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Another piston question

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GPGoverMPG
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Another piston question

Post #1 by GPGoverMPG » Mon Jun 10, 2019 8:24 am

So I'm running the 390 pistons that I balanced. I took the rods and pistons to the machine shop to have them married and the shop called to see if I had clearanced the skirts for the crank. He said he had to do it on a previous 300 build. Does anyone know if this is something I need to look for with my combo. He didn't want to but things together just to take it apart so I could rebalance the pistons.
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BigBlue94
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Re: Another piston question

Post #2 by BigBlue94 » Mon Jun 10, 2019 9:27 am

Can you get a pin centerline to bottom of skirt measurement? I can compare to my 4.060" 351w pistons at home and give you an idea. Though I'm sure someone here has the specs
1985 Bronco. 309ci I6, NP435, 4.56 gears, Detroit locker and tru-trac, 4" lift, and 37" swamper tires. The 309 is 9.75:1 CR with a Schneider 140H cam, 4bbl, roller rockers, larger valves, and headers.

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Re: Another piston question

Post #3 by CNC-Dude » Mon Jun 10, 2019 9:50 am

If he's speaking from experience, then you may need to look into it. Since the 300 stroke is longer than a 390's, and the 300 rod is shorter than the 390's, it stands to reason as the piston approaches the bottom of the stroke, that contact with the counterweighted could occur.
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Re: Another piston question

Post #4 by 54-4x4 » Mon Jun 10, 2019 9:53 am

I have 352 V8 pistons .030 and have no problems with piston skirt clearances.I think the pistons for 352,360,and 390 are the same design just different bore size.

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Re: Another piston question

Post #5 by Max_Effort » Mon Jun 10, 2019 10:09 am

If any doubt, mock it up. If the press fit pin is a problem for mock-up , grind or belt sander an old pin so it just slips in.

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GPGoverMPG
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Re: Another piston question

Post #6 by GPGoverMPG » Wed Jun 12, 2019 8:11 am

Mocking it up is the way to know. He's looking for one of my old pistons to compare to we'll see. If it's even close I'd be best served by mocking it up. The only question is how many times can you install and torque bearing caps before you need to replace the bearings?
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Re: Another piston question

Post #7 by Max_Effort » Wed Jun 12, 2019 10:28 am

GPGoverMPG wrote:Mocking it up is the way to know. He's looking for one of my old pistons to compare to we'll see. If it's even close I'd be best served by mocking it up. The only question is how many times can you install and torque bearing caps before you need to replace the bearings?

More than once. However you don’t need to torque it, just run the nuts down slightly snug. You can mock up with a used bearing too. A few thou of extra clearance isn’t a big deal for mock up.

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Re: Another piston question

Post #8 by CNC-Dude » Wed Jun 12, 2019 8:49 pm

You only need to use and install the front and rear mains to install the crank to check the deck height. Just use used bearing as has been mentioned and stick the upper thrust bearing in the block and your good. You don't have to fully torque the bolts if you don't want to, but they can be torqued and retorqued dozens of times as long as you oil the threads and under the bolt heads.
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Re: Another piston question

Post #9 by GPGoverMPG » Thu Jun 13, 2019 8:25 am

Yea, shouldn't be any problems. I need to call my machine shop today and find out where I am. I was reading the thread about priority oiling and I was wondering if oil restrictors were used to the top end. FE motors I've built reduce the oil when using roller rockers. Guess I'll be putting the bottom end together to verify piston skirts as well as check deck height.
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GPGoverMPG
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Re: Another piston question

Post #10 by GPGoverMPG » Sat Jun 15, 2019 8:32 am

The machine shop turned down a wrist pin so I could test fit my H395p speed pro pistons. The piston skirts missed the crank counter weights by at least .25inche. So much in fact I did not bother with an actual measurement. I also used this time to measure piston deck height. Using A straight edge and feeler gages and I got .040 which backs up the math. I am considering leaving the pistons in the hole .010 to reduce the compression a little bit. So here is the question, do I leave it in the hole .015 so I have room to play with timing or do I max out compression and run sub optimal timing to prevent detonation. I plan on some dyno time once it's running in the truck but it gets expensive quick. Thanks for any recommendations
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Re: Another piston question

Post #11 by Max_Effort » Sat Jun 15, 2019 9:07 am

GPGoverMPG wrote:The machine shop turned down a wrist pin so I could test fit my H395p speed pro pistons. The piston skirts missed the crank counter weights by at least .25inche. So much in fact I did not bother with an actual measurement. I also used this time to measure piston deck height. Using A straight edge and feeler gages and I got .040 which backs up the math. I am considering leaving the pistons in the hole .010 to reduce the compression a little bit. So here is the question, do I leave it in the hole .015 so I have room to play with timing or do I max out compression and run sub optimal timing to prevent detonation. I plan on some dyno time once it's running in the truck but it gets expensive quick. Thanks for any recommendations


Are those flat-top pistons that you modified?
Is there still a flat quench area?
If so I would try to achieve .040" to .050" piston to head distance.

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Re: Another piston question

Post #12 by pmuller9 » Sat Jun 15, 2019 11:50 am

Max_Effort wrote:Are those flat-top pistons that you modified?
Is there still a flat quench area?
If so I would try to achieve .040" to .050" piston to head distance.


They are flat tops with 4 centered valve pockets.

I agree with Max. Keep the pistons at .010" in the hole for a .050" quench distance.
If you go further you lose effective quench for detonation resistance even though the compression ratio is decreased slightly.

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Re: Another piston question

Post #13 by GPGoverMPG » Sat Jun 15, 2019 9:07 pm

They are flat top with 6cc valve pockets. Standard 360/390 FE pistons which makes them .050 oversize for the 300. I have opened up my combustion chambers for 78cc and I'm running big valves in the ported head. The Schneider 142f solid lifter cam and Harland Sharp 3002 roller rockers. So I am going to leave the pistons in the hole (below deck) just the .010. I wonder if the ARP head studs with their increase in clamping force will reduce the gasket thickness to less than the .039 from the Fel-Pro site. I'm only going to run 93 octane fuel. I'm guessing around 36 degree total timing which means I will have 18 degrees initial timing when I start it. Currently I'm running no vacuum advance because my 2100's have no ported vacuum outlet. I'm having better luck finding 1.14s but I think the 1.08 would be better guess Ill be installing screw in air bleeds to help tune. Thanks for the help again
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Re: Another piston question

Post #14 by pmuller9 » Sat Jun 15, 2019 10:25 pm

The 1.14s are only 300 cfm each for a total of 600 cfm which is equivalent to a 425 cfm 4 barrel carb.
The 300 six with the Schneider 142F cam and big valve ported head requires a 650 cfm 4 barrel to maximize performance.

It would be ok to use a pair of 1.23 or 1.33 carbs

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Re: Another piston question

Post #15 by GPGoverMPG » Sun Jun 16, 2019 8:16 am

Ok, I remember putting down several 1.23s. I will go look again just cause I don't remember seeing 1.33s doesn't mean their not there.
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THE FRENCHTOWN FLYER
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Re: Another piston question

Post #16 by THE FRENCHTOWN FLYER » Sun Jun 16, 2019 8:47 am

Are you going to run TWO 2V carbs? If so I would like to offer a differing opinion. This is purely anecdotal evidence based only on my own experiences racing my own junk which include two 2 x 2V equipped drag cars for what its worth.

On my drag truck in particular, I have it set up for maximum consistency and repeatability. With a smallish circle track roller cam (.600 lift Schneider) and 2.47 rear end gearing and two-speed Powerglide it runs high elevens using a Clifford intake with two 1.02 Autolite 2100s on a race prepped big valved head. I use these because it provides crisp throttle response with no bog when the throttles are snapped open. I have instructed my driver to shift it at 5500 RPM (the bottom end is stock!) These two carbs have a combined 4V equivalent of 340 CFM. He does say that above 5000 RPM it starts to lay down compared to other larger carb setups we've tried (650 double pumper, 600 vac sec, 480 vac sec) but up to 5000 RPM it runs better than anything else we've tried. I am looking to find a matched set of 1.08s to try in the future to see if we can enhance the performance above 5000 without hurting the throttle response off the line.
So my conclusion is if you are not going to run above 5000 RPM then 340 CFM will be all the airflow you will need, even with a fully prepped U-flow head.

My other junk is my street / strip Willys coupe which is using two 1.08 carbs on a pretty stout engine build up. It also works well and most of the time when I race it I just put 'er in "D" and let it upshift automatically at around 4200. When I manually shift it at 5500 it runs quicker.

A typical setup:

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FORD 300 INLINE SIX - THE BEST KEPT SECRET IN DRAG RACING

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Re: Another piston question

Post #17 by pmuller9 » Sun Jun 16, 2019 9:16 am

There are differences.

The 142F cam will pull hard to 5500 rpm and shouldn't be limited by the smaller carbs where power is falling off after 5000 rpm.
The 142F cam is also not so large where the WOT engine response needs to compensated by using a smaller carb especially considering the very long runners on the custom made intake manifold.

The 1.08s are working because the two plenums are connected together where both carburetors are available to each of the six cylinders to draw on.

In this case the two plenums are separate and each cylinder can only draw from one carburetor.
This has to do with peak flow versus plenum volume versus carb size.

I would not use less than a 1.23" carburetor.

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Re: Another piston question

Post #18 by GPGoverMPG » Mon Jun 17, 2019 8:23 am

I do have two very small plenums and straight runners about 14" long. The carbs will work at the same time and be syc'ed like motorcycle carbs. Runner length should be for peak torque around 3000rpm first time building intake so there is a lot I don't know. Will need to purchase two wide band O2 sensors so maybe I won't case my butt all over the place trying to get jetting right. I plan on setting them up one at a time on my current engine so they should be close enough to start the new motor safely. Not sure if I could run my mostly stock set up with my new intake and carbs for testing purposes. Then again all it can do is not work very well. Thanks for the great input.
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72 F250 4x4 4speed 300 I6
72 F100 2x 428 Tri Power
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