I have a stock 350 short block with stock head gaskets with 9.5:1 compression. What size gasket would I use to bump it to 9.8-10.0:1?

What is the highest you guys have run on cast heads without detonation?

------------------
1986 CAMARO Z28 -> 151,000 original miles, 43,000 on 89' vette 350 block, Holley 650 DP, Weiand intake, 1.6 rockers, 1 5/8" headers, no cat, 2 1/2" Flowmaster catback, Mallory coil, March pulleys, T5 with 3.35 1st gear and 0 miles, 90% Centerforce clutch, 3.73 posi, Eibach 1" drop springs, Spohn LCA's, Spohn adjustable panhard rod, Subframes connectors, polyurethane swaybar bushings/endlinks, 2 12" Sound Streams, 2 Infinity 6X9's, 2 Pioneer 6X9's, 800 watt Lanzar Vibe amp. ET 13.22@ 106.4MPH 3300lbs less driver and speakers Next mods-> Homemade ram air, B&M shifter, Extreme Energy 230/236 cam.

 

if you have the stock shim gasket you aren't going to find anything thinner. you're going to have to mill some off your heads and/or deck surface to increase compression.

------------------
ICON Motorsports
1st & 3rd

 

I thought stock gaskets were .039? Can't I use a .015 gasket? I've seen people use them in CHP and other car magazines for increased compression.

------------------
1986 CAMARO Z28 -> 151,000 original miles, 43,000 on 89' vette 350 block, Holley 650 DP, Weiand intake, 1.6 rockers, 1 5/8" headers, no cat, 2 1/2" Flowmaster catback, Mallory coil, March pulleys, T5 with 3.35 1st gear and 0 miles, 90% Centerforce clutch, 3.73 posi, Eibach 1" drop springs, Spohn LCA's, Spohn adjustable panhard rod, Subframes connectors, polyurethane swaybar bushings/endlinks, 2 12" Sound Streams, 2 Infinity 6X9's, 2 Pioneer 6X9's, 800 watt Lanzar Vibe amp. ET 13.22@ 106.4MPH 3300lbs less driver and speakers Next mods-> Homemade ram air, B&M shifter, Extreme Energy 230/236 cam.

 

i believe all stock gaskets are the shim type, if so they're .018 i believe, after market are around .04. if you have a .04 gasket you can use a shim gasket if you have a good finish on the head and deck. if not use a comp type gasket ,i tihnk you can get a coated shim around .025.

------------------
ICON Motorsports
1st & 3rd

 

Yes stock shim type gaskets are .018. You might be able to find a .015 shim gasket but the compression increase would be very small with a .003 change.

------------------
Follow my racing progress on Stephen's racing page
and check out the race car

87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
454 Big Block almost ready for the 2001 racing season

Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

 

Are you guys sure? Have you done the research yourself? I've had other people tell me the stock ones are .039?????

------------------
1986 CAMARO Z28 -> 151,000 original miles, 43,000 on 89' vette 350 block, Holley 650 DP, Weiand intake, 1.6 rockers, 1 5/8" headers, no cat, 2 1/2" Flowmaster catback, Mallory coil, March pulleys, T5 with 3.35 1st gear and 0 miles, 90% Centerforce clutch, 3.73 posi, Eibach 1" drop springs, Spohn LCA's, Spohn adjustable panhard rod, Subframes connectors, polyurethane swaybar bushings/endlinks, 2 12" Sound Streams, 2 Infinity 6X9's, 2 Pioneer 6X9's, 800 watt Lanzar Vibe amp. ET 13.22@ 106.4MPH 3300lbs less driver and speakers Next mods-> Homemade ram air, B&M shifter, Extreme Energy 230/236 cam.

 

The majority of factory motors I have ever torn down had one of 2 types of gasket: either steel shim, or red Victorcore. Every single steel shim one leaked like hell everywhere. The Victorcore ones were usually intact unless that was why the motor was in teardown in the first place. The factory seems to have been changing over from shim to composition over a period of time, probably due to warranty problems; I would bet that most if not all motors nowadays are composition.

IMHO it is very bad policy to use the head gasket to increase compression. Head gakets should be chosen on the basis of their ability to seal the specific components in use, which should be chosen or machined to produce the desired chamber size. It may seem to be more expense up front, but it's worth not having to re-torque the head bolts and deal with leaks no matter what you do. I would strongly suggest gettting the heads milled and using FelPro or Victor-Reinz gaskets since freedom from failure should be worth the $35 you'll pay for milling the heads.

------------------
"So many Mustangs, so little time..."

 

It only costs 35 bucks to get heads milled???? How much for a basic bowl blend on the intake side? I heard the L98 heads respond better only doing the intake side when using a dual pattern cam.

------------------
1986 CAMARO Z28 -> 151,000 original miles, 43,000 on 89' vette 350 block, Holley 650 DP, Weiand intake, 1.6 rockers, 1 5/8" headers, no cat, 2 1/2" Flowmaster catback, Mallory coil, March pulleys, T5 with 3.35 1st gear and 0 miles, 90% Centerforce clutch, 3.73 posi, Eibach 1" drop springs, Spohn LCA's, Spohn adjustable panhard rod, Subframes connectors, polyurethane swaybar bushings/endlinks, 2 12" Sound Streams, 2 Infinity 6X9's, 2 Pioneer 6X9's, 800 watt Lanzar Vibe amp. ET 13.22@ 106.4MPH 3300lbs less driver and speakers Next mods-> Homemade ram air, B&M shifter, Extreme Energy 230/236 cam.

 

let me get this straight you're asking if we've done our research when you're going by what other people have told you? did you insult them like you did the people that took the time and effort to reply to your thread?

------------------
ICON Motorsports

1st & 3rd

[This message has been edited by ede (edited January 16, 2001).]

 

Whoa whoa whoa buddy!! That wasn't meant to INSULT anybody, maybe I shouldn't have put so many question marks in but that was not a flame! It's just that this is very important and I wanted to make sure I was getting correct info. I didn't want to put on the wrong head gasket and end up with less compression or something else in that nature. Try the left side of the bed tomorrow morning.

------------------
1986 CAMARO Z28 -> 151,000 original miles, 43,000 on 89' vette 350 block, Holley 650 DP, Weiand intake, 1.6 rockers, 1 5/8" headers, no cat, 2 1/2" Flowmaster catback, Mallory coil, March pulleys, T5 with 3.35 1st gear and 0 miles, 90% Centerforce clutch, 3.73 posi, Eibach 1" drop springs, Spohn LCA's, Spohn adjustable panhard rod, Subframes connectors, polyurethane swaybar bushings/endlinks, 2 12" Sound Streams, 2 Infinity 6X9's, 2 Pioneer 6X9's, 800 watt Lanzar Vibe amp. ET 13.22@ 106.4MPH 3300lbs less driver and speakers Next mods-> Homemade ram air, B&M shifter, Extreme Energy 230/236 cam.

 

Last set I had milled, I stood in the shop while they milled them; took less than 10 minutes, and he charged me $35. Of course that was a long time ago, probably in July or thereabouts, the price may have changed. Of course also, it varied from place to place, and according to what else you're having done; alot of the racing shops include it in their standard price. I just walked in with 2 heads under my arm and asked if he could mill them.

------------------
"So many Mustangs, so little time..."

 

no big deal, just seems if you wanted cold hard facts this isn't the place to come. i guessed at .018 being the shim thickness and stephen backed me up on it, but i still giuessed. maybe an educated guess but still a guess. rb tends to say things better than i do, but if you go back to the first reply i said mill your head and resurface the deck on the block. i'd never use a shim gasket, i always use fel pro composition gaskets with a coat of k&w copper spray sealer. don't believe everything in the hot rod magazines, have fun, and visit thirdgen often.

------------------
ICON Motorsports

1st & 3rd

 

As said above, steel shim (stock) are about .018 give or take a couple.

The aftermarket ones are about .039.

The .039 is just about a plug gap.

Next time you have a feeler gauge check out .015, thats pretty thin.

I wouldn't use the head gasket thickness to gain comp. While they are off just have them milled and use a good quality composite gasket.

------------------
ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R

GO #3

[This message has been edited by Engineboy (edited January 16, 2001).]

 

easy shave your heads or use a .15 thousands steel shim felpro head gasket!

------------------
1989 firebird formula

Mods: converted from T.B.I. to a carburator 305 to a 350. Flowmater exhaust,hedman shortie hedders,202 heads,350 horse cam,bored.40 over, Edlebrock torker2 intake.

Future mods performer rpm air gap intake (polished) and 600 edlebrock carb, comp roller cam, and way better headsa 400 defintely in the works!

 

A question to ask now that you have have that answered, might be how much gain will a .3-.5 raise in compression net you? I'm curious of this myself. Isn't there some sort of guidelines about .1 compression = x amount of HP?

------------------
Working on:
'84 Z28 LG4 305 with 200,000 original miles!
Added dual elec fans.
145 MPH IROC Speedo
Building 430 HP 350
using primarily GMPP parts.
Block is in shop!

ASE Certified Master Tech

Starting to look like the Kicker poster child!

 

Sorry if I offended anybody.

I would say probably 1hp per .1 increase, a rough estimate.

The reason I want to increase my compression is to ensure I retain my low end when I swap cams. The cam specs are 230/236 duration and 110 lobe sep

How much do I have to have my heads milled to obtain 10.0:1. Is that too much for cast heads? You guys have been great help. thanks


------------------
1986 CAMARO Z28 -> 151,000 original miles, 43,000 on 89' vette 350 block, Holley 650 DP, Weiand intake, 1.6 rockers, 1 5/8" headers, no cat, 2 1/2" Flowmaster catback, Mallory coil, March pulleys, T5 with 3.35 1st gear and 0 miles, 90% Centerforce clutch, 3.73 posi, Eibach 1" drop springs, Spohn LCA's, Spohn adjustable panhard rod, Subframes connectors, polyurethane swaybar bushings/endlinks, 2 12" Sound Streams, 2 Infinity 6X9's, 2 Pioneer 6X9's, 800 watt Lanzar Vibe amp. ET 13.22@ 106.4MPH 3300lbs less driver and speakers Next mods-> Homemade ram air, B&M shifter, Extreme Energy 230/236 cam.

 

JDM,

10:1 NA is not too high for pump gas, but you'll have to keep the heads and intake charge as cool as possible, and probably use 93+ octane constantly to keep respectable timing settings. If you can keep the EGR in your setup, you'll benefit a lot at highway cruise by reducing detonation. Remember, a properly working EGR doesn't cost any power at WOT since it's closed at WOT.

A cooler thermostat and fan setting can help with the head cooling, and a slightly rich fuel mixture can "cheat" you into a couple more degrees timing advance, and mixture adjustment at various ranges is at least possible with the Holley carb. A cold air induction would help, too.

As far as offending anyone, I don't really think you did. In general, it would help if you had a clear statement of the question and expectations in the original post. You probably got the correct answer for your original question, but the question didn't ask what you apparently needed to know.

Besides, most of these guys have been offended far worse, since they've probably had to stage up next to Fords at the track - the NERVE of those people!

------------------
Later,
Vader
------------------
"I cannot take this any more... Saying everything I've said before..."
Adobe Acrobat Reader 4.0
KaleCo Auto Parts

 

Just to get back to the gasket thickness part. The stock steel shim is .018 +/- depending on the part number. I've never disassembled a "newer" engine to see if the factory still uses the steel shim gasket but I'm assuming they still do.

The .039 thickness is for a composite gasket such as a standard Felpro type. These type of gaskets seal better and don't usually need to be retorqued after use. Felpro offers a couple of gasket thicknesses .039 and .041 compressed thickness. You can even get very thick copper head gaskets in the .080 and thicker range.

If the engine is designed properly you could theoretically go to 12:1 on pump gas without detonation but it wouldn't be benificial. Other factors play a part as well. The higher in altitude you live, the more compression you can run with pump gas. Using aluminum heads allows more compression but cast iron will also work. I think my 383 was around 9.7 with cast pistons. Until I cc the heads on my BBC I'm guessing it will be around 10.5

 

Regarding the effects of increasing compression ratio to HP; its not linear. A .5 increase in compression ratio has a far greater effect on HP on an 8.0:1 engine than on a 11.0:1 engine. Or, to get the same effects in HP by raising an 8:1 engine .5 requires a much higher raising of the compression ratio on a 11:1 engine. Also there is a point of diminishing returns where increasing the ratio has minimal effect.

 

My car does not have an egr. I plan on making a ram air for my car. I have a 160 thermo and fan switch. I live in Michigan so the altitude here is pretty low. I figure if I can run 87 octane with 9.5:1 and stock cam I can run 10.0:1 with a radical cam and premium gas.

I agree with you, it is hard to predict how compression will affect hp output and there are factors that play a role. But on a typical 9.0:1 engine a good rule of thumb is 1hp per .1 increase in compression.

------------------
1986 CAMARO Z28 -> 151,000 original miles, 43,000 on 89' vette 350 block, Holley 650 DP, Weiand intake, 1.6 rockers, 1 5/8" headers, no cat, 2 1/2" Flowmaster catback, Mallory coil, March pulleys, T5 with 3.35 1st gear and 0 miles, 90% Centerforce clutch, 3.73 posi, Eibach 1" drop springs, Spohn LCA's, Spohn adjustable panhard rod, Subframes connectors, polyurethane swaybar bushings/endlinks, 2 12" Sound Streams, 2 Infinity 6X9's, 2 Pioneer 6X9's, 800 watt Lanzar Vibe amp. ET 13.22@ 106.4MPH 3300lbs less driver and speakers Next mods-> Homemade ram air, B&M shifter, Extreme Energy 230/236 cam.

 

I would be more concerned matching an appropriate compression ratio to the cam you are using, its not really a cut and dry situation. Contrary to popular opinion, I have a 350 with a 224/232 cam running 10.3:1 compression and no EGR in a relatively hot climate, its seen hot and humid too, and I havent had a detonation problem. It will even run on 87, although it loses power and will detonate on really hot days with the 87 in there. Theres too many variables to pick a number, and call it safe on everything. If you stay under 10:1, then any problems you may encounter are the result of an untuned combo or busted parts. But the cam and heads you use lead into what compression will work well also. Take a look at a Crane cam book sometime, and you will notice that they give a recommended range for compression with each cam. Thats the way to pick compression, not because you want 1 more HP from an extra .1 in compression.

 

I couldn't agree with you more. The reason I want to increase my compression is to help any lost low end I might get from the large cam, not to increase power, plus I know the cam might run better with a little more compression. BTW. How does you engine run with the 224 cam? What heads do you run? I think I should be just fine with 10.0:1 compression running 92 octane.

------------------
1986 CAMARO Z28 -> 151,000 original miles, 43,000 on 89' vette 350 block, Holley 650 DP, Weiand intake, 1.6 rockers, 1 5/8" headers, no cat, 2 1/2" Flowmaster catback, Mallory coil, March pulleys, T5 with 3.35 1st gear and 0 miles, 90% Centerforce clutch, 3.73 posi, Eibach 1" drop springs, Spohn LCA's, Spohn adjustable panhard rod, Subframes connectors, polyurethane swaybar bushings/endlinks, 2 12" Sound Streams, 2 Infinity 6X9's, 2 Pioneer 6X9's, 800 watt Lanzar Vibe amp. ET 13.22@ 106.4MPH 3300lbs less driver and speakers Next mods-> Homemade ram air, B&M shifter, Extreme Energy 230/236 cam.

 

It has a pretty good lope to it, and I can tell you that a stock chip doesnt work but you have a carb so who cares, right? I have the vette aluminum heads on it, and a 100% stock untouched, unsanded, unported, unmolested TPI intake and it runs low 14's in an untuned G-body with no traction and I am pretty sure a lack of fuel not to mention air. I feel it has 12's in it, because if you put it in second and drop the throttle at 80MPH it breaks the tires loose.
You can find out more about the car and engine, along with what it sounds like here: http://home.earthlink.net/~madmax0/gp.htm

Oh, and it has plenty of low end power. I dont think that is going to be a problem of yours.

[This message has been edited by madmax (edited January 19, 2001).]