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PostPosted: Thu Jan 18, 2018 9:58 pm 
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Joined: Sun Dec 14, 2014 11:06 pm
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Location: Portland, OR
Limited prep rule 9.1.5.2.g.1:
The block can be rebored no more than 1.2mm (.0472 in) larger than the maximum dimension
given on the specification line for that make, model, and displacement. A cylinder block from
any model from the same manufacturer, which is of the same material and dimensionally identical
throughout, except for non-critical bosses, is permitted.
Oil passages can be re-routed,
enlarged, restricted or plugged.

What is involved in proving the block is identical? Since the rule excludes "non-critical bosses" instead of including "critical dimensions" there could be a radius, chamfer or rib that has changed if you didn't define every dimension.

I ask as the machine shop doing my engine called today that the block is no good. I have two others but they are already bored over and have other questionable issues. Searching it looks like 1 car in the area in a junk yard might have the right engine, Honda D16A6 from 88-91 Civic Si/EX and CRX Si. Possible alternate block is from the D16Y7 in almost every 96-00 Civic out there. Same bore, stroke, rod length, bearing sizes, deck height, material.

Is this a rule you could defend that you applied? Or too many possible details to ever be sure you're "dimensionally identical"?

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Ian
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PostPosted: Fri Jan 19, 2018 8:06 am 
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Hi Ian-

I think you could defend the Y-block swap. The Y-block uses a different oil pan, oil pump, and rear main seal housing, but you can mount the D16A6 oil pump (direct fit) and the rear main housing (with some modification - I run a D16Y oil pan, oil pump housing, and rear main on my D15B block, so you can probably go the other way as well) to the Y block, and therefore use the D16A6 oil pan, too. Non critical bosses I would take to mean accessory mounts, alternator mount, etc...


Just my $0.02

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Jonathan Spiegel
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Big Island of Hawaii Region and Colorado Region
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PostPosted: Fri Jan 19, 2018 8:55 am 
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Joined: Tue Dec 31, 2013 10:40 am
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Location: Huntsville, AL
I think if you can show that the block is pretty much the same, crank main bores, cylinder bores, bore spacing, block height, etc, you should be fine. Pretty sure that rule is meant to keep out aftermarket blocks and the like.

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Brett W
Huntsville, AL


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PostPosted: Fri Jan 19, 2018 9:17 am 
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The M3 and the (EP Legal) 328is have the same head and block. The pistons, crank, and cams are different. I wouldn't hesitate to use the M3 block. I think it has the same part number as the 328 block.

I know the miata engine was available in other vehicles (ford escort, Mazda 323) so I think this is what they're talking about.

Since the rule is pretty clear about "dimensionally identical throughout" I think you'd be OK with one that was slightly different externally, as long as block height was the same, journal locations, water passages, etc.

If one block had say, a different boss for mounting the oil pump, you'd have a hard time convincing anyone it was dimensionally identical (even tho, yes, oil pumps are free).

I'd be careful.


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PostPosted: Fri Jan 19, 2018 9:45 am 
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And Ian, when looking for parts remember your best friend is carpart.com. Everyone will ship.


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PostPosted: Fri Jan 19, 2018 9:54 am 
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Location: Portland, OR
At this point I am looking at buying a car just for the engine block, I am worried about defending this. Welcome to vintage racing right? I do see need for clarification on this rule. Maybe I'll write my first rule revision request.

I think this needs clarified to something that helps define the intent. As soon as a boss changes the part number will change so you would need to defend. I think something that captures the machined elements of the block except those machined for bosses. It could be that a manufacturer changes a rib mid-production or has multiple suppliers with slightly different designs currently and isn't known within the current spec line.

I've dug a little deeper on this and there are some variances but they fall into other allowable mods.

    Y-blocks use different size head bolts. Per 9.1.5.m.1 allows alternate fasteners. Downer on this is I already bought the new bolts for the A6.
    Y-blocks moved the oil control jet from in the blocks deck to in the head. The shop would have to bore the oil passage to insert the oil control jet. But this is permitted per 9.1.5.g.1
    Y-blocks use a steel girdle, but this is permitted by 9.1.5.g.3

Other option but a little less common is the D16Z6 block from 92-95 Civic EX/Si. My worry here is these are "Vtec" blocks. But the Vtec has nothing to do with the block, just the head. But someone might see the "Z6" mark on the block and call foul.
Similar to the Y-block:
    Z6 block moved the oil control jet from in the blocks deck to in the head. The shop would have to bore the oil passage to insert the oil control jet. But this is permitted per 9.1.5.g.1
    Z6 blocks use a steel girdle, but this is permitted by 9.1.5.g.3

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PostPosted: Fri Jan 19, 2018 9:55 am 
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Location: Portland, OR
zChris wrote:
And Ian, when looking for parts remember your best friend is carpart.com. Everyone will ship.


I have looked at that. I see a bunch of errors in their descriptions and it worries me about not being able to see that it's right (or fair condition) before it ships. May be it though.

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Ian
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PostPosted: Fri Jan 19, 2018 11:28 am 
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Ian Green wrote:
zChris wrote:
And Ian, when looking for parts remember your best friend is carpart.com. Everyone will ship.


I have looked at that. I see a bunch of errors in their descriptions and it worries me about not being able to see that it's right (or fair condition) before it ships. May be it though.

I have had mixed success with verifying stuff like this before it ships.. some places you call and they are more than happy to take a couple extra photos and/or verify condition. others will tell you exactly what you want to hear to sell the part and get it out of their building.
ALL of the parts have a VIN associated with it, especially the engine blocks.. I would think for your purposes, it should be relatively easy to have the seller verify whatever numbers on the block you need (with photo?) prior to purchase. and then pay with credit card to it's easy to dispute the charges if there are problems with it later.

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Matt Blehm
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PostPosted: Fri Jan 19, 2018 12:58 pm 
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I think the 88/89 blocks have the steel girdle and the 90/91 blocks have the all aluminum one. I have both at home and they have D16a6 on them.

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Blake Meredith
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PostPosted: Sat Jan 20, 2018 5:26 pm 
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Location: Huntsville, AL
Agreed, I have an A6 block with steel main caps and aluminum girdle, I can check the serial number, the later Vtec engines had the aluminum main caps and girdle. I don't think any A6 block came with an all aluminum girdle. A quick phone call to HPD should be able to verify what is what. I just checked my other pictures, the original engine from my 90si shows cast iron main caps as well.

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Brett W
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