For Those Considering a Turbo SBC

[Scottie-GNZ]

This looks like it might have potential for fitting in the Z engine bay.

http://hi-techperformance.net/turbosmitty2.jpg

[SuperDan]

Oooooh, Ahhhhhh, Mmmmmmmm

[Guest Anonymous]

I'll take one... That does look like it puts the turbo in the right place for sure. I like it alot..

 

Regards,

 

Lone

[pparaska]

MMMM. I like. I wonder if that turbo wouldn't hit the inner fender though. Of course, that's nothing a little cutting and welding of the inner fender couldn't fix .

 

With a not-too-low compression (8.5:1 or 9.0:1) 350 or 383 SBC and TWO small snails, would all my whining about lag be nil? Seems like two small ball bearing turbos that made power up to 6500 (I don't need even that much rpm)would be awesome and have little to no lag. Could two be selected and engineered into the car to have boost at 1500 rpm or lower?

[Kevin Shasteen]

Scottie,

 

Nice pic & very clean install-only one question...why only one turbo-dont we need two (haha). Turbo looks like it might be close to the strut tower. Worth checking into for anyone starting their turbo'd V8Z.

 

Pete,

 

Its my understanding that you wont get immedieate boost down low & also get the same response way up high. It's gotta be one or the other or a broad response spread thruout the rpm range.

 

The Boost Threshold (lowest possible rpm where boost is created) is determined by the A/R Ratio of the turbo itself.

 

The "kick in the seat of the pants" (absence of Lag) is fine tuned, for your rpm needs, by Hybridizing your turbo housing.

 

A larger A/R ratio (A/R meaning Air/Radius Ratio) inhibits airflow & increases "lag" while a smaller A/R ratio increases airflow & decreases "Lag". Too small of an A/R ratio will give the car a [jumpy] & [touchy] on its throttle response. A too small A/R ratio will give the same effect of a HiPerf engine w/too small of a carburetor-it runs great at low rpms but seems "choked" at higher rpms.

 

At least this is my undestanding thus far.

 

Kevin,

(Yea,Still an Inliner)

 

[ August 28, 2001: Message edited by: Kevin Shasteen ]

[Modern Motorsports Ltd]

Nice setup. That turbo would clear my strut tower and likely inner fender(and hood), what's the items on the drivers side upper fender area??

[Kevin Shasteen]

Driving a V8 TT has got to be an incredible kick in the pants adrenaline rush; I guess I'll have to put that on this years Christmas list as "Things I Need TO DO" before the year ends....probably wont happen but I can dream.

 

Kevin,

(Yea,Still an Inliner)

[BLKMGK]

I'm a lousy driver but... 12.15@118mph - 2.2 60ft. Come third gear it MOVED! 4th gear passing felt like my old 3rd gear on the highway. Idled and sounded stock too.

 

I raced a guy with a somewhat hopped up Mustang once. He left me at least 2 to 3 cars off the line. His friend later told me they thought they had the race sewn up. Suddenly they hard this screaming whoosh sound blow past them at just past half "track" (street race)! The top end charge was incredible (lol). A friend at the finish line said it was a wild race to watch as I screamed past him - several cars ahead of the other Mustang.

 

I couldn't hook it up out of the hole and pretty much resigned myself to playing catch up whenever I raced. Somewhere here I documented a street race that nearly ended in a fist fight when a friend drove. Briefly - we were racing a TPI Camaro and my friend had never driven the car before. He ran the race "soft" but coming through third he matted it to try and get "a little ahead" to win the race - we were sandbagging. The fist fight nearly broke out because the kid swore we were running NOS, something we had claimed we weren't running - and weren't. Seems when my friend matted third the car pulled away that fast! Eventually we let him peek under the hood after he had already checked the trunk and backseat - not sure what he saw except for lot's of polished stuff but he handed over the cash swearing. turns out his "mostly stock" 350 TPI had "everything" done to it in the way of bolt-ons or so he said afterwards (no blower, no NOS). Oh well, that's street racing for you (lol). I did beat a few NOS cars too but my driving pretty much sux.

 

Done right a turbo car sleeps real nice...

[DavyZ]

Hmm, good story. I can't believe that I am actually contemplating building a turbocharged V8 Z. Shoot, I'm not even finished with the NA version yet! Oh well, I guess it just never ends. Who knows, I may scare myself so much with the NA V8, I may not ever build the TT V8--of course I may do it...the platform may just change...

 

Davy

[Guest Anonymous]

Ahh, friends, remember we're not talking a little 4 banger than has no low end torque, remember our V8 advantage lowered compression or not... With twin turbo's, what would be lag in a dimer motor is just a push of torque until you get kicked in the back when the turbo's spool. As Pete was saying, that much RPM wouldn't even be needed, 6k (or maybe less) would probably be just fine to set the scenery going by the window at a great clip.

I know I for one would like to test pilot such a car...

 

Regards,

 

Lone

[Scottie-GNZ]

Lone,

 

excellent point. Even a low-compression SBC will still have enough torque to make lag less perceptible. Remember that lag is the difference in torque felt between a turbo motor with no or low boost vs one at high or full boost. This is primarily caused by the engine not moving enough exhaust (yep, power) to turn the turbine wheel fast enough as a result of the turbine wheel being too big (heavy). There are other causes of turbo lag, too much advance at low RPMs and too rich, but those can be tuned out.

 

The best way to avoid or at least minimize it, is by working with the turbo manufacturer to help you configure a turbo that will give crisp response while not sacrificing (too much) top-end power. That, of course, is the principle behind the t3/t04 hybrid. Use the t3 turbine to maintain the crisp response and a t04 compressor to give the top-end. However, many of the L28T folks running the stock turbo know that the low-end response is actually a detriment to performance unless you think wheelspin is cool .

 

Where am I going with this? Guess I am just rambling

[BLKMGK]

My experience with my Ford twin turbo should help. Matting the pedal at a low RPM in a high(ish) gear would result in about 2-3lbs of boost before 2K RPM. By say 3500 RPM I would be looking at close to full boost up till redline. I limited boost to about 10lbs on that setup - compression was stock at about 9.2:1 or so.

 

Figure it was just like a hopped up stock Mustang until boost was pushing and when it was even faster IMO even when boost isn't showing on the dial the turbos ARE helping, they've just not overcome the breathing ability of the motor. It's the diffence between having to draw air through a straw and having someone pushing a little air for you - you may still have to work but just not as hard. Make sense?

 

Trust me guys, turbos on a V8 are plenty spunky and boost isn't a big issue if they're sized right. With twins you go for smaller turbos for quick spooling but together thay have quite a bit of airflow capability. A T25 is a small turbo but a pair on a 302 is enough for a streetable 450HP and a TON of torque. I had an issue with the wastegate once on one of the turbos. I saw a spike of 15+ PSI before I let out of it. That was pretty much one turbo doing that work since the other would've had it's wastegate open past 10lbs. there was LOT's of unused airflow potential in my setup One of these days I'll find soemthing to put those pig heavy cast manifolds into!

[Guest Anonymous]

I was told that a supercharger was better for off line acceleration than turbos as it is driven by a belt and turns all of the time. I also heard that it provides better gas mileage and isn't as hard on parts as the turbo setup. Can anyone prove or dispute this?

[SleeperZ]

Superchargers can give boost right off idle, but in a V8's case here, with the limited traction of a Z car, it seems that turbocharging a V8 would work very well, as the boost will build once you've left the line and hooked up. A supercharged ZV8 has a better chance of just smoking and sitting there. Sorry, off the topic, but I've not posted anything for a while and I just wanted to jump in.

[BLKMGK]

Careful Sleeper - there's more than one type of supercharger. A Root's style does indeed make instant boost - it compresses the air within it's housing and delivers the compressed charge right into the intake. A centrifigul (sp?) supercharger has to pile the air up in the intake and discharge tube and has a response curve much like a turbo. Heck, it even looks like a belt driven turbo Some centrifigul blowers are more efficient than others too.

 

Look ast the boost curve for some of the blowers being put on modular Fords, late boost that looks like a turbo with lag but they rev so high that it would boost off the scale if it made boost lower down. You don't usually see wastegates for blower cars but I guess in the case of a high revving motor it could make sense?

[Scottie-GNZ]

Boy, Les,

 

you jumped into one that I do not know will ever be settled. Each user has their own preferences, biases and opinions and too many of those opinions are based on hearsay and the infamous turbo lag stigma.

 

Here is my bias, er, $.02 . S-chargers have better off-line acceleration. I say yes, in general, but not as a rule. The problem with turbos is usually a lack of understanding of the technology and turbo systems that are not configured and/or tuned correctly. People buy used turbos or generic turbos w/o understanding how their engine will perform with it. With a turbo, just like a carb, bigger is not always better. The neat thing about a turbo is that there are 2 parts to it and you can go "half-bigger" . Another problem, especially those w/o programmable systems, is the use of large injectors or high fuel pressure to satisfy fuel demand at high boost. There is a high probability that the mixture will be too rich at low RPMs, resulting in LAAAGGGG. I will try to be modest here, but I use my setup as an example of how well a turbo system can perform off the line. I 60' better with a turbo and DRs than almost all s-charged cars, with slicks, that are in my ET bracket and like Darius' awesome s-charged hybrid, I will fry street tires at 50mph.

 

S-charged cars will get better gas mileage. Hmmm, I do not know about that one. Everyone will agree that at any speed or RPM, a s-charger has parasitic loss. A turbo cruising off-boost is going to get the mileage of a low-compression, low-cammed NA. Given the same engine and state of tune, I have to wonder.

[Drax240z]

I've always thought that turbos would get better fuel economy than superchargers, but I suppose its possible to use a magnetic clutch on a supercharger so it won't spin when you don't want it to. I would think that cruising ont he highway, the turbo should get better economy than the same engine with a supercharger...

 

However if you are comparing apples to oranges, who knows. The only way to really compare is the same engine, tested with a turbo and tested with a supercharger.

 

Lets just concede that if you are adding either, economy isn't your primary concern.

[Brad-ManQ45]

Centrifugal superchargers have next to no mileage penalty when off boost.

 

Roots types incur the biggest penalty as you are constantly driving the mechanism compressing the air depending upon the speed of the engine.

 

Turbo motors will always have a negligable amount of penalty due to the restriction of the exhaust necessary to spin the turbo during normal acceleration. Thisis nowhere ////near the amount of penalty from driving a Roots type Supercharger tho.

 

Just like in a normally aspirated engine, with a turbo setup, you need to pick the ~3K RPM range you want to make your power in. The higher the rpm range, the more "lag" experienced at low speeds, and the more of a RUSH you get when the turbo starts doing its' thing!

 

I think a 302 or 327 with a cap of 6500 rpm would work well for drag racing, cutting down on the low end torque (8.5 - 9/1 compression) allowing you to hook up, then coming on strong.

 

It's what I have envisioned for my '75 anyway...

 

That said,