So I have a built 420a that I've been driving for a while and slowly gathering turbo parts. I'm stuck on a few things tho. My motor is 10.5 compression and I'll be running a 20g.

1. What's the best external Wastegate and bov to run? Does size matter?
2. Can I get away with running a 3inch downpipe and 2.5 inch all the way back?
3. I have arp head bolts but do I need arp rod bolts or anything else?

My goal is to start around 250-300hp and work up to 350+

Any tips or suggestions would be awesome thanks.

1. The new Tial Q bov seems to be the preference these days. Wastegate- there are several great options, just get a known brand. Depending on the turbo size, you need to make sure your wastegate can move enough air without creeping. On a 20g with a 2.0L motor, a 38mm is fine.

2. The 2.5 will increase backpressure, which is always bad on a turbo car. Either dump it or go full 3"

3. No clue on a 420a. 4g's are g2g on just studs.

Dont 20g's have internal wastegates?? Only place I'm lost at really.

As for the exhaust, most people run 2.5" downpipe and usually run the same size all the way through. You realize some have had luck with a 3" DP and got to keep A/C, but most get rid of it because of fitment issues. I know a few guys that run a 2.5" downpipe to a 3" car back and have had no issues.

Says you have eagle rods in your profile, did they not come with arp 2000 rod bolts?

Only thing I would suggest is a way to tune and go cause hell. Slo2gen on here had a 25g on e85 and the thing was quick from what he told me. That is until his melling oil pump went out.

jayson427 said:

So I have a built 420a that I've been driving for a while and slowly gathering turbo parts. I'm stuck on a few things tho. My motor is 10.5 compression and I'll be running a 20g.

1. What's the best external Wastegate and bov to run? Does size matter?
2. Can I get away with running a 3inch downpipe and 2.5 inch all the way back?
3. I have arp head bolts but do I need arp rod bolts or anything else?

My goal is to start around 250-300hp and work up to 350+

Any tips or suggestions would be awesome thanks.

Click to expand...

1.) Wastegate depends on displacement, turbo size, power (massflow) goal and projected boost to reach that power goal. Sort of a balancing act.

To simplify though:
More boost = smaller gate(s), because less exhaust needs to bypass the turbine. Less boost = larger gate(s).

20G on a 2.0 looking for ~350whp? You could get away with a single 38mm if not using an internally gated housing.

2.) Really you would be better off just running 3" all the way back. Spool, power and overall efficiency benefit greatly.

3.) If you have a "built" block, what fasteners are holding your rods together currently?

You guys rock I definitely didn't expect to get such great responses!

The turbo I have I bought used (going to rebuild it soon) so it didn't come with an internal Wastegate. I was assuming 38mm would be good. I just wanted some reassurance before I started buying more parts.

Yeah I guess I'll have to go 3inch exhaust all the way. Just sucks because my current exhaust is 2.5 inch.

I have eagle h beam rods now. Just wanted to make sure if I needed any other arp hardware before I turbo'd it.

I'm not sure how much hp my block will hold. I wanted to start at 10psi and work up to 18psi max maybe a little more. I don't want to push it hard I'd rather be on the conservative side.

Is it a t3 flanged 20g or Mitsubishi?

Hrc 20g

jayson427 said:

1. What's the best external Wastegate and bov to run? Does size matter?

Click to expand...

I went with a TiAL 38mm and 1g BOV. After doing the research, those offered the best combination of performance and cost efficiency at the time (about 5-6 years ago). I'm sure there are newer/different/better models available now, though, but those should get you by with your setup.

jayson427 said:

2. Can I get away with running a 3inch downpipe and 2.5 inch all the way back?

Click to expand...

Like everyone else said, you can get away with it, but it's not ideal. Either upgrade to a 3" exhaust, or use a 2.5" downpipe. I believe the S20G has a 2.5" turbine outlet, so you won't necessarily be gaining a lot by switching to a 3" exhaust.

jayson427 said:

3. I have arp head bolts but do I need arp rod bolts or anything else?

Click to expand...

Eagle rods usually come with ARP rod bolts. I have ARP head studs and stock TTY main bolts. ARP main studs and exhaust studs would be nice, but that gets expensive quick.

Would my head lift if I have stock head studs? Because I only have arp head bolts. Which I just got my head redone and didn't think about doing that.

My concern with the exhaust is having to much back pressure with stock ports and my egt's getting to hot. So I'm unsure of that.

I'm definitely leaning towards the tial Wastegate just not sure on the bov yet.

You have ARP head bolts or stock head bolts, or ARP head studs? Little bit confused...on the EGT issue though, Hahn rated this system at 210ish on the factory exhaust system, like others said it is recommended that you upgrade the exhaust but the 2.5 vs the 3.0 I don't think would be an issue with them. If you where going for 350whp on the stock exhaust then it would probably be a concern. Another contributing EGT issue would be cam selection, are you going to be running stock cams?

Please explain your EGT concerns more thoroughly.. I monitor my EGTs both up- and down-stream of the turbine, so I can probably help you

Right now I have arp head bolts, stock head studs. I'm running Crower stage 2 3/4 race cams.

I would be happy with 300whp because I know traction will be an issue. My motor is 10.5 compression with stock ports on the head. My exhaust feels like a 4 stroke dirt bike, at idle it's got a lot of backpressure. So I've read that to much back pressure will kill a turbo.

I don't know if I can make the switch to e85 and 91 is what we have in Arizona. So that's my concern I'll have to much back pressure/ drive pressure. I'm unsure of my static compression too. I've never had a turbo car so it's all new for me.

jayson427 said:

Right now I have arp head bolts, stock head studs. I'm running Crower stage 2 3/4 race cams.

I would be happy with 300whp because I know traction will be an issue. My motor is 10.5 compression with stock ports on the head. My exhaust feels like a 4 stroke dirt bike, at idle it's got a lot of backpressure. So I've read that to much back pressure will kill a turbo.

I don't know if I can make the switch to e85 and 91 is what we have in Arizona. So that's my concern I'll have to much back pressure/ drive pressure. I'm unsure of my static compression too. I've never had a turbo car so it's all new for me.

Click to expand...

You can pretty much bet that you don't have "high backpressure" on your NA setup, especially at idle.

Consider that many factory turbos are subject to drive pressure ratios of nearly 3:1, even at lower boost. at 15psi boost, that would make for 45psi drive. A 14B for example, at high rpm and upper teens for boost could easily be >2.5:1 on most setups.

So that tells me what? Still doesn't answer my question or concerns. How can I find out what my pressures are? I'll have to post a video soon and see what you guys think of it.

No need to be rude, guy. That post should tell you those concerns are misguided and the focus would be better spent elsewhere.

The only way to find out what your drive pressure is.. would be to measure it. Like myself and several others do.

At this point though I'm not convinced you would know what to do with that data if you had it though. You keep mentioning "stock ports," like that's some sort of issue too. It's not.

You're only looking for 300whp? You say you've got a built block already? Find a turbo that can move the air you need (hint anything from a 14B on up can do this) a way to tune fuel/spark, and get to work!

You're over-thinking this, and not in a good way.

Not being rude it's just hard to get any answers in this section because Alot of people could care less about a 420a. I appreciate your time and input.

But my first post says I'll be running a 20g turbo. Already have it along with other parts. Ultimately I'll be running megasquirt but I might try to get by with my safc2 and sfmu.

You're right I am over thinking this but I want to do it right the first time and not be rebuilding my turbo or motor again. I want to start out with 10psi.

You know Alot about turbos I know that. I just need it to be broken down a little bit so I can understand. I've been told different things about my set up hence why I made this thread to set it straight with my concerns.

I used a 14B as an example that would do it, even with the small hotside creating that would have "high" drive pressure.. T3 20G? Only 10psi.. no real drive pressure to worry about unless you have a drinking straw for an exhaust system.

If you want to do it right.. erase FMU and SAFC from your vocabulary.

Of all the things to do right.. a proper solution for fuel and timing control should be your number one priority.

Alright thanks man appreciate it again

Nice. so your deciding to come to the boosted side.

Jason had been wanting to for a while now, just finally gaining the courage to do it

Yeah he mentioned that when i talked to him last. Going boosted gives u more bang for your buck if done right. I recommend it to everyone.

If only courage equaled money I would of done it ten times over by now . I have a wedding in June so it's been hard to buy parts.