Inliners International Forums General Discussion Hi Performance Turbo charging a 292 chevy

I have read many helpfull hints on turbo charging. I am a lobsterman here in Maine. I have a 30 wooden lobsterboat with a 292 (fresh motor) I have a turbo charger from a saab 900 80s model. I have fabricated all the plumbing. I guess I will start with 8 lbs of boost, work from there. I am at the point of the carb and timing and cam. From what I understand the stock cam is ok, not the best but I am on a tight buget. I have a 1 bbl rochester, I can get bigger jets, but can it handle boost pressure? What do you guys recomend for timing, from what I understand 5-8 degres retarted is good, where do you dump the oil return back into the block, I was thinking a fitting drilled into the pan? I can assume h20/alachol injection will be a must. I also found dawesdevices.com has a great fuel/air sensor for like 50 bucks, just wanted to share this, a must so not to burn valves. In a marine application, the engine is under constant load, like going up hill allday. What affect do you think this constant load will have on my set up? What a great site! you can e mail me hodgdonbrett@yahoo.com THANKS!

My first warning to you is about the type of air/fuel ratio meter you are going to use.

DO NOT USE IT!

I looked at dawesdevices.com and went over their aif/fuel meter and it is based on a "narrow band" o2 sensor. These sensors are not analog sensors. They are essential binary. It's voltage will tell you wether you are rich or lean and other than that will tell you almost nothing. A true "wide band" o2 sensor has a voltage that varries with o2 air/fuel ratio burned, usually from 0-5v.

With a narrow band you can tell if you have 14.7 or not (the switching point) and nothing else. This is why they are commonly used, because they are good for cruising and idling. Which is emmissions territory.

I recommend you grab a few books and do some more research on turbo charging. What you want is doable, but it will have to be done right because turbos are very capable of destroying engines.

I think the rochester will have to do. Wether you blow thru or draw thru i don't think it has the capacity to supply that much fuel plus enrichment. But I'm not sure on this.

The oil has to be returned to the pan. Anywhere is good so long as it is NOT submerged by the oil in the pan.

The constant load makes a difference in approach. You have a constant supply of cool water and that is PERFECT for air/water intercooling. 8lbs of boost is a fair bit for continuous duty. Have you considered something more like 4 or 5 and excellent intercooling? This would probably yield the same power but with less strain on the engine. Better all around really.

Thanks Greg! Do you know where I can get a sealed carb. In other words one that will not leak when pressurized, although @ 4 or 5 lbs I do not really see this being a problem, I just do not want fuel leaking out of the accelerator pump are and the float. I can set the wastegate for 4 lbs easy enough, what inexpensive way would you manage your timing? I hear you can get away with retarding it a few degres. I will only turn 3500 rpm maybe close to never 4000 rpm, mostly I will be cruising @ 2800 rpm or so. Turbo lag is no concern for me in this marine application. Are you fimilliar with a design to increase fuel pressure only during boost, not @ idle. I understand a holly makes a regulator and I can make a pressure activated switch to activate it during boost. What is exactact O2 sensor you recomend for this application? Have you done this before? I am not looking to double the HP just gain a few x-tra ponies. Thanks!

I've heard of richening the mixture using boosted pressure on EFI systems but I'm not sure I've ever heard of doing this on a carbed system. I would think you'd just overwhelm the carb and would just be dumping in fuel, not metering it in any way.

I guess I'm kinda useless. I'm going for a custom manifold, EFI turbo setup with computer controlled ignition. I've heard of getting after market vacuum cans for HEI's that do retarding under boost as well as advance under vacuum. That might be worth looking into. Other than that I can't help a whole lot..........

hey Greg? I think you know more than you are letting on...usseless...come on now! Dumping the fuel from what I understand can be acheived with a holly blue pump with a pressure regulator activated with something as simple as a converted mechinal fuel pump with a smaller spring hooked with a vacume line to activate the regulator, so the system does not run lean. You definetly know what you are talking about....tell me what make O2 sensor to use...you are right need a sensor with more voltage gain and reduction to monitor..here is a guy that turboed a 173 ci flathed http://cancermn.net/TS/TURBO.html his trial and tribulations real grassroots hotrodding. I already have a manifold and plumbing lets talk fuel and carbs...the timing is irrelevent with the boost your recomend 5 or so...I think you are right with continous duty...after talking with you I will utlize the ocean H2O to cool the fuel and air, will use a boat heat exchanger, cool it with ocean H2O. I would ideally like to put the carb befor the turbo, I just dont know where to dump the wastegate, seeing how it will be full of fuel, turbo lag is not an issue here.....any ideas, I just don't want to develope a leak in the carb and dump fuel on my exhaust manifold, although on 5 lbs of boost I do not think this will be an issue.....keep talking Greg

Well, I like to be careful when I'm advising other people. Especially since I haven't actually built a turbo conversion. But I am in the process of building one, and I've read a lot of material online and in books so I suppose I can go a little further.

Intercoolers are really important to turbo systems. Low heat in the intake means greater charge density; same idea as a cold air intake but on a bigger scale. I would be you can make the same power with 4 or 5 lbs intercooled than 6 or 7 lbs non-intercooled.

Most car intercoolers are limited because of size constrains and the need to limit intake volume to reduce lag. You don't have either limit really. You could plumb in a fairly big air water intercooler and get good results without worrying about lag.

Now, the intercooling will not work with a draw through system (carb feeding into turbo). You know how starting and driving is hard when the intake and engine is cold? That's because the fuel vapor condenses on the intake walls and cylinder walls and anything cold as it goes though. Now imagine how much will condense inside an intercooler. Add all that tubing and the fact that it won't be all down hill to the engine and you get puddles of fuel in the intake tract with no where to go. A very dangerous intake setup.

I would do it blow-through if I was going to do it. Big intercooler, feeding up to a enclosed box for the carb. The box wouldn't be too difficult because you've only got 4 or 5 lbs. Blow off valve before the carb so you can dump air and not worry about fuel.

I say a box because from what I've heard it's easier to enclose the carb often than to go for some kinda of sealed carb system. I'm not sure though, so this is worth looking into. The only bugger I see is the throttle shaft sealing, not sure about that.

Since you're not talking about a lot of boost either you should be able to setup the timing without any extra parts.

Returning to Brett's opening request, the most simple of the options is a suck through for several reasons including no need to rework the carb, still got vacuum and no fuel pressure problems. Maybe even use stock ignition.

I have done this conversion on a 250 and it has taken several years (this isn,t my day job, fortunately) to realize the errors of my ways. If cost is a problem, get a kit from Turbo City in Santa Ana, CA (I can't find the web site address), use a suck through design and use the stock exhaust manifold. The kit comes with a GM computer and a harness. They are very accomodating and will program the chip for your application. Do not use the Buick turbo, you can get more HP from carbs, ignition and kicked up compression, the compressor is completely wrong. Get the correct turbo for your application. I think Turbo City has rebuilt units. Pay the bill and get it done. It is worth it in painfull problems. Good luck.

Brett,
I remember in an old Super Chevy(?) an article on modifying a Holley regulator so it was referenced to engine vacuum.
It was fitted with a hose fitting on the diaphram side and a hose run to the intake.
High vacuum gave low fuel pressure, low vacuum gave full pressure.
Might be able to do what you want too.
Disclaimer: I have a suspicion I'm forgetting some important detail.

Q: Do you have to use a marine carb on your boat?
Any Coast Guard regs for turbocharged engines?

hey thanks for the advice, do you have a holly part number for the fuel regulator? I have found an electric one from JC whitney I was thinking of using...not sure...would like to have a vacume regulated one though...do you have any carb sugestions?

With the Holly regulator it will need to see boost pressure to increase fuel pressure, not low vacuum.
Just a small correction.
The vacuum/boost hose will tap into the top of the regulator.
Hope this helps.