I am going to be running a N/A 97 GT with a PI head swap and new forged internals. I wanted to use flat top pistons and was wondering if anyone knew if I needed valve reliefs on them or not.
Do I need valve reliefs on Flat Top Pistons?
- Thread starter 53BigDog
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53BigDog said:
DropTopPony said:
What's the matter......the stock 10.4:1 compression ratio isn't enough for ya? 
steveb24
New Member
Hummmm that sucks monkey nuts. I found a great set of flat tops on ebay (w/o reliefs) and I bought them. I'm in the process of a lower end rebuild and a PI head swap. I am staying N/A and looking for a 10-11:1 compression (hence the flat tops). I was planning on going with Stage one cams (possibily stage 2) but I guess that throws a wrench into my plans. Hey how much benefit is there from stage 1 and stage 2 over stock?
steveb24 said:
I had to ask the same question in another post! no question is a dumb question!!!
stangGT97
New Member
You do realize that the stock dish in the NPI GTs is enough to give you a 10.5:1 cr when using PI heads. If you just bought forged rods and forged pistons (w/ the stock dish, not sure what the cc's are), you would be in the 10:1-11:1 range, which is what you said you wanted. I think flat tops might push you a little too high.
First of all, you do NOT need valve reliefs. I don't know where some of you are getting this.
Here's why...
The portion of the piston that is closest to the valve during the intake closing event is the small, flat area (approx 10 mm wide) around the outside perimeter of the top of the piston. This 10mm area is present on ALL pistons, regardless of dish size. Therefore, there is no need for reliefs.
That being said, only if you plan on running some pretty aggressive cam timing will you need to consider this. Also, if you're going to deck the block (take material off the head deck face), you may need to consider it. The stock deck to piston (compression deck) clearance is 0.3 mm.
Also, there are ALOT of guys running flat tops with no reliefs.
Here's why...
The portion of the piston that is closest to the valve during the intake closing event is the small, flat area (approx 10 mm wide) around the outside perimeter of the top of the piston. This 10mm area is present on ALL pistons, regardless of dish size. Therefore, there is no need for reliefs.
That being said, only if you plan on running some pretty aggressive cam timing will you need to consider this. Also, if you're going to deck the block (take material off the head deck face), you may need to consider it. The stock deck to piston (compression deck) clearance is 0.3 mm.
Also, there are ALOT of guys running flat tops with no reliefs.
That's not true. And it's not theory...it's the geometry of the engine. Re-read my post and try to visualize what I'm saying.
I have VT stage II cams, and I have zero issues with valve clearance. Flat-tops or not, the area of the piston that is closest to the valve is flat on ALL pistons.
Degree your cams and you WON'T have any problems!
I have VT stage II cams, and I have zero issues with valve clearance. Flat-tops or not, the area of the piston that is closest to the valve is flat on ALL pistons.
Degree your cams and you WON'T have any problems!
This is why I love Stangnet! Thanks guys keep the suggestions and education coming!
So besides VT and Comp what other cam companies live up to their name?
So besides VT and Comp what other cam companies live up to their name?
i'll help with the visualizationModFever said:
View attachment 449197
The reason i said yes to reliefs is that for some reason people are not getting cams degreed...they think a straight up timing install is all you need. but its not my engine that is getting bent valves and scratched pistons.
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