[RayzerFish]

OK, Building my 4.6. Rather, rebuilding after my CAI sucked water into and thereby snapping a forged piston & rod. I want to take the opportunity to increase the CR.

4.6 Romeo block (+.030) w/std. crank - std. stroke & rod lenght (Forged H) -
Patriot Stage 3 (1006W) SOHC Heads w/46cc chamber
Comp 270 Cams w/ .550" lift

The guy built the motor for a blower w/ a CR of 9.48:1
I want to put flat top pistons in it raising it to between 11:1 & 12:1 but I don't know if the pistons will hit the valves? Is there any way of figuring this out? Can I calculate somehow to put a thicker head gasket? There has to be a 4.6 guru out there that can teach me. I'M A SPONGE!!!

Also, will this still run on pump gas? I read a little, but would like to hear more on this.

[mpboy]

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Short block with at least one piston/rod assembly installed.
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It is required that on engines such as the big block Chevy that has different handed pistons that you do at least two cylinders so as to verify each design. You should have already completed machining of the engine block. Deck heights, align honing, bore/hone, etc
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The cylinder heads, with milling and valve job complete.
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All modifications need to be completed on the cylinder heads you plan on testing. You may use the head with light pressure testing springs, but chamber volume, surfacing, valve job, and lash settings must me complete or you will need to re-test.
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Cylinder head bolts or studs
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Whether you are using bolts or studs as your cylinder head fasteners, you will need to have some available. You may use used fasteners for this test.
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Head Gasket (preferably a used one for this test)
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A compressed gasket (used) will be more accurate than a new head gasket.
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Camshaft and specs for the cam you are using as well as what rocker arm ratio you intend to use.
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You must know what your cam lift values are going to be with this combo. If you plan on possibly using multiple cams through the season, it would be best to test each one. If you plan on running a high ratio rocker arm, you need to test with that rocker arm on the cylinder head.
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Razor Knife
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For cutting the modeling clay
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Modeling Clay
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You need to place modeling clay on the tops of the pistons. DO NOT use PlayDoh (a child's product made by Hasbro). PlayDoh springs back after compression and will not be accurate. Modeling clay is available at most art stores and will be perfect for this exercise, and is reuseable.
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Torque Wrench
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You need to torque the cylinder head to specified torque values for accuracy.
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Crank Turning Socket or other turning device
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You will need to manually spin the engine, and a crank turning socket is the easiest way to do this.
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Dial Caliper or other "accurate" measuring device
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After you have rotated the engine and removed the cylinder head ... you will cut the clay in various locations, and then you will use the caliper to measure its thickness.

Exactly What Do I Do To Test The Piston-To-Valve Clearance?

The process is really quite simple, but if you have not already figured out what you need to do, the description provided below will be a step-by-step procedure of the processes.

First, you need to have all your parts you plan on using for this engine ready to go. These include the block, crank, connecting rods (just need one or two for this test) with the pistons hung on them, piston rings, camshaft, cam bearings installed, rod and main bearings, lifters, pushrods, cylinder heads (with parts), timing chain set and a used head gasket.

You first assemble your short block with the crank, one or two piston rod combinations (remember that the big block Chevy as well as many other engines have "handed" cylinders. If this is the case you need to test each "hand"), the camshaft, and timing set.

Where to position clay when testing piston-to-valve clearanceWith the short block pieces assembled you need to degree in and set up your camshaft where you plan on running the engine. If you plan on making future cam or cam timing changes, you should repeat the entire testing procedure for each variation you plan on using. Each change you make can cause an interference problem even if the first time you checked your clearances you were fine.

With that done, you will place a small amount of the modeling clay on the piston(s). (see image at right) Lightly oiling the piston top, valve faces, and chamber on the cylinder heads will save you a ton of grief when removing the clay. You need to place the clay over and around the valve reliefs on the piston top. Be careful not to place too much clay or making it too thick around the edges of the pistons. The clay only needs to be about 1/4" - 3/8" thick.

You now have the clay on the piston top, so you are ready to install the cylinder head. Use your used head gasket and place it on the deck and install the cylinder head. Use normal torquing procedures for your cylinder head and engine requirements. Once the head is in place you can install the remaining valvetrain (lifters, pushrods, rocker arms) on the cylinder(s) that are to be checked. Install both the intake and exhaust lifters for each cylinder tested, and also the pushrods and rocker arms. Be aware that you must test using the rocker arm ratio you are going to use on the completed engine. If you plan on installing a high ratio rocker arm at a later date, test clearance for that now. This will save you problems in the future. When you set the lash, set it at "zero". It is preferred that you test hydraulic cams with a solid lifter installed (a used lifter is OK too), just to make sure there is nothing that can cause a variance of the valve lift in your measurement.

With all this complete, you will now be rotating the engine. Place your crank socket and wrench on the crank and rotate the engine two complete revolutions. Your engine operates over 720°, not 360° as many people believe. With your 4-cycle engine this mandates rotating the engine two complete revolutions. If when turning the engine you feel resistance beyond normal, be careful, you may have contacted the valve against the piston.

Now take the cylinder head off carefully so as to not disturb the clay. When you remove the head you will notice the valve indentations in the clay. Look closely at the clay and you will see thinner and thicker areas created by the valve contact. The main areas you need to look at are the depth and edges of the eyebrows (valve reliefs), and the edges of the piston against the block (especially on big block Chevrolets).

Carefully take your razor knife at various locations on the clay and slice it. You can cut a section out to give unobstructed access and then use your caliper to measure the thickness of the clay that is still sitting on the piston top. Do not not try to measure the clay you removed, because in most cases you will stretch it and change it's dimensions upon removal and handling. Check the clay in various locations to get a detailed view at what the valves need for clearance. If you find areas that have less than admirable clearances you will need to go to the next step, which means machining will be required.


If There is Contact or Too Little Clearance, What Must I Do?

With the dimensions you found above, you hopefully took notes and wrote down the findings. With this info in hand, you can go to your machinist and tell him what you found. An easy tip is to have one of the other pistons and you can write on top of it with a thin marker the various measurement locations. If you did get measurements that require machining, I hope you had not already balanced your engine's reciprocating parts, because you will be paying the machinist to do it again after your items are machined for valve clearance. Machining for valve clearance changes the piston weight and will require you to correct the balance of the reciprocating assembly.

In applications where you have contact, the most common contact points are in the piston valve reliefs (eyebrows). Either they are not wide enough from the use of larger valves, or they are at the wrong angle. This happens when you use aftermarket heads, larger valves in OEM heads, or you are using heads that have been angle-milled. With the information you have learned from checking the piston-to-valve clearance you will be able to tell your machinist what is needed. If you are unsure of what to tell him, simply leave the clay on the piston(s) during disassembly and take them into the machine shop for a more experienced inspection by your machinist. Remember, taking any material off the pistons will lower your compression ratio. Taking too much can cause other problems (piston top gets too thin, etc).

After you get your items back from the machinist you will need to re-test your piston-to-valve clearance. Go through the same procedure listed above.

the only way i know to do it

you could turn the motor by hand and tell if it is binding up, but you will prob not get it right and BOOOMMM


and with that kind of CR i would say pump gas would be ok, but just use a good octane

[NeverEnuff]

Um...I didn't read a lot of that...but to answer your question...yes those cams will fit with flattops...dish or flattops the modulars don't care because the valves are so close the cyl wall that the pistons dish is non-existant where it would hit.

You will be hard pressed to get the 270s in there with a good intake C/L. You will HAVE to degree them and check PTVC to see how much you have. No need for modeling clay...that is old school and doesn't give you as accurate readings. Just put a checker spring on the valve you are checking and as you roll the motor/cam over...push on the follower while a dial indictor is on the retainer and see how much your dial indicator moves till it hits the piston...there is your PTV clearance. I am telling you tho...with the comp advance ground in...and the motor you are running...giving no decking of the heads or block, along with stock PI valves...you will have to retard the shit out of the cams to get the needed PTVC.


Also...your compression should be well over 12:1, more like 12.3-12.6. Figuring a .012" deck height, flattop, 42-43cc chambers on a 3.582 bore and stock stroke. You will need 92-93 octane GOOD gas that you or your tuner trust. Put anything else in it and it will ping.

Good luck.

Edit: Just saw you put the Patriot heads at a 46cc chamber....if that is true you will be more in the 11.7-11.8:1 range...my bad.

[RayzerFish]

Thanks N,
I ran the numbers and with the custom pistons I'm having made I will be at 11.04:1 if the machinist can deck my block with .003. If not, a little higher. I am being led to believe it should run fine on 91 oct, true? I hope so because I may be in Daytona, but I don't want to spend that kind of price for gas.
I'll degree them for sure, but I'm having reliefs cut in the pistons for the oversized valves in the Patriot stage III's. I sort of understand what your saying about how to check the PTVC, but what is a "checker spring"? Beyond the fact that it's a spring used to test it with, is it a stiffer or weaker spring? Why? Can I buy one somewhere? Will I need to buy the removal tool? I know, I sound like a 4 year old asking so many questions. But I LOVE THIS STUFF!!! And I'm learning so much thanks to people like you. I'm a sponge!!!

Love you, MEAN IT!!!

[NeverEnuff]

Checker spring is a lighter spring. Can compress it with your fingers. Used to check your PTVC. You can degree a cam with stock springs in...but you can't check PTVC with stock or aftermarket springs in as you really can't push down on the valve hard enough.

Now...if you have reliefs cut into your pistons..that would help a bunch. THen you would have NO problems putting the cams in. You want to get them as close to 106-108* intake C/L as possible. It will give the most power in the power band needed. Try and get about .050 or more of the piston cut out. THat should help a ton. Stock PI valves have about a .070-.080" 'lip' on the valve, not helping with PTVC...when you go aftermarket valves...that is not there...so that gives you more clearance...but with a bigger valve...that takes some away. I think with my first 2V built, comp 270s, and +1 intake and exhaust valves, no decking of the block, but .005-.008" on the heads, I want to say I got them in at about 114* intake C/L...and they had about .068-.070" of clearance. Now honestly...most say you want .070" clearnance of piston to valve at any time...while I would agree with that on pushrods...not so much is needed on the modular or OHC motors. There is no pushrod, 'rocker' or tall 'stud'. All this stuff creates 'play' in the valvetrain. Our cars can got 9000+rpms on stock lash adjuster and followers...so they are pretty stout and hold RPMs rather well. Anyway, I would say keep it about .045-.050" to be safe. I have heard of some dipping into the .030" range but that is a ilttle close for me. I ran my first 32V bolt on cammed build in the .048-.050" range and it saw 7000rpm everyday, and when I tore it down...it still looked perfect. Got another buddy with a cammed 2V and his is at about .042-.045"...still running strong.

Also...when checking cam timing and PTVC you need to get a solid adj lifter to set zero lash. You will need to grind keyways to get the cams lined up bank to bank...our cars only read from one cam...the ECU only 'sees' the drivers cam. If the drivers cam is checking in at 115* intake C/L, but the passenger side is off from that and sitting at 108* C/L...you can see how that can cause problems, with timing, fuel delivery and with the banks fighting each other. You need to get the cams as close to the same timing as possible. I have seen cams off bank to bank more than 10*...there is power and driveability to be had in just stock motors by just degreeing the cams...this is why there are 'freak' GTs and Cobras out there.. More likely than not, they came out of the factory with gears that were pretty close...

Hope this helps...

Soak it up brotha...soak it up...

[NeverEnuff]

Oh...and You will have more than 11:1 comp...with the specs you gave me...shaving the heads, and block...with those chambers and a stock compression height on the pistons, flattop...with only 2-3cc total of valve relief...Pretty sure you will be a tad higher than 11:1...but 91 octane is fine for either...just get a good tune...