New to me 84 Corvette

[Grumpy]

I know the feeling!!! You almost want to sleep with them, they are so pretty !

don,t run that engine in the garage with the doors shut!
the fumes are getting to you big time!



if you want to sleep with something ,
it should at least vaguely look like these picture's below

not car parts

 

[Indycars]

BUT, when you don't have that choice ???

 

[Crossfire Mike]

How did you decide on the 65cc chambers over the 75cc chambers ?

Well I had heard and read that Chevy stock engines can be up to .025 piston in the hole and you can't trust GMs stated compression ratio's for these gen 1 SBC's as their up to a point lower compression than advertised. Is this really true, I don't know but I wanted to take no chances and I love the snappy nature of a high compression engine. I am also understanding due to the faster heat transfer of the aluminum you can raise compression up to a full point with little negative effect. Come smog test time I'll find out if this was a wise decision. I'm after high 9's or low 10's for compression so the 65cc head seem like it would help me get there best. Depending on what I actually find as far as piston height will determine a lot of what I actually end up with. The larger chamber AFR head while far superior in every aspect than the stock ones just seem like a wasted opportunity to make another real performance minded change at the core level being so close to the stock size. If I was going to do a rear mounted turbo or supercharge this Corvette, yes I would have gone larger chamber to keep compression near stock levels. I have no plans for that on "this" car so I got the 65cc's. Long answer.....

Those babes Grumpy posted make my car hobby budget look cheap. I can't imagine the outlay of cash just to keep them happy and interested....

 

[Indycars]

Well I had heard and read that Chevy stock engines can be up to .025 piston in the hole and you can't trust GMs stated compression ratio's for these gen 1 SBC's as their up to a point lower compression than advertised.

It's true that the deck is 9.025" from the crank centerline and the piston top is usually 9.0",
thus leaving the piston in the hole by .025".

I am also understanding due to the faster heat transfer of the aluminum you can raise compression up to a full point with little negative effect.

That's typically stated that aluminum head can handle a 1.0 higher CR than a cast iron head with everything else being the same.

The question is what size is your present combustion chamber ? What is the casting number of your heads ?

What octane fuel are you planning to use ?

 

[Crossfire Mike]

the OEM crossfire heads for 1984 are casting number 462624 76cc heads
462624 chevy head flow numbers
(these are the heads that came on the 1984 corvettes)
just a bit of info on those stock #624 head flow rates

.......intake....exhaust
.100..44..........41cfm
.200..101..........82cfm
.300.155..........125cfm
.400..182..........137cfm
.500..196..........140cfm

(THATS PATHETIC)

GM claims 9.0 compression and I'm not too sure if I believe it as I could run 87octane fuel with the timing advance from stock setting even with all my existing mods and not get a hint of pre ignition. I'm planning to have to run the CA mid grade fuel which is 89octane but if it comes down to it I'm fine with using the 91octane too.

 

[Indycars]

Near as I can tell your piston design is a flat top with 4 valve reliefs, which should add about 7-10 cc's
to your CR calculations. What do you think, does that seem right?

https://www.carid.com/1984-chevy-corvette-piston-rings-connecting-rods/



I'm not trying to be nosy and doubt your decisions, but one never knows what the other person background
is in the beginning. If you have already done the calcs, then I can stop worrying, but if you want I can go
further. But until you have done some calcs you really don't know.

Comment ???

I'm in the same boat, 91 octane is the best I can get in my area of the US, some get 93 octane.

timing advance from stock setting even with all my existing mods and not get a hint of pre ignition.

BTW, Pre-Ignition is a different animal than Detonation or also known as knock.
.

 

[Crossfire Mike]

Hi Indycars, As far as I can tell we're just talking shop here. It's nice to be on a board where other's want you to be successful and avoid mistakes. Yes best I've been able to gather the piston do have valve reliefs that will be at least 7cc's. I'm figuring on that number I have used summits compression calculator and also found this one Static_And_Dynamic_Compression_Ratio_Calculator that actually takes into account the intake valve closing degree's which my cam is 34degree's with all this info entered I'm in to this calculator is how I'm basing my final compression ratio estimation. It also gives the dynamic ratio which is pretty important to know also. I'm semi-confident I'm going to find a .025 deck height and until I'm positive on that I'm not going to get head gaskets because I'm still committed to achieving a .040 or so quench. If I end up with a 9.5 or 9.8 or 10.0 compression then thats what it is but I defently want higher than 9.0

 

[Indycars]

Is the 34° Intake Valve Closing (IVC) at .050" or when it touch the seat ?

Do you know IVC when it touches the seat? OR Do you know the duration from seat to seat?

 

[Crossfire Mike]

The cam in the car now is the Crane part number 114132 which is the one Grumpy had pointed out to me and discussed in other threads. I installed it last year and it really works well and woke the car up. the full specs are:
Small Block Chevy 1981-87

Crane PowerMax emissions legal cams produce amazing increases in torque, horsepower and throttle response while extending the rpm powerband of computer controlled performance passengers cars and light trucks. PowerMax Emissions cams also permit full function of stock engine control computers. Plus, they work great with aftermarket performance chips.
*Note: 50-State Legal. This camshaft has been granted a California Air Resources Board (CARB) exemption (an ''EO'' number), or is a direct or consolidated replacement part. It is 50-state legal, per the manufacturer's application guide.

**Note: For 1981-87 cars only.

***Note: In order to use these camshafts in 1955-57 265ci blocks, it is necessary to machine a small groove in the rear main journal of the cam to allow oil flow to the top of the engine.

****Note: Beginning in 1987, most of the V-6 and V-8 engines were equipped with hydraulic roller camshafts. There are differences in the block to accommodate a cam retention thrust plate and the anti-rotation mechanism for the lifters. These blocks are identifiable by bolt holes for a cam retention plate under the upper timing sprocket, as well as bosses and tapped holes in the lifter valley for lifter retention hardware. The camshafts on these engines have a step nose and smaller bolt circle on the front of the cam. An earlier model camshaft may be used in these blocks by using the appropriate timing chain set and adding a thrust button when using a roller cam.
1988-99 Chevrolet 305 and 350 V-8 engines (and some 1987 350 V-8 engines) use a different configuration camshaft core than the 1955-87 engines and cannot be interchanged.

GREAT FOR 305 H.O., PERFORMANCE 350 TRUCKS AND TPI-EQUIPPED 350 ENGINES. GOOD MID- AND TOP-END TORQUE AND HP. AXLE RATIOS OF 3.73 OR NUMERICALLY HIGHER REQUIRED. AUTO OR 5- SPEED MANUAL. MUST USE ADJUSTABLE FUEL PRESSURE REGULATOR. (50 STATE LEGAL IN 1981-87 267-400, CARB EQUIPPED CARS ONLY. C.A.R.B. E.O. D-225-25)



Grind Number: 2040
Operating Range: 1600-5000 RPM
Duration Advertised: 270° Intake / 276° Exhaust
Duration @ .050'' Lift: 210° Intake / 216° Exhaust
Valve Lift w/1.5 Rockers: .440'' Intake / .454'' Exhaust
Lobe Separation Angle: 114°
Max Lift Angle: 109° ATDC Intake / 119° BTDC Exhaust
Open/Close @.050'' Cam Lift: Intake - (4°) ATDC (opens) / 34° ABDC (opens)
Exhaust - 47° BBDC (opens) / (11°) BTDC (closes)


Pretty sure thats a typo from the Jegs site having two "opens" and no "close" for the intake side. This cam has proven to work very well with the stock computer and my manual transmission. Can only get better with some great cylinder heads. Keep in mind I'm running 1.6 ratio roller rockers so the actual final lift numbers are a little greater with a bit more duration added to both intake and exhaust.

 

[Indycars]

From the Seat to Seat durations and LSA you can calculate the IVC on the seat. Yours is 64°, assuming
that the cam is installed 5° advanced. (119-110) / 2 = 5°. When I use the GoFastMath website you quoted,
then your DCR is 8.78. This would be too high for 91 octane gas. With my Crower cam was installed 4°
advanced my DCR was 8.27 and I had a small problem with detonation. So I retarded the cam 4° and with
a DCR of 8.02 I'm problem free now and that's with Brodix IK200 aluminum heads. I think Grumpy will
tell you that a DCR of 8.25 is the max for 91-93 octane fuel.

But the problem with most online compression calculators is they use IVC at .050" and then GUESS at
the actual closing value. So when I plug your values into my Excel calculator I get a SCR/DCR of 9.90/7.96,
therefore I believe you should have no problems. My calculator will be a few hundredths lower then others
since it takes into account every possible space in the combustion chamber, including the volume around the
piston to the first ring.

If you have Excel or the Free "Open Office", then you can download the Excel calculator below. It will allow you
to compare 5 engines all at once. You don't have to write down your results each time you try a different combination.

http://garage.grumpysperformance.co...comp-ratio-cranking-pressure-calculator.4458/

There are a bunch of different calculators below:

http://garage.grumpysperformance.com/index.php?forums/spread-sheets-and-engine-related-forms.99/

 

[Crossfire Mike]

Thanks for running my numbers through your calculator. I installed the cam straight up but I do think there was some advance, like 4 degree's ground into it from crane but I'm not exactly sure. I will play around with your program to see what happens when different values are used. I'm glad to see that right now it seems I'm in the ball park of where I should be at for a pump gas street engine. I would be real happy with the numbers you came up with for this engine.

Question though I noticed you used a .015 thick gasket in the calculations is this too thin for good sealing and what is a good brand. I've also heard of some gaskets embossing a ring grove into the cylinder head that will need to be milled off the next time the heads are off the engine should I even worry about this.

 

[Grumpy]

this info may help/// especially if you take the time to read through it

https://www.summitracing.com/parts/sce-p110621

http://garage.grumpysperformance.com/index.php?threads/copper-head-gaskets.827/

http://garage.grumpysperformance.com/index.php?threads/sbc-head-gasket-choice.11070/#post-79067

http://garage.grumpysperformance.com/index.php?threads/preventing-leaky-head-bolts-studs.50/#post-59

http://garage.grumpysperformance.com/index.php?threads/anodes.74/#post-93

http://garage.grumpysperformance.com/index.php?threads/headgaskets.1074/#post-2072

these links may help

cooler denser air​

Im always rather amazed at the guys that don,t stop and think about the total process of making power and the failure of so many guys to think thru how each step can be improved. it really doesn,t matter if you have a single carb, dual quads or efi, cooler denser air will result in a more...
garage.grumpysperformance.com

cooling off that c4 corvette​

your stock corvette http://garage.grumpysperformance.com/index.php?threads/thoughts-on-cooling.149/page-3#post-107697 has a rather marginal cooling system if your engines been modified for significantly higher hp levels, that cooling system can be significantly improved upon.I run into this...
garage.grumpysperformance.com

Mounting An Effective Trans Cooler On A C4 Corvette​

now I know few cars with less room to mount an efficient oil cooler with a fan than a c4 corvette, and after I installed a 3200 rpm stall converter in my corvette it became obvious I needed an aux trans fluid cooler. theres very little under the hood room and ground clearance is already minimal...
garage.grumpysperformance.com

Crossfire conversion question​

I have been restomodding an 84 Vette that had already been converted if you could call it that. If you want the more detailed story of my experience so far,read my community introduction post. What I am stumped by and confused about are two things. First I should say i have read hundreds of...

www.digitalcorvettes.com

Unwanted engine bay heat.​

I have an 84 Trans Am. As you might know, these cars have tight engine compartments, no front grilles, and lower hood lines than Camaros. When I finally get the 334 re-installed, my Turbo "bulge" hood should just close - I hope. The intake manifold is a Weiand 8000, Edelbrock 1904 Quadrajet...
garage.grumpysperformance.com

 

[Indycars]

Question though I noticed you used a .015 thick gasket in the calculations is this too thin for good sealing and what is a good brand.

You said you wanted .040 quench distance, so .025" + .015" = .040". That's the only reason I used
.015" head gasket thickness. FelPro, Cometic and SCE come to mind for quality head gaskets. I don't
know if anyone makes .015", but you should get pretty close. I used SCE copper gasket, it's .021" and
sprayed it with Permatex Copper Spray-A-Gasket PN 80697. Like Grumpy has suggested in the links
above.

I've also heard of some gaskets embossing a ring grove into the cylinder head that will need to be milled off the next time the heads are off the engine should I even worry about this.

That's for extremely high compression. You do not need to worry about doing anything like that !

 

[Crossfire Mike]

I just spent a fair amount of time reading Grumpy's links and then looking at venders head gasket offerings. I got information overload and decided to call AFR and speak with their tech line. They recommend the felpro 1003 which is wrong for my application because of the 4.166bore@ .041 compressed thickness on their site. I asked about going thinner and they said no problem as long as it's installed proper. What he did say was do not go smaller than 4.125 bore size otherwise I'll have the gasket edge hanging into the combustion chamber and it will burn and leak or if it doesn't completely burn away will cause a hot spot. So with thanks to you and Grumpy's help looks like I know I need a .015-.020 compressed thickness gasket with a bore 0f 4.125. Weather its a copper one or not shouldn't matter so long as I use a copper spray. AFR also said a miniscule amount of "brinelling" may happen with the felpro gasket but like you said not to worry about it unless I'm running lots of boost or nitrous.
I'm settled in my mind if I don't get the perfect quench so long as it's not super bad like .050 or something. Perhaps knowing I have to use a larger bore size gasket than I originally thought will ensure I keep the dynamic compression number well within check to be safe on pump gas and if I lose a little bit of static compression that's fine too as I'll be way better than the stock rating. I'll look this week for a gasket that fits my needs I also decided to get some ARP head bolts just to give me that peace of mind for clamping force.

 

[Crossfire Mike]

It's been bugging me all day as to why AFR tech said to go no smaller than 4.125 bore on a head gasket. I suppose because I'm not finding one thats .015 compressed @ 4.125 bore size. So I pulled one cylinder head out of the box and made some measurements and this is what I found. I Think AFR didn't expect these to go on a stock bore 350 or smaller or at least I'd not go any smaller than 350ci. I'll keep looking for a head gasket but I know I'm going to have to make a compromise somewhere whether it's actually a larger bore gasket which brings issues on my desired compression ratio or thicker gasket which brings issues to my compression ratio and quench...

 

[Indycars]

In copper I don't think you will find anything smaller than .021". I used a SCE P11152, but for your
bore I would use the P11062. It's plenty easy to check if it falls inside the combustion chamber by
installing it over the dowel pins and looking. Even if it does, copper is easy to remove in the needed
areas. I had .041" larger than the bore, you will have .060". I only had to remove a very small amount
in a couple of areas.

Copper is re-usable, so if you ever have to pull the heads again, it won't be much more for the copper.

 

[Crossfire Mike]

I don't know why I couldn't think of that probably because I'm totally over thinking this whole thing. I measured the chamber all around and can now see like you say that only a couple areas does it over hang and very little where it does. I will order the P11062's and when they arrive custom fit them to my heads the tiny bit they will need. I appreciate your help on this as now I will get very close to what I wanted in the beginning and leave little horsepower on the table. I end up with a .046 quench which is not super great but not terrible and close to my original compression wants so I'm safe with pump fuel.

Engine 1
Bore 4.000
Stroke 3.480
Combustion Chamber 65.0
Deck Height 0.025
Gasket Thickness 0.021
Gasket Diameter 4.060
Dome (-) / Valve Relief (+) 7.00
Top Ring Height 0.300
Ring Land to Cyl Bore Clearance 0.0070
Connecting Rod Length 5.700
Intake Valve Closing Angle 64.0
Atmospheric Pressure 14.7
Dynamic Compression Ratio 7.85
Static Compression Ratio 9.76
Cranking Pressure (Gauge) 186.60

 

[Grumpy]

if you take the effort to measure accurately and do the required minor mods youll do fine with zero problems

 

[Crossfire Mike]

Thanks Grumpy, with yours and Indy's good advice I believe I'm all settled on what I need and what to do next. I plan to have the heads off in maybe a couple weeks so I'll post some pictures of that progress when it happens.

 

[Indycars]

With a quench distance of .046, you can probably wind the engine north of 7000 rpm without
worry and sleep good at night !!! LOL ! .....NOT !!!