Help with Turbo Lag, Swap gear ratio? (1 Viewer)

[Nitro]

I have a 1993 HDJ81 Imported from Japan with a 1HDT 4.2L turbo diesel. Running 33 inch tires on the 16 inch wheels. Axle gear ratio I believe is 4.11.

Thinking about running 4.88 or 5.13s to help with the turbo lag that is present from a dead stop to acceleration. Seems like the turbo kicks in around 1400/1600 RPMs.

I’m unable to find the speed/rpm calculator that you input your transmission/transfer case/differential ratios/tires size for a result of speed/rpms at 60.

Anyone have experience/input on this?

Cheers

 

[Dusten]

I have a 1993 HDJ81 Imported from Japan with a 1HDT 4.2L turbo diesel. Running 33 inch tires on the 16 inch wheels. Axle gear ratio I believe is 4.11.

Thinking about running 4.88 or 5.13s to help with the turbo lag that is present from a dead stop to acceleration. Seems like the turbo kicks in around 1400/1600 RPMs.

I’m unable to find the speed/rpm calculator that you input your transmission/transfer case/differential ratios/tires size for a result of speed/rpms at 60.

Anyone have experience/input on this?

Cheers

View attachment 3420038

You can't find a speed in gear calculator?


Transfer case ratio won't matter unless you're trying to calculate low range speeds

Gearing Analyzer with Shift Tracer

Enter gear ratios, tire and diff ratio to analyze RPM vs speed at shift points with tracer

www.blocklayer.com

 

[OffRoadScott]

Turbo lag is based off size of the turbo. You might be able to help some of the issues you are dealing with by going with a larger exhaust allowing the turbo to breath.

 

[Dusten]

Turbo lag is based off size of the turbo. You might be able to help some of the issues you are dealing with by going with a larger exhaust allowing the turbo to breath.

Gearing helps because a turbo also builds boost via load. But he's going the wrong way for that. Typically turbo cars will have a tall rear gear.

Example, most na fox bodies run a 3.73 gear gear but turbo cars tend to run a 3.27

He's hoping gears will get him into boost faster. But 4.88s and 33s are going to turn a lot of rpms on the freeway.

 

[Ragnaroek]

I'd start with more fuel and a 3" exhaust.

 

[mudgudgeon]

Auto or manual?

Stock turbo?
Stock exhaust?

Agreed 3" exhaust helps a lot. More fuel will help it boost earlier, but you won't get it boosting a lot before 1400RPM with the stock turbo.

If you're going to add more fuel, an EGT gauge is highly recommended

My hdj81 with 4.11 gears, 35" tires, stock turbo, 3" exhaust, manual trans and increased fueling had no issue with turbo lag.

If you wanted to take off hard, a quick blip of the throttle ahead of popping the clutch for take off would help it boost a little.

They can be a really fun beast to drive

 

[Nitro]

Thank you for all the replies.

 

[Nitro]

Auto or manual?

Stock turbo?
Stock exhaust?

Agreed 3" exhaust helps a lot. More fuel will help it boost earlier, but you won't get it boosting a lot before 1400RPM with the stock turbo.

If you're going to add more fuel, an EGT gauge is highly recommended

My hdj81 with 4.11 gears, 35" tires, stock turbo, 3" exhaust, manual trans and increased fueling had no issue with turbo lag.

If you wanted to take off hard, a quick blip of the throttle ahead of popping the clutch for take off would help it boost a little.

They can be a really fun beast to drive

It’s an automatic transmission, stock turbo. Looks like 2 1/2 inch exhaust. I’ll look into 3 inch exhaust.

 

[Nitro]

You can't find a speed in gear calculator?


Transfer case ratio won't matter unless you're trying to calculate low range speeds

Gearing Analyzer with Shift Tracer

Enter gear ratios, tire and diff ratio to analyze RPM vs speed at shift points with tracer

www.blocklayer.com

So is the transfer case a 1 to 1 ratio in high gear?

 

[OffRoadScott]

Get one of these!

Anti Lag

 

[Dusten]

So is the transfer case a 1 to 1 ratio in high gear?

Yea

 

[Nitro]

Yea

Do you know the low range ratio?

 

[Dusten]

Do you know the low range ratio?

2.488:1

 

[Dusten]

Get one of these!

Anti Lag

Kind of need an ignition system

Diesel tends to use nitrous for the same effect

 

[Nitro]

2.488:1

Cheers

 

[Fosters]

Do 10% under drive high range in the transfer case…it’ll get you what you need rpm wise