Hey all,

So i'm thinking of doing a custom rear mount turbo kit, and I have a question to everyone that is boosted. Does the MAF Sensor need to be before the turbo or keep it were it is? Also, can I keep the stock injectors? All i'm looking for is 4 - 6 psi btw.

Other info:
1986 L98 corvette upgrades listed in the sig.

Thanks
Kris

 

Run the MAf after the turbo and after the wastegate, it will measure what actually goes into the motor.

You could see potential problems before the turbo because the MAF will monitor airflow and the wastegate will blow it off after it has been measured, depending on how the wastegate is setup.

The L98 cars have a restirctive MAF, at a minimum remove the screens. More intrusive is to cut the heat fins carefully. It will not hurt anything and is an old L98 hot rodder trick. The heat fins are there by GM when they did the vette testing in Death Valley desert for extended WOT runs and heatsoak. Not needed in 99% street application. A modified L98 MAF is good to 500-550 FWHP.

Greg at Blowerworks.net sells an LS7 style MAF that works with L98's. You will have to have the MAF table recalibrated.

The right way for injectors would be to upgrade to larger units. The L98 injectors are small since the L98's were rated at 230-245HP depending on year. aving said that, at that low of boost a lower cost FMU setup with stock injectors would work, just dial it in right. Everyone will tell you to put bigger injectors and retune as the right way, but your boost targets are on the lower side, just beware that like all of us, once you get the extra power, knowing there is more to tap into by upping boost will become inevitable.

I only throw out the FMU option because i have 3 years and 50K miles since previous owner set my car up dyno tuned with FMU, but I know it could be a problem waiting to happen and will upgrade to 62lb injectors shortly.

Also, do some research, since L98 is batch fire you cant go too big with injector. I would think a 42lb or even smaller would work for your application. I think stock L98 are something like 26lb.

If you retune, be conservative on your timing since 86 is iron heads, unless you have a convertible and may have aluminum. That was the transition year from iron to Aluminum.

Hope this helps.

 

Wow thank you for all the info this will help for sure!

Ya i'll have pcm4less retune my pcm, and i ask about the injectors just to run it for a short period of time. My plans will include bigger injectors for sure... Cause i'm a horsepower junkie!

That's one thing i forgot to mention i do have an Adjustable fuel pressure regulator (That's what you mean by FMU, Correct?)

One last thing... Its 86E Coupe with iron heads < Also plan to replace in future

Thanks
Kris

 

An FMU is different than an adjustable regulator. It goes inbetween your existing regulator and the return fuel line.

It is a boost referenced 2nd regulator.

The stock regulator is a 1:1 regulator so as boost goes up one pound fuel pressure will increase by 1pound, not enough to get extra fuel in response the the extra forced air.

The FMU is closer to 3:1 or 4:1 and increases fuel pressure signficantly under boost. It allows stock injectors to flow more lb/hr because it increases the pressure when there is boost. This is what would allow a stock injector size to work with the additional air the turbo would push so you get more fuel flow for a given pulsewidth.

It is really a bandaid and the bigger injector route is truely the best, correct approach because for example if you push 7-8 pounds of bost your fuel pressure climbs from 40-45psi to the 85-90psi range under boost and get close to locking up the injector depending on year/model.

I ONLY brought it up because at 4-6 pounds I believe you could set up a reliable system if you were on a budget. Most shops who install FI kits throw the FMU away or on a shelf so you could probably get one for under a hundred bucks just to get it out of their hair. You just have to be really careful in setup.

One last thing about forced induction on an L98. For a naturally aspirated application the tuned port setup is very good with an automatic. An LT1 type setup works better with a 6 speed. I have had 5 C4's and I would take a tuned port over Lt1 any day on an automatic car and I have owned them both, so this comes from real world experience with both types of cars well tuned. This changes with forced induction because the boost adds in the low end torque and really wakes up the top end so a TPI's miniram type of setup will add a signficant amount of power on the top end that will get lost with the TPI setup.

For naturally aspirated, a miniram technically does this but with the wide gear splits on a 700R4 you lose pull as opposed to a TPI setup you shift ito a torque peak. This is why Lingenfelter did the SuperRam box setup was primarily for automatic cars.

With a 6 speed and small gear splits the miniram/LT1 style is definitely the way to go.

More info than you asked for and maybe contradictory to what you will read but gleaned over many years and ownership of C4's of various vintage and hot rod setup.

 

Thank you for the info. More info the better! My car is setup correct it's a l98 700r4, so in the future I should look into a tpis miniram.

Oh and thank you for clearing up the FMU...

Im hoping to get parts together in the next month,

Thanks
Kris

 

i have a custom rear mount turbo wit 80mm, its up for sale, a complete kit, ceramic ball bearing, with a meth kit also, i did 622wrhp wit 22psi, first try at 8psi 443wrhp,,

 

hey just wanted to know where is a good place or website to buy turbo kits for a c4? thank you

 

there are none.
this was as close as it was going to get,
http://www.raptorllc.net/LT1.htm

hp performance had a single as well, and it is not on their page.
http://www.vetteweb.com/tech/vemp_06.../photo_03.html

Or find one of these

 

Stock l98 injectors are 22lb

 

None of these systems IMO provides the power that systems for a C5/C6 do but the cost is about the same.

 

not entirely true.....................

been a while but I am back and have been busy....... long and short of it is no stocked kits but I am doing per order beginning October 15th. details to come... they will not be rear mounts either!

Chris

 

Welcome back, is your system going to be like the one you built a while back? Single or dual turbo?

 

Twin kit with the ability for instant spooling small turbos or up to twin 67mm units which should support upwards of 1500rwhp if desired.

 

That should be fun

 

ooh ok thanks man but any advise i can get on doing a turbo kit for my c4 because i really want to turbo my vette

 

That sounds like fun

 

ooh ok thanks man..ive been trying to find kits and i found some but it seemed too cheap for everythin but i really want to turbo my LT1 and any info or advise i can have would help.thanks

 

This is why I went the supercharger route.

 

I was thinking of going to supercharger for my next project because there was no turbo kit with real power for the C4. I had decided that I needed a F2 supercharger but mounting it and keeping from cutting the hood seems to be a problem. Now with the possiblity of ICEVETT dual system, my only question is would dual 67mm turbo be small for a 454. Time for more research.

 

Take a look at this setup