Hey guys I'm really confused on this turbo stuff. I'm going to bore my slant .060" over and run forged pistons(if I can find any geez), I'm going to put in oversized valves(1.7" intake, 1.44" exhaust) with a .430" lift cam. I'm planning on running a 4bbl intake with a Megasquirt EFI system using the Autonomics 4bbl throttle body which flows 700cfm. currently I'm confused on what size of turbo I should be running with this system? I read aftermarket gaskets have a headgasket squish of .040" whereas the stock was .020" so I'll probably deck the head maybe.040" for a bit of a compression ratio bump but I want to try and stay around 8.5, I figure thats a good place to stay so I can run bigger boost. Oh also will be running ARP studs in the rods, crank and head.

A lot comes down to how much power you wish to make, and what kind fuel do you wish to make that power on.

One thing, if you get forged pistons there is a good chance you want have to worry with the head gasket thickness, and head milling to get the compression you want.

More than likely if you go Forged pistons, its going to be a Venolia piston. They are about the only company that makes them for the /6. Although they are a very good piston maker, so no worry there. They probably would not have them instock though, and will have to make them. But they do have a piston Design for the /6. That is a good thing though, you can probably get them (Venolia) to make small ajustment on the piston to meat your needs. Like compression, or how far down the top ring land is (it helps to have it down farther to cool it in a forced induction engine) , and even the Dome/dish of the top of the piston. So I would not go cutting the head for gaining compression until you have pistons in hand and know what compression you can achive with what ever combustion chamber CC you have.

Also the difference you are probably hearing about in the head gaskets is the diff between the factory Steel Shim gasket, which is around .020 thick, and the often used Felpro head gasket, which is around .040 thick.
You can still find the Factory Steel Shim gasket, although it may take a little bit of looking, many people still have them on the shelf. There has even been some of the members here that have them left over that may offer to sale. The steel shim head gasket is a very good gasket to use for forced induction, but the Felpro or other paper gaskets can work good also. SO no real worry there on a gasket. As far as a gasket that want blow when running a Turbo, it comes down to tuning more than anything. A gasket that can blow easy can even save you from blowing the engine because it will let go before you damage the engine (like burn a piston).


Now back to the turbo, what size? Like I said a lot comes down to how much power, at what boost level, at how many RPM's, and what kinda of fuel you wish to run.

I am going to assume that you will be street mostly, and you want to make all the power you can without having to run race fuel all the time, or worry about destroying the engine very easy. The turbo choice can have a big effect on how this all comes out.

Right off, I really would not run anything smaller than a T61 T4 turbo. You can run smaller, but your really dont get what you need, and you become very limited on Boost & RPM of the engine, which in turn can cause tuning problems, blown head gaskets, and low power for the work put into the build.

The funny thing about my "smallest turbo I would run" is, that it is big enough to fit most peoples wants & needs for the slant six. With the engine you described building you could very easy make 400hp on 91 octane pump gas with this turbo and mid range boost. No less than 350hp, but maybe even as much as 500hp if the system is effecient & tuned right. This would be on mid boost levels, maybe around 16 to 18psi of boost. You would also make a easy 300 to 350hp with just running 10 to 12psi of boost. A good intercooler & proper turbo manifolding & tuning can incress the level reached and make the 450to 500hp on pump gas possible.

Many things effect the outcome of the performance on a build like this, like the right compression ratio, exhaust, tuning, Manifolding, weight of car, trans & gearing of car, Tuning, how hot the engine is allowed to run, tuning, how hot the out side air is, tuning, having the right size injectors, oh, and did I meantion the tuning.

Also this same T61 T4 turbo, if you did achive lets say 450hp with it running on pump gas and 17psi of boost, then if & when you wish to (and you will want more power latter on) you can put race fuel in the car, and then turn the boost up more & make as much as 650hp ( a Perfect setup may reach 700hp out of this turbo) and a very few exceptions have made even a slight bit over 700hp using this size turbo. But in the real world, you know, yours & mine, 650hp with race fuel & max boost with great tuning is what could be expected. And probably around 425hp with the 91 pump gas fuel and the 17psi of boost.

One thing to remember with turbo's, it does not have anything to do with BOOST. The amount of power made, or how much your engine can stand, Does Not Have Anything to do with Boost PSI levels. What boost level is, A measure of the resistance that your engine has toward the air pump (Turbo) that you are running on it. And 15 psi of boost from one turbo, is not the same as 15 psi of boost from another turbo.

OK, the T61 T4 turbo, IMHO is a very good match for someone wanting a good,powerfull, street/strip combo setup. It is small enough to spool quick enough for the slant six, and big enough to run cool enough, to be effeciant and make a pretty good level of power. It is also a good priced turbo, maybe around $800.00 for a good Garrett based turbo with journal bushings. You could step up to a double ball bearing unti for about $1100.00 and have even quicker spool and a little more efficiency.

This turbo could get by with a pretty tight stall convertor with street driving, ofcourse the higher stall you have the better the turbo will spool. But things like this is one of the reason why I think a turbo this size is one of the best all around turbo's for most people on the /6.


The next step up would get into a bit more money, a GT6776r or a GT4088r would start getting a bit more serious for a turbo. This turbo is going to want atleast a good 3000rpm stall convertor. But it is of new design and will kick ***. The low & mid boost performance would be a little more than the T61. Maybe be able to make a easy 500hp on 91 pump gas because of its efficieny from being a bigger size. But when you throw the race fuel to it & turn the boost up, very close to 800hp ( or even a little more) can be achived on the right setup. With the restricted head of the slant six (even with bigger valves), the only way to incress power is to turn the boost up higher. These turbo's can to it. And for the utmost baddest street/strip combo, this would be the turbo's to do it with. The GT6776r would be my choice because of price, and rebuildablity. Around $1300.00 for it & it can also be setup with a internal waste gate which can make install & price a little better.


To go any higher than this turbo is going to getting into pure racing setups. It can be done but probably no reason to get into all that for now. There are also turbos in between the two I have meantioned, but not much reason to really consider them unless you get into really trying to maximize a curtain setup. For the most part one of the two should fit the need quit well, and then some.


Building the proper intake, and header can make achiving these levels of power I meantion very possible. Also you must run enough injector if EFI is used. For instance with six injectors and the T61 turbo, a set of 60lb injectors is the very smallest you could run . I would use a 83lb myself and if I thought I might even begin to think about a bigger turbo latter on then a 95lb injector would be needed. The 83lb injector would be the very smallest to run with the GT6776r or the GT4088r, the 95lb injectors is what I would really run again. This is with 6 injectors. With one of them throttle bodies with only four injectors was used it would have to be refigured. Dont let anyone tell you any different on injectors either, I havnt seen a turbo engine build on this board yet that is running a proper injector size for the turbo. And then they wander why they can get it to run without detination.


A lot could be talked about with your build, even in the bottom end of the engine & its needs, the head and its build also. But you must look at your budget & your true expectation & be honest as you can about it, before you even buy the first part. I will help any way I can, in fact if your not real big on getting it done in a hurry, I might be able to offer some help with parts here in the next two months. Even before then I could piont you to some very good venders of things needed.

Research it, draw up a plan, then build it.


Jess

I just contacted Venolia this week. $60 per piston for a general flat top that copies a stocker. None on the shelf.

Well my goal isn't as much hp as you said. I am willing to spend what it takes to get a good engine and good experience with turbo's. Like I said I'll probably stick with a basically stock bottom end and run the factory forged crank and rods, with the venolia pistons. just basic flat tops. Like I said I'm not looking for huge power just a fun little engine that could show a V8 a run for it's money.
the efi I'm planning on running is a megasquirt system with a 4bbl throttle body:

It runs 4 injectors I could run 6 but that would require jumping up to the brand new v3.0 megasquirt and I'm not looking for that precise of engine control.
I'll probably go with that T61 T4 if that is a good one for my build. I'm thinking of going with roller lifters as well.

What kind of intake do you think I'm looking for? I was just going to buy the 4bbl intake and header combination from clifford but if theres something better out there let me know.

I am on a limited budget for the motor. I really don't feel like spending a ton more then maybe 3 grand on just the motor, I know turbo's are kind of pricey but I figure I could get a decent setup for like 2 grand.

Also do you think I can get sufficient cooling running the intercooler behind the bumper? seems like a pretty easy place to put it. not sure where else I could put it other then behind the grille. don't know if it would fit.

another thing. What size exhaust pipe should I run? I'm thinking 3" that goes into a single into dual muffler and 2 1/2" after that.

Your on the right track here for sure. IMHO, it would be just as easy to do a multiport system as to use that throttlebody. One thing you will have to get pretty big injector for that to feed the system good & that can get you into low Z injectors and make the system more costly & complicated.

With a multiport you could use 60lb high Z injectors that are made for Buick GN's and the cost is only $285.00 for 6 injectors. This would work very good with the megasquirt, but you would have to build a fuel rail & mod the intake which is not that hard if you go about it right. The economy & idle would be much better to, plus better fuel distribution for a much safer tune for the engine. The newest Clifford intake has EFI injector bosses built in that only need drilled. You would have to call Clifford though to see if they have it in stock because if it is not in stock it could take several months to get no matter what they tell you.


The T61 is great for your intent. With the power level you wish to achive you could skip the intercooler to help cover some of the cost to go multyport and make the system easier & cheaper to build. You would still be able to run a easy low 13's to mid 12's second quarter mile on pump gas, and then throw race fuel to it & run low 12's to low 11's depending on how the car is setup. Use a turbo that is made for the Buick GN and you can use the built in wastegate instead of having to add a external gate & this will save even more money. Plus you can always add the intercooler latter if the budget allows.


A 3" exhaust is all you will need, no use in dividing it up into duels. Infact you can get 3" exhaust for your car that will work quite easy from TTI header company, all you would have to do is run the down pipe back to it at the crossmember. The headers you meantioned may not be able to work, you just about have to use the stock manny or build a header for the turbo.


Many of the things we are talking about here I am working through right now myself. I will be a bit busy today but I will come back with some links and other info. I plan to call Clifford myself here in the next few days and deside if I am goingto build my own intake (which would be much like the ones sold for Toyota Supra's from the aftermarket) or use there intake. It will cost me more to build a intake, but it would fit and work better and part of the cost can be offset with a cheaper throttle body & ease of plumbing to the turbo. The availibility of the Clifford will have a big effect on my choice here.

Depending on your budget, you might also consider a Holley carb for your build. But getting a better idea of the full cost will help to piont you in the right direction. Like I said I am digging through much of this right now for myself to figgure out which route would be the most cost effective . I think what you are wanting to build is right inline with what many /6er's are wanting. As far as engine you dont need a all out build, just a good sound bottom end and a head that breaths pretty good will make a lot of power. Infact I intend to do it with a basic stock bottom end with just maybe ARP bolts & good rings, maybe even with the factory pistons if I have a set in that good a shape. I will PM you with some more info in the next few days.


Jess

sounds good thanks. i'm thinking of running an Offenhauser intake instead of the clifford one. I'll be buying a slant six exhaust flange from clifford(they still sell them for 50 bucks)

Anyone know if the stock rods are forged? I know my crank is but I'm curious if the rods are to.

I'm looking at dividing up the exhaust tubes just because then I can use the stock looking exhaust tipes for an even more sleeper look.

I'm not certain if the megasquirt world work well with 6 injectors it's really only meant for 2 or 4.

Stock rods are forged steel. While not the toughest rods you could possibly have, they'll hold if the motor doesn't ping.

While some of the wiring diagrams for Megasquirt only show two or four injectors, it's quite capable of driving 12 or more injectors. Six is no big deal, especially with a V3.0 or if you're running high impedance injectors. A V2.2 with low impedance injectors (like what I have on my Dart) would need injector resistors (I grabbed a resistor pack off a Toyota Cressida since I'm using Supra injectors) or a flyback board, but it can still be done.

_________________
"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Lucky, I found this info on a Turbo Coupe site

"-T61: Great for engines in the 400-600rwhp range. Full boost at 4000rpm or so with a header and supporting mods. Great for serious street cars or drag cars in the 9-10 second 1/4 mile range. Can handle upwards of 40psi."

They make it sound like even the t3/t4 hybrid doesn't come into full boost till over 3000 rpm.

The more I think about all of the conflicting info the more confused I get.

Lucky, you really sound like you know what you are talking about and you are very consistant in your responses. Don't take any offence to this but what experiance do you have with turbos? Is it real world dyno and dragstrip or are you just book smart?

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Chris'
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If it's on a Turbo Coupe site, they are probably discussing its application on 2.3 liter engines. It'd spool earlier on a slant six.

_________________
"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

So you are saying that a larger CID engine will allow the turbo to spool earlier than on a smaller CID engine?

What effect does the RPM range have then? If slants make their peek power at a lower RPM than a smaller, high reving engine does what else needs to be considered?

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You need to consider the total airflow demands of the engine. Predicting spool up time is a royal pain, but you can plot the amount of air the engine needs for its intake side. Then you'd find a turbo with the compressor side that meets the air flow demands you have. Really it's best to get a book that explains the process if you don't have examples of the turbo you're considering on similar engines. I'd recommend picking up a copy of Maximum Boost, Turbochargers, or Street Turbocharging - they all cover the process fairly well.

_________________
"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

So before a turbo is picked a person should really have the head flowed, cam picked, etc. I suppose that the intake needs to be taken into consideration also?

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Chris'
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You don't need that much work; you mostly just need to have a rough estimate of the engine's volumetric efficiency and the RPM range in which it will operate.

_________________
"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair