NOOB questions about turbo build
 

Hello all.

Noob here and yes I've already used the search bar. I want to know if anyone can help guide me in the right direction with my build as far as what parts to use. I've searched many threads and it seems everyone is going a different route with their turbo build so I didn't see anything that could help me.

I have a 95 318TI. I understand the motors are forged rotating assembly so i will be keeping my bottom end stock. I will however replace the head gasket with a thicker layer to lower the compression, upgrade to ARP head bolts and do some light porting and valve angle job to my head.

I want to make somewhere around 300 wheel horsepower. I know this is possible because I've seen plenty. My questions are as follows:

- What is the smallest turbo I can use to make this power?
- What size injectors do i need?
- Is there any kit or ready made turbo exhaust manifold that I can buy?
- how much boost can the stock internals handle?
- How low do I need to take my compression down to?

Thanks for all your inputs.

Not many people have done a turbo m42, a few have been documented on this forum if you search deep enough. Typically for a small displacement 4 cylinder the turbo I would look for that suits you power goals would be a T3 style in the 50mm range with a .63 A/R on the exhaust housing. There is an exhaust manifold and downpipe made by OBX (https://www.ebay.com/itm/OBX-Turbo-M...-/162269228973) however I've heard bad things about it's quality. Injector size depends on if you upgrade your fuel pump, it should be comparable to turbo M50/52/S50/52 injectors. Depending on how low you go with compression will dictate how much boost you can run. If you're looking to run high boost (15+ psi) you should go with a conservative CR of 8.5:1 or 8.8:1. You also have o consider the higher boost you run the greater chance of pushing oil past the piston rings, so if high boost you'll have to do pistons as well. LOTS to consider. VAC Motorsports makes and supplies a lot of M42/44 engine internals.

Thanks!

I've looked into the vac kit in the past but its way out of my budget. I think I'm just going with ARP head studs and a good and thick head gasket to lower compression to 8.5:1.

As far as fuel pump goes I already have an e85 capable 340 from rallroad.net. So in that case I'm thinking some 42lbs should suffice. And for the intake and exhaust manifold I will most likely have one them fabricated. Gives me a good excuse to get rid of that God awful intake manifold...its so hideous.

I guess my next question would be what turbos do you guys recommend. This will be my first turbo build so I'm not familiar with them at all. I'm and LS guy (have a 325is with an LS3.) To save cost could I buy a turbo off of a car with a similar sized motor, such a Saab, Evo, SRT-4. The TD04 turbos seem very reasonable and seem to be used on a lot of cars from the manufacturer so they must be reliable???

I'm willing to stay right at or under 15psi. 300whp would be nice but ill be just as happy with 250-270.

You could try to make another OEM turbo work on your setup however all of those units will be internally wastgated, setup for their stock boost pressures. If you want an external gate those would make things a bit more complicated.

Personally, I like external gates so I would go with something like the Borg Warner SXE-252 with an .63 A/R. If you're willing to purchase right now, Boostlab has a sale on their own turbos which are basically garrett housings with their own billet wheels. They have a 5757 (57mm compressor inducer 57mm exhaust) on sale for $499, this is a journal bearing turbo so it would suit your power needs >(http://www.theboostlab.com/bl-5757-turbocharger/).

I've personally also researched into a turbo for my M44 and to make about 400WHP the guys over at Boostlab suggested their 5855 ball bearing turbo. Bigger compressor wheel for more air flow and smaller exhaust wheel for faster spool plus the addition of being ball bearing compared to journal bearing. That unit is also on sale right now for around $800, but i'd only recommend that if you'd want to go for more than 300hp. You can find it here, all sale prices activiate in the shopping cart >(http://www.theboostlab.com/bl-5855-d...-turbocharger/).

Awesome. What is the difference between internal wastegate and external wastegate and what are some of the benefits and downsides of both?

Also, what is the purpose of doing a metal fabricated intake plenum? I see a lot of turbo guys convert to these instead. Looks much better IMO, but do they serve a purpose?

Also, I see some people are routing their MAF in front of the turbo and others in front of the intake manifold where it is normally.