427 engine (part 2) - RHS block - Page 71

Bob K · 01-26-2011, 04:31 PM

Quote:

Originally Posted by Rich Z

I'm talking to Vernon Hills at STSturbo and he recommends that I put two wastegates on the car. Aaron agrees if I want to go to 10 lbs of boost instead of the stock 6 lbs

Rich, I just can't express in words how badly I feel for you.

If 6# of boost will work with one waste gate I think that's the route I would go. On my '87 Buick I think the waste gate was mounted with the turbo so I don't know how one waste gate controls two turbos.

I would think with 6# you would have way more power than you'll ever be able to use but maybe you have some facts that show your power curve would drop dramatically and in that case I would go with two. Just my thoughts.

Hang in there cause it has to get better.

Bob K · 01-26-2011, 04:35 PM

Quote:

Originally Posted by Rich Z

I just asked Bryan at LME about the max boost that block could take without getting close to the ragged edge of tuning and he said it could take 25 lbs. Figure on a max of 1200 rwhp.

If the turbos will only put out around 13 lbs when the wastegate fails, then I'm thinking that perhaps I don't need the wastgates at all. I'm guessing they won't be cheap, and if I want to go with 13 lbs, then why bother with them?

Anyone able to poke some holes in my logic here?

I'm lost. I thought the waste gate got rid of excess boost. Don't you have to have one?

shakedown067 · 01-26-2011, 04:37 PM

Quote:

Originally Posted by Bob K

I'm lost. I thought the waste gate got rid of excess boost. Don't you have to have one?

I wouldn't run without one.

Bob K · 01-26-2011, 04:39 PM

Just found this Rich:

http://en.wikipedia.org/wiki/Wastegate

The primary function of the wastegate is to regulate the maximum boost pressure in turbocharger systems, to protect the engine and the turbocharger

**Rich Z** · 01-26-2011, 04:42 PM

Quote:

Originally Posted by Bob K

I'm lost. I thought the waste gate got rid of excess boost. Don't you have to have one?

On a stock engine without forged components, you have to watch the amount of boost carefully. Although I have seen some people push 10+ lbs through a stock LS6, it's not something that is recommended. When I specified what I wanted in the new engine, I stated that I wanted it to be able to handle SUBSTANTIALLY more boost than the 6.5 I was getting with that stock motor.

What a wastegate does is to allow you to set a point via a pressure spring that will bleed off any boost above a set value that the spring is rated for. This is to protect the motor from excessive boost.

The 427 not only puts out more air as exhaust, but it also DEMANDS more air into the intake. There was some question in my mind as to whether those turbos could keep up with the demand of the intake. From what I heard from Aaron, the boost reached 13 lbs indicating that the wastegate had failed. So I'm thinking that this might be the max boost that the system can deliver. Since the motor itself can handle a lot more, then do I really need the wastegates at all? Since I already had one, then I was going to keep it there and just put a different spring to provide 10 lbs. But heck, three more pounds won't be that big of a difference, and I could dodge the expense of the wastegates if they really aren't needed in my application.

This might be one of those things that looks good on paper, but not real good in practicality, however....

Bob K · 01-26-2011, 04:49 PM

Quote:

Originally Posted by Rich Z

On a stock engine without forged components, you have to watch the amount of boost carefully. Although I have seen some people push 10+ lbs through a stock LS6, it's not something that is recommended. When I specified what I wanted in the new engine, I stated that I wanted it to be able to handle SUBSTANTIALLY more boost than the 6.5 I was getting with that stock motor.

What a wastegate does is to allow you to set a point via a pressure spring that will bleed off any boost above a set value that the spring is rated for. This is to protect the motor from excessive boost.

The 427 not only puts out more air as exhaust, but it also DEMANDS more air into the intake. There was some question in my mind as to whether those turbos could keep up with the demand of the intake. From what I heard from Aaron, the boost reached 13 lbs indicating that the wastegate had failed. So I'm thinking that this might be the max boost that the system can deliver. Since the motor itself can handle a lot more, then do I really need the wastegates at all? Since I already had one, then I was going to keep it there and just put a different spring to provide 10 lbs. But heck, three more pounds won't be that big of a difference, and I could dodge the expense of the wastegates if they really aren't needed in my application.

This might be one of those things that looks good on paper, but not real good in practicality, however....

OK, now I get it. I guess you have to know how much boost they'll put out and maybe a gauge so you can keep an eye on it. I have not had one since '87 so I don't know anything about the ones you have. I'm thinking twin turbos put out way more than 13#.

**Rich Z** · 01-26-2011, 04:58 PM

Quote:

Originally Posted by Bob K

OK, now I get it. I guess you have to know how much boost they'll put out and maybe a gauge so you can keep an eye on it. I have not had one since '87 so I don't know anything about the ones you have. I'm thinking twin turbos put out way more than 13#.

It depends on the engine they are hooked up to. "Boost" is the amount of forced air that the turbos can deliver over and above what the vacuum of the engine is trying to pull into it. The more air the engine needs, the bigger the turbos have to be, or the faster they have to spin, to keep up. I have the smaller turbos on the car because I prefer faster spooling over higher top end HP. I wanted the power band to be closer to where my "more spirited" driving would be rather than focused way up in the high RPM ranges. So I'm thinking those turbos just might be maxed out at 13 lbs. What would really need to be done is to run the car on the dyno and see if the boost started DROPPING at the highest RPM range. That would mean that the engine got to the point where it started needing more air than the boost condition could supply. Which as long as it didn't drop the boost down to zero, then that would probably be OK. I don't plan on spending very much time driving the car reving above 6,000 rpm anyway.

RevXtreme 1 · 01-26-2011, 04:59 PM

Dual waste gates are a must IMHO.

Here is a thread on a custom twin turbo I just finished. Had to fab EVERYTHING as there are no kits out yet. Really turned this V6 car into a beast:

http://www.camaro5.com/forums/showthread.php?t=125470

**Rich Z** · 01-26-2011, 05:01 PM

Quote:

Originally Posted by RevXtreme 1

Dual waste gates are a must IMHO.

Ok, but WHY? If the max boost produced from them would never go above what the engine is capable of handling, why would they be needed?

RevXtreme 1 · 01-26-2011, 05:18 PM

It is an extra saftey feature and not that much more $$ to do. Each turbo is fed by your exhaust on the side the turbo is mounted. Having one on each turbo with one controller "T"'d to it will bleed exhaust quickly form each turbo. Now I know that both feed into one intercooler so it can be equalized there before it reaches the intake, but at the turbos allows each to bleed off as needed right there.

If you look at the pics of the V6 kit I just did you can see (mid-mount turbos) where each is. I used 56mm turbos on this which is overkill, but the owner wanted slower spool-up to save on the tranny shock at launch (no aftermarket hard parts for the tranny out yet) and wants it to build from 3k or so RPM and up to 7K. No boost fall off with it.