Help with LS1 v8 conversion

[Engineer]

Still think a small V8 is the way to suit the MX-5

Yes, I concur. A nice small block V8 4.5-6L is the best option for the MX5. It suits the body weight and dynamics well. You don't want something that overpowers the chassis too much. Carol Shelby always said that the best engine for the cobra was the 289 (4.7L), it was a revvy little thing that worked very well and rewarded any good driver. The 428 by comparisons was a bit of a beast and it sort of spoiled the balance in the car, it was all about the engine and everything else got drowned out in the experience. Same applies for the MX5, you can have too much engine, no point having the power if you give it full throttle and it just wheelspins in 3rd let alone 1st and 2nd. You need the just right balance to make the car a nice driving experience.

In my opinion that horsepower target is around 450HP

[Nevyn72]

V8 in an MX5 is for people who just aren't trying......

If you're really serious then you need to go for Gold with a V12 like this guy!

https://youtu.be/VzHA8B6RZ_M

[Engineer]

V8 in an MX5 is for people who just aren't trying......

If you're really serious then you need to go for Gold with a V12 like this guy!

https://youtu.be/VzHA8B6RZ_M

LOL..yeah what a great project. But its sill short on power for the amount of effort (308hp std) and the longer engine puts more weight where you dont want it...not to mention the packaging looks "cozy"...not sure how many kms he will do with it built like that...not many I would imagine. it probably wont last too long taking bumps and speed humps all day long on the road. But a great technical exercise for sure!

[Bushberger69]

Worth noting engineers can go outside the VSB14 engine-size guidelines if they feel they can demonstrate it's still satisfactory.

The preface to the entire bulletin says "advice for... the execution of modifications"

The table itself even says "recommended maximum"

This is correct, thats why you have engineers..otherwise you can write an AI bot to perform binary logic and make decisions on engineering modifications to vehicles.

For the OP Ls1 in an MX5 is outside of the vsb14 guidelines for maximum engine size..also depends on which model of MX5 you have they are all differ in TARE weight. If under 1100kg TARE its is 4 x TARE kg = MAx engine cc . If over 1100 kg its 5 x TARE kg = max end cc.

Now why the laws of physics and engineering change for the RMS at exactly 1100kg is not explainable... ROFL

If they had even thought about how absurd the model is, they would have realised that a it it should be a a sliding scale of engine size vs TARE kg...as the TARE weight increases the engine size can increase in proportion. A simple liner graph would have done it...i.e. find your TARE kg on the X axis and then go up until you hit the line to get your Maximum Engine size in CC...simple...that would have been nice.

By the RMS model and logic, a car that comes in at 1099kg TARE can have a 4.4L engine and one at 1101kg can have 5.5L...go figure

So that's why the certifier has some discretion...well hopefully...

Hey Engineer... I've been daydreaming about doing this to my NC, and correct me if I'm wrong, but my PRHT NC weighs 1153kg, which means that I can legally fit up to a 5.765L engine (ie. an LS1). A soft top NC only weighs 1110kg which limits it to a 5.55L. Is that the biggest LEGAL hurdle to jump?

[StuwieP]

Worth noting engineers can go outside the VSB14 engine-size guidelines if they feel they can demonstrate it's still satisfactory.

The preface to the entire bulletin says "advice for... the execution of modifications"

The table itself even says "recommended maximum"

This is correct, thats why you have engineers..otherwise you can write an AI bot to perform binary logic and make decisions on engineering modifications to vehicles.

For the OP Ls1 in an MX5 is outside of the vsb14 guidelines for maximum engine size..also depends on which model of MX5 you have they are all differ in TARE weight. If under 1100kg TARE its is 4 x TARE kg = MAx engine cc . If over 1100 kg its 5 x TARE kg = max end cc.

Now why the laws of physics and engineering change for the RMS at exactly 1100kg is not explainable... ROFL

If they had even thought about how absurd the model is, they would have realised that a it it should be a a sliding scale of engine size vs TARE kg...as the TARE weight increases the engine size can increase in proportion. A simple liner graph would have done it...i.e. find your TARE kg on the X axis and then go up until you hit the line to get your Maximum Engine size in CC...simple...that would have been nice.

By the RMS model and logic, a car that comes in at 1099kg TARE can have a 4.4L engine and one at 1101kg can have 5.5L...go figure

So that's why the certifier has some discretion...well hopefully...

Hey Engineer... I've been daydreaming about doing this to my NC, and correct me if I'm wrong, but my PRHT NC weighs 1153kg, which means that I can legally fit up to a 5.765L engine (ie. an LS1). A soft top NC only weighs 1110kg which limits it to a 5.55L. Is that the biggest LEGAL hurdle to jump?

First step would be talk to the engineer.

Emissions testing would be, I suspect, the biggest hurdle.

Pass that, and as long as you can convince the engineer your brake setup, chassis, suspension and all the rest are up to scratch, you'll be fine

[bruce]

So much pointless navel gazing. As said above and I've said repeatedly before, speak to an Engineer. They will ultimately say yes or no as they will be giving the approval.
(From my experience talking to Engineers in Vic, they won't approve such a conversion. But, things may have changed over the years and views changed).

[Engineer]

Hi,

The weight you listed at 1152kg is the Kerb weight. What you need to find is the official TARE weight. Its the TARE weight that gets multiplied by 4 or 5 to get the final engine capacity figure in cubic centimetres. if you cant find the official TARE weight then you need to put the car on a weigh bridge with 10L of fuel and get the TARE weight that way. The way that each engineer and each state based authority certifies modified cars will ultimately be the biggest challenge.

Make no mistake this is not a simple path. You WILL be tested at every point and at the very least for the following:

1) IM240 Emissions test to ADR 79/00 or 79/01 depending n model of car
2)Full day Brake test (not your normal rego brake test
3) Noise Test
4) Body rigidity test
5) 100+ small VSB 14 type Standard checks and tests like (suspension height, structural load calculations (FEA), proper welding used, proper electrical work (i.e grommets), fuel line routing, etc etc

Plus a whole lot more. My advice is to see the engineer FIRST. Create a plan for what you want to do and see how you go. You may find your conversation will not be entertained by anyone or you may find an engineer who is willing to help you and work with you.

The car will cost you $35K+ to convert and certify (if you can find anyone to do it).

If the car's TARE weight is over 1100kg then you are technically over that hurdle and can fit an engine that is 5 times the TARE weight.

Good luck with it...its a tough road but doable.

Cheers,

[Beelzeboss]

Use this tool provided by the RTA to find the official tare weight that they will use.

https://myrta.com/rvd/

MX5 NC PRHT says 1140kg, so LS1 would be OK.

However, and feel free to correct me if I'm wrong, but the engine must be newer than the car, or so my engineer told me when I engineered my LS1 swapped S13.
The newest LS1 we had here is from a 2005 VZ commodore (in 2006 they went to the 6L). The NC was introduced in 2005 so you'd only be able to make it work with a 2005 NC and a 2005 LS1... but I think I'm correct in thinking the PRHT NC didn't come out until a little later on, so... yeah, it's going to be difficult to convince an engineer.

In terms of cost and the process, I completed the entire LS1+T56 swap on my S13, including the cost of all components and full engineering in NSW for engine, gearbox, brakes and wheels for around $7,000. The engineering portion of it was $1200, it definitely pays to shop around for an engineer.

[bruce]

I'm believe the price of anything LS has gone up too.

[Engineer]

Hi,

VSB 14 from memory doesn't stipulate that an engine needs to be newer than the car. The engineer has told you this to make the emissions aspect easier. An engine that is the same year or newer than the car will ensure that any emissions requirements are met without issue. However, If you have any (and I mean any) modifications, this logic will be invalidated and an IM240 test can be asked for to meet compliance. The car will need to pass the Emissions targets set for its year of manufacture.

The IM240 Emissions test thresholds (HC, NOx and CO levels) for your car's year of manufacture can be found here:

https://www.infrastructure.gov.au/vehicles/environment/emission/files/Emission_Standards_for_Petrol_Cars.pdf

So its not exactly true that you need a newer engine than the car, the engineer was trying to make it easy for you and him/her. You can still get an IM 240 emissions test in Sydney NSW at the Botany testing centre. It takes about 30-40 mins. Not sure if Victoria is still doing them.

I agree with Bruce, almost everything has gone up in price recently and expecting a total front/back conversion with engineering to cost under $10K is not realistic. A solid, good condition, low km second hand LS3 engine, ECU and gearbox package will cost $15K alone. The whole car needs to be modified for this conversion to work. Its not a weekend job to do in your driveway. But again it all depends on the type of result you want... OEM levels of fit, finish and reliability or something less.

Overly modified cars (like a V8 MX5) tend not to do too well in the reliability stakes unless properly modified across all the subsystems of the conversion. You will be surprised at how many problems the engineer's solve at the OEM level to ensure your comfort and the cars reliability. When you modify a car in its entirety front to back, you need to solve all these problems again...yourself..and that costs time and money, plus a few cuts and bruises

Cheers,