Turbo on a budget: 91 Z28 rear mount build
 

Started to work on my 91 Z28 finally. Been busy with the black car and was on the fence about what i want to do with this car. Thought about a cam only type setup to keep things simple but in the end i think i can turbo for less money.

So this is a build for ultimate budget. Its a stock 305 TPI car with 130k miles. Well kept and clean. Runs great, but its stock and slow. Being a 305 and that i have a spare 305 tpi motor, i want to boost this and not do a big expensive build like the black car. This is to be a daily driver type deal and just needs to have enough power to be interesting. I sold my 99 ls1 trans am for this car so i need to get back into the mid 12's.

So here we go. The car

Attachment 324481

Just finished a 4th gen disc brake rear swap along with plastic gas tank with new 255 pump. Got rid of drums and the 2.73 peg leg. Now 3.23 posi. I upgraded rear springs to global west lowering springs and also a 23mm sway bar. Front i replaced stock 34mm swaybar bushings and added global west springs as well to match.

Easiest and cheapest way to turbo this car while keeping stock engine bay and ac system is to rear mount. Since muffler and i pipe were shot, it only made sense to replace it.

Re: Turbo on a budget: 91 Z28 rear mount build
 

Bought a brand new walker replacement I pipe from cat to over axle. Car is bone stock down to manifolds and ypipe and cat. Factory 2.25" exhaust it is perfect for small turbo spooling. Walker replacement crush bent type is only 20$

Turbo i am using a on3 T70 t4 .96 i got in classifieds for 280 shipped. It was new and never used. Saved few bucks on it
Attachment 324479
I have a couple friends using on3 with great success.

Plan is to have vsracing wastegate for 99$, and bov for 52$.

Exhaust in place, quick trip to autoparts store to buy some more tailpipe cheap exhaust pieces to extend to turbo.
Attachment 324480

I needed an 18" piece, a 45 bend and an adapter to flare to a 2.5" round to the turbo t4 flange i got from columbia river bends i believe. Its a round hole inlet instead of typical rectangle. Made it easier.

There is more room on the driver side frame rail since no spare tire buldge so i chose to mount turbo here

Re: Turbo on a budget: 91 Z28 rear mount build
 

Attachment 324477

Basically the setup here. Small piece of 2.5" pipe i cut at near a 45 angle to the t4 flange. Catback to t4 flange i have less than 60$ into i believe.

Using factory rubber mount trimmed down and bolted it to the compressor housing bolts to support the turbo abit more
Attachment 324478

Re: Turbo on a budget: 91 Z28 rear mount build
 

Camera angle sucks but it is level and straight back. Tucks up well
Attachment 324473

Attachment 324474

Attachment 324475
Keeping this section slip fit with two tabs that bolt together to keep it tied in. Will have copper rtv to seal slip joint. Whole turbo section can drop out and go back to stock muffler if i ever want to remove it
Attachment 324476

Re: Turbo on a budget: 91 Z28 rear mount build
 

Most expensive part of this is basically the turbo and the oil return pump. Cant really skimp out here. I was able to find a lightly used turbowerx exa pump for 310$ shipped instead of the new price of 399+ ship. Same pump i have been using on the black car for 4 years now. Well worth it.

For now, i will run a -4 line to turbo feed from the china wall fitting in back of the block. I had a left over nitrous feed line so i will reuse it. For return i plan on using a -6 size from pump to engine, likely going into the fuel pump block off plate. I'd prefer oil pan but doesnt look like i will have that off the car to weld a fitting. Wanted to avoid braided AN line for cost reasons so i may look into some cheap rubber line that can handle oil. We shall see.

Cold side will likely be a mix of aluminum and mild steel exhaust where possible, as i can weld steel and not aluminum. Want to keep it somewhat light weight but up over axle and around the engine k member may need some bends so i have some 2.5" pipe left over and will use what i can.

Going to be hot air low boost for now to get it running. Eventually do a front mount intercooler or meth kit depending on what room i have and how much i wanna mod front end for a cooler. Plan to run on code $59 stock 730 ecm until i can get ebl flash or p4.

Going with 42 lb injectors i got off here for 100$. Should be plenty for up to 400 whp

Re: Turbo on a budget: 91 Z28 rear mount build
 

Very interesting.. I will be watching this thread closely to see how well this goes.

Re: Turbo on a budget: 91 Z28 rear mount build
 

deleted

Re: Turbo on a budget: 91 Z28 rear mount build
 

Me TOO ! ...Get it dynode ...would love to see the HP numbers. :driving:

Re: Turbo on a budget: 91 Z28 rear mount build
 

Attachment 324457

Cold side started. Had some old piping from my other turbo car build laying around. Trying to go up over axle so i can still strap this thing down on the dyno lol. Else i would just go under sway bar. its tight in there between panhard bar and upper bar so i may clearance upper or remove it all together.

Re: Turbo on a budget: 91 Z28 rear mount build
 

Just looking from the pictures, which I realize can be dimensionally deceiving, it looks like you have only a couple of inches of suspension movement above the turbo hot pipe around the track bar. Just looks pretty tight to me. I'm sure you've checked, but how much travel is there in the track bar? And are putting a piece of flex anywhere in the exhaust pre-turbo?

Sounds like it ought to be a blast to drive!

Re: Turbo on a budget: 91 Z28 rear mount build
 

The hotside has plenty of clearance for suspension. Its the cold pipe goin over axle under track bar that is tight. I may have to revisit this issue and remove track bar or clearance the sides of the stamping. Cutting off the rounded stamped edges of the track bar around the pipe will give me almost an inch but does compromise track bar strength.
I dont have a upper bar on my other car and never noticed a difference without it so i may just remove it. Idk how much suspension travel to expect there

At this time no preturbo flex pipe. That may change later on but it has some movement to it and turbo is supported by the factory rubber mount above frame rail. Should be ok but we shall see

Re: Turbo on a budget: 91 Z28 rear mount build
 

this should be interesting. thanx for the pics too. lookin good!

Re: Turbo on a budget: 91 Z28 rear mount build
 

Anyone know if the stock fuel pressure regulator can be plumbed to boost? Or do i need a check valve to prevent pressurizing it?

Re: Turbo on a budget: 91 Z28 rear mount build
 

i boost refrenced mine with no issues when i had the tpi on the original motor

Re: Turbo on a budget: 91 Z28 rear mount build
 

Cool. Just didnt want to blow the diaphragm out

I guess i should get an adjustable regulator but not sure i'd need it if it does boost reference some. Even tho its not designed for it. Dont wanna over work the single 255 pump

Re: Turbo on a budget: 91 Z28 rear mount build
 

deleted

Re: Turbo on a budget: 91 Z28 rear mount build
 

I'd be more concerned with overworking the injectors, rather than the pump. That is, if you still have the stock 18 or 19 lb ones installed. I think the 255 will be just fine IMO. How much boost you planning to put to this? (Or did I miss that in a previous post?)

Re: Turbo on a budget: 91 Z28 rear mount build
 

Good size turbo for the app. I like the install.

With the stock engine the ECM will be in single fire mode at idle and low loads with the 42#/hr injectors. Idle will be slightly rougher than the normal double fire mode.

One 255 lph pump is way more than what you need. Stock puts out 40 gal/hr (40*6/.58 = 413hp). I was making about 380hp crank at 10 psi with the stock pump and 11.5 AFR.

Since it is a hot air build I am guessing max boost will be 8 PSI. Stock 91 305ci is at 210hp crank. So 1.54 * 210 * .9 = 291hp crank. You're gonna be unimpressed and put either alky or FMIC or both and crank it to 16psi..........and then comes the 212/212 cam. That would give about 240*2.1 = 500hp crank. Let's face it, these TPI motors were designed for a pickup truck, not high HP. Look at the torque curve it will make!

EDIT: Stock fuel pressure reg is fine for boost. It will do 1:1 fuel pressure raise in boost as required.

Since it is a budget build. Consider getting a $0 stock TPI or vortec roller cam and send to Delta for $150 round trip to have the grind you want put on it (within reason). 14Point7 has WBO2 kit with the sensor for under $100. Maybe get a $20 used ebay shurflo 45 psi pump and remove the pressure switch. Add one of the $5 garden spray nozzles and $20 worth of lowes line and fittings.

Re: Turbo on a budget: 91 Z28 rear mount build
 

Wow turboing a second third gen huh? I didn't expect this to be your thread!
What are your expectations with the spooling? Seems like a pretty big turbo for a stock 305 but I don't know much about this particular turbo. Are the On3 T70's actually a 70mm inducer? Should be a torque monster (well relatively speaking, can't compare to your other car lol) down low if it spools in the meat of the TPI torque range. I'm curious how responsive it'll be. Is it an auto? If so are you are keeping the stock converter? That would make a big difference in the spooling too I'm sure. Very clean car, I like it! You could always throw a bulkhead in the valve cover for the turbo drain, my friend it dumping in the valve cover with a rear mount and it works great.

Re: Turbo on a budget: 91 Z28 rear mount build
 

I will be using 42's for now. I have no worries on the idle i have run these inj before on cars but little bigger motors. I'll get it to work

Its gonna be hot air for now just to dial in the setup, see how it works, spool etc. i have .96 and .68 housings that should fit this thing so i will experiment. Also will wrap pipe if need be. But if i find a deal on a cooler i may throw it in right away. My buddy may have a small one. We shall see.

Stock tpi for now but would like a stealth ram or single plane with elbow someday. Or upgraded tpi parts

Believe me i would love to rebuild bottom end port the heads and add bigger cam, but for now this is just for quick and easy lol
If all goes well more mods over winter break

It is automatic and stock converter for now. Want a 2600 ish stall later on. Def would help spool but stock tranny so i am worried about its life

Re: Turbo on a budget: 91 Z28 rear mount build
 

The idle will be fine, just not as smooth as it was. The 42#/hr in a mild cam 350 are at min BPW of 1.2ms double fire so I know they will be single fire in the 305.

Sure is a pretty car. I would run .96 to start and keep the TPI on it if the rest of the eng compartment is factory. I have one rig with basically the same setup. 305 with low 200 duration cam, stock long block and TPI, 70mm with 1.28 T6 turbine engine mounted. Starts making boost at 2600 RPM and full boost at 3200. Stall is rated at 2000, but foot braking stalls at 2600 due to more torque. It is a fun ride, but feels like a turd at anything less than 10 PSI. The injectors are 58#/hr Peak & Hold (96 bux for 8) fired alternating bank and double fire using a 1995 TBI PCM.

I messed with a used Shurflo 45 psi pump yesterday. Took the press reg apart. It is simple to shim the spring to make more pressure. Could bypass the press switch all together. It is a cheap way to get cooler IATs with -32 washer fluid with some denatured added in.

Re: Turbo on a budget: 91 Z28 rear mount build
 

Well thats one thing i will have a problem with. No matter what i do to this car it will always feel like a turd. I'm to used to my 1100 hp car now. Even that car feels like a turd on gate spring pressure and its a mid 9 car on gates!

Looking into a 100$ intercooler idea from cxracing. Goin to measure size and see where i can fit it in the front nose without cutting up car too much. Gotta plan pipe routing. Be nice to relocate battery to trunk or gut charcoal system since its no longer in use with 4th gen gas tank. I may pull it but maintain the cruise control stuff. We shall see.

Doing injectors and oil feed line off back of block this week.

Re: Turbo on a budget: 91 Z28 rear mount build
 

32x12x3 or 4 fits with a lil trimming of the latch support and works great.

though with a rear mount turbo if u use all aluminum tubing fromt he rear to front it actually cools the air charge alot , not as good as an intercooler but the air is nowere near as hot as a front mount turbo plumbed directly to the tb

Re: Turbo on a budget: 91 Z28 rear mount build
 

deleted

Re: Turbo on a budget: 91 Z28 rear mount build
 

I was considering something alittle smaller like a 18x12 or 25x12. Maybe not as tall as 12.
Also thought of something like a 25x7 and laying flat like procharger intercoolers with a small air duct scoop

Re: Turbo on a budget: 91 Z28 rear mount build
 

You are in the same situation I am in with the TA. Only looking to cool for 600HP and don't want to cut the car up. I have been thinking of putting two small ICs by the turbo / rear end with an air scoop. How much room you got in front of the rear end?

With a car this nice, I would try to leave as much factory as possible including the evap.

Re: Turbo on a budget: 91 Z28 rear mount build
 

My 25x12x3 fit right in front of the stock radiator (without A/C) without having to really modify anything besides slight trimming on the brace that angles from the hood latch area down the bottom of the core support. Obviously if you have A/C that won't be the case. The air deflector underneath pulls all the air through the intercooler and my IAT's are very cool and stable. Any intercooler will cool it down for a few seconds when it acts as a heat sink. It's how well it prevents temperature creep under a longer pull that really makes a difference. I also run water injection and now that I've experienced both I wouldn't hesitate to only run water/meth injection since you want the install to be minimally invasive.

Re: Turbo on a budget: 91 Z28 rear mount build
 

Thats the idea. Its bone stock and really clean. Idea is to do this on the cheap yet not cut the car up in case i wish to sell it and someone doesnt want the turbo. I can just unbolt everything and go back to stock

Like the idea of injection. Just would have to do it on the cheap lol i dont have any expensive water alky inj on my race car let alone my daily driver lol

We shall see

It all depends on how well this all works and how fast car goes. It will be easy to go 12's but i would love to see 11's out of it. At that point boost bug hits and you start adding on to push for 10's etc. thats how black car got to the point its at

Re: Turbo on a budget: 91 Z28 rear mount build
 

It'd probably be close to a wash cost wise vs an intercooler. $100 or so for a pump, $40 for a nice nozzle setup, and then a cheap Hobbs switch since I'm guessing you can't trigger it off the ECM. Could use your stock washer tank as the reservoir. I bet labor wise it'd be pretty close to the same too. Either way you have to fab some brackets and figure out how to plumb everything. I like how intercoolers are more reliable, although I bet you could have better cooling with the water. Or just run E85 and you probably can get by with neither. Ha.

Re: Turbo on a budget: 91 Z28 rear mount build
 

If you get this car into the 11's without drastic motor and drivetrain changes I'm gonna be mad! Lol.

Re: Turbo on a budget: 91 Z28 rear mount build
 

As light as it is i dont see how i couldnt in good air if i get enough converter to 60' right lol. I may run it at track bone stock to see where its at to get an idea how well motor is working

If i get injectors in before end of thursday and retune for them, i can go saturday lol

Re: Turbo on a budget: 91 Z28 rear mount build
 

Subscribed for updates. Can't wait to see how this turns out!

Re: Turbo on a budget: 91 Z28 rear mount build
 

I think the chronicles 9sec car went a lil under mid 11s with a big cam, heads, ported TPI. Well, there was some timeslips posted but then they were questioned so who knows. Will be interesting to see if you can get it into the 11s. I had mid 12s as the best for this stock TPI 305ci setup.

The cxracing fox body vertical IC looks decent sized. I saw some shurflo 60 PSI (mod to 100 PSI) pumps that can do 50/50 water/alky go on ebay for $35 shipped.
A simple 4 resistor and one NPN transistor ckt board ($5 in parts) tied to the 2BAR map signal can turn on the pump via a relay.

Re: Turbo on a budget: 91 Z28 rear mount build
 

My 3700 lb ls1 car ran 12.5's with only 320 whp. This z is several hundred lbs lighter and i think 350 whp is doable once intercooled. That should go high 11 lol i went 11.4 at 392 whp

Its all in the 60 ft, which will require stall. I wont have quite yet lol

My injectors are 42 lb at 58 psi so they will be 36 on stock regulator for now. That will limit things a touch. But like said this is just being thrown together to get it running with what i have and then i can pick at the things that need upgraded later

Re: Turbo on a budget: 91 Z28 rear mount build
 

It will be interesting to see what you can get out of that stock 305ci.

Ah, now I understand your 255lph concerns. I thought your 42s were at stock fuel pressure. At 36#/hr stock pressure it should be in double fire mode at idle. 59psi+15psi drops the lph output quite a bit.

Check out discounthydraulic.com for the hose. Good deals on crimp made hoses or push on hose. Both oil compatible.

Re: Turbo on a budget: 91 Z28 rear mount build
 

Yup. My black car had some fuel pressure issues with 255 pumps. Anything over 60 psi flow goes to the crapper. Lol simply adding a 3rd one did not overcome the pressure deal of the small line size out the tank. I should have went 340 lph single on this blue car lol oh well

13-15 psi should get me my goals but we will see. I just be happy to have good spool response and make it in mid 12's again like old trans am

Re: Turbo on a budget: 91 Z28 rear mount build
 

parker pushloc hose is cheap and so are the fragola fittings , also check ur local napa they can make hyd hoses up that will work as well fairly cheap ,

Re: Turbo on a budget: 91 Z28 rear mount build
 

I was looking at the parker pushloc for return oil. I have 15 ft of -4 an for feed.

The turbo and oil shouldnt be near as hot as some of those front mount setups lol

Re: Turbo on a budget: 91 Z28 rear mount build
 

i have a bunch of it on my cars no issues , its a shame the stuff isnt rated for fuel use :(

Re: Turbo on a budget: 91 Z28 rear mount build
 

Attachment 324391

Doing injectors and this thing is filthy. Got oil sludge and grime built up around intake so deciding i am gonna pull base manifold and clean it up, regasket everything to make sure its not gonna leak

Also helps get to the little plug on china wall i plan to use for oil feed. Couldnt get it out last night with manifold still on so once off it will be easier i hope lol. That plug square is odd size and tight!!!

Re: Turbo on a budget: 91 Z28 rear mount build
 

u know what this means , time to port the base while its off lol, anyways im out for a while going to try to get the engine in my car today , my buddy/trans builder will be here tommorow night and the goal is to get that th350 finished now that i have the missing parts for it so i can get that in the car as well

Re: Turbo on a budget: 91 Z28 rear mount build
 

Lol thought about that and painting it. Guess it wouldnt take long but not sure how much it would help with stock runner and heads
I wanted all this done by end of weekend so its ready to get inspected. Not done with whole turbo build but just get it inspected in stock form, but i guess no rush now

Re: Turbo on a budget: 91 Z28 rear mount build
 

porting will help no matter what , and since u have it off and are going to clean it may as well just get it done even if it is just a quick cleanup in the ports

Re: Turbo on a budget: 91 Z28 rear mount build
 

Oh boy, don't go down that rat hole. Stick some paper towels in the ports, wire brush it and blow it off. It will look fine.

I would pull oil from above the oil filter. Much easier to get at and no TEE needed. Just a 1/4" NPT to what ever fitting you use. Piece of 1/4 or 1/8 brake line works well.

I talked to walbro about the 400lph pump. They test them down to 8 volts. As is, the stock return line is too small. I am going to put a resistor in series to drop the voltage to limit pump flow. Then bypass the resistor when at x amount of boost.

EDIT: The push lock at discounthydraulichose is fuel compatible. Way cheaper than NAPA usually.

Are you planning on returning oil to the fuel pump mount area? Are the later 305s drilled for oil return?

Re: Turbo on a budget: 91 Z28 rear mount build
 

Lol probably notgonna port it. Just redo gasket seal. Clean base with powerwasher

This motor has the oil pressure sending unit in filter area, leaving behind block open for fittings. Thats what i used on my other car

This one should have a block off plate. My spare 91 motor did. Its lower than valve cover so shouldnt have a problem getting oil up to it. Else i'd have to go valve cover as i am not gonna pull oil pan

Re: Turbo on a budget: 91 Z28 rear mount build
 

nice to know ill have to take a look for when i put that hp 1800 pump in the car

alot of rear mount turbo builds ive seen drill and tap the oil fill on the valve cover for an an fitting so it does work but id want to return it as low in the motor as possble ,

another option is to return the oil right into the timing cover , this option is pretty nice as it drains right into the pan and is much easier to get to then the pan

Re: Turbo on a budget: 91 Z28 rear mount build
 

I forgot they moved the oil press sensor in the later years.
Make sure you look into the fuel pump mount floor area and check that the block was drilled with a hole going to the oil pan.

Thumbs up to the 15psi and cooler IATs.

EDIT: If it turns out that the fp area is not drilled, weld fitting to a piece of 1/8" thick plate. grind area on oil pan for return. Punch hole for oil return. Weld 1/8" plate over hole with the pipe lined up to the hole. This way no metal gets into the pan.

Re: Turbo on a budget: 91 Z28 rear mount build
 

I have had a lot of success with pushloc on off-road stuff, and it's pretty cheap too (compared to -an)



it's a slippery slope my friend! :lmao:

Re: Turbo on a budget: 91 Z28 rear mount build
 

Oh i know it gets slippy. Already want to do a single plane now cuz i dont wanna reassemble this tpi!!

Down this far might as well throw 1.6 rockers on lol

I gotta use self restraint. Lol keep budget idea in check

Welding on pan makes me nervous! Can the heat and sparks flash oil vapor off?? Or ignite left over oil residue in pan even if i drain it?

Re: Turbo on a budget: 91 Z28 rear mount build
 

i was always taught to weld the pan without draining the oil out of it , its harder to ignight the oil when its full, unless of course the car runs really rish and theres a ton of fuel in the oil. then u drain it and refill it with fresh oil