Turbo gods! Please talk to me!

[RideShoot&Drink]

Hi all,

I'm contemplating turbo upgrade. Currently I run stock 87 3.3 CIS Turbo motor with 915 trans. The only thing other than stock is full GHL exhaust. Basically, I don't have any specific goals in mind at the moment, I just want more! More power, more torque, faster spool, etc. Everywhere, low end, mid range, top end. So, which turbo should be the best to achieve that? And how that specific turbo would change the character of the car?

Thanks!

[RarlyL8]

You have a good start with the exhaust. Turbo by itself won't get you better driveability, that is done with cams and compression. As for the turbo, it depends on your power needs and red line. A K27-7200 is great for 400HP motors at stock redline. The K27-7200HF and other variants do better up top. It's all a compromise, you need to match the cams, EFI, turbo, etc to achieve a specific goal.
You will find with the 915 that your needs can easily be met

I'll give you (my) example. SC cams, K27-7200, Euro exhaust, 0.75bar spring, B&B intercooler, 915 tranny.
The car drives wonderful. It has more power down low than my 3.0L SC engine had and it explodes to life before 3000 rpm for a rocket ride. The short gears of the 915 allow you to get on boost quickly while also giving a nice smooth power transition at partial throttle.

[RideShoot&Drink]

Rarly thanks for your reply. I guess, you can't have it all with just a turbo upgrade. I personally, love top end rush. So, probably K27HF would be a better choice. I plan on doing sequential bolt on upgrades without going inside the engine. The goal is to have a kick ass combo without sacrificing reliability. Please, tell me what's the deal with IC's...there are short neck, long neck, full bay, etc. IC's. How do you pick the right one? I heard Kokeln and C2 Turbo are good upgrades. I have to tell you, I'm confused with IC's as much as I'm confused with turbos. Also, I heard that some go step further 964 cams and use 20/21 cams on their 3.3 CIS engines, heard anything about it? Once again, your reply is greatly appreciated...thanks!

[RarlyL8]

Yes, I understand. SC cams are no longer "en vogue" due to the availability of 964, GT, etc, etc. While they may not be the cam of the day anymore they are still very very good at giving low end torque and improved drive-ability for minimum cost.
Intercoolers. You need to match the heat dissipation characteristics of the IC with the requirements of your engine. For example, a mildly modded 930 engine (say 400HP) can use the stock intercooler if the boost level is also kept stock. If you increase the boost level you increase the need for intake air cooling in order to keep the engine from pinging due to the increased C/R from higher boost. The higher the effective C/R the more intercooler you need. Intercoolers provide free HP due to cooling the intake charge, but only to a point. They also contribute to lag due to the volume of intake air that they hold. This increase in lag is probably not significant until you get to the full bay mega-coolers. For what you are wanting to achieve a full bay cooler is not required. You may want to look at the Kokeln / Ruf / or B&B units like I use. They are physically the size of the later C2T stock units.
Long neck coolers require the elimination of the stock BOV assembly which is replaced by an aftermarket or C2T unit. Short neck coolers will bolt up to what you have now.
You can start your quest with a new turbo followed by a larger intercooler and then a 1.0 Bar spring. Those mods will complement your aftermarket exhaust and should get you significantly more power than you currently enjoy.

[RarlyL8]

[Lukesportsman]

I have 20/21's in the 3.0 that I'm building up currently. It should be running by summer, but no feedback so far. I think any cam that works with CIS should function well with a turbo. By going with the bigger cams, allowed by the EFI it should allow more boost at a given octane level. This is being discussed currently in the engine forum.

Are you running euro headers or aftermarket? Get rid of backpressure to spool. Yes upgrade the IC before adding boost. Look up factory IC efficiency and you'll see why.

[bkreigsr]

check out Bell Intercoolers too for 'custom' sizes.
Bill K

[RideShoot&Drink]

Rarly, I thought C2T IC is larger in size, more like full bay IC...am I wrong? How's B&B unit working for you? I heard that B&B exhausts had some troubles quality wise...how's your IC holds for you? Are you happy with your selection?

Luke, I run full GHL exhaust (headers w/heat and 2 out muffler). Once full system was installed, it greatly improved the character of the car, even with engine being totally stock. It definitely did more to this turbo car, than to my 85 Carrera (I went with SSI's, Monty sport muffler and chip). Going with full GHL system was great improvement, more power and quicker spool are very much evident, so I'm very happy with this upgrade.

Bill, do you know if anybody used those Bell IC's? Are they happy with the results?

Thanks!

[Lukesportsman]

DonE is running Bell and I've heard of others on Rennlist too.

[RarlyL8]

The 965/Ruf/B&B are the same approximate size. I am very happy with this unit. This size is very good if you run A/C. It is also good if you like to fiddle with the CIS and change your oil filter without having to remove the intercooler.

[look 171]

Rideshoot,

I know this isn't your original question. Have you also look into changing ring and pinion gears in the tranny. I did, and it is a hell of a lot of fun to drive. Not that it wan't fun before, but I'll tell you in a half a second, you are rocking down the road. I notice that you like the top end rush. Changing the R/P is going to lower that a bit. My top speed in 4th is at about 168 mph according to the gear chart. I haven't gone that fast yet, nor do I want to. I $hit in my pants doing 130ish. This thing keeps on pulling at that speed. Are you doing mainly street driving?

Jeff

[RideShoot&Drink]

Jeff
Yeah, that's one of the things I'd look at if I was running 4 speed 930 trans, but I have 915 with shorter gears anyways, I have no idea what's the top speed would be with 915. What I notice is that with stock turbo power flats out at around 5.5-6k, wish I had a bit more ;-). I did about 155 on mine...but, hey it's never enough!

[RarlyL8]

With the '78 US 915 the top end is gear limited to about 160mph at nearly 7000rpm. The K27-7200 starts to drop out above 6000rpm in 4th and 5th gears. You can't notice it in the lower 3. With the 915 and typical mods you can get from a dead stop to top end in around 30 seconds.

[RideShoot&Drink]

Rarly, when does K27HF drops out, have any idea? Thanks.

[William930t]

RarlyL8, very tidy engine bay!!

[RarlyL8]

Talk to Stephen at ImagineAuto about the HF. I've no experience with it, just what's beed read. From what I understand the HF is supposed to be fatter in the midrange and on top than the 7200 and supports more horsepower. For mild hp engines the 7200 is a good value at half the price of an HF.
The engine bay is spartain, the way I like it. Getting rid of that monster stock air cleaner was the last push in making that motor as easy to service as possible. The sound the breather lets out during initial acceleration is awsome as well. WHOOOOOOOOOSHHHHHHHH !!

I'm really surprized that more 930/915 guys have not chimed in. They usually don't miss a chance to talk turbos and mods.

[air-cool-me]

Randy... it just looks like you have this one covered! [chIme]


a 915 is the best mod you can do for driveablility(sp)... IMHO

150mph and its close enough to the red-line... not a tI'me to nitpick over a few hundred RPM!? jk!

the stock muffler is heavy and flows like crap... ditch it and get something lighter..

bell only makes cores or common shapes, correct?

overlap with a turbo bleeds boost pressure out the exhaust ...
turbo's and CIS both need very little overlap.. so what works for CIS should work for a turbo (but I'm not 100% sure..) ask someone who knows more..

also slightly lower tire profile will make taking off from a stop a bit easier... due to lower gearing effect..

[/chIme]

[rattlsnak]

Along with the bigger turbo and 1.0 spring, putting on an IC like this from a C2T will help greatly, but you have to change some piping as well.

[RideShoot&Drink]

Rattlsnak,

What do you have to change in order to go from stock IC to C2T IC. How difficult is it? I have to manage $$$$$ spent too wisely these days. Do you know how C2T IC compared to units such as Kokeln or B&B efficiency wise. What are pros/cons?

Nick

I already ditched the stock exhaust and very happy that I did, I have full GHL and love it.

Thanks all!

P.S: Oh, and by the way, this is the girl who waits to be upgraded...

[rotorhead]

Originally posted by RarlyL8

RarlyL8,

tell me about that air filter you have....

Steve