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Hey guys just had a question about an engine rebuild. . Why would someone use an NA cylinder head on a NB SE engine rebuild?

Cheers,
Brad

Both are non-VVT?

There's a much wider availability of hot cams for the non VVT head which is an important consideration depending on your application. Edit: though yes the SE head is not VVT anyway!

I seem to recall sailaholic saying once that the NA8 head has more potential for porting than NB heads too, but I might be wrong about that so not a for sure thing.

NA8 uses a BP05 head, whereas NB8A (VICS) & NB8 SE uses a BP4W head. NB8B & NB8C (VVT) uses a different head again. Another reason is BP4W heads were/are scarce & expensive, although becoming more common as NB8A's become older.

Look at using a BP low port head with a high port cam cover. There are more options for porting using the low port head.

I know MrBrad is in the market for an SE, so with that in mind I guess he's asking if he should be wary of someone selling an SE with a built engine using an NA cylinder head, or if it sounds a bit suspect?

93_Clubman wrote:NB8B & NB8C (VVT) uses a different head again.

BP6D

I would check the casting marks on the rear of the cylinder head. If it is a 'BP05' head then the intake manifold will not line up and you need an adapter or modification to fit. In factory form the BP05 head does not flow as well as the later BP4W BP6D high port heads

The only reason to use an NA head would be for something highly modified.

sheep wrote:The only reason to use an NA head would be for something highly modified.

Or it's cheaper.

hks_kansei wrote:

sheep wrote:The only reason to use an NA head would be for something highly modified.

Or it's cheaper.

Is it? The intake manifold doesn't fit... So add the cost of modifying the SE manifold to fit... And deal with the fact that it won't fit well, I would say an NB head would be a far better option. Unless said SE has an NA8 intake manifold on it, which wouldn't bother me but it's no longer how an SE was intended. I have had plenty of experience when it comes to rework to change a 'cheaper option' back to the correct option.

This is also assuming the NA head has all of the SE valve train swapped over... Surely no one would leave the HLA's in there?

The SE was never intended to be the ultimate, it was intended to be what could be achieved under Californian emissions laws at the end of a dying model.

So while I understand a possible want to keep an SE original, only someone who has never dríven a well sorted NA8 turbo would have a problem with an NA head/manifold on a well sorted SE. If the car has an aftermarket ECU an NA8 head manifold and sensors makes a LOT of sense, ask the guys with aftermarket ECU controlled SE's about the myriad of issues they have had trying to run the SE's electronics on aftermarket ecu's back in the day before they were well supported, many to this day still run NA alternators for this reason.

Its such a common thing here to see SE fans who have never dríven other models with turbochargers to type out responses as if the SE is the epitome of what a turbo MX5 can be. Im sorry but it was never designed to be that.

Dann

NitroDann wrote:The SE was never intended to be the ultimate, it was intended to be what could be achieved under Californian emissions laws at the end of a dying model.

So while I understand a possible want to keep an SE original, only someone who has never dríven a well sorted NA8 turbo would have a problem with an NA head/manifold on a well sorted SE. If the car has an aftermarket ECU an NA8 head manifold and sensors makes a LOT of sense, ask the guys with aftermarket ECU controlled SE's about the myriad of issues they have had trying to run the SE's electronics on aftermarket ecu's back in the day before they were well supported, many to this day still run NA alternators for this reason.

Its such a common thing here to see SE fans who have never dríven other models with turbochargers to type out responses as if the SE is the epitome of what a turbo MX5 can be. Im sorry but it was never designed to be that.

Dann

The only reason I would use the NA head is if it was heavily ported, because only then, will it out flow the NB head. In any case, I don't think we're talking about that level of engine here. The engine in question (assuming) has had the head replaced to rectify a failure, not for any performance goals...

My concern is why not repair the SE using the correct (or closer to) parts. If the SE in question has a standard turbo arrangement, standard cams, and a stock NA or NB head, then the NB head is the better option is it not? The extra costs involved in buying a used NB head are outweighed when you factor in what it takes to use the NB manifold on the NA head. If you do use the NA manifold, then it's cheaper, but the NA head still does not flow as well as the NB head in stock form. The SE that was for sale a while ago had the NB manifold, so I can only assume the holes were redrilled or flanges swapped. This adds to the cost, making the NB head a far better option. Regarding Aftermarket ECU issues, the head plays little to no part in this.

It is also possible that an NA8 engine was used if the SE threw a rod. This would be done to retain the oil/coolant ports on the block, but again, if it was me, I would pair another NA8 block with an NB8A head to get as close to correct as possible for an SE.

This is all just speculation and opinion. Forums are a great source of both if that's what you're after, but if you want more factual information, OP should discuss this with one of the many MX5 workshops around. Perhaps a chat with the guys that built the engine, followed by a second opinion?

Lol, I run a workshop that specialises in turbocharging and upgrading turbocharged MX5's.

Dann

NitroDann wrote:Lol, I run a workshop that specialises in turbocharging and upgrading turbocharged MX5's.

Dann

Ok

NitroDann wrote:Lol, I run a workshop that specialises in turbocharging and upgrading turbocharged MX5's.

Dann

Ahh...I nearly cracked up. In all fairness, not everyone would know that. Plus you also had one mad little NA.

So will you be finished with my exhaust before Saturday?