Assuming 93 octane fuel, 8:1 compression, 15 PSI boost, intercooled and a good choice of components all around, does it look likely to be able to hit 850HP from a TT 383?

 

I dont think you will hit that on 93

 

i think thats very possible...ppl running cobras and LS1s with 10 psi boost with nice components are running 500 to 600 and with 15 psi and twins i think ull be right at around 750 to 800...you could prob go with 8.5-9 comp ratio if you only want to run with 15 psi...if your running 8 to 1 then u could do much more boost and go with like 20 psi ...and im sure ull make 800 to 900 then and i dont see why that couldnt be on pump 93 octane either
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im not an expert but from what i do know i think im pretty accurate

 

http://www.gnttype.org/techarea/turbo/turbocalcs.xls

According to that calculator, it is possible if you use good parts like you said. Take a look. You will probably have to only rev it to 7500rpm or so. I recommend an intercooler.

 

Tuned right, its possible. With 93, You will need alky injectoin though...

 

Assuming that you’ve got a reasonable setup you should be able to run that much boost with 8:1 compression without the intercooler, so that won’t be a problem.

Lets assume that you get things pretty well matched and you’re at an adiabatic efficiency and intercooler efficiency in the high 70% range, just short of 80%, that will result in a density ratio of 1.9, so you need to build a setup that will make 850/1.9 = 447hp without the turbo. Assuming 100% VE, that works out to about 5400rpm.

So yea, it can be done. Real world, that low compression will hurt you, so I’d figure at something more like 85% VE at your hp peak, even with very good heads, so I’d pick a cam that will give you a hp peak in the 6200-6400 range and heads that flow >225cfm at least .050” below your max lift and exhaust ports that flow at least 175cfm at the same range (small, fast exhaust ports will do you more good then ones that flow a lot). Of course, unless they’re iron heads you should be able to run a bit more boost with that compression, probably 18-20psig or so, maybe more with that big a cam.

I’d probably shoot for a little more compression and a little less rpm or a little more boost and a little less rpm, or keep things like they are so you don’t have to get things as spot on to make the power you want.

 

Sounds promising. I've just really been starting to get into turbo systems over the last few months. I have decent retention and am picking it all up pretty well except that I sometimes have trouble finding the time to read. So far, I've yet to come across a table which illustrates the max DCR + boost against octane ratings -- probably because there are too many factors to make a simple table from. I was hoping 8:1 would be good to ~2.0:1 PR. This is even better because I can build it as an NA street engine and add the turbos later. 8:1 is kinda low, but a 383 with that CR will be better than my worn out 305 as it stands right now. I'll bump it up as high as I can go on 93 octane and no more than 20 PSI at the throttle body. That's the highest I would EVER ru nit on 93 and probably wouldn't go >15 unless I was on race fuel. I most definitely intend to intercool.

My end goal was nothing crazy. I initally wanted ~11.5 sec passes and would be OK with that for quite some time. I did some math and found a few calculators on the internet and came up with:

850 FWHP = ~720 RWHP (Give or take a bit)
720 RWHP = ~138 MPH @ 9.88 sec @ 3500 lbs

I know these are real loose estimates, but this is much better than I had set out to achieve in the first place.

Here's some calculators for anyone who may want them (and the math below, please rview for accuracy):

http://www.speedworldmotorplex.com/calc.htm
http://www.dsm.org/tools/calchp.htm
http://www.wallaceracing.com/et-hp-mph.php
http://car.race-cars.net/calculators/et_calculator.html

hp = weight / (ET / 5.825)^3
hp = weight * (speed / 234)^3

 

it’s nowhere near that easy. Even NA, DCR is only a vague guidline and you play a game of “what can I get away with.” The fact is that better parts, better quench, better chamber design, port design, better tuning… will have a great impact on what DCR you can get away with. Just becase someone has a rule of thumb that says that “yea, 8.3:1 DCR is fine” doesn’t mean that when you slap together your big bore, big block with iron heads and a bunch of old school parts that it won’t rattle.

Boost effects this like it does everything else, it broadens the range and increases the effects of changes just like it increases the airflow through a given induction system. Secondly, it doesn’t seem to effect things as much as any reasonable number crunching predicts, and it is not uncommon for actually CR + boost to = the equivalent of 14-16:1 CR and the engine still running fine on pump gas. The higher above your torque peak you’re at, at whatever boost level you’re at the less the boost has an impact on the detonation sensitivity of the engine. This is especially a big deal if you’re using the blower to extend the rpm range of the engine.

8:1 is on the low side for NA, and to make it run well you’ll have to run the rest of the engine to match that, which will not necessarly be the same combination that will work well with the turbo, but don’t let that stop you or the “it will be a dog off boost” crowd stop you, it will be much easier to make power on boost and it can be tuned to work off boost. Loads of production stuff in the 70’s came with compressions in that range and lower, and loads of turbo cars came with compressions lower then that (some of the faster turbocharged porsches were in the 6’s, some older saabs are in the low 7’s, and even things like the turbo sunbird, which was a good performer for what it was, was in the high 7’s).

You’re going way, way conservative on your estimates. The equasions that you used actually assume flywheel HP, and it will only take about 450 hp to do what you expect to do.

Build an engine that will make you a reliable 500 hp and you’ll be there easily, assuming half way decent tuning.

 

OK...got some more time to read today and here's what I'm thinking. Does it sound OK to you guys?

A pair of TO4 turbos with 0.96 A/R. Intercooled, 383, up to ~6200RPM. Sound like a good start for 850HP?

 

Is that turbine A/R ? It seems a bit big to me. In a T4 turbine, I would go with a .69 or something like close...spool better and work better with Your relatively low redline rpm...

 

Most of the 355's that don't turn a lot of r's I've came across were running .58 or .69. So for only 6200 I say a .81 max.
There's a guy with twin H3's on a 355 running .96's.
Full boost around 3800 rpm. But he has a 3500 stall and shifts at 7500 or so.
The .81's might make it a little easier to drive on the street by slowing the boost up a little down low.
I know of one person who went up to .81 on his 60-1's so he had an easier time getting on the freeway w/o wheel spin.
You also need to take OC vs Tan housings into account.