mos90

i have a 396ci 11/1 cr brodix t2215heads cam 250/262@.050 .650 lift 112 lsa.. fast xfi. dynamic c/r 8.8/1


decided to go with custom turbo install... in the process of building a 383 8.5/1 but for the mean time im gonna use it on my current motor.

not sure if twins are the way to go and a larger single.

was looking at a garrett 42r bb..74mm . ive decided that 1000hp at the fw is plenty lol..

or maybe 2 57mm turbos. not sure..


my motor now puts down 490 rwhp. so my goal is to boost maybe 10psi and shoot for 650-700 rw with this motor and 750-800rw when new motor is done..

id like some of your opinions...

mn_vette

Single vs twin will depend mostly on where you can fit them. I'm sure BTF will have some good suggestions on what to get for either setup.

As far as boost goes, I'm not sure I would run more than 6psi on your compression. It would be good enought to feel the turbo setup out and work out the kinks until you rebuild the engine.

And you'll really want to change out that cam.

mnstrlt1

I am curious to know the reason for stepping down to a 383 instead of sticking with the 396 with low compression pistons?

93 ragtop

My understanding is, a low compression 396 piston has to have the pin located up in the ring groove area. This is not good for a FI motor as it can allow for blowby easier.

mos90

yes. this is true. cant get the compession low enough even with 74cc head. i think a -16 dish is the lowest i can go. maybe 9.8/1 without going to a .070 head gasket, and i dont think thats a good quench for a turbo setup.

also, if i understand turbos correctly, more displacement= larger turbo to make boost. this usually means more lag.. correct me if im wrong.

i plan on leaving the cam in for the time being. dont want to start ripping things apart while new motor is being built.. it still should make good power with that cam.

AKS Racing

Shorter rod? 5.875" vs 6.000". I agree, a very thick head gasket is not the proper route for a force fed engine. Quench (target 0.032 - 0.042") is quite important for any engine that is susceptable to detonation.
Aaron

Baldturbofreak

hmm thats an awefull lot of cubes to feed for a 42. If it's a front mount you will be stuffing the tubine soo hard, you'll have exhaust valve float issues.
Even out back a 396 thats almost 500whp NA will be restricted up top by the smaller turbine. IF your all about power below 6K I guess it will be alrighty. We'll have to double check using your flow data against the compressor map.

I think if a single is what your all about you should be around the 81mm+ mark for that motor combo. Esp with that cam, the 112 will require very low turbine inlet pressure to be effective (big *** turbo)

IMHO
it should have a GT4718R out back, or a GT55R out front. That would keep you well out of choke and make for a very powerful car.
Or if twins is your game, pair O GT3582R's or my personal fav thats going on my own car- Rockin a pair of GT4094R's. Up to 1680+FWHP without being a laggy turd, or a hyperactive freak.
Just smooth,punishing torque from 3500 until 8Krpm.

Want the second pair of headers off my jig.....?

Baldturbofreak

Bigger motor, high compression = more tubine impetus= earlier threshold.

A motor with too small a turbo will spool the instant you open the throttle then fall off as the cmpressor cant keep up wiht the air demand.

A motor with too big a turbo will act like an NA motor for the most part until boost threshold. Then it will pull long and hard up top.

What size to use really has more to do with proposed HP, then we look at compressor/turbine size to make sure it will be a good match in the proposed engine rpm range. Then it's jsut a matter of how much pressure is required to stuff the mass flow for your HP target thru @ your rpm peak.

mos90

i shift at 6800 rpms. can turn more if i wish but starts to drop off about 6700, but still make good power to 7400..

i see you mentioned something about a extra set of headers.. what are they for twins or single.. and for what year vette.. i dont have a/c so thats not an issue.. email me a few picture of your setup so i can see the layout.. if you dont mind. mos90@twcny.rr.com

i guess we can talk about other components after i figure out a combo.

another question, will a journal bearing turbo be efficent or is bb that much better?

the guy that is going to do most of intall said he would like to use an 88mm bb turbo. but ill mention the 55r..

lcvette

for that rev range I think for fitment and his power goals I would use a precision PT88, this has a nice sized turbine and is proven to be a killer on the 402-408 LS1's, not laggy and makes good clean power through mid to high 6's. packaging that unit is MUCH easier then the garrett units as they have smaller housings. Anti surge housings on that size cubic inch motor are really kind of wasted anyways and hurt compressor efficiency as far as flow is concerned.

as for the proposed motor of 383 cubes.. a few things I would consider is your cam selection.. that monster you have in there is way overkill for a turbo motor, and unless you just like to rev to the moon which is hard on parts? making incredible power with a turbo does not require use of a gigantic cam shaft so downsizing that bear of a cam will help driveability and not take away from your power potential.

motorwise I say this alot to all I talk too... even the 383 in my opinion weakens the piston too much for 1000hp... and a 3.75" crank with a 5.7" rod is kinda ..well...not my favorite combination, not saying it doesn't work but I prefer a more vertical rod angle on the crank from a longer 6" rod.

this being said.. my motor of choice is the good old 355 3.48" stroke and 4.030" bore.. call Ross, they built some pistons to my design request for "alottaboost" extra thick top ringland, dish milled further from edge but a little deeper in center to maintain the ringland material thickness, light weight in the right places and designed to yield a 8.7 SCR with a .035" cometic head gasket and a 62cc chambered cylinder head. Notice what I am trying to keep strong??? this is the number one failure point for boosted engines is the piston ringlands from detonation.. unfortunately even as safe as we try to be in our tuning, it still happens and when it does this adds a little room of forgiveness so we may correct and try again.

the boosted community is a different world, here we make up displacement with boost. the old adage holds true though.. no replacement for displacement, but... that means more torque (traction problems) down low or oversized ridiculous turbos which break the bank and make packaging require a complete redesign of the engine bay.. for your goals with good flowing heads a nice sized cam, a 355ci motor and a 76-78mm turbonetics unit or a precision PT76GTS... there are some other units available as well but these turbos will easily hit your 1000fwhp mark and have great street manners to boot!

get ready to start gasping when you put your fuel system together

Chris

69427

Can you expound a bit more on that?

Baldturbofreak

Speakin of which chris I think I still have a wiped out turbo of your somewhere....
I agree onthe 88mm. PT's do package nicer than this one will Rock & Roll, but smaller housings create a tighter Caudual and flow loss's accompany them from the separation caused by it. If you can fit the big housings, use em. It's always worth power.

Ballbearing will withstand much more abuse as in
2 steps,
stick cars
crazy boost with the above
but the wont drop the boost threshold that much. transient response (say from a gearshift) cant be compared though. Lightening quick.

Baldturbofreak

Turbine pressure will be so high that the valve will hang a bit as the piston starts traveling back down. Backflowing inert products into the ever increasing volume(from piston travel) until intake pressure can overcome. you'll find alot of carbon in the intake port.

Ask Brian (MNvette), he was having just a mother of a time with TIP. not to long ago.

mnstrlt1

ICvette, Please fill us in on fuel requirements for a 1000hp package. Not to mention the tuning needs (I assume a stock ECU will no longer be sufficent in an application like this one?).

I agree that any more low end torque (and really any more than stock) just goes up in smoke. In fact, in a combination like this one, i would be more than happy loosing a little low-end to make crazy mid-and top-end. Only because you'll be moving, thus making use of the power.

mnstrlt1

I was curious to know of any of the aftermarket blocks (like world products or merlin) would be able to support big boost applications but still have the benefit of huge cubic inches?

Baldturbofreak

Personally I wish I had spend money elsewhere when it comes to the crankshaft. To get a 6" rod and 8.8-1 I had to have a 37cc dish and a funny-*** ringpack.
The extra 33 cubes wernt worth it unless you were buying a little M or the like and are going for the bore instead.

I jsut used two walbro255's with the relifes plugged, right inside the tank. But I can also accelerate the fuel away from the pickup with ease unless the tank is 3/4 and above. That sucks.
If I do it again? 2 words Belt-Drive

lcvette

Well said on the back pressure issue... basically in laymen’s terms, the exhaust wheel is too small to flow enough at higher rpm/boost pressures from sheer air movement.. It corks the motor up as a 2" single exhaust would on a 502ci big block race motor so to speak..

so using a larger flowing exhaust wheel on the turbine side of the turbocharger reduces backpressure pre-turbo but will unfortunately generate slower boost response (more lag) this is where turbocharger sizing and knowing what your building is pretty crucial.

too large and you will make nothing but peaky horsepower that hits so hard at the end it is fun for a bit but the uselessness of it gets aggravating.. too small and it will light up the tires off idle and nose over after your midrange. Sizing just right will give you good response, good midrange, and good top end.. but in most cases a full all around street car is better suited with a little bit smaller housing/wheel combination for instant response but one that may become marginal if you plan on running high revs. Just a matter of deciding what you want the power band to be..

a prime example is my 2.0L eclipse.. I run a GT4088R turbocharger on it.. it has a 63.5mm compressor inducer diameter.. I am currently close to maxing it out on my engine running right around 42psi and moving near 70lbs/min of airflow.. In order to make this much power (~700whp) this turbo was required.. the drawbacks are I don't see full boost until 5800rpm. While this sounds crazy in a corvette world, my power band on the smaller engine is 5800-9500 which gives me a very broad area under the curve to work with.. sooo for the street it is very easy to get caught with your pants down if a car starts toying with you and hits it, by the time you find the correct gear and drop the pedal, it still takes a few seconds to bring the turbo online.

When it comes online it is a menace to say the least.. But it has a very Jekyll and Hyde personality.. It’s either all or nothing.

In comparison, my vette (355ci) spooled a 74mm turbo MUCH sooner. I would see boost start in the low 2000rpm range with threshold at around 3600 (21psi) and pulled strong to redline... the time between hitting the pedal and having full power was a fraction of the time as with this 2.0L 4 cylinder. so shifting the power band and onset of boost can be determined with the sizing of the turbo unit used.

why don't you give us your specific goals to better help fine tune a turbo selection.. getting close is fine and housings can be changed at that point to make smaller adjustments up or down. I like having two housings, one for street and one for long tall gear roll outs on the highway which net a higher broader power band... after all it is something else to get out and stretch the legs of a high boost turbo car from time to time!

Chris

lcvette

As for the fuel system... I have my eye on the new Fuelab pumps, DC Brushless motors which are fully compatible with straight methanol, ethanol, race gas, nitro methane.. Pretty much about any fuel type you throw at it. While methanol is hard on other parts of the fuel system and creates a generous amount of maintenance (not good to leave methanol in the lines for long) the new fuel us boosted people are turning to is E85, E95 ethanol fuel. While it takes more volume of fuel to achieve the same air fuel ratios using E85 or E95, there are a few very distinct advantages. the first being the obvious... ethanol when mixed with the same amount of air as gasoline and mixed to its proper Stoich ratio yields more power than gasoline, roughly 4-5% more power meaning by adding fuel you do actually get some results.

The second being that upon its phase change from a liquid to a gas, it has a higher latent heat of vaporization characteristic, meaning it cools the intake charge down (a dream for boosted cars especially in summer months.) This also has a second advantage which I will hit upon in the next section.

The third wonderful thing about Ethanol fuels (especially E95) E85 has an octane rating of 105, E95 has an octane rating of 109.. Hmmm now we're getting somewhere.. As we all know boosted engines are more detonation prone then NA motors. so now we take the higher octane rating of 105-109 and couple it with the wonderful phase change cooling effect and we can now go to a gas station and fill up with a fuel that is comparable in price to premium 93 octane gasoline, but net much higher boost pressure with a higher margin of safety and make more power from the fuel used all on its own to boot. Sounds like a no brainer right?

Now finally on to a fuel system.. The DC brushless motors in the Fuelab pumps will tolerate these new fuels (they are designed too) but more importantly, for the money they offer some serious flow capability even at high pressures which turbo/blower cars find useful since most regulators are boost compensating on a 1:1 ratio. while 6,7,8 even 10 psi of boost may not seems like an issue, people running higher numbers 20, 30, 40psi will see total fuel pressure requirements of between 70-100+psi. You must size your fuel pumps to deliver an adequate volume at these elevated pressures. if you dig a little you'll find that fuel pumps like to flow less as pressure rises. So making sure you have enough pump(s) is important. These get spendy fast when you’re dealing with 800-1000hp engines.

Next are fittings and lines...-AN, stainless steel braided, rubber or Teflon coated inner sleeve? When you start laying the system out and building a list of fittings and hose needed you start seeing the dollar amount climb rapidly. Most companies are very proud of -AN fittings and hose. This will add in most cases unanticipated expense as a lot of people always seem to think of big ticket items and the little items which add up quick are overlooked during the estimation of a build.

Next, the tank itself, As BTF stated, with that much power you can get the fuel level vertical in the tank and hold it there while accelerating.. This causes the dreaded pump starvation and fuel system aeration.. This can hurt your mill if not cured. a rear facing sump with baffles is really a good idea for higher end power levels. Don’t skimp on fuel.. It will cost tenfold to fix what skimping can damage. other routes would be a fuel cell but in most cases... staying as close to stock is important and the factory tank can be used with a sump if done correctly.

Moving on to injectors... a good estimate for sizing injectors is take your rwhp goal, divide by 10 and add lb/hr at the end. Next, see what sizes are available near this number. Preferably the next available size larger is a good idea. Example.
Power goal= 900whp
900/10=90+lb/hr
96lb’ers are the next size up this should support your fueling needs provided the pumps can maintain rail pressure and flow.

I would bump up to 96lb/hr injectors for some cushion. One might ask why not just get the biggest injectors they sell? Well, most injectors are either low z (impedance) or high z (impedance). Factory is high z which means the injector absorbs the heat from functioning. You would destroy a low Z injector without a resistor box in the factory system which is why they are sold, they bring the impedance delivered o the injector down and the box absorbs the heat. Low Z injectors work faster and are commonly known as peak and hold type. The quicker cycle rate generally helps to more precisely tune fueling.

Back to topic, when you get too large of an injector they tend to get lazy, don't react as quickly, they also have such a high flow rate (example 160lb/hr) that they are required to have a tremendously short pulse width to accomplish low rpm fueling. This begins to make part throttle drivability very tough to fine tune and you can often times have stumbling, hiccups, stalls and overly rich conditions which can't be tuned out. Now as stated before the newer ethanol fuels becoming available in various areas in the States require more fuel. If you plan to run this you will be able to increase injector size as the E85 requires longer pulse widths at the same airflow rate as gasoline. This will help get part throttle tuning back inline and more manageable.

So if it’s available and you think you might want to try it out (E85) take this into consideration. Stoich of E85 is 9.76 parts air to 1 part E85 Vs. Gasoline’s 14.7 parts air to 1 part gasoline this will need to be accounted for in your tune. This can be done by adjusting injector flow rate in the PCM in your current good tune to reflect the percentage difference or even using fuel pressure since the fuel demand is changed globally due to its nature.

Sorry for writing a book, went off a bit on a tangent, but the short story is the fuel system will need careful consideration to accommodate 1000fwhp!

Chris

mnstrlt1

thanks a lot Icvette.

I hear large injectors are not "street friendly". that you cannot "get large injectors to idle". So, this leads me to believe that high horsepower cars are truely not streetable (i.e. ability to also pass emissions). Sounds like a standalone would be the only real option here (again voiding it from being emissions-thus street legal).

Are there vendors that offer fuel cells specifically for vette's? I was familiar with the need for stronger (and larger diameter) fuel lines, not to mention the size of the fuel rails as well.

mnstrlt1

the "iron eagle" Dart block can be punched out to a 455ci. Would this maximum cubic inch effort also cause the problem you guys are finding with the ring locations on the stock block and 396 ci's?