Building an 8v with as much mi parts as possible

[Tom Rallye 3 1 Cars]

So, after rebuilding my mi16 the second time after it got full of sandblasting grit (long story, stupid mistake) the same problems surfaced, because, although it has been cleaned with ultrasound, it still is full of grit...

I invested quite a bit of mony in special parts for the mi: lightened and balanced bottom end, bigger oil pump, new injectors, ...

Because legislation has changed, it would be better to convert it back to 8v, but I want to use most of the parts I invested in.

So what are my options to make a fast 8v block with as much of the mi16 parts and running the standard ignition or the mi16 ingnition? I will be starting from a 1.9 rallyeblock (DFZ).

[Tom Rallye 3 1 Cars]

I should ad that I have a spare mi16 bottom end too, so that could also be used in combination with an 8v head.

[Andy 105 1 Cars]

Afternoon,

 The problem will centre on the pistons. The 16v ones have cut outs machined into them which will make a mess of the CR when you try to use them with the 8v head. Swapping to 8v pistons using the 16v rods is tricky, so I think you will need the 8v rods and pistons in your Mi16 bottom end to ensure you have the correct CR with the 8v head. The 8v and 16v water pumps are slightly different and you will only use the tapping on the timing end of the block for the 8v tensioner . However, the engine mounting that bolts onto the block is different between the 8v and 16v. If you use your 16v mounting on your 16v block, I think  you will be o.k, but have no direct experience of using that arrangement with an 8v Head and timing belt . Others on here are far more knowledgeable and will , I am sure, add extra detail as needed. 

[Tom Rallye 3 1 Cars]

Been reeding here all day and I hope it will be possible to use the total mi16 setup, including pistons and rods, with the 8v head. That head needs to be skimmed to get a CR of about 11:1. In combination with bigger valves and a camshaft of about 275°. That would make a nice engine I hope, but I'm far from sure if it's achieveble or not, so some encouragement (or discouragement) would be greately apreciated...

[petert 588]

I've built an 8V with Mi16 pistons, rods, liners and crank. It works well. You can tell it's not your average 8V.

[Tom Rallye 3 1 Cars]

So basically a mi16 bottom end with 8v head works fine. How much would i need to skim of the DFZ head with bigger valves in combination with bigger cams (about 275°) to get the compression around 11:1, and wouldn't the pistons hit the bigger valves?

[welshpug 1,661]

8v combustion chamber and valve inclination is quite different to a 16v, valves are pretty much straight up from the piston crown so they can open a hell of a long way at tdc before you come near the pistons.

 

 

however if you have a failed engine due to grit in there I wouldnt want to use any parts in a new engine.

 

 

using a flat topped mi piston under an 8v head which is 8cc smaller chamber will unlikely need any skim to get healthy compression, dont forget to make sure the valve springs can cope with the peak lift you want yo use.

 

lastly, you will need a mappable ecu, or find someone to map the Motronic ecu, I would try and find the map based system rather than afm too

[Tom Rallye 3 1 Cars]

The head would be from a DFZ, wich has a bigger chamber than a normal 8v, so might need a skim. 

I will use an other mi block. I' ve had it with this one. Don't see much harm in using the pistons and rods.

[wicked 103 3 Cars]

The dfz head has smaller valves than the dkz/d6b and has a lazy cam. Would not be my choice for custom build. Probably a 2.0 8v head is a better choice. A bit higher compression asks for wild cam....

[petert 588]

The DFZ chamber is 49cc from memory. Thus even with Mi16 pistons the CR will only be 9.1:1. You would need to skim 2mm off the head to get it anywhere near a decent CR. Add small valves, poor flow etc. and it's best just to walk away from a DFZ head.

Edited October 19, 2018 by petert

[Thijs_Rallye 87 4 Cars]

On 10/19/2018 at 7:27 AM, Tom Rallye said:

So, after rebuilding my mi16 the second time after it got full of sandblasting grit (long story, stupid mistake) the same problems surfaced, because, although it has been cleaned with ultrasound, it still is full of grit...

You got to be kidding me. How did that happen this time?

[Tom Rallye 3 1 Cars]

We had it cleaned with ultrasound, checked and doublechecked. Put it back together with new bearings, oilpump, ... . Started it up and after 20km the same problem. Must still have been somewhere in there, despite the ultrasound. Aint gonna try it a third time...

[Tom Rallye 3 1 Cars]

I'm gonna look for a 8v head with bigger valves than (306 xsi). Will I be able to use the motronic from the mi? I thought there could be a problem with the dissie, but not sure?

[Thijs_Rallye 87 4 Cars]

2 hours ago, Tom Rallye said:

Will I be able to use the motronic from the mi? I thought there could be a problem with the dissie, but not sure? 

That is not going to work since the Mi has a stepper motor for the idle and it's maps are not suited for running an eight valve engine.

 

I can imagine you're not going to try for a third time, but if you want to use the bottom end you will still risk the same problem since the grit will likely be present in the oil galleries. Ultrasound isn't suited for removing blasting grit in an engine but unfortunately you've now found that out the hard way :(.

[Tom Rallye 3 1 Cars]

No, I'm going to use a different bottom end, but I would be using the pistons, rods, flywheel and sensors from the "gritted" mi, just another crankshaft , oilpump and all new bearings.

Will have to search for another solution for the ignotion than. Would the jetronic of the Dfz be able to run it, bearing in mind it will have a bigger camshaft, higher cr and bigger valves?

[Thijs_Rallye 87 4 Cars]

I'd personally go for the DKZ Motronic engine management. If this is going to be a road going car I would not get too excited on big cams and thus compression, unless you are going the stand alone management route. The L valve will start to resonate with big cams making it practically undriveable at low revs.

[Tom Rallye 3 1 Cars]

I was thinking about stand alone management with cr of around 11:1 and a cam of 275°.

Would that work for a road car?

[petert 588]

A good combo, but I'm confident the standard dizzy won't like it without modification.