher rpm?

2) How much of an overbore could you realistically do and still use a stock head gasket?

3) How much much more of an rpm window do you think the shorter rod would allow?

4) If I decided to be a guinea pig, would you help me out in terms of knowledge (aka answer a million stupid questions since I know zero about internals)?

Thanks in advance for any answers.

Tom

The question that begs asking is why would you destroke the motor when you can offset grind for a longer stroke?

As you note, not much needs to change electronically for higher RPM operation. While it's not really a good rod ratio for high RPM work the stroke on the BP miata is plenty short to accomodate 8500 RPM redlines without serious work other than the rods. The stock rods tend to fail under extended tensile loads at high RPM, but the aftermarket rods do not. You will need some cams capable of taking advantage of the extended RPM range and springs to match. Preferably you'll use shim under buckets to reduce weight on the valve train allowing you to use lighter valve springs at higher RPM. I used R&D springs dual spring setup at 65 PSI installed and 175 PSI open.

There is a gasket available that allows for an 85mm bore, but for boosted apps most people stick to 84 mm or 84.5 mm. While they say there is no replacement for displacement, that's not quite true... It's called boost, and lots of it! Ric Stevens had a junkyard 1.6 running 8000 RPM with a GT3271 at 24 PSI making over 325 RWHP and pulling 11.40's at the track. I know that displacement does a lot of good things but don't chase it at the expense of hard earned dollars. There are better places to put your money, especially when trying to keep costs down, having to buy a $250 head gasket vs a $100 headgasket for 50cc's of displacement makes no sense.

Your money will go farther with cams and a decent valvetrain than it will on adding displacement. Add as much displacement as possible without incurring significant additional costs. Personally I consider an offset ground crank cheap displacement. The stock crank is plenty strong so offset grinding it is a non-issue. The scat rods are $299.00 which is a bargain, especially since they come with 3/8" ARP 2000 bolts. I don't know how strong they are, but I haven't held back on my motor.

As far as the longer rod goes, there is a piston out there that moves the wristpin up to compensate for it. I believe a number of companies including stoid have built motors in this manner.

Mark
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Old 12-06-2006, 09:55 PM   #13
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that ****'s great
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Old 12-06-2006, 10:13 PM   #14
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Quote:
Originally Posted by Markp View Post
The question that begs asking is why would you destroke the motor when you can offset grind for a longer stroke?

As you note, not much needs to change electronically for higher RPM operation. While it's not really a good rod ratio for high RPM work the stroke on the BP miata is plenty short to accomodate 8500 RPM redlines without serious work other than the rods. The stock rods tend to fail under extended tensile loads at high RPM, but the aftermarket rods do not. You will need some cams capable of taking advantage of the extended RPM range and springs to match. Preferably you'll use shim under buckets to reduce weight on the valve train allowing you to use lighter valve springs at higher RPM. I used R&D springs dual spring setup at 65 PSI installed and 175 PSI open.

There is a gasket available that allows for an 85mm bore, but for boosted apps most people stick to 84 mm or 84.5 mm. While they say there is no replacement for displacement, that's not quite true... It's called boost, and lots of it! Ric Stevens had a junkyard 1.6 running 8000 RPM with a GT3271 at 24 PSI making over 325 RWHP and pulling 11.40's at the track. I know that displacement does a lot of good things but don't chase it at the expense of hard earned dollars. There are better places to put your money, especially when trying to keep costs down, having to buy a $250 head gasket vs a $100 headgasket for 50cc's of displacement makes no sense.

Your money will go farther with cams and a decent valvetrain than it will on adding displacement. Add as much displacement as possible without incurring significant additional costs. Personally I consider an offset ground crank cheap displacement. The stock crank is plenty strong so offset grinding it is a non-issue. The scat rods are $299.00 which is a bargain, especially since they come with 3/8" ARP 2000 bolts. I don't know how strong they are, but I haven't held back on my motor.

As far as the longer rod goes, there is a piston out there that moves the wristpin up to compensate for it. I believe a number of companies including stoid have built motors in this manner.

Mark
Gotcha. Thanks for the input. So it looks like the SCAT rod for the Honda + a shorter piston would fit within "reasonable" specs for the BP motor without needing to do anything radical. Stronger internals for a cheaper price and from what you've been throwing at your engine (at much higher rpms no less) seems to be pretty sturdy. Rebuild the shortblock with a modest overbore for a little more displacement. Hmmm....
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Old 12-07-2006, 09:44 AM   #15
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Quote:
Originally Posted by Markp View Post
The question that begs asking is why would you destroke the motor when you can offset grind for a longer stroke?

As you note, not much needs to change electronically for higher RPM operation. While it's not really a good rod ratio for high RPM work the stroke on the BP miata is plenty short to accomodate 8500 RPM redlines without serious work other than the rods. The stock rods tend to fail under extended tensile loads at high RPM, but the aftermarket rods do not. You will need some cams capable of taking advantage of the extended RPM range and springs to match. Preferably you'll use shim under buckets to reduce weight on the valve train allowing you to use lighter valve springs at higher RPM. I used R&D springs dual spring setup at 65 PSI installed and 175 PSI open.

There is a gasket available that allows for an 85mm bore, but for boosted apps most people stick to 84 mm or 84.5 mm. While they say there is no replacement for displacement, that's not quite true... It's called boost, and lots of it! Ric Stevens had a junkyard 1.6 running 8000 RPM with a GT3271 at 24 PSI making over 325 RWHP and pulling 11.40's at the track. I know that displacement does a lot of good things but don't chase it at the expense of hard earned dollars. There are better places to put your money, especially when trying to keep costs down, having to buy a $250 head gasket vs a $100 headgasket for 50cc's of displacement makes no sense.

Your money will go farther with cams and a decent valvetrain than it will on adding displacement. Add as much displacement as possible without incurring significant additional costs. Personally I consider an offset ground crank cheap displacement. The stock crank is plenty strong so offset grinding it is a non-issue. The scat rods are $299.00 which is a bargain, especially since they come with 3/8" ARP 2000 bolts. I don't know how strong they are, but I haven't held back on my motor.

As far as the longer rod goes, there is a piston out there that moves the wristpin up to compensate for it. I believe a number of companies including stoid have built motors in this manner.

Mark
Sorry if this seems like a dumb question but what in all of this is a honda piece? The Scat rods? I'm still not getting this.
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Old 12-07-2006, 09:50 AM   #16
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Originally Posted by brgracer View Post
I hear ya, and I know you are not criticising.

I'm not totally clear on the whole idea myself, which is why I am asking for more info from markp. From my limited knowledge, I only mentioned the longer rod b/c I think the stock honda rods that mark was referring to are a bit longer than the miata rods which is why you have to destroke a bit so that you don't have issues with the piston rings coming down too low on the down-stroke? I also assumed that this would be accomplished when regrinding the crank to fit the rods as well. Also from what I gather, the shorter stroke (in combo with a fancy valvetrain ) allows for higher rpms via less strain on the piston in terms of velocities.

I am still thinking about building a 94 shortblock + 99 head engine for my next FI project. So $700 for stronger internals + a "unique" setup sounds like more fun than spending the same amount just for some stronger rods. Plus, if you can improve the flow with a 99 head/oversized valves/Begi intake manifold/etc, you would probably be able to take advantage of any added upper rpms.

p.s. I didn't know you were also in the fancy valvetrain business....if I do decide to go down this route, I may ask for your assistance, and by ask I do mean $.
Ahh ok I see. Thanks Unfortunately the only thing Jesel makes for over-head cam engines are fancy finger followers, and the miata doesn't use those. I can assist you with a turbo kit though
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Old 12-07-2006, 12:39 PM   #17
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Sorry if this seems like a dumb question but what in all of this is a honda piece? The Scat rods? I'm still not getting this.
SCAT makes rods for the honda that are stronger than stock Honda rods and are $299 a set. Offset grind the crankshaft and find the right piston and you have a stroker motor.

Mark
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Old 12-07-2006, 01:09 PM   #18
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SCAT makes rods for the honda that are stronger than stock Honda rods and are $299 a set. Offset grind the crankshaft and find the right piston and you have a stroker motor.

Mark
Do I hear the makings of the ghettostroker? :gay:
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Old 12-07-2006, 08:15 PM   #19
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SCAT makes rods for the honda that are stronger than stock Honda rods and are $299 a set. Offset grind the crankshaft and find the right piston and you have a stroker motor.

Mark

I seriously think I'm going to try this...
Just a few questions for now.

Which Honda engine are the SCAT rods for?
Any ideas on what pistion specs should be?

Where can I find more info on this?
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Old 12-08-2006, 01:16 PM   #20
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Originally Posted by lukydvll View Post
I seriously think I'm going to try this...
Just a few questions for now.

Which Honda engine are the SCAT rods for?
Any ideas on what pistion specs should be?

Where can I find more info on this?
I really don't know where to get more info on it, if I had done this personally I would have more answers.

Mark
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