How Much Power can you get out of a NA 4.6 2v?

MadStang

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I have a problem with decking the block of an NPI (assuming thats what you were talking about) would that not rob you of the very little PTV clearance you have to start out with? valve notching the pistons can only do so much.

I have valve notches that are .080 deep. Flat top pistons, Zero decked block, .030 decked 39cc heads, and Stage 4.5 cams. no valve clearance issues. you'll have plenty of PTV with notched pistons.
 

twovalveterror

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I have valve notches that are .080 deep. Flat top pistons, Zero decked block, .030 decked 39cc heads, and Stage 4.5 cams. no valve clearance issues. you'll have plenty of PTV with notched pistons.

don't you have a new edge though? are you running an NPI block in it? I have valve notches, but I want to run the biggest cams I possibly can, so I did't deck the block anymore than had to be done to get it nice and true.
 

MadStang

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don't you have a new edge though? are you running an NPI block in it? I have valve notches, but I want to run the biggest cams I possibly can, so I did't deck the block anymore than had to be done to get it nice and true.

there's no difference between blocks. for clarification I'm running a 97 cobra teksid. the heads are the difference but personally I'd never build an NPI motor for n/a power. IIRC npi has a 52cc chamber and PI 44cc? but anyway NPI are severely handicapped compared to PI. I don't know if you have a PI swapped motor or not but there should be no clearance issues on a PI car if you have decent valve notches.

Edited for accuracy
 

MadStang

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NPI block refers to using NPI dished pistons with PI heads.

in that case on a PI styled head, the valve clearance issue is the same for all dished or flat top pistons. it's the very out side corner where the PTV generally occurs.

As can be seen here from my valve notch location.

teksid_006.jpg
 

twovalveterror

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ok. I was under the impression that the NPI deck height was shorter, and that was the reason for the bump in compression when doing the PI swap. thanks for clearing that up. I have a NPI block, but have PI style heads, so technically I'm not building a NPI motor for N/A power, I'm building a hybrid for N/A power. lol.

one more nagging question though. if there is no difference in deck heights, why then does the NPI have more PTV clearance issues? does the smaller combustion chamber put the valves closer to the block? I guess that would depend on whether they decked the heads to achieve the smaller chamber or if they just took less material out around the valves as compared to the NPI.

I may have just answered my own question, but I would still like to know the method employed for curiosities sake.

thanks guys.
-Jake
 

MadStang

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I actually retract my previous statement. I was thinking about TFS head cc volume not stock npi and PI. Stock NPI has a cc volume of 52cc and PI has 44cc, so scratch the idea that the NPI has a smaller chamber I was incorrect. as for npi having more clearance issues, I'm not sure if that's the truth or the case as I've never owned an NPI.

NPI has more compression with PI heads do to the smaller cc dish in the piston. I believe it's 10.49cc for NPI and 18.1cc for PI. the bigger the dish, the less compression.
 

twovalveterror

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they do have clearance issues. and them having a much smaller dish in the pistons is undoubtedly why. thanks for working that out with me guys. this should be posted in that "what to change?" thread as the right way to tell someone they are wrong! lol. this is easily the best tech I have gotten from this forum yet.
 

MadStang

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they do have clearance issues. and them having a much smaller dish in the pistons is undoubtedly why. thanks for working that out with me guys. this should be posted in that "what to change?" thread as the right way to tell someone they are wrong! lol. this is easily the best tech I have gotten from this forum yet.

yes and no I think. Because as I said the piston is going to make contact at the outside edge of a piston (which is basically flat top/ level with the deck).

NPI Piston making contact with a valve:

diynotch.jpg


Yes it's making contact with a little bit of the inside diameter of the dish, but most of the interference is on the outer diameter. still enough to cause issues on the ID? yes and a notched piston is required. but is it the main location for PTV clearance issues? no, the OD is. but again, regardless, a piston notch would be required on both PI and NPI because the OD is flat on both style pistons, no matter how deep the dish is.
 

twovalveterror

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well I'm back to square one then. I will have to check with a couple people I know who run big cams on NPI motors and maybe even shoot an e-mail to nick at modular headshop. I'll post the results up if I can remember.
 

03DSGGT

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I would definitely talk to Nick at MHS. I have a set of his TFS head specific Stage 3 cams in my car, and I did a lot of brain picking with him. If I remember correctly, you car run a monster cam (compared to a PI head) with a NPI head because the intake valve sits higher in the head with it being a bigger combustion chamber. Also, Ive read that a ported NPI head will outflow a ported PI head from about .450 lift and up. I actually want to build a nasty N/A NPI 2V car for my next project...
 

twovalveterror

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I would definitely talk to Nick at MHS. I have a set of his TFS head specific Stage 3 cams in my car, and I did a lot of brain picking with him. If I remember correctly, you car run a monster cam (compared to a PI head) with a NPI head because the intake valve sits higher in the head with it being a bigger combustion chamber. Also, Ive read that a ported NPI head will outflow a ported PI head from about .450 lift and up. I actually want to build a nasty N/A NPI 2V car for my next project...


that answers my question. if the valves sit higher in the NPI, it would only stand to reason that when you do the PI swap, you reduce your PTVC! I have never heard that the ported non PI would outflow PI before. I guess I can find solace in the fact that my stage III ported livernois heads will most certainly outflow my stock NPI's!

duff, those notches look sick! your short block reminds me of mine, just much, much cleaner.
 

vermilion

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the clearance is very minimal. in order for an npi to outflow a set of PIs, is much needed work. it can be done but its not the average porters task.
 

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