How much compression to use on a 383 with stealth heads

[frederick]

Hi guys, I pulled the heads today and measured how far the pistons are down the bore: 0.040"
With a 440source head gasket which is 0.044" and 84cc chambers this would give 8.57:1 compression.
My question is: should I up the compression by skimming the heads, 8.57:1 seems a little low to me. 0.084"means no squish however.
What would you recommend, the car will run on 98 RON which is 95 octane gas in the USA if I'm correct.

Another option would be 0.020" steel shim gaskets, but I dont believe the gaskets are compatible with aluminium heads.

Frederick

car specs:
4000 lbs
2.91 diff
4-speed manual
383 +0.030
440 source heads
Weiand Action+ manifold
lunati 60301  0.454@213, 0.475@220
1.75 Headers
600 cfm Edelbrock 1405
14"x 3"K&N

[firefighter3931]

I would shoot for 9.5:1 if at all possible. 

That will mean some head milling of course....to both the deck surface and intake surface. 



Ron

[frederick]

Hi Ron,

Thanks as ever for helping me out.
If I'm correct the stealth heads need a cut of 0.0043"/cc.
To get to 9.5 would mean a head mill of 0.05" which seems like a lot to me.
Are you sure the heads wil support this?

Frederick

[firefighter3931]

Hi Ron,

Thanks as ever for helping me out.
If I'm correct the stealth heads need a cut of 0.0043"/cc.
To get to 9.5 would mean a head mill of 0.05" which seems like a lot to me.
Are you sure the heads wil support this?

Frederick

Sure, the heads will support a .050 mill....but you will also have to shave the intake manifold or the intake surface of the heads .060 to maintain proper manifold port alignment. The rocker shafts will also need to be shimmed or you will need shorter pushrods.



Ron

[Musicman]

It would be nice if you weren't .040 in the hole either... a zero deck or 0.010 in the hole would be nice for a quench factor with that .040 gasket compression.
Maybe a different piston would be a more economical fix. 

Mike (just thinking out loud again)

[frederick]

Just spoke to 440 source on the phone.
The maximum head mill they recommend is 0.065"-0.070", after that you run into trouble with the inlet valve seat.

I also went to my machinist to inform about the prices, but he was still on vacation.

It would be nice if you weren't .040 in the hole either... a zero deck or 0.010 in the hole would be nice for a quench factor with that .040 gasket compression.
Maybe a different piston would be a more economical fix. 

Mike (just thinking out loud again)

I know, but I don't really want to pull the engine and completely disassemble the engine again.
It will depend on what they charge for the milling, I do know it is a lot more expensive then in the states....

If I do decide to go with the pistons which ones would you recommend?

Frederick

[Musicman]

Milling the heads will raise the compression, but it won't do anything for the .080 gap in the quench area. I guess you'll just have to wait until you can speak with your machinist. I was unaware of the fact that the engine was currently assembled and installed. Which ever way is cheaper for you, that would be the way to go. As long as you are satisfied with the end results, that's all that really matters. It would be nice to get your quench at .050 or less, but I can certainly understand your situation.

[firefighter3931]

Milling the heads is the easiest way to go in this instance considering the engine is allready in the car and running fine. As for quench, i agree with Mike....it's allways a good idea to build it with tight quench.... but with 9.5:1 and aluminum heads you aren't exactly pushing the pump gas compression envelope. It will run fine on pump gas, even without a tight quench build.   


440 Source has comfirmed that you're fine milling the heads .050 which is what i suspected they would say. 



Ron

[frederick]

but with 9.5:1 and aluminum heads you aren't exactly pushing the pump gas compression envelope. It will run fine on pump gas, even without a tight quench build.   
Ron

Thanks Ron I was worried about that.
I hope you don't mind me asking another few questions:
Is the 0.040"in the hole the cause of the block or the pistons?
The pistons are the original cast ones, if I do fit new pistons at what spec do I have to look to get them higher in the bore?

Milling the heads will raise the compression, but it won't do anything for the .080 gap in the quench area. I guess you'll just have to wait until you can speak with your machinist. I was unaware of the fact that the engine was currently assembled and installed. Which ever way is cheaper for you, that would be the way to go. As long as you are satisfied with the end results, that's all that really matters. It would be nice to get your quench at .050 or less, but I can certainly understand your situation.

The story behind the engine is a long one, I'l give you the short version.
The engine that was in the car was a 383HP but seized.
At the rebuild it was found it was much cheaper to get a reconditioned engine from the states than reconditioning the old one, so that was what we did.
The engine was put in a car in the states a friend bought an shipped together to save on shipping costs.
Unfortunately when the friend picked the car up from the port and drove home with it on a trailer he had an accident... he was ok, but the new engine tumbeld across the street damaging the heads.
So back to the machinist who was able to repair the damage.
Engine went into the car without problems. But final restoring was done at a restoration company.
They found the engine didn't produce much power but found nothing wrong after taking it apart 2 times.
Car was delivered home but was barely driveable.
To find the source of the missing power we took the car to a dyno shop, which confimed the lack of power: 140hp at the rear wheels, they were able to up it to 180hp but it is stil a slough with 4000lbs.
Early this year I found out about the stealth heads and decided to go with them and fit a new cam and some headers at the same time, $ is cheap for us now.

You see why I am reluctant to take the engine apart again.

Frederick

[firefighter3931]

but with 9.5:1 and aluminum heads you aren't exactly pushing the pump gas compression envelope. It will run fine on pump gas, even without a tight quench build.   
Ron

Thanks Ron I was worried about that.
I hope you don't mind me asking another few questions:
Is the 0.040"in the hole the cause of the block or the pistons?
The pistons are the original cast ones, if I do fit new pistons at what spec do I have to look to get them higher in the bore?

Frederick, the only way to riase the compression in the shortblock would be to swap in new pistons or you could deck the block to achieve the same result. Decking the block creates other issues though...same thing as milling the heads. Both will alter the intake manifold alignment and rocker arm geometry/pushrod length requirement.

Basicly, you would need a piston with a taller compression height so that it sits closer to the deck surface. That means disassembly and most likely a custom piston if you wanted to go forged.

If it were mine, i'd leave the shortblock intact and work the top end of the motor to increase compression & perfomance. 



Ron

[frederick]

Basicly, you would need a piston with a taller compression height so that it sits closer to the deck surface. That means disassembly and most likely a custom piston if you wanted to go forged.
Ron

Custom pistons eh, so thats probably going to cost more than having the heads milled, plus having to take the engine out.
Thank you again Ron for taking the time to answer my questions.
I'll let you now what I'll do once the machinist is back.

One last question: can you install a camshaft with the engine in the car?
I've got room in front of the engine, but I've got the Don Hayes book on rebuilding the engine which say you have to guide the camshaft from below.

Frederick

[frederick]

Just out of curiosity, how much of a difference in hp will raising the compression from 8.5 to 9.5 make?
Which lunati cam would you recommend for this, I was thinking 60301 but that may be a bit mild with 9.5 compression.

Frederick

[firefighter3931]

Sure, the cam can be installed with the engine still in the car.....i've done many that way. 

Increasing the static compression from 8.5 to 9.5 is a significant improvement.  The higher the static compression the less noticible it becomes.....so 8.5 > 9.5 is more "seat of the pants" power than say 10.5 > 11.5 

I'd look at the next grind up VooDoo cam (#302) for your build.....to take advantage of the better flowing heads. It's a 112* lsa grind and i would install it on a 108* intake centerline. 



Ron

[Musicman]

Just out of curiosity, how much of a difference in hp will raising the compression from 8.5 to 9.5 make?
Which lunati cam would you recommend for this, I was thinking 60301 but that may be a bit mild with 9.5 compression.

OK, Ron beat me to it... the difference in compression will result in mild gain.
I agree with Ron... move up to the Lunati 60302 with your build. Not a huge difference, but noticeably better.

The original build that you have outlined above should be producing roughly 330-HP and 380-TQ as is...
Rear wheel HP should be coming in around 280-HP


What's your guess RON 

[firefighter3931]

What's your guess RON 

Mike,

With good flowing heads, lunati #302 VooDoo grind, a 9.5 static compression ratio, the Wiend Stealth dual plane, 1.75in primary tube headers and a 750cfm carb it should make 400hp/450tq pretty easy. 


Ron

[Musicman]

Mike,

With good flowing heads, lunati #302 VooDoo grind, a 9.5 static compression ratio, the Wiend Stealth dual plane, 1.75in primary tube headers and a 750cfm carb it should make 400hp/450tq pretty easy. 


Ron

Yes, I agree with you there... I was just looking at his current build and wondering why he is only seeing 180 HP at the wheels when he should be seeing closer to 280... any thoughts?

[frederick]

Mike,

The "current build" with which I was getting 180 rwhp, was:
stock 383 +0.030
I haven't measured the cam lift but it will probably be .425
stock log exhaust manifolds
stock intake manifold, which was cracked, although it didn't show a lean mixture on the dyno.
stock distributor which was wobling a lot and probably didn't help either, I have upgraded now to a new distributor with electronic ignition.
The 600cfm edelbrock and 14"k@N filter were purchased at the dyno centre.
Torque curve was strange to it peaked just above idle at 400ftlbs and dropped thereafter trougout the rev range.
With hindsight I think they may have put the cam in wrong, to advanced.

I put these specs into engine analyzer and got around 230hp.
I was shooting for around double that, around 350hp at the flywheel, not to high in the revs cause the bottom end is stock.

400HP I'd better fix the play in the steering before trying it out then
Do you have any idea at what rpm?

Will the 600cfm hold it back a lot you think?
And will it still make enough vacuum for the brakes?

[Musicman]

Mike,

The "current build" with which I was getting 180 rwhp, was:
stock 383 +0.030
I haven't measured the cam lift but it will probably be .425
stock log exhaust manifolds
stock intake manifold, which was cracked, although it didn't show a lean mixture on the dyno.
stock distributor which was wobling a lot and probably didn't help either, I have upgraded now to a new distributor with electronic ignition.
The 600cfm edelbrock and 14"k@N filter were purchased at the dyno centre.
Torque curve was strange to it peaked just above idle at 400ftlbs and dropped thereafter trougout the rev range.
With hindsight I think they may have put the cam in wrong, to advanced.

I put these specs into engine analyzer and got around 230hp.
I was shooting for around double that, around 350hp at the flywheel, not to high in the revs cause the bottom end is stock.

400HP I'd better fix the play in the steering before trying it out then
Do you have any idea at what rpm?

Will the 600cfm hold it back a lot you think?

Well Frederick... that explains a lot 
I was using the info you posted at the start, and the numbers just didn't add up

Using the Lunati 60302 you should see your highest HP numbers showing up on the curve between 4500 to 5500 RPM. Your torque curve will be running close behind it, peaking about 1000 RPM's behind the HP curve.

[frederick]

Well Frederick... that explains a lot 
I was using the info you posted at the start, and the numbers just didn't add up

Using the Lunati 60302 you should see your highest HP numbers showing up on the curve between 4500 to 5500 RPM. Your torque curve will be running close behind it, peaking about 1000 RPM's behind the HP curve.

Good, because I don't think I'm going to rev it above 5000.
Engine analyzer also predicted the peak to be at 5500 although it did also it for the 60300, 60301 60302 and 60303, which is why I'm asking you guys. - I don't have anything to compare it to.

Frederick

[Musicman]

Sorry, forgot...

The 600 cfm Performer you have now is a good carburetor for a 383 street build and should satisfy your needs without to much complaint. It may starve the engine a tad bit at WOT in the higher RPM's however. That's where a slightly bigger carb. like Ron mentioned comes into play. It just depends on what you plan to do with it really. If your just chugging around town and cruising, the 600 is a good responsive carburetor on a 383, but if your spending your day at the track a bigger carb will provide more power on the high end.

[Musicman]

it did also it for the 60300, 60301 60302 and 60303, which is why I'm asking you guys.

There's more than just your cam at work here... everything in the engine works together as one unit remember. Change your exhaust, the peak changes... change your intake, the peak changes again... 

[frederick]

This is intended to be stricly a street build, it will never see a strip and rarely more than 4500rpm.
It is not a daily driver and not intended for around town, but it has to be able to cope traffic of course.
It is a recreational vehicle, driven only in summer.
The power brakes will still have to work on engine vacuum.

Oh yeah and the rear axle I don't know, it is either 2.91 or 3.31 but most likely 2.91 because it was converted to a manual in the 60's.

Frederick

[frederick]

it did also it for the 60300, 60301 60302 and 60303, which is why I'm asking you guys.

There's more than just your cam at work here... everything in the engine works together as one unit remember. Change your exhaust, the peak changes... change your intake, the peak changes again... 

Exactly my point. It is why I was doubting what it was predicting; all cams peaked at the same rpm without changing any of the other specs.
Do you think the 60302 will work with power brakes, if it does, you've got me turned from the 60301 to the 60302. (lunati say in their cataloge the 60301 will work with them.)

Well, Mike I'm off,  it's already 0:35am here, thanks a lot for answering my questions.

Frederick

[frederick]

Hi,

I just spoke to a local shop, they recommend an even bigger cam with my combo, at least 60303.
What do you guys think.

Frederick

[Musicman]

If you use the 60303 you will have to move up to a 2500-2800 stall as Ron said... You will gain a few extra ponies at very high RPM's , but you will loose more of your low end torque on the street. You will also loose a small amount of vacuum, about 3 "HG.

Myself, I would stick to the 60302... it's a really good street cam... idles smooth, plenty of vacuum, and a great overall performer. You could still move up to a bigger stall with the 60302 if you wanted too, but at least it wouldn't be a requirement.

You've already stated that your build is for the street, rarely if ever exceeding 5000 RPM, so why start looking at a cam that enhances power at higher RPM's. Once you start to cross that bridge, you may as well go all the way across, and that requires a lot of extra support that is not currently part of your build.