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Speed pro power forged piston clearance .001!!!

General engine tech -- Drag Racing to Circle Track

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bentvalves
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Re: Speed pro power forged piston clearance .001!!!

Post by bentvalves » Sun Jul 12, 2020 11:49 pm

riv187 wrote:
Sun Jul 12, 2020 9:44 am
Boring a 396 .060 over right now, and trying to decide on piston clearance. On the box it says minimum clearance .001, that sounds ridiculous. This will be a street build with 5500 max rpm and weekend cruising. What have you done?? .003 is our best guess but want feedback on one who has used these. Thanks
I like how you used the plastic clamp to hold the stylus driver against the bore.

are those suggested bore finish values on the tape courtesy of sealed power?

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Re: Speed pro power forged piston clearance .001!!!

Post by 1980RS » Sun Jul 12, 2020 11:52 pm

.001 on a forged piston? Yikes. Not for me, run it at .004 that what I did on my last BBC and they were Speed pro's that were calling for a tight clearance. Heck I even add .001 more when using Hypers too. If you are going to run it hard than run it a bit looser, don't need to be a lot, just a little in my book.

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Re: Speed pro power forged piston clearance .001!!!

Post by frnkeore » Mon Jul 13, 2020 1:44 am

Mark O'Neal wrote:
Sun Jul 12, 2020 9:22 pm
frnkeore wrote:
Sun Jul 12, 2020 12:34 pm
The skirt clearance, is based on the aluminum alloy and not if they are forged or cast.

My Speed Pro catalog, calls for .0015 clearance, for that piston.
Skirt clearance is based on skirt profile, gauge point and application.
Are you trying to say that the expansion rate of the type of aluminum alloy is not taken into consideration?

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Re: Speed pro power forged piston clearance .001!!!

Post by Geoff2 » Mon Jul 13, 2020 5:52 am

[1] Would think the piston maker knows what clearance is best for his design....
[2] 0.001" might be a minimum clearance. More clearance might be ok, but create noise/piston slap
[3] I think the original TRW/SP alloy was known as VMS75, known today as #4032 alloy. It has a lower expansion rate than #2018.
[4] If the pistons have a slot [ instead of holes ] for oil drainage behind the oil ring, you can generally run tighter bore clearance because the slot reduces heat transfer to the skirt.

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Re: Speed pro power forged piston clearance .001!!!

Post by Old School » Mon Jul 13, 2020 10:33 am

Which piston is it? The newer ones have the lightning bolt on the skirt. They take less clearance. The old TRW style with nothing on them expand a lot, call for .005 minimum.

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Re: Speed pro power forged piston clearance .001!!!

Post by gmrocket » Mon Jul 13, 2020 10:40 am

Old School wrote:
Mon Jul 13, 2020 10:33 am
Which piston is it? The newer ones have the lightning bolt on the skirt. They take less clearance. The old TRW style with nothing on them expand a lot, call for .005 minimum.
How old are you talking? I have a box here that’s over ten years old with no lighting bolt on the skirt, uncoated. Right on the outside of the box it says .001”

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Re: Speed pro power forged piston clearance .001!!!

Post by riv187 » Mon Jul 13, 2020 10:50 am

Charliesauto wrote:
Sun Jul 12, 2020 3:52 pm
riv187 wrote:
Sun Jul 12, 2020 9:44 am
Boring a 396 .060 over right now, and trying to decide on piston clearance. On the box it says minimum clearance .001, that sounds ridiculous. This will be a street build with 5500 max rpm and weekend cruising. What have you done?? .003 is our best guess but want feedback on one who has used these. Thanks
If that's your block in the photos, I would take it to a shop that has and uses torque plates.

I would not be "guessing" on the clearance. If the manufacturer calls for .001" minimum, add a few tenths and proceed. If you make it .0015", that's 50% more clearance than called for. .003" is 3X the recommended clearance.

If your bearing manufacturer specs .002" are you going to build it with .006"?
Yes thats my block,,,I remembered the head bolts but forgot my head gaskets,,so he bored it within .010" till I got the final spec and I'm taking the gaskets back tomorrow night to finish boring with torque plates. On clearances,,,I agree to a point. To tight though and it seizes or scuffs...too loose and it rattles but still live on.

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Re: Speed pro power forged piston clearance .001!!!

Post by CGT » Mon Jul 13, 2020 10:57 am

gmrocket wrote:
Sun Jul 12, 2020 2:27 pm
i add .002" to the nominal bore clearance and measure across from the pin. not only that, they are meant to be pressed and come with about .0003" pin bore clearance..thats way to tight and contributes to the scuffing . open the pin bore up to .0007 to .001"
I remember seeing a lot of them with stuck wrist pins back in the day. It was the first thing that needed done to those...was to open up that clearance.

I would do some measuring on them. I agree that .001 is a little scary, but if they only have that built into the skirt. I'd probably be unwilling to make my fresh bore and hone .002 or so too big right off the bat....just to run some cheap pistons. Depends on the situation I guess.

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Re: Speed pro power forged piston clearance .001!!!

Post by riv187 » Mon Jul 13, 2020 11:05 am

I got through to speed pro tech line!!!! The fellow who I spoke with was a older gent also a hot rodder and said in my application of a hot rod driver/maybe some strip use to go .002-.0025"....is good range,,,but .0025 for me. He said normally they add .001-.0015 to min for a hot rod use that is going to get on it now and then. Of course the old TRWs would be .005-.006" ,,,but the new high silicone material and skirt design like tighter. He said .003" is OK, but a little loose and the skirt won't be fitting the cylinder as well in this application. He said things like boost/nos/(no plans for boost for me, maybe a tiny NOS shot down road) also play into the skirt spec. He also said SLP-232K moly rings with 280 finish would be good match. Hope this helps anyone else and I appreciate everyone's suggestions.

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Re: Speed pro power forged piston clearance .001!!!

Post by gmrocket » Mon Jul 13, 2020 1:08 pm

CGT wrote:
Mon Jul 13, 2020 10:57 am
gmrocket wrote:
Sun Jul 12, 2020 2:27 pm
i add .002" to the nominal bore clearance and measure across from the pin. not only that, they are meant to be pressed and come with about .0003" pin bore clearance..thats way to tight and contributes to the scuffing . open the pin bore up to .0007 to .001"
I remember seeing a lot of them with stuck wrist pins back in the day. It was the first thing that needed done to those...was to open up that clearance.

I would do some measuring on them. I agree that .001 is a little scary, but if they only have that built into the skirt. I'd probably be unwilling to make my fresh bore and hone .002 or so too big right off the bat....just to run some cheap pistons. Depends on the situation I guess.
Tunnel ram, and it’s wants to “rev up” 🤪

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Re: Speed pro power forged piston clearance .001!!!

Post by gmrocket » Mon Jul 13, 2020 1:17 pm

riv187 wrote:
Mon Jul 13, 2020 11:05 am
I got through to speed pro tech line!!!! The fellow who I spoke with was a older gent also a hot rodder and said in my application of a hot rod driver/maybe some strip use to go .002-.0025"....is good range,,,but .0025 for me. He said normally they add .001-.0015 to min for a hot rod use that is going to get on it now and then. Of course the old TRWs would be .005-.006" ,,,but the new high silicone material and skirt design like tighter. He said .003" is OK, but a little loose and the skirt won't be fitting the cylinder as well in this application. He said things like boost/nos/(no plans for boost for me, maybe a tiny NOS shot down road) also play into the skirt spec. He also said SLP-232K moly rings with 280 finish would be good match. Hope this helps anyone else and I appreciate everyone's suggestions.
Well there ya go. So if they say .001” at bottom of skirt and he said your ok with .002 to .0025”,, or even .003” max..that’s fine

Because they taper about .001 to .0012 up just under the oil ring , you’ll end up with about .0035” .0037” under the oil ring using the .0025” at very bottom of the skirt point.

That’s good ..the VMS-75 Has 11% silicon which almost the same as 4032 ...and 4032’s can be run with that clearance or slightly more...like .0042” max in your Bore size

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Re: Speed pro power forged piston clearance .001!!!

Post by rebelyell » Mon Jul 13, 2020 1:36 pm

riv187 wrote:
Mon Jul 13, 2020 11:05 am
I got through to speed pro tech line!!!! The fellow who I spoke with was a older gent also a hot rodder and said in my application of a hot rod driver/maybe some strip use to go .002-.0025"....is good range,,,but .0025 for me. He said normally they add .001-.0015 to min for a hot rod use that is going to get on it now and then. Of course the old TRWs would be .005-.006" ,,,but the new high silicone material and skirt design like tighter. He said .003" is OK, but a little loose and the skirt won't be fitting the cylinder as well in this application. He said things like boost/nos/(no plans for boost for me, maybe a tiny NOS shot down road) also play into the skirt spec. He also said SLP-232K moly rings with 280 finish would be good match. Hope this helps anyone else and I appreciate everyone's suggestions.
Curious, how the tech guy did Not mention the skirt-coating and its thickness spec and how that thickness figures into the clearance spec; it does.
suggest call another pro.

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Re: Speed pro power forged piston clearance .001!!!

Post by gmrocket » Mon Jul 13, 2020 1:54 pm

rebelyell wrote:
Mon Jul 13, 2020 1:36 pm
riv187 wrote:
Mon Jul 13, 2020 11:05 am
I got through to speed pro tech line!!!! The fellow who I spoke with was a older gent also a hot rodder and said in my application of a hot rod driver/maybe some strip use to go .002-.0025"....is good range,,,but .0025 for me. He said normally they add .001-.0015 to min for a hot rod use that is going to get on it now and then. Of course the old TRWs would be .005-.006" ,,,but the new high silicone material and skirt design like tighter. He said .003" is OK, but a little loose and the skirt won't be fitting the cylinder as well in this application. He said things like boost/nos/(no plans for boost for me, maybe a tiny NOS shot down road) also play into the skirt spec. He also said SLP-232K moly rings with 280 finish would be good match. Hope this helps anyone else and I appreciate everyone's suggestions.
Curious, how the tech guy did Not mention the skirt-coating and its thickness spec and how that thickness figures into the clearance spec; it does.
suggest call another pro.
I have a coated one here..the coating on it is about .0002”

Comparing to an Uncoated one, they did not reduce the original skirt dimensions to make up for the coating and it doesn’t matter because they provide a window where there is no coating to measure..

Coating is not an issue

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Re: Speed pro power forged piston clearance .001!!!

Post by Mark O'Neal » Mon Jul 13, 2020 3:15 pm

frnkeore wrote:
Mon Jul 13, 2020 1:44 am
Mark O'Neal wrote:
Sun Jul 12, 2020 9:22 pm
frnkeore wrote:
Sun Jul 12, 2020 12:34 pm
The skirt clearance, is based on the aluminum alloy and not if they are forged or cast.

My Speed Pro catalog, calls for .0015 clearance, for that piston.
Skirt clearance is based on skirt profile, gauge point and application.
Are you trying to say that the expansion rate of the type of aluminum alloy is not taken into consideration?
I don't pay it any mind at all.

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Re: Speed pro power forged piston clearance .001!!!

Post by cjperformance » Thu Jul 30, 2020 2:42 am

I've used loads of them (brand/type) in Clevelands , .0025" gives no scuff and no noise. .003" if using a bit of n2o or block filler , can 'just' get some noise at cold start, gone within half a minute. Or .0035" if running in a boat/cold water but they do make a little noise for a minute. But no scuff!
Craig.

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