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Discussion Starter · #1 ·
I have a 73' 240 with a rod sticking out of the block :( However, on the upside, this gives me the oportunity to build another engine, and test out a theory of mine. My budget doesen't allow for a 3.1 or anything, so I decided see if I could come up with an old fashion hot-rod style combo. Here's what I came up with: L28 block, L24 crank and rods, 280zx flat top pistons, and an E88 head that has been re-worked but not shaved. What I think I should end up with is a quick revving engine with great low end tourqe, and fairly high compression. It seems like this combo would be the most bang for the buck possible, especially since I have all the parts laying around. Anyway my installed piston height would be +.05mm. This is where I came upon some questions:
1) Has anyone destroked one before?
2)Should I take that .05mm off the pistons?
3) Would the valves clear?
4) Can I get away with the stock head gasket or do I need the 2mm HKS one?
5) How do I calculate the compression?
If anyone can shed some light on this subject, or give me the benefit of their experience on this one I would be very grateful!!

Tony Rohn
 

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See Nov/Dec '97 issue of Z-Car mag.

With respect to clearances/head gasket/valves clearance.....calculate - measure - measure - measure......like any custom job: If it was easy, everyone would be doing it! ;-)

With respect to compression ratio - see Bob Hanvey's compression page. The URL is <A HREF=http://www.geocities.com/MotorCity/Track/6997/compression.html>http://www.geocities.com/MotorCity/Track/6997/compression.html</A>

good luck

tomh

> I have a 73' 240 with a rod sticking out of
> the block :( However, on the upside, this
> gives me the oportunity to build another
> engine, and test out a theory of mine. My
> budget doesen't allow for a 3.1 or anything,
> so I decided see if I could come up with an
> old fashion hot-rod style combo. Here's what
> I came up with: L28 block, L24 crank and
> rods, 280zx flat top pistons, and an E88
> head that has been re-worked but not shaved.
> What I think I should end up with is a quick
> revving engine with great low end tourqe,
> and fairly high compression. It seems like
> this combo would be the most bang for the
> buck possible, especially since I have all
> the parts laying around. Anyway my installed
> piston height would be +.05mm. This is where
> I came upon some questions:
> 1) Has anyone destroked one before?
> 2)Should I take that .05mm off the pistons?
> 3) Would the valves clear?
> 4) Can I get away with the stock head gasket
> or do I need the 2mm HKS one?
> 5) How do I calculate the compression?
> If anyone can shed some light on this
> subject, or give me the benefit of their
> experience on this one I would be very
> grateful!!

> Tony Rohn
 

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my take on it

by using the L-24 crank you will have a motor that revs faster and higher as opposed to the L-28. However, you will not gain much if any torque in n/a applications. you will also lower your compression too much. I think for my engine, I calculated the compression to be down to 6.5:1. This is much too low for an n/a motor and on the low side of a turbo motor. You reduce the stroke 6mm which reduces the piston deck height by 3mm when going from the l-24 from the l-28. Your concepts are good if you were to build a destroked turbo motor where the turbo could give you all the torque you need. This is off course, if you are using the l-28 block instead of the l-24.
 

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Discussion Starter · #4 ·
Re: my take on it

Tom,
I think we must be on different pages! I'm not saying you're wrong, I just want to make sure my figures I have are reliable. Here is my engine (in theory) with figures that I got from Jim Wolf's L28 bore and stroke combo's that he presented at a Z club of San Diego meeting. My L28 piston pin height I found on the 3.0 and 3.1 liter In-line 6 cyl. FAQ on IZCC's webpage.

Piston pin height (l28) = 38.1mm
Rod length (L24) = 133.0
Stroke/2 (L24) = 38.85
This adds up to 207.95
Which is my IPH or installed piston height
Block Height = 207.9
For a possitive difference of = + .05mm

I would think that an IPH that is more than my Block height would give me a relatively high compression ratio. If my figures are false I apologize, but I'm just going by what I have available, and the sources seemed pretty reliable. Tell me what you come up with.

Much apreciated

Tony Rohn

> by using the L-24 crank you will have a
> motor that revs faster and higher as opposed
> to the L-28. However, you will not gain much
> if any torque in n/a applications. you will
> also lower your compression too much. I
> think for my engine, I calculated the
> compression to be down to 6.5:1. This is
> much too low for an n/a motor and on the low
> side of a turbo motor. You reduce the stroke
> 6mm which reduces the piston deck height by
> 3mm when going from the l-24 from the l-28.
> Your concepts are good if you were to build
> a destroked turbo motor where the turbo
> could give you all the torque you need. This
> is off course, if you are using the l-28
> block instead of the l-24.
 

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Discussion Starter · #5 ·
Re: my take on it

Tom,
I think we must be on different pages! I'm not saying you're wrong, I just want to make sure my figures I have are reliable. Here is my engine (in theory) with figures that I got from Jim Wolf's L28 bore and stroke combo's that he presented at a Z club of San Diego meeting. My L28 piston pin height I found on the 3.0 and 3.1 liter In-line 6 cyl. FAQ on IZCC's webpage.

Piston pin height (l28) = 38.1mm
Rod length (L24) = 133.0
Stroke/2 (L24) = 38.85
This adds up to 207.95
Which is my IPH or installed piston height
Block Height = 207.9
For a possitive difference of = + .05mm

I would think that an IPH that is more than my Block height would give me a relatively high compression ratio. If my figures are false I apologize, but I'm just going by what I have available, and the sources seemed pretty reliable. Tell me what you come up with.

Much apreciated

Tony Rohn

> by using the L-24 crank you will have a
> motor that revs faster and higher as opposed
> to the L-28. However, you will not gain much
> if any torque in n/a applications. you will
> also lower your compression too much. I
> think for my engine, I calculated the
> compression to be down to 6.5:1. This is
> much too low for an n/a motor and on the low
> side of a turbo motor. You reduce the stroke
> 6mm which reduces the piston deck height by
> 3mm when going from the l-24 from the l-28.
> Your concepts are good if you were to build
> a destroked turbo motor where the turbo
> could give you all the torque you need. This
> is off course, if you are using the l-28
> block instead of the l-24.
 

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Do not shave pistons or use 2mm gasket

The following is based off of an original compression ratio of 8.8 for a 73 motor.Your new swept volume with 280 pistons will be 429.16 cc. Your E88 head clearance volume including gasket and crevice volume is 51.09.Subtract .2904 from 51.09 due to .05mm positive deck height and this yields 50.799. Divide Swept volume by head clearance volume and add 1 to get compression ratio of 9.448. This will run fine on pump gas.You do not need to worry about .05mm positive deck clearance this is only .002 of an inch above block. Your valves will not be bothered at all by such a slight increase. Hope this helps, norm
 

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Discussion Starter · #7 ·
Re: Do not shave pistons or use 2mm gasket

Norm,
Thanks for the info. It's nice to know I'll be able to run pump gas, as that was one concern of mine. Any ideas on what kind of performance I can expect out of this setup? I realize this would fall in the realm of speculation, but hey it's all theory so far right? I know four cylinder datsuns that have had similar mods done have real high red-lines and get there in a hurry, so hopefully this'll turn out along those lines!
Thanks again.
Tony Rohn

> The following is based off of an original
> compression ratio of 8.8 for a 73 motor.Your
> new swept volume with 280 pistons will be
> 429.16 cc. Your E88 head clearance volume
> including gasket and crevice volume is
> 51.09.Subtract .2904 from 51.09 due to .05mm
> positive deck height and this yields 50.799.
> Divide Swept volume by head clearance volume
> and add 1 to get compression ratio of 9.448.
> This will run fine on pump gas.You do not
> need to worry about .05mm positive deck
> clearance this is only .002 of an inch above
> block. Your valves will not be bothered at
> all by such a slight increase. Hope this
> helps, norm
 

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Protecting my reputation.

Tony,

You are referring to the compression ratio quoted in the post by 240Z Turbo, no???

All I offered in my posting to your question was to point you towards a back issue of Z-Car mag. & to a page on Bob Hanveys web page.

I am curious though & I will fire up my compression ratio spread sheet & see what it reports for your desired build.

later....tomh

> Tom,
> I think we must be on different pages! I'm
> not saying you're wrong, I just want to make
> sure my figures I have are reliable. Here is
> my engine (in theory) with figures that I
> got from Jim Wolf's L28 bore and
...snip...
> I would think that an IPH that is more than
> my Block height would give me a relatively
> high compression ratio. If my figures are
> false I apologize, but I'm just going by
> what I have available, and the sources
> seemed pretty reliable. Tell me what you
> come up with.

> Much apreciated

> Tony Rohn
 

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Discussion Starter · #9 ·
Re: Protecting my reputation.

Tom,
Yes, I was refering to the CR posted by 240z turbo. Incidently I noticed that he deleted his message. I wasn't trying to offend him, but merely stating that my data indicated a positive piston height which would make for a relatively high CR. I apreciate everybody's responses. BTW, I'm going to go and check out that web page now, thanx for the lead!
Tony Rohn

> Tony,

> You are referring to the compression ratio
> quoted in the post by 240Z Turbo, no???

> All I offered in my posting to your question
> was to point you towards a back issue of
> Z-Car mag. & to a page on Bob Hanveys
> web page.

> I am curious though & I will fire up my
> compression ratio spread sheet & see
> what it reports for your desired build.

> later....tomh
> ...snip...
 

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> I have a 73' 240 with a rod sticking out of
> the block :( However, on the upside, this
> gives me the oportunity to build another
> engine, and test out a theory of mine. My
> budget doesen't allow for a 3.1 or anything,
> so I decided see if I could come up with an
> old fashion hot-rod style combo. Here's what
> I came up with: L28 block, L24 crank and
> rods, 280zx flat top pistons, and an E88
> head that has been re-worked but not shaved.
> What I think I should end up with is a quick
> revving engine with great low end tourqe,
> and fairly high compression. It seems like
> this combo would be the most bang for the
> buck possible, especially since I have all
> the parts laying around. Anyway my installed
> piston height would be +.05mm. This is where
> I came upon some questions:
> 1) Has anyone destroked one before?
> 2)Should I take that .05mm off the pistons?
> 3) Would the valves clear?
> 4) Can I get away with the stock head gasket
> or do I need the 2mm HKS one?
> 5) How do I calculate the compression?
> If anyone can shed some light on this
> subject, or give me the benefit of their
> experience on this one I would be very
> grateful!!

> Tony Rohn

Tony - I finally got around to firing off my spread sheet. I do not have the compression height or dish of most of the stock pistons since I did the spread sheet for looking into the 3.1 L stroked and bored motor that I am planning on building.

I substitued stock L24 compression height with no dish & came up with just below 9.5 to 1.

I'd attach my spread sheet (MS Excel 97) for all to snag, but there is no means to do it here. If you would like a copy, post a responce to this & I will e-mail copies. It works quickly & is a fun way to do what-if's!

tomh
 
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