Heads/cam + STS

Just a quick question, pardon the ricer math here. If you are making say 400hp with a heads/cam combo and then you add a STS turbo kit, will that put me at upward 400s? Or does the 100hp gain advertised by STS only apply to a stock engine?

There are alot of variables... but it is safe to say expect around 15-20hp per 1psi of boost... so 5psi should gain you 75-100hp.

Ok sounds good. Thanks!

Uh oh...
So I made 560 at 20 psi... That means I make 160 Na? Probably right.

Ok, realistically I made 560 at 15 psi. Figure the rough side because my motor is not ideal - I'm probably somewhere in the middle. 275NA 275 from boost.

Many many factors - If its a turbo friendly cam you may make even more, if its lots of overlap (guessing so if its 400 NA) then it may not gain as much per psi. #5 will make some sort of difference though.

Well basically I can get an STS kit locally for hopefully pretty cheap and was wondering if it was worth throwing it on and getting another tune for it. The LSA is what was kinda making me think twice as you pointed out.

If you can get it for cheap I would go ahead and get it. It can't hurt unless you compression is really high and you can always change the cam.

Ok that was the plan, if anything it would make for a good intimidation at redlights ;)


Another question, a local shop is telling me the stock crank can't take more than 500 hp, is that true?

Jason Warren-9.3@142, 95 Z/28, 355 LT1, TH-400, LT4 TrickFlows, LT4 intake, stock crank, stock pcm w/recalibration, solid roller, 300shot, 3578lbs.

Thats from LS1tech's fastest LT1 page

If I make say 500hp crank and spray a 100shot, will that be too much for the stock rods?

How much overlap does your cam have? Thats probably one of the most important aspects of a cam when it comes to turbo's. Less overlap will make for less reversion.

Check out my LT1 with an STS. http://www.camaroz28.com/forums/showthread.php?t=664161 Lots of pics and videos.

It was a kick in the nuts difference goin on the stock car. My best guess is around 24hp per pound of boost.
I would say that the typical power produciton numbers would definitely apply to your motor as well. With your heads/cam you've made it breath more air in each breath, less restriction. HP potential is based on airflow through the motor, so adding boost should compliment your setup well.

And yeah, I've also heard that 500hp is the generally accepted limit of what a stock LT1 can reliably produce.

Um, well LSA is a ummm lovely 107..... ;)

The stock crank will be ok. The stock pistons won't take much abuse. The stock rods should take 500RW with ARP bolts and keeping the rpm within reason (6000rpm). The stock main caps will probably be walking around and should get ARP studs.

You cant really rate any rod by horsepower.

Your best bet for a budget build is stock crank, stud the mains, Scat forged rods 7/16 bolts, SPR or other budget dished piston. If your stock bore is ok just hone it and run a standard bore piston to save $$ on machine work (ie - none)

-Scott.

Well plan is def new forged pistons, looking at a set of Mahles now. Maybe a set of Scat I rods and of course all ARP. If I keep the rpms below 6k, should the stock mains be ok if I use ARP?

My take on it is if you want 500-600 Flywheel HP then 2-bolt mains with ARP studs will be ok.

Here is a link to the Scat rods I think would be good with larger 7/16 screws

http://store.summitracing.com/partdetail.asp?part=SCA%2D26000716&autoview=sku

When looking at pistons you want a dish to get you around 9:1 SCR with boost.

Good luck,
Scott.

http://www.kmjent.com/cart/product.php?productid=622&cat=7951764&page=1

These a step above stock rods and would most likely still be overkill for my project.

Boosted- What kind of CR are you running?

Right now I have -24cc SRP's with stock stroke, stock ported heads and Felpro 1074 gasket. That's real close to 9:1.

I'm in process of building a new engine with a 3.75 stroke, -31cc dish, same heads and gasket and minimum decked off of the surface of the block. At this point I'm making some assumptions on actuall CC of the combustion chamber and where the piston deck will end up. Should still be 9:1 +/- 0.3

-Scott.

If the engine will most likely never see more than 10psi, is dropping the compression that much really needed? I am just thinking along the lines of how the STS kit is advertised for a stock LT1 no mods needed. And since I would be running forged pistons and maybe better rods wouldn't it be fine?

Yea

Yes, dropping the CR to around 9 is needed or I don't need to drop it that much?

If you stay below 10 psi you should be between 9.0-9.5 to 1 and be fine with a good tune.

You don't NEED to drop the compression to run below 10psi.
I'm running 7psi just fine on my stock LT1, thinking about running 9...

If you're buying new pistons anyway, I'd get dished and shoot for about 9.5 to 10 compression ratio, this would work great for under 10psi of boost.
Of course an intercooler and/or methanol always helps too.

If you run good pistons and not junk you can get away with it. Like MikeGyver said an intercooler and meth/water injection will make it pretty safe.

Good pistons = Mahle?

I looked at them and ended up going with diamond.

When they say good forged piston they mean one out of 2618 alloy which is more tolerant to detonation than a 4032.

So if you get into detonation with a higher CR, you might not grenade the pistons. Detonation still is very hard on other engine components - head gaskets and bearings - It is not wise to operate any motor while detonating!

You wont lose much of any driveability comparing 10.5 to 9.5, or even high 8's. Efficiency goes down with lower compression ratio, but it is also important to lower CR with increased load.

Gains will be minimal running a 'high' compression ratio on pump gas while the risk of damaging engine components goes up. At 10psi you could probably run 9.5-10.0 ok, but I guess my point is why not just build the motor to handle boost?

-Scott.

Well the whole boost/CR is new to me, so pardon me coming off as an idiot. Any advice is greatly appreciated. I just don't want to get worse gas milegae than I do now.

Hey no problem. It's good to see new people interested in supercharging and turbocharging on this forum.

You're adding a turbine wheel in the exhaust path out of the engine, so in theory you will lose gas mileage even at cruise. You will certainly lose mileage when your foot is in it - which will be quite often with a turbo :)

-Scott.

Ok, another question for you guys, the turbo that comes with the STS kit, is it a GT40? If so how much would a rebuild cost?

Ok, another question for you guys, the turbo that comes with the STS kit, is it a GT40? If so how much would a rebuild cost?

you can get a couple different turbos with the STS kit, best bet is to get the part number off the turbo and call a shop.

Well I don't have the kit, so I am kinda in the dark here. But in general how much is a turbo rebuild and is it possible to do by yourself?

I am trying to weigh a rebuild versus a new turbo.

You're adding a turbine wheel in the exhaust path out of the engine, so in theory you will lose gas mileage even at cruise.

I do not agree with this statement. Based on my experience and everything I've seen, turbo's are capable of Increasing fuel mileage.

The turbine wheel creates virtually no opposition to exhaust gas flow at cruising speeds. On my car my MAF is reading in the vicinity of only 25gm/sec of airflow through the motor while cruising, for comparison it goes to over 350gm/sec at full boost.
But at the same time the compressor wheel is helping feed the motor fresh air, making the motor work less hard to get it, resulting in less throttle to maintain speed.
I would like to hook a gauge to my exhaust (before the turbo) to measure back pressure.

My friend drove the exact same route on the freeway before and after installing a turbo on his truck. He gained 6mpg(!!!) and was only getting like 18 or something before the turbo. Both times were on cruise control going the same speed, running a 'there and back' route.

The turbo STS uses is a 60-1 with a TO4E compressor cover and a T4 turbine housing, it flows about 60lbs/min of air; enough to produce around 550-600hp.. The upgrades are 67mm, 70mm, and 76mm compressors, and can all be had in journal or ball bearing, and I believe comes with a 1 year warranty?

Any piston is going to hold these power levels if tuned well. The better the piston, the more forgiving it is. Like many others I run the high silocone content SRPs with no problems on 20psi.... if something happened in my fuel system they would break before a better piston.

Gas mileage shouldn't be affected much either way really. Even with my little bitty turbo its not spinning much at 1500ish rpms. If I get to 2 or above its making a good noise for sure. The exhaust and turbine housing are going to cause more restriction than the spinning wheel inside it.

Does any one have any pictures of how the STS kit mounts the turbo behind the car?

http://www.ststurbo.com/camaro_lt1

Yea I had looked at that, and I was curious about how the turbo was attached, if at all. I can see the air filter is attached via the driver side hanger and the exhaust tip I assume grabs the passenger hanger, but the turbo just hangs in between them?

Not really sure. These guys here added a a pretty simple bracket to help support the weight (seen about half way down)

http://www.exoticperformanceplus.com/projectCar.php?car=32

Has any one tried to fab up their own version of the STS kit?

I made all of my own pipes except the one that loops up and over the axle, and used a huge intercooler.

The majority of the weight of the turbo is held by the exhaust pipe that's welded to the stock exhaust. The turbo is also located by the intake pipe that loops up and over the axle, the air filter pipe, and for people using an exhaust 'tip", that has a hanger as well.

Here's some pics of my install.
http://i39.tinypic.com/vrybtc.jpg

http://i43.tinypic.com/rsvhab.jpg

http://i42.tinypic.com/n4lh.jpg

http://i42.tinypic.com/ztw46s.jpg

http://i39.tinypic.com/rhtssz.jpg

So the turbo is supported mainly by the exhaust tube?

umm, well you can undo everything and it'll hang by the exhaust pipe, but it'll droop a couple of inches. So everything is really responsible for kind of "triangulating" it into place.

It's not really hard mounted though, it floats like an exhaust system should.
I just went out and layed under my car. I grabbed the turbo and can only wobble it about 1/4" or so in any direction.

I do not agree with this statement. Based on my experience and everything I've seen, turbo's are capable of Increasing fuel mileage.


Mike,

Dicussing this may be better served as a seperate thread so as not to hijack, but it certainly seems interesting. At steady cruise: I think what you are saying is that the compressor wheel is reducing pumping losses associated with the pistons pulling in air, but I'm not sure it is actually relavent. I don't doubt what your buddy was seeing, but could that be due to a different tune or other changes?

Regardless, I think we can agree that a large object placed inside of a volute is not going to flow as well as a straight pipe. Both the exhaust and intake have to flow through such. The exhaust is certainly being restricted as it passes through the turbine & housing. The real question is if the speed of the compressor - at cruise - is helping to reduce engine pumping loss, OR is its rotational speed slow enough at cruise to also cause an intake restriction?

At steady cruise there is XX net power required from the motor which remains the same for turbo, blown, NA. So which of the three systems has the least total-loss at low flow levels? Which requires the lowest airflow (and fuel) to produce that XX net power?

During even light acceleration, additional exhaust energy is spent accelerating the wheel from rest.

At WOT, you get a significant pressure rise across the comp. which increases intake flow, engine VE, and power but at higher specific fuel consumption than NA.

In summary, my opinion is that a turbo will reduce mileage under all three of these scenarios (cruise - when at same A/F ratio, acceleration & WOT) when compared to the exact same motor (save for intake/exhaust changes) before adding the turbo.

Thanks,
Scott.

I don't doubt what your buddy was seeing, but could that be due to a different tune or other changes?

The tune wasn't changed, and it never went near boost during the test. Keep in mind this was a pre-conceived test, not just a 'hey looking back, I got better mileage" kinda thing.


Regardless, I think we can agree that a large object placed inside of a volute is not going to flow as well as a straight pipe. Both the exhaust and intake have to flow through such. The exhaust is certainly being restricted as it passes through the turbine & housing. The real question is if the speed of the compressor - at cruise - is helping to reduce engine pumping loss, OR is its rotational speed slow enough at cruise to also cause an intake restriction?

This is a hard scenerio to speculate on, I can see it either way, I understand exactly what you mean. Sure the turbine housing creates quite a restriction on the diameter of the exhaust pipe, but at cruising airflow rates I think the restriction would be negligible. My friends vehicle also has a rear-mounted turbo, which replaces the muffler, so muffler backpressure couldn't be a factor in any way. So when his turbo was off he even had very little backpressure.

Image this... Say we have a syringe, that when pulled back rapidly (as we all know) requires quite some effort. Liken this to the piston (pumping losses).
Now if you repeat this while -slighlty- blowing into the syringe, it will be easier as it'll create less vacuum. Overcoming the pumping losses will net more power, and in an effort to maintain the same cruising speed, will require less throttle. Less throttle decreases engine load and requires less fuel, hence an increase in fuel economy.

Now this isn't a perfect analogy. I'm sure it has flaws, but it portrays the basic principle as I see it, and of course I may be wrong.

I'm going to tap a pressure gauge into my exhaust so I can monitor back pressure during all driving conditions, as I'm now very interested in gathering some data.
I may even remove my turbo since it only takes 15 minutes, just to test this myself (and of course have the intake suck air from up front again).

LOL well this a good read guys, I don't mind the hijack its good stuff!

haha sorry

I think measuring exhaust pressure would be a good idea to better understand how well a particular system performs. I was almost thinking of mounting a boost gauge in-car that could be swapped from a pre-turbine fitting to a post-turbine fitting.

Nice car Mike!

-Scott.

I'm jumping on this kinda later but according to everything i've been reading here i'm driving a time bomb, I have a completely stock 96 Z with an intercooled sts and I have been blowing 11 psi for the entire summer in my daily driver, and I have to say it loves it.

Has any one tried to fab up their own version of the STS kit?I built my own setup back in ~2004 on my old old formula, ran a mp t70. I have pics somewhere, but not sure where it's been so long, really the build wasn't that hard. Although I have since had a rear mount ls1 and two front mount lt1 kits, I HIGHLY recommend a front mount setup. I used realquick's hot parts and the spool time is a HUGE difference between the rear/front. Don't get me wrong, you can make a rear mount setup work, but just not a fan of it after having a front mount setup.

I built my own setup back in ~2004 on my old old formula, ran a mp t70. I have pics somewhere, but not sure where it's been so long, really the build wasn't that hard. Although I have since had a rear mount ls1 and two front mount lt1 kits, I HIGHLY recommend a front mount setup. I used realquick's hot parts and the spool time is a HUGE difference between the rear/front. Don't get me wrong, you can make a rear mount setup work, but just not a fan of it after having a front mount setup.

What A/R turbine housing did you use?

.84 on the t70 rear mount
.96 on the front mount t76

The rear mount was a le3 heads, futral custom cam, 355 also. A .68 housing would've chocked it back on the top end which is why I never went with that.

The stock heads/cam front mount still out spooled it. I say sell the heads/cam and use that money for a front mount setup, you can easily push mid 10's on stock heads/cam, I went 10.80 with a slipping STOCK tranny, 42lb injectors at 70lbs fuel pressure(maxed out), and only 11.5lbs of boost, all on stock heads/cam with lt4 valve springs.