well i have run into another problem trying to redo my 383. i bought a comp xr294 and the clearance is so close it would hit if i took away the gasket. my current pistons have a 5.5cc valve relief and i have .008 deck height and a .039 thick gasket with afr 1034's


i am at a loss. does anyone have any ideas on what i can do. id hate to have to take the rest of the motor out of the car and redo the bottom end.

if i do take it all apart can anyone reccomend good pistons and rods? at a reasonable price.

 

Sure they'll touch if you take away the gasket but you're not going to assemble the engine without a head gasket.

Get some modeling clay. Put a 1/8"-1/4" thick piece in the valve reliefs about 1/2" wide and put a little bit of oil on the piston and on the clay so nothing sticks. Install the head with gasket and snug down with a few bolts around that cylinder. They don't have to be torqued down.

Now to properly check clearance, you need solid lifters. Install lifters for that cylinder, pushrods, then adjust valve lash if you're using a solid cam or adjust to zero lash if you use a hydraulic cam.

Rotate the engine 2 full revolutions and pull the head back off.

The valves should leave imprints in the clay. Cut through the depression with a utility knife and measure the thickness.

Absolute minimum thickness is 0.100" on the intake and 0.125" on the exhaust. If the thickness is less than that you have a few of options but none are easy.

Use a camshaft with a different grind. Valve timing and duration can change the piston to valve clearance just as well as the lift.
Use a thicker head gasket although your .039" head gasket is close to the thickest available.
Pull the engine apart and have the pistons flycut if there's enough metal under the reliefs or replace the pistons with ones that have deeper valve reliefs.
Is the cam installed straight up? Advancing it may add or subtract piston to valve clearance depending where the interference is.

I see a 2 different listings for the XR294HR cam and both having .540/.562 lift. There's no way you can use that aggressive of a cam with a factory style piston with the 5-6cc valve reliefs. Are the heads even set up to accept that much lift?

 

they are aftermarket pistons. speed pro hypers. i think that was the brand. and the clearance is very small. .050 intake and like .020 exhaust. all afrs come with 600 max lift and due to the minmal clearances i already have i dont think advancing or retarding the cam can help. can u fly cut the pistons while they are in the motor if you tape everything off and have the piston at tdc?

 

No plus taking off that much metal means the engine needs to be rebalanced.

 

I strongly disagree with Stephen. I've been a professional automotive machinist for 9 years, and you can do this without any issues. And FelPro offers gaskets thicker than .060", but that's still not enough clearance, and it hurts quench. The correct solution is to just change the cam. If the cam you have has a 110 lobe sep. Then replacing it wit the same lobes on a 114 sep will help with clearance, as would using the next smaller lobes. Also, what size intake valves are you using? If they're larger than 2.02", then flycutting would still be wise if you cannot change pistons. However, that cam is large enough that with adequate valvetrain control and head flow you could shift above 6500 rpm, and those pistons are a poor choice for that RPM, you should be using forged pistons. Bottom line, get some good forged pistons. SRP and such generally come with plenty of valve relief even for 2.08" valves, standard, while SpeedPro L2256Fs or LW2256F are still only intended for 2.02s.

 

i was told by fel pro today that i could use 2 gaskets which would be ok. it will bring my compression down to 9.5:1 which is what the cam calls for and clearence will be close but i think it will be doable. ever heard of that?

 

if this is a fresh build pull the pistons and rods and get the pistons machined for valve clearance .

 

the motor is still in the car. i did clearance checks with 2 head gaskets and came up with around .090+ for each exhaust and intake and it was close around the one edge but still more than .010 almost double that. everything will be close but maybe ok. what does everyone think about these numbers?

a guy from a machine shop said they have a motor that has been running off of .065 exhaust clearance and also said hydraulic lifters will give me some additional clearance is that true?

 

doubled gaskets will actually increase the likelihood of detonation, due to a complete loss of all quench. Take those pistons out and get some SRPs or some such.

 

Double head gaskets and clearance is still too close.

You have the block almost zero decked then you want to double the head gaskets to compensate for piston to valve clearance. Even if the deck was still at the original height with the pistons approximately .030" in the cylinder, using one head gasket would still have clearance issues.

Change the pistons or use a different cam that will work with your current pistons. Your current combination of parts just won't work together.

 

if i do rip all this apart. how do these pistons look

http://store.summitracing.com/partde...0&autoview=sku


http://store.summitracing.com/partde...0&autoview=sku

 

ok so i am thinking of going down to the comp xr288h grind will that help get me where i need to be clearance wise?

 

you've got the heads off and you already have the other cam right? Just pull the motor and get the pistons machined for clearance . Unless it's got a million miles on it and needs a rebore ? you have to drop the pan to get the timing cover off anyways . You're only looking at about 20 minutes to have it sitting on the floor .

 

the motor has about 2500 miles on it now. i just dont have a hoist to get it out to machine it for clearance. the other thing is i dont think my current setup will hold much over 500 hp which the 294 cam should put me well over that. afr has a setup with the 288 grind which is right at 500hp. so i think i should go with that for that reason as well as the clearance reason. what are your thoughts?

 

I'd rent or borrow a cherry picker and do it right . 2500 miles I'd be tempted to use the same rings even . Why don't you think the motor will hold up ? If you used new rod bolts and built it right the first time why not ? The weak link if you buzz the motor lots are the hyper pistons but there's lots of guys using them and nitrous so why not ? If the pistons were full floaters it's even easier as you don't have to pay to get the rods pressed on and off . I'd do what I had to to make the cam you chose work rather than use what you're forced to by stuff you can adjust . You got the cam you chose as part of a kit with the AFR heads ? I'd try to make the combo I chose fit but that's just me . Stubborn I guess .

 

wow you have just got a bunch of problems there.
eliminate them all - rent a cherry puller - and get the pistons done - problem solved - but this is a good lesson for anyone doing a build - READ READ READ then buy buy buy, not the other way around.
my friend atilla the fun turned me on to www.competitionproducts.com. ok we are not really friends but i have asked him 4 or 5 thousand questions. they have good prices on lifters, rockers, springs, and ss valves - so they might have what you need.
good luck and take pics of the build so we can watch it happen.

 

well the cam i have in there now didnt come with a head combo kit. was all bought sperate. the other cam i am thinking of going down to which is just one size down will be the 500hp 383 combo that is listed on afr's web site. i have a steel crank and stock 5.7 rods with arp rod bolts. which from what ive heard is good to 500hp/6500rpm give or take a few hp. so i dont want to over do it. i am stubborned at times myself but i just think it will be better to use another cam than to cut into the pistons and weaken them if the slightly smaller cam will give me the clearance i need. i also dont want to cut into them unevenly and end up with slightly different comprerssion in other cylinders. correct me if im wrong but thats my opinion. whats your thoughts on that?

 

ok so here is where i stand now. i have downgraded to the xr288 which should put me right at my goal according to afr. i have upped my clearances to intake .080 and exhaust .110 by using a .041 thick gasket and a .015 shim and advancing the cam 4 degrees. and my compression will still be at 10.27:1 and according to afr this cam and 9.5:1 compression with my style heads made 500hp by 5500rpm. how does this sit with everyone. i know my quench is a little high at .064 but not as bad as it would have been before at .095 with the other cam and what it would have taken for it to work. i know everyone wants me to change my pistons but i am just out of money right now and need to try to make do with what i have. but let me know what you think. thanx vinnie

 

Your minimum clearance is better but still not at the recommended tolerances. You can assemble it any way you want. You've been given a lot of advice on what to do. Trying to save money by not using proper parts can cost you a lot more money by having an engine that doesn't perform the way you expect or has a major failure. You're still trying to do a bandaid solution to a mismatch problem.