Are you Bored? Bang for Buck Engine recipe required.

[ed.harris]

Round 2

[ed.harris]

Round 3

[ed.harris]

Last ones.

[ed.harris]

Oh, the head has been machined past the Thumbprint.
Sorry for the inverted images, senior moment...

The block has a B prefix and I believe the head is also around that era with a heater plug and a temp sensor.

Cheers Ed.

[ed.harris]

Another omitted fact, the piston dome height is 8mm.

Cheers Ed.

[ed.harris]

Bore.3.125 inch from memory.

[Craig Allardyce]

Hi Ed,

I'm going to weigh into this one now with regards to running high comp, camshafts, heads, etc.
Firstly I'm running a similar set up i.e. high top pistons, head, carb, exhaust and cam work. Standard diff ratio of 3.89
From experience you will need to run 98 as minimum due to detonation risk, and this is especially due to the possibility of getting a one off crap tank of fuel and as result torching a piston. Many think they'll hear it first, but many people do not know about inaudible detonation. Once that happens for a period, the damage is done, and you wont know till its all too late.

I'm running 9.9:1 comp, 19.92cc dome, and 50.4 cc chambers. No matter what I'm running you must cc your chambers, dome, and accurately calculate your clearance volumes. You need to know exactly what you are playing with.
You also need to weigh up your dynamic compression ratio and inlet valve closing point in order to work out your affective comp ratio. This leads me into camshaft. Going back to a reduced duration camshaft will affectively increase your dynamic compression ratio. This will well and truly increase the risk of detonation. Longer duration camshafts reduce the risk of detonation at lower rpms as they realistically decompress the cylinder until the design rpm is reached, then the cylinder gets its full or better charge. Detonation is less prevalent at higher rpms as there is reduced combustion time at those higher engine speeds, therefore less or no time for detonation to occur.

I'm dancing with the devil on mine as I too wanted streetable, so am running a high lift and low duration camshaft. With 9.9:1 comp my cranking compression pressure is around 270psi! But, I have done extensive dyno testing in order to set fuel mixtures through out all rpm and load conditions, and importantly I have a mappable ignition curve. Initially I experienced detonation at around 2600rpm (peak BMEP cylinder pressure and peak torque rpm) and have been able to reduce ignition timing at that point.
If you're adamant about running less cam duration, you must run 98 as a minimum. Crap fuel these days makes this a necessity in my opinion.
With 10.5:1 comp you going to need to run the best fuel you can, keep your gear ratios low, stay above peak torque, or run a really light right foot if you're going to run a mild cam.

0d850711-afac-45f2-8513-e82342fba19c.jpg (153.34 KiB) Viewed 168 times

[ed.harris]

Thanks Craig for you detailed reply.

I see you are also using one of Harvs gaskets.

I will be calculating the static compression ratio as I picked up some placticene this arvo to measure the Dome, and I will have a crack tomorrow if I can find a graduated syringe.

I do not understand what calculating clearance volumes is?

You have made me think about using the existing unknown Cam.
The previous owner said power didn't come on until about 3000 rpm but I did not know what is was like before that.
If I stick to the existing Cam the opel 4 speed lower gear and 4 gears instead of 3 also helps with drivability.

I was also thinking of at least measuring lobe lift of the Cam in the Engine and comparing the lift with the 1433 clives grind.

I believe the engine just had a standard distributor fitted sometimes with and sometimes without electronic conversion.

I don't want to be playing around too much trying to tune it.
Another option is to get another compromise Cam.
I will be running an AFR gauge in the car should get a bad batch of juice, was going carry Octane booster.
I have used NOS octane booster on another car that is boosted.

Keeping the existing Cam may be the way to go.

Another option I was thinking was to do some work to the Combustion chamber shape by removing material and making the shape more moder.

Any thoughts on that idea?
Has it been done before?
I know it could cause other detonation hot spots, possibly.

Thanks again for your hands on experiences.

Cheers Ed.

[Blacky]

Compression = lots

for a grey at least. No real way of telling without plenty of measurement. Just send it

[Craig Allardyce]

Clearance volume is the volume of the head gasket thickness and combustion space, and the crevice volume is from the top ring to the top of the piston. Best way to measure all this is to fill the cylinder with the piston .300" down the bore, then recalculate it if it was a flat top piston. This will then work out your dome volume as well. Measure all this with an old compressed head gasket fitted and a piece of perspex clamped down on the block. Make sue the fill hole through the perspex is at the highest point. Use a burette to fill the cylinder for accuracy. Syringes aren't.
Re the chamber, piston domes are bad for flame propagation and can in fact send an engine backwards with regards to combustion harshness. With some heads softening the chamber and reducing valve shrouding can get some breathing gains that better offset the lowering of compression, even though compression ratio is reduced.
You would also benefit from putting gas flow grooves in the piston dome. This allows gas in the squish area to be transferred across to the spark plug area during compression to aid in better combustion. Domed pistons can be awful for trapped gases and flame travel. Repco went through all this when they were developing engines for Jack Brabham. Lots of money developing high comp pistons and engines with no gains and loss of hp.

And BTW, an AFR gauge will not warn you of detonation, it only monitors O2 in the exhaust.

[Craig Allardyce]

I have amended a few things in my post above.
Below is also the spreadsheet I made up over the years for calculating the comp ratios.

It may be too much for some, but if you're handy with spreadsheets they make the task a lot quicker and easier.
Take note of the Octane listing vs comp ratio and brake thermal efficiency at full throttle. Also you have to understand RON and MON with respect to octane ratings. 10:1 needs 100 octane (at full throttle conditions)!

Compression ratios.xls

(35.5 KiB) Downloaded 10 times

[Fud]

Hey Ed, if you go over to my engine thread HOT GREY 2.0, you will find my the last build I did, it ran 141hp on the engine dyno, I’m in the process of building another hot grey, this next one will be another solid one, hopefully with a little more power


Sent from my iPhone using Tapatalk

[ed.harris]

Thanks Craig,
I will check it out.

Thanks FUD I checked it out.
Is the new engine having higher compression, or is it going to be boosted?

Anyway, I did some ccing today and have some values for people to check my calculations.

I also noticed a couple of interesting things.
Firstly I used an old spark plug from my J motor (Champion RC9YC), it seems not correct and screws too far in, takes up volume and hits the pistons when I drop the head on the block without a gasket, the head sat up about 8mm.
What plugs do people use?

Also, I can see the angle part of the piston through the plug hole.

This has me thinking it would be best to clock the plug so the earth strap going to the electrode is down.

I I was thinking that if the strap is up, the strap would should the Spark from the combustion chamber reducing efficiency.

Anyway, the values.

Combustion chamber volume 50 cc.
Domestic volume 22 cc.
Head gasket volume around domestic. 4 cc
Bore 79.5 mm
Stroke 79.4 mm
Assuming compressed head Gasket thickness 1.5mm, what Compression ratio does everyone get, just to check.

Fitting correct spark plug will increase combustion chamber volume slightly.

Does anyone else want to do the calculation to check my calculations?

[Errol62]

Swept area or cylinder displacement 379.24cc. 139cui near enough. Do we know the deck height Ed?


Sent from my iPhone using Tapatalk

[ardiesse]

Ed,

That is definitely the wrong spark plug. Waaay too much reach. You want something like the Champion J12Y (13/16" hex, 14 mm thread, 3/8" reach). Grey motors take the same plugs as small-block Chev V8s, but with a different heat range.

ETA: 3-1/8" bore, 3-1/8" stroke equals 143.8 cubic inches.

Rob