pskel350

i think my engine has 8.5 compression ratio now(stock). well i want more speed, so i think more compression would be the answer. i would like to get to about 10:1 CR, i did a search and came up with about milling off 10 cc would give me about 10:1. is this figure correct, or would i have to have more milled off. also people on this board have talked me into getting a Weiand stealth intake, will i be able to have this milled to match the heads?? is this the best way to abtain more power?? also is there anything else i have to be aware of when having this done??
:hail: :hail: :hail: SPEED

Mark A Shields

What engine do you have now, I wasn't aware that any stock 3rd gen motor had that low of compression.

Just remember you'll prolly have to get you intake done to for the ports to match.

pskel350

i have a 350 over .40. it isnt a stock third gen engine, it is a truck engine i know it isnt the best choice but it was cheap, 900 for a whole rebuilt engine. when i first got the engine i put some mild ported heads and a used cam in it for a month till i parked it for the winter. now i am going to redue the top end to give me good power for a daily driver in the summer. i am not looking for a 500 hp 350 but i want some good power. how much could i have milled off from heads and intake before something bad happens? will the stock bottom end be able to take higher compression? sorry for all the dumb questions but i know you guys can give me the right answers. thanks

Mark A Shields

What pistons are in there?

I know how you feel, I basically have a truck replacement engine too, and crap compression. I just bought some new heads to help compression, but have to still use a thin head gasket to keep the compression up.

pskel350

they are the stock pistons, not sure exactly what they use. how thin of head gasket are you going to use Mark? You just bought those pro lighting heads right? i wish i could afford a set of those right now, those look like really nice heads.

camaro_1983_383

you can mill the heads but i personally wouldnt go that route. you will have to mill the intake also. what cam do you have in there?

pskel350

camaro_1983_383: just wondering why you wouldnt go that route, cause that isnt the first time i have heard that and i am curious why i shouldnt. i am going to put in a Lunati Bracket Master 2 cam, .455/.455 lift. i will have 1.6 rockers so the lift will be about .485 by mine calculations.

Mark A Shields

Well, if you plan to use the heads later, milling is irreversible, though if you don't plan to use them later on, I don't see the harm in it.

I'm going to use a .015 gasket, but I'm not going to put that many miles on it, before I tear it down to stroke it.

F-BIRD'88

1.. When you mill the heads to increase compression, you mill the intake face of the heads to correct alignment, not the intake manifold.

2. If you have a dished piston motor with open chamber 76 cc
style heads (about 8.?? cr), milling these heads even to the max will not get you 10.0:1 cr.

You want to start with a 64 cc or 58cc based head, and mill those to get the cr you want.
Any/all of these 64cc or 58 cc heads will out perform the 76cc heads with some porting and equal sized valves.

Sell off your low compression 76cc heads to some one who needs them.

Allthou there are other routes to take, the $budget$ method
is to find a set of 305 heads (416's) and port them your self
with 1.94x1.60 valves. Give them a generous porting job and you'll have a knockout street/strip performance head.

Mark A Shields

Yup, I sold my old heads thru the classifieds, granted I didn't get much for them , but I had no use for them.

pskel350

so what CC are these 416 heads. i cant seem to find a head file for them on DD2000. what kind of compression would those heads give me? and even after porting and polishing would they flow enouh with my cam selection? and can i use my 1.6 roller rockers on them?

F-BIRD'88

416 casting 305 heads have 58cc chambers.
If you replace a 76cc head on a 8:1 cr motor with a 58cc head
all else being the same your new cr will be 9.58:1
If you then substitute a .015" shim gasket for the felpro .040" composite head gasket you would then have 10:1..

These heads can be ported out to very respectfull fow figures
with 1.94 and 1.60 valves.

I got flow figures of 243 cfm intake and 189 ex on the last set I did.
It's not hard or rocket science, just time consuming.


Thats more than any readilly available out of the box
aftermarket cast iron head of the same port volume and better
than some bigger ones. More than enough to run 12's

U can use 1.6 roller rockers but yu may need to elongate the pushrod slot in the head to clear. The push rod gets moved closer to the rocker stud with 1.6's. I do it with a rat file in a drill.

pskel350

well i think i am going to find a set of 416 heads. what vehicles did they come on exactly, anything else than a camaro or firebird?

F-BIRD'88

They came on just about any pre 87 305 with a carb or early tpi
with perimeter valve covers. Monte carlos, regals, cutlass's, trucks
caprice's etc... A set of 87-92 "081" castings from a late 305 tpi
would be a good starting point too.

pskel350

sorry for all the questions, i hope you guys dont think i am totally dumb. but what is the difference from 416's to 081's? is it just the center bolt and the perimiter bolt hole pattern? thanks for all the replys.

F-BIRD'88

yes

rjmcgee

Just curious, what are the flow numbers of the 416 heads stock?

ede

you don't want to adjust your head gasket thickness to reach or increase the compression, you want the gasket to reach your ideal quench, or get very close to it. how far i nthe hole are the pistons, or out of the hole?

Mark A Shields

Yup, but like Vader said if you have dished pistons, that will be near impossible to do.

F-BIRD'88

I haven't flowed a 416 head in stock form yet.

But here are the numbers for the 081 head. The 416's are going to be real cose to this as the ports and valves are the same.

0.050 31 0.050 15 49
0.100 63 0.100 37 58
0.150 92 0.150 61 67
0.200 116 0.200 78 68
0.250 134 0.250 92 69
0.300 157 0.300 101 64
0.350 170 0.350 105 62
0.400 182 0.400 107 59
0.450 189 0.450 109 58
0.500 195 0.500 110 56

pskel350

EDE: what do you mean by wanting the head gasket to reach my idea quench??? i dont know how to tell how far the pistons are down or up in the hole, but it is totally stock bottom end.

Marshall89ws6

or you could get a set of world products 305 heads they sell....... they come with 58cc chambers and good valve sizes..... plus they are probably better than a stock casting and most likey there is more room to port........ go here .........http://www.jegs.com/cgi-bin/ncommerc...41&prmenbr=361

pskel350

Marshall89ws6: i will keep that in mind, but i am trying to keep this on a pretty small budget. cuz i am trying to work out a 02 camaro ss next year.

Marshall89ws6

haha i must have missed that part

ede

to find your deck clearance measure from the deck surface to the top of the piston with a depth mike, or depth rod on a dial caliper. i never tried it but you might be able to with a straight edge and feeler gage too. most likely it'll be around .030 in the hole. ideally you'd want 0 for most applications, but there isn't much you can do at this point to change it. knowing the number will help in your gasket selection.

Guest

Just for future searchers...

Do NOT mill the heads to increase compression. Its a last ditch effort when there are no other options available to do so. Factory heads dont really have thick decks either, so milling just makes them that much thinner. If you want more compression, get different heads or different pistons. Milling is to true the surface. And trying to mill 10cc's off a stock head, you'd be lucky if there was anything left after you were done.

Marshall89ws6

or you could find someone with a set of zz4 heads..... 58cc's also..... if i still had mine id get em to ya cheap.

pskel350

ok, i am really lost now. today i used the compression ratio calculator on DD2000. i used the infomation giving to me on this site, and it said i have 9.34 compression. but i still want more. how much compression should i run on the street, and how much compression will my stock bottom end handle?? and do you guys think that it really is 9.34 compression or 8.5? i have no clue now.

Mark A Shields

10:1 compression is almost the max I believe for iron heads. For 93 octane at least.

Marshall89ws6

yea past 10:1 u need some sort of lead in there or race gas to eliminate detonation.....my buddie has 11:1 on his chevy 302 heads. (iron) but he runs race gas..... the exhaust could knock u out with just a whiff lol

mine is somewhat like that but he runs like 110 Octane Cam II



fuel i think its called. I just run 108 octane. and plus hes got lead substitute in there... shiOt is lethal stuff.

F-BIRD'88

To find the compression ratio you need to know
the head vol in cc
the piston displacement
the valve relief or dish volume
the dome volume
the deck height clearance of the piston to the top of the block @
TDC
The volume of the head gasket.
On a typical stock 350 dished piston motor the #'s are
4" bore 3.48" stroke, 76cc heads, 13cc dish/ relief volume .025" or .045"deck clearance.
gasket volume will be 9.1cc's for a .040" felpro gasket
or 3.5cc's for a .015" steel shim gasket

depending on the actual deck clearance and head gasket used
the cr of this stock motor will be 7.69:1 low side or 8.35:1 high side.

Swapping on a set of 58cc heads would change that to
10.02 high side or 9.03:1 low side. again depending on the actual combination of head gasket and deck clearance used.
The deck clearance of a typical stock dished piston motor
is .025" to .045" below the deck @TDC.

You can download a more user friendly compression ratio program from www.download.com.
It's called Engine CR 1.0
Just go there and search for compression ratio.

A half a cr does make a difference. It's worth the bother to get the cr right for what you are trying to achieve. Measure your deck clearance when you remove your heads and get the gasket that will do the best job for ya. The more cam yu use the more critical this is.
A true 10:1 compression ratio usually requires 92 octane gas minimum.
Different engine combination will require slightly different octane gas but it won't vary that much really.

pskel350

so i shouldnt use 416 heads to raise compression, or isnt my compression really 9.34?? i have no clue wha it really is now?? any more help would be awesome.

Marshall89ws6

it actually probably is 9.3:1..... thats what a stock tpi 305 and 350 are..... and the tbi's as well.

F-BIRD'88

You'll only know by measureing the deck height and calculating the cr properly, not by guessing. The info you need is in the thread above. Just re-read it.

87Formula4bbl

While on the topic of the 081 heads, can anyone tell me if the 081's will bolt right up to the carbed LG4 305 since they are originally from a 92 TPI (I think)? Will there be any forseen problems in doing this?

F-BIRD'88

What heads are on your car now? You may already have 081's.

87Formula4bbl

I am not sure, I have never had them off, let alone I dont even know where to find the casting number. The reason I ask is because I need to know before I purchase these heads. I plan on purchasing this set of heads (assuming they will fit correctly), port and polish, and pretty much rebuild this set, and since my car is my daily driver, I need to swap within the time period of a couple of days. That is my main reason for purchasing another set instead of doing the work to my current set. I cant afford to have my car out of commission for the time it takes for a porting job. I am in school right now and don't have the time to mess around with my car as much as I'd like, I'm still in the learning process. Can you tell me where to find the casting numbers?

Concerning compression, if my original set are the 416's, will the 081's set my compression a little higher, I think I read in my Haynes manual that I too have 8.5:1 right now, and I'd like to go a little higher eventually, so I'm keeping tuned to this thread.

Thanks for any help.

pskel350

dammit.....i just downloaded Engine CR 1.0 and it doesnt work at all, piece of crap, guess i have to download it again.

87Formula4bbl: if you are gonna sell your 416's let me know

Mark A Shields

I dl the trial version and works very well.

pskel350

Mark A Shields: thats what i dl twice now and it wont work at all. what windows program to you have, i think that is the problem. i have windows XP.

87Formula4bbl

pskel: If I do sell my heads, it won't be for another 2 months at least, I want to do some work to this other set, and swap them when I find the time in between work and school. If I do though, I will be listing them in the classifieds on here if your interested.

pskel350

87Formula4bbl: thats cool, cuz i wont be ready for heads till about then, so maybe i will see them on the classifieds.

Mark A Shields

I'm runnin XP as well, did you unzip it? I know you have to hit enter several times before you can get to the actuall program once you open it.

F-BIRD'88

You're new at this eh....
If the heads are the ones in your picture, they are not 416's
416's are on 86 and back cars and have perimeter bolt valve covers, 081's are on 87+ cars and have center bolt covers.
There are other casting that could be on there too. the ones with the swirl vane and pushrod bulge in the intake port are to be avoided. Some of these heads have a different intake bolt pattern angle on the center 4 intake bolts. You can mod around this to fit one to the other.
Look at your intake bolts to see. You'll have to remove a valve cover to see which head you have. The casting number is between the rockers. the 081 chamber cc is 58cc's
The haynes manuals specs for cr and only nominal specs
your actual cr will be differnt trust me.
Won't know till you get the heads off and measure the piston deck height on your motor.

pskel350

Mark A Shields: yeah i unziped it and installed it, then when i go to start it, it just starts to open then an error pops up. damn thing!!

87Formula4bbl

pskel: I am also running XP. I just DL EngineCR too, and I have the exact same thing happen with the error MSG. While installing, I noticed the setup program attempted to overwrite some of my newer files, so it must not be compatible with the XP drivers.

Mark A Shields

I am using XP and had no problems with it.

Mark A Shields

pskel, if you want, when you know all the #s needed, just post them and i'll run it thru the program for you.

87Formula4bbl

Thanks F-Bird88, that helps a lot! You probly just laugh at how dumb people like me are sometimes, but I guess everyone has to learn at some point right? HAHA

F-BIRD'88

You can download a good working demo cr program from
Performace trends

http://www.performancetrends.com/

The Engine CR 1.0 workes fine on my computer.....