Valve to piston relief spec's ?

[OLD H2S]

Time for No. 47 to hit the spa for the winter. Trying to get some flat top cast pistons from ModMax and I need to machine the intake notches in the piston tops. Do you know the angle and dimensions of the cut so I can set up a fixture to hold the pistons?

 

[96blak54]

Good idea! I dedicated a damaged short block and heads for piston valve reliefing. I intall the piston, mount the modified head, and relief away. I dont have a piston fixture and im not a fan moving my milling machine out of tram, so I impervised.

Send me your pistons, ill do them

What is you build idea?

 

[OLD H2S]

I do not have the pistons yet or the engine out of the car yet. Got used SVT rods, rest will be stock but the cams, they are Bullit stock duration but .525 lift. Heads, you have seen pics of on another thread, the have the top side opened up and when I get the motor apart I will finish the porting and fly cut some off the heads. Block will be bored .020 over for the new pistons and deck the block .020 with a FelPro .036 thick gasket.
Thanks for the offer to cut the pistons. I have a small mill at home and a Bridgeport at work to play with. I was planing to use a sine plate to get the right angle on the pistons and use my 1" fly cutter shaped to a radius edge and plunge cut down into the top of the piston.
Some ARP head studs,Hurricane oil pump, windage tray, 7 quart oil pan, Ford GT cam followers,JBA shorty headers,BBk varitune mufflers,Exedy 16 pound steel flywheel, Exedy stage 2 clutch kit, Ford aluminum drive shaft,T45 Source parts kit for the trans I am looking for 250 HP.
Stopped by Burtonsville Performance Machine Services, House of Balance and Horsepower by Herman for pricing on what I need, so I am off to a slow start and doing the 3.73 rear and panhard bar with rear coilovers first since the parts are all here. Flame on guys .. I need the input.

 

[whiplash473]

You should be able to call the company that your heads were built at and ask them. TFS, Edelbrock, etc should be able to tell you.

Just curious why you would fly cut your heads and not either use an insert cutter or a surface grinder

 

[96blak54]

So the heads are npi? If the bullet cams are stock duration, why use them? I dont understand this one...

Anyhow, if youre using stock npi heads undecked their will be no need to notch the pistons. If you decide to deck the head .100" then piston notches will be needed. The npi heads have a ton of room unlike pi heads. Also, you can deck npi heads .100"! The deck thickness compared to a pi head is nearly double.

 

[whiplash473]

So the heads are npi?

^^^

What is the engine anyways? I'd like to move this thread to the appropriate section .

 

[OLD H2S]

It is a '96 GT NPI. I am trying to cut the pistons myself but the engine block and heads will be done by BPMS because a big cutter works better decking the block and fly cutting the heads. Block will be cut .020 and the heads maybe .130? Yes, no?

 

[OLD H2S]

I did the rough head porting before on another thread and I will do the finishing work, they are stock NPI heads. The big why??? See my other threads, I have done 3 Terminator engines in my Marauder that I sold and am now doing a low HP motor for my SN95 toy.

 

[96blak54]

Hotrodding at its best. More fun this way! Taking the underdog to new hight! I got enough friends with 1000+rwhp cars and watching them struggle with harnessing it....that aint me. I help them work on it, solve problems, but it aint me.

If you could score a set of 5.4l heads half of your work is done. All that will need porting is the intake port.

.130" decked is do-able. Ive heard pi heads decked .070" and survived fine n/a on an iron block. .130npi and .070pi is roughly the same thickness after decking.

Youre gonna need some deep pockets. Roughly .100" possibly deeper depending on camshafts. Valve reliefs is what kills compression potential with flat top pistons. Gonna have to dome the pistons next...lol

 

[96blak54]

If you dont achieve 320rwhp, sumtin is wrong!

 

[OLD H2S]

Maybe i'll go to the "auto recylcler" and get some 5.4 heads. I really liked the photo of the exhaust ports you showed. One reason I do like my '96 NPI is I bought this car new and it has not been abused till I started road racing it this year. I bet the cylinders still have crosshatching. I am not really trying to do a cheap build, I just have had parts laying around for years just waiting for the next build, I did not know it was going to be the wife mobile. I am knee deep in replacing the bathroom floor that collapsed so hiding car parts in the bathroom rebuild budget is easy but I have to act fast.

 

[OLD H2S]

So now I am chasing 5.4 heads, Rock Auto wants 525.00 ea. for a set of rebuilds, that's the price for a set of ported heads from ModHeadShop. I have been chasing down the local recyclers that are good in this area and I will let you know the price later.

 

[96blak54]

Their are a few recylers on ebay listing specific year heads "buy it now" for around $150ea shipped free.

 

[OLD H2S]

Now I need some help and input: When I run the numbers for the CR I come up with 11.4:1, which is wrong for a stock NPI head, I am using.
Bore, 90.2
Stroke, 90.0
head gasket bore 92.0
gasket thickness 1.0
chamber cc's 49.77
piston dome -15.3
piston deck clearance -2.5


Where did I go wrong, should come up 9.3:1 cr.

I am getting heat from vendors about doing a close clearance build but I should be able to do -.020" on the block, -.100" on the heads, a .036" gasket and have at least .016" clearance between the head and piston? I am trying to figure out the cr for this set up. Where did I screw up?
Your thought's and flames are welcome.

 

[lwarrior1016]

[MENTION=14727]96blak54[/MENTION] would be the one to answer that.

 

[OLD H2S]

Found the valve angle is 11 degrees.

 

[lwarrior1016]

Close clearance builds are awesome! Doing things different and out of the norm is how to win (I quoted that from a good friend of mine). Make sure to factor in thermal expansion and what your rotating assembly is made of. Have you read the sticky about squish?

 

[96blak54]

Mathmatics are great! To bad the figures are only hypothetical,...BUT is necessary! Homework gets us there.

Im missing how you came up with chamber volume. Did you measure the cc volume? Decking the head .100" will dramaticly alter the volume that no mathmatics can figure. If the chamber was perfect shape like a pringles can, mathematics would work. Since the chamber has ramps and undercuts and to throw in fords chamber tolerance being within +/- 2cc, liquid cc'ing is the only way to know.

I noticed your piston dome has a number. Shouldnt it be 0 for flat top piston?

.016" nominal distance is close! Just be sure to measure everything once the short block is together. Youll have multiple headgasket thickness options to aquire what works for you.

 

[OLD H2S]

Those numbers are the stock numbers I found, some must be wrong. When I switched the deck height and the piston numbers to negative I only got the cr down to 11:1 so I am messed up somewhere. I and tryig out the calculator to check if it is accurate before I input my build numbers to see how thing shape up.

 

[96blak54]

Without cc'ing the head and purely speculating probable chamber size at 40cc, your compression ratio comes in around 13.5:1. And I assure you is not a problem in a 3800# car. Add in low gearing and aftermarket cams, engine stress becomes minimal. Low engine stress ='s mo squeezable!