Inliners International Forums General Discussion Blown and Injected Calling carb experts.

I need some help. I have a 53 stude bracket car with a 292. I'll explain a little about the setup. It's bored .040 with a set of Tom's pistons, 1.94 intakes with some porting and lump ports, delta turbo cam with .544 lift, Tom's 1.75 roller rockers, Clifford intake with a homade exhaust out of SS ells. The turbo I've got on there now is totally wrong but it was given to me so I will use it until I can afford the right one. The turbo is a Garrett Gt4288 with a T6 exhaust which means it doesn't start making boost until I get to about 3500 rpm. Now for my main problem. When I bring the car up to about 2000 on the converter and nail it to the floor it will just die if I keep my foot down. The car won't move 5'. If I roll into the throttle easy it runs pretty strong. Ive got two carbs with the Hanger 18 modifications. A 650 Holley dp and a 750 Holley dp. Currently I've got 73-83 jetting with the secondary pv blocked. I have replaceabe jets in the primary pv circuit with .046 orfices. The car idles with about 12 inches of vacuum so I have a 9 pv in it. I,ve tried squirters from 25 to 40 0n both carbs with no change. Different cams with no change. It idles 14.5 afr and wot it seems to be about 10.5 with the current jetting. It produces more power with the 750 so I hope to keep that if I can. At least it feels that way on the short stretch of narrow road I can test. It will start spinning my 13-31 Hoosiers when the boost starts to come on. I guess I've been lucky with carbs in the 50 plus years I've benn building cars because I've never had this much trouble. Sorry for the long post. Any HELP would be great.

Its probably more of a turbo being too big problem than a carb problem.

Harry,
Glad to hear you came over to the turbo side!
A few questions.
What is going on with the timing?

Put a lower PV in it. Like a 2.5. I bet it is dumping way too much fuel in.

My car likes 12.75 AFR at idle and cruise. around 11 at WOT.

I'll try a lower pv. My timing is 10 initial 35 total all in by 1800. I'm also going to try it tonight with out the hat on it to see if I can eliminate the turbo as the problem. I know it's not the correct turbo but for now it's what I'm stuck with. Thanks for the help.

How much boost and does it start at what RPM and goes up to what?

My engine was found to be getting way too much accel pump shot. Lowered that # and it will RPM faster.

Your converter is too tight, need a least 4500 stall.

Harry

Harry 6674 II 5760,

What is the A/R on the turbine housing?

The specs of your camshaft?

What size are your SS els?

Sounds like acceleration circuit is not working correctly.
Too much or not enough squirt? Hard to say, need more info.


That is a big turbo T6 housing is really huge!

Idle A/F ratio is lean.

MBHD

Harry,

You said the turbo does not make boost until 3500, if you try and take off at 2000 the turbo is a restriction and will not have any power, it must be in boost to work, That is why you need a 4500 or higher converter. That's why when you roll into throttle it works. A 4500 stall will work fine on the street.
Stall is a factor of how must torque is applied to the converter not if it's on the track or street

Also on a carb turbo you must run a 2.5 power valve to hold the extra fuel back until you are in boost. It's best to use a boost referenced power valve to hold back untill under full boost.

Harry

Last night I took the hat off the carb to eliminate the turbo from the equation. It still does the same thing. Nail the throttle and it dies. I didn't have 2.5 pv so I will try to find one tonight. I fully understand about the converter and turbo not being the best for this engine. The last engine in this car was a 500 cube cadillac, thats the reason for the tight converter and the 3.50 gears. I kept reading that these were torque engines so I kept the same converter and gears. Maybe with right turbo I'll find some touque. If I can't get the 2.5 pv locally I may try it plugged until the pv comes in. I may look into one of those cheap GT45 turbos for the heck of it or maybe a Holset HX50. I won't spend a lot of money on a turbo. I've got about 4 other wheeled projects to help remove my money from my person. Thanks for the help and I'll look into boost referenceing the pv. I've heard of it just don't know how to do it.

Harry,

Even with the hat off the turbo is still a restriction, these engines only make enough torque for a tight converter if they are under a lot of boost, keep the gear.

Harry

If this helps the trouble shooting with the 750 I disconnected the secondarys and wired them closed, no hesitation. Thanks.

I would think if it was too lean it would back fire, maybe it's too rich? Or too much pump shot on the secondarys?

Last night I bought a 3.5 pv, it's as low as I could get local. I'll do the mods to boost reference it and give it a try. It might be a few days, I found a broken exhaust stud and of course I can't get to it to drill it out. Thanks for the help.

Consider installing a wide band O2 sensor after the turbo... it'll tell you whats going on. If you get one with a dash gage they can log the data to look at after the run...

I have an Innovate wide band with gauge. The AFRs are workable if I take off easy, If I nail it it dies so fast the gauge can't tell me anything.

I'v been thinking, with a very tight converter at only 2000rpm and no boost, the engine has very little air flow to pull fuel through the carb, thats why when you only use the primary side, with the secondary wired shut, the signal is stronger when you snap the throttle open.

It needs a lot more stall.

Harry

Yup,
& w/having a T6 turbo, that turbine housing has to be huge!

Maybe a 1.41 A/R, that will definately be a dog.

MBHD