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Post by warpspeed on Dec 3, 2023 9:31:10 GMT
Detonation should not be a problem with well thought out intercooling, and I am not planning on running crazy high boost levels anyway. The rest has to do with sufficient fuel octane and proper tuning.
If you look at the compression ratios that successful forced induction factory road cars have run over the last few decades, they are all in the mid to low eights, many with factory boost pressures in the low teens.
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Post by dickie on Dec 3, 2023 12:43:32 GMT
Hi, Warpspeed.
It is not a mega thin head gasket I am after but need to have one to take into account how much the pistons come out of the bore and allow for squish clearance. So I will be looking in the 030 to 040 thou range which Cometic do 030 / 036 / 040 Thou gaskets ( Compressed Thickness ) I need to bring my CR up to compensate for the loss due to using a shorter stroke which is the reason for a big head skim. I need to measure the piston volume above the deck next, so I need to make an 85mm bore ring to go on the deck to measure the actual CC of the installed piston crown then work out my required Combustion chamber volume to get the compression up.
Cheers Dickie
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Post by warpspeed on Dec 3, 2023 20:00:50 GMT
An alternative to a bore ring might be measuring with the piston a known distance down the bore. Easy enough to set with a depth gauge.
From what I have read, 040 squish is just about optimum for all engines regardless of size.
Looking at some of the pictures on the internet of sectioned BP heads, there would appear to be plenty of material in the head face. That seems to be a better way to do it than having a ridiculously high piston dome that is going to really hurt flame travel. Ignition advance requirement is a pretty good indication of how well it burns.
A bit of each sounds like a good compromise. Less dome also usually suggests a bit less piston weight. It all sounds like an excellent plan.
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Post by dickie on Dec 3, 2023 20:36:47 GMT
Hi Folks,
Your idea of measuring with the piston down the bore is a good idea I will look into it. I have taken a couple of measurements. The piston protrudes by 17 thou. Piston Crown is 8 mm above the deck. The VVT head has a chamber depth of 17 mm The valve seats are the limiting factor on how much can be skimmed from the head. I will be fitting + 1 mm inlet valves which will be the limiting factor. The Wossner pistons have a deep valve cut. If I take the head down by 3.4 mm it will leave 13.6mm above the piston crown without the head gasket thickness.
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Post by dickie on Dec 9, 2023 18:19:13 GMT
Hi Folks,
I have made a bore ring so that I can do the measurements at TDC. It will be to difficult to set the piston in any other postion. The ring is easy to measure and calculate its volume then check the piston crown volume at TDC with a burette. I will have to fit the sump temporarily and set the block up level before I can do the volume measurement. In the meantime I have stripped the VVT head down ready to take to work and get it milled down for chamber measurement and valve clearances etc.
Cheers Dickie
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Post by dickie on Dec 10, 2023 21:11:27 GMT
Hi Folks, More ramblings of a Lunatic. I have been playing more engine calcs and measurements. I have got a piston above deck volume of 9.45 cc If I use a 30 thou Head gasket thats 4.32 cc This brings the volume of piston with gasket down to 5.13 cc Swept volume is 449.42 cc Which has enabled me to do some head volumes to get the CR
Head chamber volume
50.2 cc = 8.9-1
42cc = 10.7-1
38cc = 11.82-1
36cc = 12.48-1
34cc = 13.21-1
32cc = 14.04=1
31cc = 14.4-1
30cc = 14.9-1
I Think the head on the car has 42 cc chambers assuming 52cc OEM then an 80 thou skim so If I used that head as it is I should have 10.7-1 CR on the new block. All good fun and games !!!
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Post by dickie on Dec 15, 2023 12:43:39 GMT
Hi Folks, The VVT head is now in the machine shop at work waiting for a chance to be put on the Mill and have 2.5 mm removed. It will not be done till the machinist has a bit of slack time, so early next year.
I will have to start building the engine for my 90 year old Austin Seven instead ! Also with billit crank and rods custom camshaft slipper pistons etc. The fun never stops.
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