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Speed pro power forged piston clearance .001!!!

General engine tech -- Drag Racing to Circle Track

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riv187
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Speed pro power forged piston clearance .001!!!

Post by riv187 » 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
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Re: Speed pro power forged piston clearance .001!!!

Post by af2 » Sun Jul 12, 2020 11:20 am

More like .0035" or .004" if they are forged 2018.
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riv187
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Re: Speed pro power forged piston clearance .001!!!

Post by riv187 » Sun Jul 12, 2020 11:32 am

L-2240NF 60 is part ,,I read that they have high silicone/12%,, and at that less expansion(?)

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

Post by frnkeore » 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.

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

Post by rebelrouser » Sun Jul 12, 2020 12:37 pm

I think this would be worth a phone call to Speed Pro. I am seeing a trend that piston clearances are getting tighter in a lot of engine combinations. It gets on my nerves pressing buttons trying to actually talk to a real person, but many times it is worth the trouble. The machinist that does my blocks tells me some of the LS engines he does for the local dealership actually have zero clearance until some of the coating wear off. This quick advertisement is what I think the trend is.

https://www.bing.com/videos/search?q=ti ... &FORM=VIRE

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

Post by BillK » Sun Jul 12, 2020 1:44 pm

Riv,
First of all, why would you not believe the manufacturer ?????? I dont understand that thinking.

That being said there are plenty of forged pistons that are run at those types of clearances. The "good old" L2256F small block pistons have been that way for almost 40 years ? The material and design of the piston determines the clearances. I am not a piston engineer so I do what the manufacturer says. They almost always say that you may have to add clearance for certain conditions like boost or nitrous and in marine applications.

Also if it is a coated piston and you have to measure on the coating they probably take that into account when they say .001

Ask the guys that are telling you to run .003 -.004 if they are going to pay to fix the engine if it is noisy or uses oil etc.
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Re: Speed pro power forged piston clearance .001!!!

Post by PackardV8 » Sun Jul 12, 2020 1:56 pm

My machinist is one of those who works to tenths every day, but doesn't follow the directions on the box they came in. He says that .001" is for a perfect world. The customer who doesn't pay for a new water pump, radiator, oil cooler, distributor, won't warm it up before running hard, introduces too many variables. His take based upon forty years in the business is, " another thou-and-a-half; more is less trouble."
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Re: Speed pro power forged piston clearance .001!!!

Post by gmrocket » Sun Jul 12, 2020 2:27 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
And thats the exact reason them piles of junk pistons are usually scuffed and for sale on ebay!

i cant tell you how many times ive had to redo a build that had TRW/speedpro heavy slugs in it that were scuffed because they followed the .001" recommendations ...and to note, that .001" is at the very bottom of the skirt. EG: if they are for a bore of say 4.125" , make it 4.127"

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"

the only reason i will ever use that junk is if the customer supplied them

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

Post by rebelyell » Sun Jul 12, 2020 3:33 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.
same here .0015" also says it IS skirt coated
L-2240NF 60 probably made of 11 - 12% silicon 4032 (f.k.a their proprietary VM-75) and not NO-silicon 2618.

If a SP/FM/TRW forged piston has SLOTTED oil drainbacks behind oil ring, it's probably 4032. But if forged but has round DRILLED drainbacks, it's probably 2618.

Some coated skirts have a small naked spot with no coating where you should gage.

Call their tech line.
1-800-325-8886
Hours:
Monday – Friday 7:30 a.m. – 4:30 p.m. (CT)

https://drivcat.com/LiveDocs/1104.pdf
Last edited by rebelyell on Sun Jul 12, 2020 3:58 pm, edited 1 time in total.

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

Post by Charliesauto » 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"?

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

Post by modok » Sun Jul 12, 2020 4:05 pm

The skirt profiles on many pistons are getting better so they can run tighter at the guage point.
Not just "cam and taper" anymore, it's....like a curve. If you only ever measure pistons at the gauge point then your not seeing the full picture and what's going on.

So....I'd add .001", but I don't think you need to add .002", unless those are some old NOS pistons.
396 maybe ok to not have a torque plate, probably using cast rings. It'll work. If it was a 454, chrome or moly, no

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

Post by af2 » Sun Jul 12, 2020 4:51 pm

BillK wrote:
Sun Jul 12, 2020 1:44 pm
Riv,
First of all, why would you not believe the manufacturer ?????? I dont understand that thinking.

Ask the guys that are telling you to run .003 -.004 if they are going to pay to fix the engine if it is noisy or uses oil etc.
Not knowing what the piston was is the reason I said 2618.(actually misstated 2018) The 4032 can be at the .0015" but why wouldn't you go to .0025" to not scuff the piston? I have a few with 4032 at .003 and no noise at all.
Ask the guy that set it at .001 how are you going to pay for the seizure.
GURU is only a name.
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Re: Speed pro power forged piston clearance .001!!!

Post by econo racer » Sun Jul 12, 2020 5:45 pm

With 1 or 2
thous. clearance after you run it to 200 degrees. Shut it off then try to restart it in about 15 minutes. You will think your starter just went out. Too tight IMO.

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

Post by gmrocket » Sun Jul 12, 2020 6:47 pm

Google; scuffed Speedo pro or TRW forged piston...lots of fun

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

Post by Mark O'Neal » 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.

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