trying to figure out the most i can mill my heads/ deck my block to get the most compression out of it as possible, and run the biggest cam as possible

im running 2.4cc dome pistons .060 over with a 3.48 crank

ive calculated my compression with a bunch of different senarios, but id like to find out how much space ill have before ill have PTVC problems

- as is with a .040 gasket with a 4.125 diameter im at 9:4 compression
- if i put a .015 gasket with a 4.100 diameter im at 10:1 compression
- if i deck the block to 0 and mill the heads .008 and run the .040 gasket im at 10.2:1 compression
- if i mill the heads .020 and run the .040 gasket im at 10:1 compression
- if i mill the heads .020 and run the .015 gasket im at 10.6:1 compression
- if i mill the heads .010 and the block .005 and run a .020 gasket with a 4.100 diameter gasket im at 10.3:1 compression

my goal is to have OVER 10:1 compression, safe PTVC and maintain the proper quench which i think is .040

 

How many cc are the heads?
What's the intake closing point of a cam your thinking of?
How far are the pistons down in the hole?

 

thats what im trying to figure out, the heads are 882 with 76cc chambers, i can mill these up to .020 max, the block has a .025 deck height that i can mill, and the higher i can get the compression, the bigger the cam i can put in, but for what im thinking off, the intake closing is anywhere from 58 ABDC to 76ABDC depending on what i get the compression to

 

Scrap the 882's there one of the worst flowing heads (unless ported hard).
Get a set of Vortecs (64 cc) milled (60 cc).

 

i have the heads and this is a budget build.... as far as cam goes, im thinking 224/234 .465/.488 234/244 .488/.510 or the ***** thumpr

 

That's a lot of machine work for a "budget" build.

 

machine work and labor is free, i have all tooling i need (taking an engine rebuilding class)

 

FYI, there is no sure way to determine PTV clearance besides a very thorough mockup of the parts with the camshaft you intend to use. The camshaft determines the outcome, and it's not just the valve lift that makes the difference.

 

Yep, you need to do a mock-up with the cam degreed-in as you plan to run it. I use the clay method with one head installed with a few head bolts on the head gaskets I plan to use and solid roller lifters adjusted to zero lash..

Complete directions are probably on CompCams' website, in their catalog, etc.

Once you know how much clearance you have you'll know how much you can safely remove.

CompCams recommends a minimum of .100" intake and .125" exhaust. Deviate from that at your engine's peril.

Jake

 

i always like a dial indicator set up on the valve spring retainer. trying to measure a piece of clay doesn't make sense. i always deck my blocks to 0 and use the inexpensive stock felpro head gasket at 0.041" thickness. 9.5:1 compression is plenty.

 

i know how to check it once everything is assembled, i just wanted to see if theres a forumla or something that i can measure it with... everything ive been seeing with people get away safely with 250/250 .650/.650 cams, so i dont see how i could even be close

and the cams im looking at have the intake closed like 67-76 ABDC bleeding off like 3 points of compression... i need 10.3-10.5 SCR to maintain an 8.0-8.5 DCR

 

Attention to detail is the key to a well built engine. If you don't measure you're only guessing and assuming.

Jake

 

That mild cam won't have any P-V-C issues.

What is the part number for the .060" over 2.4cc dome pistons?

 

trw L2304 060

i didnt think id have any ptvc issuses, but just wanted to see how much material i can take off safely without having any problems... when i talked to a machiniest, he said as long as i stay at or under 244/244 and .600/.600 i wont have any problem at all, but those numbers seemed high to me...

will i have any piston to head problems? as long as i stay at or over a .040 quench i shouldnt right? since these are forged pistons i have to give them more clearance to expand too, so should i give it some extra quench?

i do plan on measuring, but im pretty sure im not even close to harming anything, id like to determine how much compression ill have before i order a cam so i can get the biggest cam possible (my dad wants a really lopey cam) i dont wanna order a cam that will bring my DCR under 8.0 cuz i can only have 10:1 SCR and not the 10.5 i thought

 

Reading Comprehension. Once you read and understand the clay method it makes perfect sense. That's why it's been one of the most recommended methods for so many decades.

It eliminates the differences in the closest point of piston travel where minimum valve to piston clearance occurs due to differences in camshafts.

Most people don't really know where the closest piston to valve clearance point actually is. They don't realize how a camshaft's specs determine where that point actually is.

A simulation program, like Engine Analyzer Pro, has a feature that shows exactly where the closest piston to valve clearance occurs and the amount of clearance there is. Absent a $500 program like that, the most recommended way is by measuring the thickness of the depressions made in the clay by the valves.

Of course, for the uninitiated, I'm not about to fight over this. Whatever floats your boat.

Jake

 

Forged TRW pistons, lumpy ***** cam (or 234/244 ancient grind flat tappet cam), and 882 heads --- Who else can see a problem with this setup?

You'll be burning 93 octane to have a car that has no low end, and runs out of steam at the top end, and pings like an SOB all over town

Keep in mind when doing the CR, that the 882's have DISMAL flame path characteristics.

Below .600" and below 250° as you mention, shouldn't cause any PVC problems. Make sure you check your valve spring clearances however, and the valve retainer to guide clearance.

.040" quench is fine. You don't have to enlarge that due to the forged pistons. Make sure you bore the block and hone it based on the recommended clearance for the forged pistons (diametrical clearance).

 

so what would you recommend to combate this?

should i go with some camel hump heads? i found a decent set with all the work done for $350 with 2.02 1.60 valves and 64cc combustion chambers, just didnt wanna spend the money cuz i know 882s flow good

 

ah, no! Camel hump heads flow better, but the flame path is still poor. Why are you so hell bent on using 40 yr old technology?

Get a set of vortecs from a local wrecking yard, and machine them yourself? Since you have access to the machining equipment eh? They flow great, and have better burn characteristics. ie, only shoot for 9.5:1 cr and burn regular fuel...

 

im not looking for this motor to make 400hp, just want it to be reliable, have power, and sound like it has a huge *** cam... any suggestions, and as stated it is a budget build, so i dont wanna go pay 300 for heads that are still ganna need 200 in parts to make them good for a .500 lift cam

 

Do you, or do you not have access to machine tools to machine heads on your own?

My motor build is a pretty good budget build.... 416 heads came off a 305. Heavily ported they work just swell. A solid flat tappet cam and it sounds pretty aggressive alright. Makes in the 350 HP range.

 

i have tooling to do most of the machine work, but there are certain things that we dont have tooling for, and i have never used most of this tooling i am just learnings, so porting my own heads wont net me nearly the same results as a professional porter by any means... i know for a fact i have mill the heads, port n polish, grind/cut valve seats, grind valves, and test springs, but thats all i KNOW we can do

just how bad are the flame fronts? and why would my build ping and have no power, im always ready to learn, but i thought this build was going to be pretty decent for a low price (getting pistons from my roommate)

 

See thread;
https://www.thirdgen.org/forums/engi...eads-sale.html

That's CHEAP horsepower.
Cutting the valve pockets to run better springs is super easy. You'll be able to do that no problem.

Flame fronts - I just mean if you use old low tech heads, and you push your CR to the limit, it'll ping under load unless you use very high octane fuel. It's a waste of money. Use better parts up front (a bit more cash typically), and you save money on fuel in the long run, and it runs better, etc etc.

For a first build (right?), don't shoot for the sky. Don't try to push the limit. Build something that's not up at the very edge of detonation, and enjoy driving ALL THE TIME. You can sacrifice 15hp so that you're not explaining to that hot blonde why your car won't start when it's hot, etc etc..

 

piston to head clearance should not be a problem with a 0.035" head gasket and 0 deck clearance. there is no formula to calculate this that i know of. i think with your combo you'll have tuning issues though.

 

if i get the vortecs, and i mill .005 off the heads and .005 of the block (to true everything up) and run the .040 gasket, ill be at 11:1 compression, and 8.5:1 DCR with the big ***** thumpr

how does that combo sound? i think i should be at a solid 350rwhp with that combo... and unfortunately this would make the motor im building for my dad have more power than my car :-(

 

your quench area would be too big

 

so 11.5:1 compression and run an even bigger cam??? or is 9:1 DCR okay?
is 11.5:1 compression even safe on an iron head and still be possible to run 93 octane

 

i would just get a set of stock dish pistons ($100) with the vortec heads, 0 deck block, .041 head gasket, and a mild/lumpy cam. roughly 9.5:1 comp

 

Using clay is still done by top assemblers these days.
I admit IDK alot about quench//cam//piston clearances.
My friend clay'd my last motor, ( Bigblock, .250 dome, .544 lift, closed chamber 112 cc heads ) a tame motor but was fun in my '74 Camaro.
I agree also to degree the cam. It's self-insurance!!
A guy around here did a 383, BIG cam, did NOT clay or degree it--
rumor had it on start-up, all he had was an expensive piece of iron between his fenders!!

 

I've heard ppl do this-- I've never seen it but hear it's accurate.

 

measuring something that isn't hard/solid doesn't make sense to me. one of my instructors once said "pass a piece of jello around the class and ask everyone to measure it and everyone will have a different measurement"

 

LOL--good point!! If I have the chance, I'd like to see how another friend sets up his S/C valvetrain-- This stuff is Very Interesting!!

If greatskiiiier goes .600, is that big for 9.5-10.0?

Thanks for your input skirkland1980--
education for some of us!!

 

with vortec heads i would stay around .500 lift

 

You're not looking for an exact measurement, you just want to know that there is an acceptable minimum.

You can disassemble the valvetrain, reassemble it with checking springs, sit there and poke away at a valve with a dial indicator advancing the crank a fraction of a degree at a time through the overlap period until you find what you think is the CPA, then disassemble it again and put it back together with real springs... and then if it turns out that clearance is marginal, you can look forward do doing it again 7 or 15 more times to make sure that clearance is consistent on the other valves.

Or you can put a piece of clay on top of the cylinder, put the unmolested head on, spin a few of the bolts down finger tight, lash the valves to the point where the valve is just about to open, turn the crank over once, unbolt the head, and check the thickness of the clay. The thickness of the clay is the clearance at CPA. If you mess up and stretch the clay a little thin while you're cutting it or peeling it off the piston to measure it, it doesn't matter because you're only looking for enough, not an exact measurement.


To the OP though, you're building a mess. You're going to go through a bunch of hassle and work using odd and most likely more-expensive domed pistons just to recover some compression so that you can use a set of some of the absolute worst heads GM ever made, and then you're going to throw in as big a cam as you physically can, which is most likely going to have more lift than those crap heads will ever be able to use.

Power doesn't come from compression, it comes from airflow. Airflow comes from good heads. 882 heads are not good heads. Get some reasonable heads, get some cheap flat-top pistons, get a cam reasonable to the flow potential of your heads. The results will be much better than whatever you're trying to do right now.

 

He is trying to work with what he has...He can't afford a good set of heads but wants to build the motor to perform once he can afford it.

The 882 heads are just to get the motor running. He is looking for a good cam for an all street car that will sound good. He wants the dome pistons because he is getting a really good deal on the entire balanced rotating assembly ($320 for everything including a Holley 600 Vac.)

 

i always check clearance with the springs i'm running. i check exhaust clearance 10 deg before tdc on the exhaust stroke and intake clearance 10 deg after tdc on intake stroke. i've never heard of a "acceptable minimum" when building an engine.

 

and chaston saves the day! lol
this motor doesnt have to perform like a freakin hotrod, i have my ls1 for that... this is a cruiser motor for my dad that he just wants "to sound like it has a huge cam"

EDIT: id also would like my time and effort go into something that will put some power to the ground... if i can get some vortecs ready for a .500 lift cam for under $350 it would be worth it... even if my dads car will be able to hang with mine lol

 

Just a few things which I hope will help:

First: Since, in matters like these, there will be differing views on what and how things should be done, you need to decide on whose advice to respect and follow. Then, when issues like these arise, turn to that source to determine how to proceed.

Second: The selection of parts and the actual build of the engine go hand in hand if you hope to achieve your goal. You must select the right parts AND build the engine correctly; one without the other won't cut it. Attention to Detail and Precision are the keys and all the best running engines cover those two bases.

Lastly, just as points of reference: Taken from CompCams' newest catalog, #106-07, page 378 -

"The easiest and possibly most accurate way to check piston to valve clearance is to place strips of modeling clay on top of one piston, then rotate the engine over by hand with the head bolted in place and all of the valve train with valves adjusted."

Also, same source, same page:

"COMP Cams strongly urges you to check the piston to valve clearance on larger street cams and on all race cams. We recommend at least .100" clearance on the intake valve and at least .125" for exhaust valves."

Now, I've cited my source from a company whose advice I respect and follow. Others may have different sources they rely on, which is fine. Comp is just my choice.

Hope this helps.

Jake

 

yep, got the funds and new build time... lmao
same as everything before, but vortec heads machined to accept .550 lift... called comp and they said with 11:1 compression and to run on pump gas im ganna need a 240/246 .507/.510 cam

how will this perform on the street? i think it should haul @ss at the track lmao.... im planning on retarding the timing 4 degrees to make it more street-able

 

I'd strongly second Apeirons suggestion.
Stop getting hell bent on long duration cams and huge compression.
Keep the STATIC CR around 9.5:1, and run a decent cam, then brag about domestic V8 TORQUE, and beat the pants off your buddies eh?

I have a 240° duration cam (albeit solid tappets, so it acts a smidge smaller). I ride the clutch through parking lots, lug it around to park it. It's annoying as sin! It's got NOTHING below 2000RPM (nothing).

I also saved some money ($300) by not balancing the rotating assembly (dumb!)

Instead of paying $400 of machine work to deck my 416 heads (and put in valve guides, cut valve seats, etc etc), I could have just bought some vortecs, and kept my compxe268h cam, and ran circles around myself.

My engine is still cool and all that, but it SUCKS as a daily driver due to the cam. Weekends only.

If you're going to drive it a bunch, shoot for torque. Keep your CR low to let you use normal gas. You'll have more fun with torque then revving the crap out of it searching for HP.

New cams don't need to be installed retarded or advanced to make them more streetable. They have 4° of advance ground into them already. You retard it to gain more top end - which is the opposite of streetable IMHO.

 

this is going to be for my dad in a car that he will only drive on the weekends in nice weather, and itll be an auto... i already have the 2.4cc dome pistons so im going to use them, if i only take off like .005/.004 off the block and the vortec heads i plan on purchasing (numbers respectively) then ill be at 11:1 compression exactly with the cheap felpro gasket

 

Are you 100% certain of your deck height? ie. your pistons depth at TDC? Have you measured it with a dial indicator and feeler gauges? I know TRW/speed-pro mis-printed and put 1.56" vs the actual 1.54". This might only be the non high performance ones, but for something like piston depth, I prefer to measure than assume.

11:1 CR is too high i'd say. My personal opinion is to switch pistons to a dish or something. Pistons are cheap, under $100, I wouldn't get caught in a bad build due to that. You'll have a heck of time working around 11:1 CR....

 

is says they have a .100 dome and its a 2.4cc dome according to summit

i havent measured yet, but it has a pretty bad lip on it (which is why im boring to .060) which is PRETTY thick... but like i said i havent assembled anything yet

if nothing is milled i will be at 10.75:1 compression and have a .065 quench

EDIT: dont have my tools here but the dome is the same height as a quarter, which wikipedia says is .07"... but the numbers are still in the head of the pistons so idk

 

I agree with SONIX. 240ish @ .050 is a lot of duration for a 350 CID sized engine operated on the street. Of course, some don't mind the loss of low end torque and actually prefer the lopey idle/sound, but his account is typically what results.

Several months ago, when I was shopping for a new cam for my son's 96 350 LT1, I deliberately kept the duration on the short side just to maintain the low end and street-ability.

Many guys stay in the 218 - low 220 range on a streetable 350 but I chose lobes even slightly shorter in duration than that. I then spec'd a tighter Lobe Separation Angle and went with high ratio rockers to get the valve lift I wanted.

My thinking is that to have to move to such a longer duration cam (like Comp recommended) just to address gas and CR isn't a good approach. Sort of like a band-aid approach.

To me, a better way would be to choose heads with larger combustion chambers and/or different pistons to lower CR. Then you could run a more "streetable" cam without having to worry about detonation.

I wouldn't go the thicker head gasket route since doing that negatively effects quench.

Just me views.

Jake

 

which is more important static compression or dynamic compression? i thought dynamic is what REALLY matters and as long as im within 8-8.5:1 i can run on pump gas with no problems

 

most people don't have the tools to check clearance with a dial indicator. mine was over $200, then you need a tool to move the rocker arm and a degree wheel ($$$). using clay is the easiest method.

 

i have the tools (my teacher has been collecting em since 1850! lol) i just havent begun putting anything back together... i want to get my new heads before i hot tank everything

for the last time THIS IS NOT GOING TO BE DAILY DRIVEN... its a weekend/ nice weather motor for my dad who, and i quote, "why are you so against putting a huge cam in it" he wants it to sounds stupid lopey and want to die at red lights... if he wants to drive a car for performance he knows were my camaro's keys are

 

My note on the dial indicator was just to check how far up the bore the piston was at TDC. The dial tells you where TDC is, then a steel straight edge and feeler gauges tells you the depth. Harder with pop-up pistons, but I imagine still do-able. Has nothing to do with PVC clearance though.

Dynamic is loosely based on cam timing, and while slightly more accurate, is still not perfect. Keep in mind, altitude, car weight, stall speed (if auto), engine running temperature (coolant temp), ambient air temp, intake air temp, etc etc all have an effect as well. My 10.3:1 iron headed engine has NEVER pinged on me, because I have a lot of those factors working in my favor. If you don't, then you don't want to be very close to the razors edge right?

If this engine isn't going to see mega nitrous, or 8000RPM, i'd avoid forged pistons anyway. Speed-pro hypers cost under $100 for a set, and would work fine for your application...

 

As per your PM :


Try something like;
http://www.summitracing.com/parts/SUM-17350-30/

These should be ;
Speed pro- STL-H345NP30 just rebadged as "summit".

They are hyper, flat top, and right around $80 a set. You can get them in .060" over, but find out if that's what you need first. The link above is for the .030" over size.
I think pistons come with new wrist pins, but ask summit. They are cheap either way.

If you want to re-use your stock rods, you really really should get new rod bolts. Then you typically need to have the rods machined to be re-sized. I priced it out, and new rods at $180 each from Ohio crankshaft were cheaper than resizing and new bolts... Your call. Chevy rod bolts are the weakest link. A stock crank is fine, ARP crank bolts help, but rod bolts are the big one.