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Discussion Starter · #1 ·
Just bought a set of Manley 11cc pistons.

Have Comp stage 2 cams 475,450 and 265,267

Intake valves are 1mm oversized

Does anyone know if I will need to have valve releifs cut to make this setup work correctly.

I know how to check this....just seeing if someone has does this so I can same some time.


Thanks
Dan
 

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9cc CP pistons with no reliefs here with .006" deck squaring (.006" piston to deck clearance), 1 MM OS valves, .495" intake lift and .475" exhaust lift with similar duration and lobe centers had .090" intake clearance and well over .120" on the exhaust.
 

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Discussion Starter · #9 ·
9cc CP pistons with no reliefs here with .006" deck squaring (.006" piston to deck clearance), 1 MM OS valves, .495" intake lift and .475" exhaust lift with similar duration and lobe centers had .090" intake clearance and well over .120" on the exhaust.
Awesome!! Thank you this was the answer I was looking for.

Dan
 

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9cc CP pistons with no reliefs here with .006" deck squaring (.006" piston to deck clearance), 1 MM OS valves, .495" intake lift and .475" exhaust lift with similar duration and lobe centers had .090" intake clearance and well over .120" on the exhaust.
On what centerline?
 

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Lobe separation is 116*
Intake center line 114*
If 114 is where you plan on putting the cam, then valve reliefs PROBABLY won't be necessary. You'll want to check p/v clearance to make sure adequate clearance is there. If you were wanting to advance the intake cam, depending on how far you wanted to go, a valve relief would be necessary. As Michael mentioned, you are limited with your current piston in that arrangement.
 

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Discussion Starter · #13 ·
If 114 is where you plan on putting the cam, then valve reliefs PROBABLY won't be necessary. You'll want to check p/v clearance to make sure adequate clearance is there. If you were wanting to advance the intake cam, depending on how far you wanted to go, a valve relief would be necessary. As Michael mentioned, you are limited with your current piston in that arrangement.
Thanks BLK_03

I'm going to assemble it at 114*. Made good power there before on the old/same setup but with 17cc JE's. Still going to check clearance. Just wanted hear that there is a chance it will work before I pull the pistons out of the boxes.
 

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On what centerline?
Within a few degrees of his intended centerlines. These are custom Comp Cams. So, I keep the rest of the specifics to myself. The P/V clearance was not at the closest point at TDC. I took measurements with the checker spring as the piston was approaching TDC and after. I kept the closest measurements, but not where in relation to TDC.
 

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Within a few degrees of his intended centerlines. These are custom Comp Cams. So, I keep the rest of the specifics to myself. The P/V clearance was not at the closest point at TDC. I took measurements with the checker spring as the piston was approaching TDC and after. I kept the closest measurements, but not where in relation to TDC.
Tightest p/v is usually after TDC.

Super secret shit!!! KB 2.8, built engine, sounds strong. Any track times?
 

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Within a few degrees of his intended centerlines. These are custom Comp Cams. So, I keep the rest of the specifics to myself. The P/V clearance was not at the closest point at TDC. I took measurements with the checker spring as the piston was approaching TDC and after. I kept the closest measurements, but not where in relation to TDC.
Depending on rod length, stroke and cam profile shape; the exhaust is close around 8 degrees BTC, the intake 8 degrees ATC.
 

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Tightest p/v is usually after TDC.
Aware, but not sure where exactly ATDC in my case. I was more concerned with with finding the lowest clearance, and less concerned where exactly it was at the lowest.

Super secret shit!!!
Something like that. These were Nazman's cams that he was working on with John at MP for a larger PD blower and ported heads that never got further then grinding cams. I got a deal on them and built the rest of the engine to make use of them with ported heads and a 7.75:1 DCR.

KB 2.8, built engine, sounds strong. Any track times?
Two track outings and two AAA flatbed rides home since the rebuild, but it is all fixed now. It will be next year before I can get back to the track. I have the dyno sheet though: FileDen.com | Free file hosting and online storage.
 

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I've done two sets of Comp Stage 2 cams now. Both engines were different. Each had generous flycuts.

At 105.25 ICL, the intake cleared at .164 around 3 degrees ATDC, 9cc dish piston. At 106 ICL on my engine, I had .112 around 7 degrees ATDC. Flat top piston. Dish or not makes no difference, as the outer band of the piston is the interference point. The CS2 can be run at the card or a little forward without trouble. The CS3 (238 duration @ .050) will see .067 clearance at 115.75 ICL on a stock style piston without flycuts.
 

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It is prudent as the engine builder to actually check your engine's PTV yourself. There is always a danger involved in using someone else's experience and then firing your engine w/o checking and setting your own PTV clearance. As Michael and Tony have already pointed out, your pistons are skinny in the crown dept and not candidates for fly-cutting to achieve proper PTV clearance.

You will need to check PTV clearance every degree of crank rotation from TDC past the point of closest clearance. As Steve has already pointed out that point and its actual clearance will change as you move the cam phasing, relative to the crank, around.

Although we call it a piston to valve collision it is actually a valve to piston collision. The collision occurs not because the piston hits the valve but because the intake valve hits the piston - a subtle but important distinction. The cam in the case of the intake actually opens the intake valve faster than the piston moves down the cylinder. FWIW it is just the opposite for the exhaust.

To do this checking you will need to use a checking spring and dial indicator among other things. Steve's (03Steve) engine building thread in the TToC provides a great primer for how to do it correctly. It is well worth the time to read.


Ed
 

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Discussion Starter · #20 ·
Manley's came in today.....not impressed.

The reason I'm replacing pistons is I had to go .30 over from going lean on the dyno with a 100 shot.

I had JE's in my motor for 2.5 years. They held up great but I was looking to save a few bucks this time around. I saw the new MMR 2500R pistons (rated to 2500hp) and gave them a call. They said they didn't have any .30 over and would take 2+ weeks to get. They told me it was private labeled by Manley. I called Summit and bought a set of Manley platinum .30 with coated skirts.

I was not impressed with them. The main thing was crown. It measured .220 compaired to JE .280. There was also a lot less material under the piston. I called MMR and asked if there crown was any different than an off the shelf Manley and they said no.

I deceied to return them. I called LM engine and ordered a set of there custom pistons with valve reliefs from Michael. His crown measures .300. He was very knowledgable and nice to deal with. Will not have to worry about PTVC. Thanks again for all you guys help.
 
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