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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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Post by dickie on Apr 28, 2024 14:39:42 GMT
The cylinder head is still on the machine shop at work.
The chap that was going do the work has now retired and the machine shop has got busy with real work so I might have to pay money to get it done !!
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Post by dickie on Sept 19, 2024 8:50:51 GMT
Hi Folks,
Its update time !
I finally got the chaps at work to mill the head for me they took off 2.3 mm or 90 thou ish.
The chamber volumes are now 43cc
The piston crown is 8.24cc
so with a 40 thou Cometic gasket that works out at 12.09:1 compression ratio according to an on line calculator.
By the time the actual head that I will be using has had the oversize inlets fitted with de shrouding work that figure will drop slightly.
This is in my target zone with the 285 cams.
I can now check the valve centre lines and piston pocket to valve clearances at TDC
I have 1.24 mm Inlet Lift at TDC
And 1.06 mm Exhaust Lift at TDC
So I need to make sure I have safe clearances for the valves as the next priority.
MOT has just Expired and I have just changed the front upper ball joints and the Rack tie rods and one upper wishbone bolt.
I am waiting for some longer front brake lines to arrive as the original braided hoses were just too short with extended lower ball joints on the front and the old hoses had been kinked at full lock.
I am able to make progress this week as I am on Holiday at home having sent my Wife off to Spain for the week !!!
Cheers Dickie
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Post by dickie on Sept 26, 2024 17:42:10 GMT
Hi Folks,
More Lunacy on the way.
I am on the hunt for another Mk 2 1800 cylinder head, there should be a complete engine available locally very soon.
This will be the donor head which will be modified as I will leave the car in working order for the time being.
I am investigating fitting a plate ( Glueing ) onto the intake side of the head so that the ITBs can be moved upwards and angled downwards by moving the port entrance up by 20mm or thereabouts.
I am thinking of starting off with a 25mm Alloy plate which could be bolted onto the original threads with the plate milled to a wedge shape and new manifold stud threads. then the lower part of the ports being filled and the upper part being moved up. Time to do more experiments on the skimmed VVT head.
I will try and see if this is possible without any Tig Welding.
There appears to be plenty of height under the strut brace to do this.
I might do an experiment with a sheet of rigid foam first to see what is practical or possible.
Please do not send the men in White Coats around just yet.
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Post by dadbif on Sept 28, 2024 7:12:50 GMT
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Post by dickie on Sept 28, 2024 10:04:57 GMT
Hi Dadbif,
It is the ports in the head that I am thing of moving upwards to align with the valves better.
The OEM inlet face has a negative rake I am looking at changing the face angle and moving the inlet ports upwards. This will mean removing material from the upper part of the port where it protrudes just below the injector ports and adding material at the lower section of the port.
I have already cut a lump of high density foam to do some experiments with and I have a Danst Manifold adaptor plate to help with alignment.
The Jenvey manifold only lifts the ITBs up and gives them a down angle which does not alter the inlet tract in the head.
I am already using a set of BBR ITBs on a Mk2 1800 head.
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Post by dadbif on Sept 28, 2024 16:14:11 GMT
Whilst I applaud your constant quest for improved air flow, will all the effort be rewarded with more power?
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Post by Zed. on Sept 28, 2024 16:29:25 GMT
Whilst I applaud your constant quest for improved air flow, will all the effort be rewarded with more power? Rich. |
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Post by dickie on Oct 2, 2024 19:23:51 GMT
Whilst I applaud your constant quest for improved air flow, will all the effort be rewarded with more power? Hi I have no idea what if any the power improvement will be as I am doing a lot of experimenting with this engine but as horspower goes up with revs I am hoping for an improvement.
It will be capable of over 8000 RPM as it is now an oversquare design with longer conrods forged pistons etc.
By tilting the inlet ports upwards instead of downwards and moving them upwards it will straighten up the inlet tract, it might also allow longer inlet trumpets to be installed.
I have now collected a Mk2 1800 head from an engine with a blown head gasket.
I just need to remove the inlet manifold and strip it down then clean it before I butcher it.
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le sigh