Ok, I've been working on a turbo setup for my car for about 3 months now and I thought that it was going ok... however I still cannot get this piece of junk to run right! Here's my setup followed by the problems Small Block 355 Chevy T70 Turbo 38mm wastegate @ 5.83 psi Mighty demon 750 blow thru Summit 110gph boost pressurized fuel pump Timing set at intervals of 2 between 10 and 20 (tried every combination, right now at 14*) A mock up boost retard ignition system(retards timing by 10 degrees at boost) Accel Shorty Plugs Accel 8.8m wires Problems: Car makes a huge backfire a few seconds after shutdown Car drives fine up until about 3500rpms than hesitates almost as if an RPM limiter was active...For some reason the car builds boost according to my boost gauge its just that the car isn't going anywhere, I can still shift it but up until what I'm guessing is the turbo kicking in and the secondaries on the carburetor opening up it runs fine, its just that when boost starts it becomes sluggish Do you think an auto body place would be able to determine whats wrong? I've tried an exhaust place but they said no... Or perhaps one of your guys insight would be able to help me? Thanks alot I appreciate any info Jim

That wastegate seems kinda small? I use a 50mm, and was told with my setup dont go smaller then a 50mm with my low boost levels.
Are you running 14* timing wot at 5.8psi? I am running like 19-20* on 7PSI and thats still WAY to low.

Try giving the car some more timing.

Jay

I dont think the wastegate is the problem cause it is venting properly and controlling the boost, no spiking or compressor surging or anything

and i mean 14* at idle, too be honest I dont know how to get a timing reading at WOT or under boost cuz the car only makes boost while driving

Mines a bit different as i am EFI, but what I do is when I see boost 3800+ (WOT) i dropped my timing. so when my MAP see's 90-100KPA(1 bar) my timing drops from 40ish down to 20 (ramps down slowly till 4000 and stays pretty steady)

Also maybe you should get a wideband on the car so you can make sure your getting the right fueling. Maybe its leaning out?

Jay

throw your carb in the garbage and get efi.

while efi may be a better setup for a turbo, a carb will work just fine, no reason to just throw it in the garbage because of a tuning issue

Worst advice ever. Give the carb to me! Plenty of very fast carb turbo guys out there including a guy I know just a couple blocks from me.

You have fuel in the exhaust. It sits in there, gets hot, and lights causing the backfire. This is a problem with the carb. Incorrect float levels and/or too much PCV or main jet.

Is this a double pumper holley or vacuum secondary? I only know of double pumpers working for boost.

Auto body won't figure it out. Try posting in the carb section of www.theturboforums.com.

Did you install the D1941 module and switch? If so, have you tested that it retards by 10*? If you did and it is set up right then you can run your distributor as normal in terms of timing. That is set the base timing to 8* or what ever is best. Then about 40* during cruise from the mechanical advance and vacuum can. Under WOT boost the vacuum advance is zero so you will see your base+mechanical-retard which should be something like 8+14-10 = 22 - 10 = 12*. If you want more you could bump up the base timing a little.

Only fast easy way to check all this is with a timing light and Wideband O2 sensor. Two tuning tools I swear by.

there are plenty more faster turbo efi guys out there. Do it right do it once.
if u didnt notice but no car manufacturer for the last 20+ years uses a carb.
I own 2 turbo cars so how is my advice worst than someone who doesnt even own/race a turbo car like yourself???

Yes and no. I prefer EFI also, but a well tuned carb can do quite well. Can it start a twin turbo T76 1400HP engine in the northern US dead of cold winter and Arizona hot sun in the summer and make 1400HP in all cases after warm up...........no it can't. Can the EFI do it.........yes it can.
That is an extreme case that most don't care about when trying to make boosted HP. Most are just looking for something good and fun. A carb. can do quite well under most conditions when tuned properly.

Notice he is using a "T70 turbo". That is a an Ebay T70 so you know this is a low budget build. I am all for low budget turbo builds. For under $1000 a cheap carbed, T70, mechanical dizzy setup can acheive 500-600 FWHP. Try to do that NA for under $1000........won't happen. Try 3-5 times that dollar amount.

So, I would spend $50 on a Holley jet kit and plan a weekend of tuning. Find a friend with a WBO2 sensor. Or better yet.......go to www.14point7.com and buy a WBO2 controller for $50 and the $60 WBO2 sensor. Put the stuff together and you have a WBO2 sensor for under $120 that you can use on anything and use a laptop PC to record. You could go without the laptop and get the display for $40 I think.

the d1941 retards proportionally, that is i tested it without using the hobbs switch and at 14* it retards it to about 6-7* and at 20* it retards to about 9-10*

also i screwed with the link on the carburetor to make it one to one, that is the secondaries open the same with the primaries

I actually retarded the idle timing to 10* and its running a hell of alot better, that is with proper tuning, i made it a little more leaner than the ridiculously rich condition it was at

btw the carb is mech secondary double pumper

That is good that it is a mech. double pumper.

It sounds like you are getting the hang of it. It also sounds like it was overly rich. As you lean it out keep an eye on detonation. Although, you are not running a lot of timing right now so that is in your favor.

Overall, it sounded like it was overly rich causing the bog and as lean it out it will rev quicker. Without a WBO2 I would keep an eye on the spark plugs.

Those D1941 modules come in handy for a cheap NOS and boost timing retard setup. They also work good if you run a lot of base timing. You can add a toggle switch with one side to ground and the other to the D1941 input. Suppose you have your timing advanced a lot and the starter won't crank the engine........you fill the toggle switch to retard 10* and then it starts easier. Once running you flip the switch back to add in 10*.

The wideband thing on that website looks intense plus it says they are out of stock on em =/ Im gonna pull the plugs again tomo and check em, can i just run an 02 sensor and use an AFR gauge or does that require the ECU?

The WBO2 on that site does not require an ECU. You can just read the display. All that is needed is the LSU 4.2 WBO2 sensor, a 5 amp fuse, and wiring.

If you use a stock NBO2 (narrow band) it will not read the AFR accurate like a WBO2 would. You would need a gauge to read the NBO2 sensor. No ECU necessary. This setup is not that good though because it is not accurate at reading the AFR. The NBO2 will only say rich or lean, not how rich or how lean. Right now you know you are rich so it wouldn't tell you much.

The WBO2 is accurate at reading the AFR. If I was in your situation I would keep checking the spark plugs and not run a NBO2 with gauge because it won't help much.

taking the spark plugs out requires me to dissassemble the entire turbo setup btw, do you think i could get away with a decent narrowband afr gauge? such as http://www.summitracing.com/parts/ATM-7375/?image=large

I am not sure what to say. I always use a WBO2, but I do compare it against my NBO2 logs. Usually a NBO2 around .8 volts is in the 11-12 AFR range but it varies.

Be very careful if using just the NBO2. The cost is about $80 and a NBO2 is about $30. I think the Innovate LC-1 WBO2 setup is $200, but I am not sure if that comes with a sensor.

Maybe try ebay for a used NBO2 gauge. I just can't see spending $80 on an item that is not that useful.

yeah it comes with an o2 sensor but thats really pricy im already almost 400 over budget on my project lol

i can prolly get one of those "jdm" air fuel ratio gauges on ebay just to mess around with for the time being... they are 30 bucks... if i dont like the results ill have to "borrow" the wideband from my friends turbo altima

When that motor was put together was the cam set straight up or advanced? Was that motor running right before the turbo, or was it put together along with the turbo setup. Im dont know too much about carbs, but from what u said, sounds like your getting enough fuel.

motor wasnt exactly put together lol it was taken out of a blazer its a gmpp 350 that the only mod was bored out thats about it and yeah i ran it for about 2 years b4 the turbo and it ran great... it also runs great without the turbo hooked up, just using the carb feeding in n/a

im going to autozone tomo to pick up a cheap sunpro afr gauge and a bosch o2 sensor...hopefully itll be decent i mean itll prob read all the way in the right red zone cuz i have the screws to the point they are about to fall out of the carburetor

almost sound like a boost referencing problem. just a stupid question you ever try setting the boost a bit higher see if the problem starts subsiding

Oooh mr turbo racer puffin his chest up Your advice of just tossing the carb away is just stupid. There's a reason for him using a carb so why not just freaking help the guy with what he has?

As soon as I read that that's what I thought, I'm using a carb because I cant afford some $2000+ setup, injectors, electronic gizmos and stuff for an efi setup.

And TTROC I took off the boost controller and it seems to be doing alot better now too, I been using one of them ebay boost controllers, and maybe they are just pieces of garbage. So than I turned the screw out on the boost controller and it spiked through the roof, I'm probably gonna end up with an EBC from summit or something.

Maybe Ill throw the 15 pound spring in there, see how the stock motor likes that guy

ok when you do swap the springs lets us know what the out come is.

And honestly i think the best boost controller is a 5 valve from home depot or lowes from the plumbing section

I had a similar problem with a similar motor in my Malibu. In my case it was the design of the carb hat that was at fault. Boost blew across the bowl vents, sucking fuel out and down the carb throat, causing a severe rich condition. I tied the bowl vents together with a piece of fuel proof hose with a cutout at the top & gained great drivability & 100hp. Good luck, Mark

HMMMMMM.... I'm using Spectres carburetor hat...

http://www.summitracing.com/parts/SPE-9843/

I wonder if this thing is causing the problem cause its not necessarily made for turbo applications

Can you explain what you mean by tying the vents down? Did you tee the two of them together and cut a hole in the hose so that boost couldn't suck fuel out?

I just hooked a length of fuel hose to both vents and then made a slit across the top of the hose. Yes I guess you could hook a short piece of hose to each vent then hook them together with a T fitting & leave the other end of the T open. Mark

That's not a bad idea at all, I'll add that to the list of things to try

So I'm gonna swap out the springs
Hook up the AFR gauge to get a reading
Tie off the Bowl Vents
Tune the jets and maybe reset the fuel bowls

Hopefully this goes good and I can get a video or something, does anyone else car start to burn out around 3000 rpms out of no where?

Something else to consider is your plug gap, didnt mention where is is set but definately something to double check while your checking everything over.

It's at 40 came stock at 35, is that too much or too little?

running even worse now... when I floor it it stalls out

you need to tighten that plug gap up, youre not running crazy boost numbers but still should probably be around .025", you wanna tighten it up to prevent boost blowing out the spark. good luck

I know you're not running a ton of boost but are you just running a stock HEI ignition? I had a 8.5:1 blower motor and we started having problems with the iginition at under 10 pounds of boost that were similar to what you're describing. A 6AL fixed everything.

did u do everything at once? How does it stall out, sputters and stalls, or just bucks pops and stalls?

It just feels like its dumping the fuel in and boom stall kinda like it wants to do it but than just fails...

I did the Bowl Vent mock up thing, hooked up my gauge which says Im ridiculously still rich

just for kicks I'm gonna try and take it around the block without the carb hat on, see if its a turbo problem or a carburetor problem

tomo ill regap the plugs to .25 and astro did you just get the 6AL or did you have to get a new distributor and all that stuff

i run a msd 6al w/ btm, with a msd pro billet distributor locked, using the btm to lower timing under boost, and havent had any spark related problems or what its worth. also run two steps colder spark plugs gapped @ .025"

that stuffs expensive but its worth it when youre standing over your car in the garage wondering what is wrong...

I have to run shortys so Im limited on the heat range of the plugs but Im gonna gap em to .25 like you suggested, I also ordered a more powerful Ignition Coil Upgrade Package 55,000v (coil cap rotor and wiring) for added fuel burning to hopefully stop the backfiring.

HOPEFULLY, the problem was the plug gap and the spark getting blown out, I mean I had to take the whole turbo setup apart just to get the plugs out so I might as well do a quick check on everything. So far the pressurized fittings on the fuel pump are still secure, the wastegate piping was filled with water(my fault I had to hose off the motor) thank god I didnt run it like that.

If it turns out not to be the plug gaps and the coil doesnt do anything, is there anything I can try?

update: apparently one the spark plugs is cracked right down the center, and was half bent Im guessing from rubbing into the manifold...

any progress?

I shoulda ordered overnight shipping lol, I'm waiting for my parts to come today, I will intsall later and update...

Apparently the spark plug was arcing against the manifold... putting a decent amount of voltage into my headers lol, thats probably what made the first fire Number 6 & 8 were fouled out horribly and there was a huge amount of carbon build up in the turbo manifolds and down the downpipe a good 3 feet right before the cat, so apparently its still running rich minus the fact that 6&8 werent firing

GUESS WHAT!

Still doesnt work lol

Im scrapping the whole system I give up, Ive spent almost two grand already and its still running like a pos.

I'm gonna save up and get this bad boy

http://www.summitracing.com/parts/PFS-70026/

Self tuning =D, comes with 2.5 Bar Map Sensor good for 20 lbs of boost, 220lph fuel pump, boost pressure fuel pressure regulator, ecm, 4 60 lb injectors, wideband o2 sensor, plus its all contained inside the throttle body itself, no bulky mess or anything like that

It's highly doubtful that is the wastegate. I run two 38mm TIAL Wastegates and on my lowest setting I am making 600 rear hp and on the high setting 850 rear hp at 9-18#s boost..my car drives as good as a stock car.

I also highly doubt that your spark is being blown out with the amount of boost your are running. I ran 18#s using NGK TR6 Plugs gapped at .034". Everything was/is fine. With FI you have to make sure the tune is good.

Have you hooked it up to a wideband or put it on a dyno to see what your afr is?

Running like **** has to do with air, fuel, and spark...granted all of the mechanical things...which you have stated did.

I mean I suppose a dyno would have a wideband o2 sensor they can put on to check the air fuel ratio and all that but honestly I cant even drive it down the block so getting it to a dyno would be a challenge...

I drove it down the block today and I think I narrowed the problem down to its running out of fuel cause I managed to rev the **** out of it and it ended up stalling and than not cranking until I pumped more fuel into the carburetor, so could it be possible the problem lies in the carburetor and that the fuel isnt moving from the bowls into the engine properly?

After a little searching it turns out you can get a simple wideband AFR gauge, controller and bosch for about $150, which I guess I will pick up
I'm also gonna go with an electric fuel pump and boost fuel pressure regulator
And for added tuning a complete jet assortment

The jets for my carb are 75's for primaries, and 83's for secondaries, any suggestions on what to up them too?

got any updates

Any progress?

http://www.thirdgen.org/techboard/po...ml#post4230889 (Whelp, it works (for those of you following my turbo build))