11 replies to this topic

[gpskipton]

Greetings,

 

I have a 1988 1275 Metro engine that I purchased that is very clean and I am in the process of supercharging it prior to installation in my 87 Mayfair.  The prior owner did a VTEC swap and the shop and owner said it was a very good engine.  I have a basic SC kit (much like the Janspeed one).  I do not plan on rebuilding the engine at this time, but I will measure to make sure it has not been mucked with.  I know a decompression plate is not ideal, but that is my plan for now.  Someday I wall do a 1293 rebuild with dished pistons.  I have a few questions:

 

- I understand the Metro runs at about 10.5:1 CR, with Janspeed's 6CC plate it brings it down to 8.4.  I have contacted them and they said that is on the high side, but doable.  I think they offered a 9CC plate at one point which would be perfect and I asked them about it, but I have not heard back yet.  Is 8.4:1 OK?  Is the VMAXSCART plate thicker?? I am in the states and have access to 93 octane which I think is 98 RON.  I could add octane boost.

 

- I found out that the distributor on the engine is not standard.  It is a 59D4.  I checked the stamping on the block (12HD24) and it is an 88 Metro 1275 for sure.  The specs on the dizzy run 1-20 degrees (vacuum).  I know this is an older style dizzy, but from my readings this may play to my advantage?  It seems like at 20 degrees max, this will give me some boost insurance.  Thoughts?  I could get a 123, but hey if this works for now...

 

- I plan on ordering the Janspeed needle for my HIF44.

 

Thanks!

[Turbo Phil]

I think you need to recalculate your compression ratio. A 6cc decomp plate will not take your compression ratio from 10.5-1 down to 8.4-1.

Phil.

[gpskipton]

Greetings Turbo Phil

 

This is my first time trying to calculate CR.  I heard back from VMAXSCART, and their decompression plate is 2MM.  Assuming a 71mm bore, I calculate that to be about 7.92 CCs.

 

I am assuming the head gasket is about 3.3CC (bk450)... this is what the bk450 is roughly and it sounds like a good one to use.

 

I am using a CR calculator and have entered 70.6 bore, 81.4 stroke, 0s for the head gasket as I am adding the CCs to the combustion chamber volume.  21.4 is what I am using for the combustion chamber volume starting point.  In order to match the current 10.5:1 CR in the calculator I added 1 gasket (21.4+3.3=24.7) to account for the original head gasket and back calculated the piston deck clearance (which I don't know) as 2.25.  This yields the 10.5:1.

 

I then simply add the decompression plate and one more gasket to the combustion chamber (21.4+3.3+7.92+3.3=35.92) which yields 8.1:1.  This sounds like a pretty good number?  

 

Any help is appreciated.

[Hpal]

I'm currently doing an 1100 engine in Australia, with a sc12 toyota supercharger. I've build my engine with about 9:1 comp ratio. My mini guy has seen/worked on supercharged engines recently with 9:1 and no problems at all "with the right cam". I'm using a 266 cam, so apparently because of the hotter cam used there is more overlap of the valves so effectively the comp ratio is lowered a bit because a bit of pressure is wasted out the valves. I read that a metro cam is similar to the one i'm using. So anywhere in the 8's will be fine, but you may need the decompression plate to bring it down from 10.5

Edited by Hpal, 11 August 2020 - 10:32 AM.

[Steve220]

I'm currently doing an 1100 engine in Australia, with a sc12 toyota supercharger. I've build my engine with about 8.8:1 comp ratio. My mini guy has seen/worked on supercharged engines recently with 9:1 and no problems at all "with the right cam". I'm using a 266 cam, so apparently because of the hotter cam used there is more overlap of the valves so effectively the comp ratio is lowered a bit because a bit of pressure is wasted out the valves. I read that a metro cam is similar to the one i'm using. So anywhere in the 8's will be fine, but you may need the decompression plate to bring it down from 10.5

CR remains the same, no matter what cam you use. The MD266 has less overlap than other cams, which is why it's good for turbos.

[Turbo Phil]

He’s talking about dynamic compression ratio Steve. While cam choice has no bearing on static compression, it does effect dynamic compression ratio. The inlet valve closing point is the influence on that.

Phil.

[Steve220]

He’s talking about dynamic compression ratio Steve. While cam choice has no bearing on static compression, it does effect dynamic compression ratio. The inlet valve closing point is the influence on that.

Phil.

I think i wrongly assumed he was talking about static because of the CRs he was mentioning.

[gpskipton]

Thank you for the help.  I am not a CR expert, so maybe I should just ask.  Is a 2MM plate good (about +8CC +extra gasket CC)?  I have a stock 1988 Metro which I believe runs at an advertised CR of 10.5.  I reverse calculated from there using a CR calculator to come up with about 8:1 with a 2MM plate.

 

I am not rebuilding the engine so I want to be conservative.  Later on I plan to do a 1293 build, but for now I'd love 100hp or so would be great.

 

Things I know:

- Metro CAM

- Metro Head

- I know I will need to work with the timing - I am thinking either a 123 (can a 123 sense boost? all I see is vacuum retard specs)

- Cooler plugs

- hf44

[gpskipton]

For whatever reason, I never noticed the CR sticky post.  Using that calculator (I used a different one before) I also come up with between 8-8.5 CR.  So, I think I am good to go.  I plan to run the Aldon Amethyst for timing.  I know MJ is a little better, but I am trying to keep it cost efficient and simple.

 

One question: Were do I pull the boost from for the Aldon Amethyst?  I am doing a suck through almost identical to the JonSpeed.  I assume I need to tap the intake manifold or SC and use the same tap for a boost gauge and the Aldon?

 

Thanks for the help. 

[HUBBA.HUBBA]

The vmax decom plate is 12cc inc the gaskets

Edited by HUBBA.HUBBA, 04 June 2020 - 04:19 PM.

[HUBBA.HUBBA]

For whatever reason, I never noticed the CR sticky post.  Using that calculator (I used a different one before) I also come up with between 8-8.5 CR.  So, I think I am good to go.  I plan to run the Aldon Amethyst for timing.  I know MJ is a little better, but I am trying to keep it cost efficient and simple.

 

One question: Were do I pull the boost from for the Aldon Amethyst?  I am doing a suck through almost identical to the JonSpeed.  I assume I need to tap the intake manifold or SC and use the same tap for a boost gauge and the Aldon?

 

Thanks for the help. 

yep Amethyst off the boost gauge line is fine. FYI i have a Vmax decomplate and inlet manifold with the boost gauge take off I would sell. The decom plate I have will bring the CR on a 1293 to 8.4 which is perfect. To be honest mate you don't need an Amethyst or mega jolt on a super charged set up and vacuum advance dizzy without points will be fine.

Edited by HUBBA.HUBBA, 04 June 2020 - 04:25 PM.

[JonnyAlpha]

How did this end up - all ok?