SR20 swap into Datsun 620

[Kami04]

I wanted to reach out and see if anyone has done this swap and used a TOP MOUNT turbo set up I’ve got the mounts figured out but wanted to do a top mount if possible although I know that the brake booster may get in the way

[Wildcat Walker]

I have done the swap, many years ago. I currently still own an SR swapped 620, albeit in project mode at this time. My plan is to run a top mount using the Mazworx manifold, and likely a Mad Dat Booster. Special care must be taken to insulate from the turbine heat. Blanket the turbo, blanket the booster, and a treatment to the hood. 

 

Mazworx - Mazworx SS Series SR20DET/VE RWD TopMount Turbo Manifold #70001 GEN2 30

 

Mad Dat Brake Booster and Master Kit – Mad Dat Motorsport

[Kami04]

3 hours ago, Wildcat Walker said:

I have done the swap, many years ago. I currently still own an SR swapped 620, albeit in project mode at this time. My plan is to run a top mount using the Mazworx manifold, and likely a Mad Dat Booster. Special care must be taken to insulate from the turbine heat. Blanket the turbo, blanket the booster, and a treatment to the hood. 

 

Mazworx - Mazworx SS Series SR20DET/VE RWD TopMount Turbo Manifold #70001 GEN2 30

 

Mad Dat Brake Booster and Master Kit – Mad Dat Motorsport

Thank you! I’m gonna try using the ISR ram top mount and I’ll let you know how it fits I’ll swap the booster though!

[Kami04]

3 hours ago, Wildcat Walker said:

I have done the swap, many years ago. I currently still own an SR swapped 620, albeit in project mode at this time. My plan is to run a top mount using the Mazworx manifold, and likely a Mad Dat Booster. Special care must be taken to insulate from the turbine heat. Blanket the turbo, blanket the booster, and a treatment to the hood. 

 

Mazworx - Mazworx SS Series SR20DET/VE RWD TopMount Turbo Manifold #70001 GEN2 30

 

Mad Dat Brake Booster and Master Kit – Mad Dat Motorsport

Would you know the OEM brake line size? 

[Stoffregen Motorsports]

There's more than one way to skin that cat.

 

One option is to move the brake booster closer to the firewall. Obviously it is mounted where it is because of the proximity to the clutch master, but if you move the clutch master over to towards the fender, you can make room for the booster mounted directly to the firewall. To get the correct pedal position, just bend the pedal or cut the pedal off and move it over on the pivot bushing.

 

Another option is to ditch the booster. These trucks are so light you don't really need power brakes anyway. Besides, that booster is so small, it's not doing a ton anyway.

[Kami04]

6 minutes ago, Stoffregen Motorsports said:

There's more than one way to skin that cat.

 

One option is to move the brake booster closer to the firewall. Obviously it is mounted where it is because of the proximity to the clutch master, but if you move the clutch master over to towards the fender, you can make room for the booster mounted directly to the firewall. To get the correct pedal position, just bend the pedal or cut the pedal off and move it over on the pivot bushing.

 

Another option is to ditch the booster. These trucks are so light you don't really need power brakes anyway. Besides, that booster is so small, it's not doing a ton anyway.

I’d like to do a brake booster delete but I can’t find anyone that makes a kit

[Stoffregen Motorsports]

Kit? Basically just remove the pedestal, and make a bracket/plate that will bolt the master to the firewall.

[Stoffregen Motorsports]

Or better yet, get a Wilwood master. They come in about four different styles, from modern to classic looking, and with various mounting styles. Veritcal holes, horizontal holes, etc.

 

The compact tandem master has that goofy screw on lid, but is really short, for  dual circuit master.

[]2eDeYe]

https://zcardepot.com/products/brake-master-cylinder-1-wilwood-240z-260z-280z?variant=19275615436913&currency=USD&utm_source=google&utm_medium=cpc&utm_campaign=google%2Bshopping&srsltid=AfmBOore8Ij_7AwEvfLpgr92ZJjcaaWWEZ603zuvg4BGQhK-4Iu2XE4bAy8

[Kami04]

Awesome thank you guys will get the brakes set up

[Stoffregen Motorsports]

A 1" bore master might be too big to be used without a booster. I had one of those like in the link and the pedal was way too firm.

[Kami04]

1 hour ago, Stoffregen Motorsports said:

A 1" bore master might be too big to be used without a booster. I had one of those like in the link and the pedal was way too firm.

Any link recommendations? 

[Wildcat Walker]

27 minutes ago, Stoffregen Motorsports said:

A 1" bore master might be too big to be used without a booster. I had one of those like in the link and the pedal was way too firm.

We might agree on this. ^   I ran a larger bore master when I was driving my 620, with the stock booster, and Jason Pope's D21  Brake "kit" and the pedal was too firm. I have never taken the time to draw a free body diagram of the stock 620 pedal assembly and determine the forces required to get baseline brake pressures, but It might be good to do. If nothing else, just to emulate the stock pedal feel with upgraded braking components.  One thing that does need mentioning is that all else being equal, upsizing the master cylinder bore will require more pedal force to generate the same brake line pressure, but with less pedal travel. The pedal travel really isn't a huge factor as it's not something your foot is as sensitive to, but the force required to achieve desired braking definitely is.  

 

I would probably avoid modifications such as moving the booster, but deleting it entirely is an option. I personally wouldn't delete it from a turbo application. As you can imagine in a boosted Datto, a guy needs all the brakes he can get. So that leaves two options, finding a booster that is suited to the braking and sizing needs, or not running a top mount manifold. The Mad Dat booster diaphragm, based on the measurements in the images, appears to be about 100mm whereas the stock 620 is 178mm. This works out to be about  a 62% loss in brake boost force, but that remaining 38% assistance is still very useful compared to deleting the booster entirely. 

 

I would personally rather run the manifold, so Mad Dat it is. The reman 620 boosters from AutoZone were over $100 back in 2009 when I bought mine, so the $256 for the Mad Dat doesn't seem so bad since its brand new in a post china flu world. 

[datzenmike]

Keep the booster. It roughly doubles the brake line fluid pressure. If you stop at a set rate using 66 pounds pedal pressure, in order to stop without the booster it will require 132 pounds. I know, doesn't seem that much but in stop and go in town the fatigue adds up. At 132 pounds pedal pressure you generate 875 pounds line pressure without the booster. With the booster 1,425 pounds of line pressure. When it comes to brakes, too much is almost enough. With an SR in it, it's not at all enough. 

 

These are not light trucks, they are 500 pounds more than a 510. That is if empty.

[Kami04]

So what is reading from all the responses is that I either change manifolds or I delete the booster but if I delete the booster it will be a extreme pain to drive?

[Wildcat Walker]

20 minutes ago, Kami04 said:

Any link recommendations? 

 

5 minutes ago, datzenmike said:

Keep the booster. It roughly doubles the brake line fluid pressure. If you stop at a set rate using 66 pounds pedal pressure, in order to stop without the booster it will require 132 pounds. I know, doesn't seem that much but in stop and go in town the fatigue adds up. At 132 pounds pedal pressure you generate 875 pounds line pressure without the booster. With the booster 1,425 pounds of line pressure. When it comes to brakes, too much is almost enough. With an SR in it, it's not at all enough. 

 

These are not light trucks, they are 500 pounds more than a 510. That is if empty.

Mike, can you please detail your calculations so I can follow? You're giving force units (lbs.) not pressure units (lbs./in^2).  We can neglect the slave to shoe relationships and just work from pedal to slave. The stock master and slave diameters are .750". 

[Wildcat Walker]

6 minutes ago, Kami04 said:

So what is reading from all the responses is that I either change manifolds or I delete the booster but if I delete the booster it will be a extreme pain to drive?

No, keep some sort of booster. Preferably stock. Find a manifold that fits stock booster or a smaller booster (Mad Dat). You can manipulate components to give the proper pedal feel and required braking, you will just need to do some simple math. 

[datzenmike]

The numbers are pounds of foot pressure and line pressure in in PSI. I should have said this. All are from the '78 620 FSM

 

The '78 used a 13/16" master (front disc)

The '78 master vac booster was 6"

 

The '73 booster made 1,250 PSI @ 132 pounds of foot pressure

 

Sorry I don't have a '75-'77 FSM. It's likely slightly less than the '78 but more than the '73. If you have a working brake booster. Disconnect it some time but beware. The change is dramatic.

[Stoffregen Motorsports]

4 hours ago, Wildcat Walker said:

No, keep some sort of booster. Preferably stock. Find a manifold that fits stock booster or a smaller booster (Mad Dat). You can manipulate components to give the proper pedal feel and required braking, you will just need to do some simple math. 

Math or trial and error.

 

I personally would delete the booster. This means running a smaller master, but as long as you have enough brake pedal travel, that's fine.

 

Ok, so my Wilwood suggestion may have been ambiguous. They don't make a master with a bore smaller than 1". Stock Datsun masters run from 7/8 to 15/16. I'd go with a 7/8 master and ditch the booster.

 

But then, what are you doing for brakes? Four wheel discs? Different calipers? If larger, they could require more volume. Though it takes time, and some possible parts swapping, there is no substitution for trial and error. Even math doesn't always translate.

[Wildcat Walker]

FYI, if you don't post pictures you will be banned. 🤥

[paradime]

There are manifold options that can give you more space. The Artec moves the turbo forward about 1 3/4". Another advantage is the V-band connection to the turbo and waste gate allows for a some rotation to point the down pipe away from the brake MC a bit. My SR20 swapped track 510 has a similar setup with a GT-X 2867r making an easy 378 whp on stock internals. Your truck is going to be stupid fast, and the ability to control it is a necessity for your survival so build accordingly.

 

As to the the need for a booster, here's my $.02 worth. The 1974-75 620's curb weight is 2286 lbs. The reason for the booster is handle it's 1441 lb payload capacity. If you'er not using it as a work truck, ditch the booster.

 

Relying on standard calculations is meaningless here, because various pad compounds can make a HUGE difference. My 510 might be lighter, but it has to reliably brake from high speeds, over and over again. It has a shortened Wllwood MC with a Big Brake kit and PolyMatrix pads. Even under punishment, the brake response is consistent, predictable, and linear. Not heavy or stiff at all. Theres more than enough power, and if you're not careful, it can lock up sticky 205 track tires at any speed. For street driving, the race clutch is a PITA, the brakes are not.

 

Here's a link to that top mani.

 

https://www.enjukuracing.com/products/artec-cast-stainless-top-mount-turbo-manifold-sr20det.html?gad_source=1&gclid=Cj0KCQiA4Y-sBhC6ARIsAGXF1g7zJ_n_J4OLacE6AcZ7R7vsAasB7tdVboYzJyNN9QIrHJvCv03onIcaAozjEALw_wcB

 

 

Edited December 23, 2023 by paradime

[Kami04]

15 minutes ago, paradime said:

There are manifold options that can give you more space. The Atec moves the turbo forward about 1 3/4". Another advantage is it's V-band connection to the turbo and waste gate allows for a some rotation to point the down pipe away from the brake MC a bit. My SR20 swapped track 510 has a similar setup with a GT-X 2867r making an easy 378 whp on stock internals. Your truck is going to be stupid fast, and the ability to control it is a necessity for your survival so build accordingly.

 

As to the the need for a booster, the 620's curb weight is 2286 lbs. The reason for the booster is handle it's 1441 lb payload capacity. If it's not being used as a work truck, ditch the booster. Relying on standard calculations is meaningless, because various pad compound can make a HUGE difference. My 510 might be lighter, but it has to brake reliably down from high speeds over and over again. Ii has a shortened Wllwood MC with a Big Brake kit and PolyMatrix pads. Even under punishment, the brake response is consistent, predictable, and linear. Not heavy or stiff at all. Theres more than enough power, and if you're not careful, it can lock up sticky 205 track tires at any speed. 

 

Here's a link to that top mani.

 

https://www.enjukuracing.com/products/artec-cast-stainless-top-mount-turbo-manifold-sr20det.html?gad_source=1&gclid=Cj0KCQiA4Y-sBhC6ARIsAGXF1g7zJ_n_J4OLacE6AcZ7R7vsAasB7tdVboYzJyNN9QIrHJvCv03onIcaAozjEALw_wcB

 

 

This is very helpful have you seen anyone use the ISR ram top mount manifold? 

[paradime]

Not sure if the ISR I saw on a 620 was a RamHorn or and older IronMan. Owner didn't say.

[Kami04]

21 minutes ago, paradime said:

Not sure if the ISR I saw on a 620 was a RamHorn or and older IronMan. Owner didn't say.

https://share.icloud.com/photos/075grreypsMUBCdye9tygVjNA this is partially what it looks like I’ll have to try and get better pictures

[Wildcat Walker]

On 12/21/2023 at 4:15 PM, paradime said:

 Your truck is going to be stupid fast, and the ability to control it is a necessity for your survival so build accordingly.

 

As to the the need for a booster, here's my $.02 worth. The 1974-75 620's curb weight is 2286 lbs. The reason for the booster is handle it's 1441 lb payload capacity. If you'er not using it as a work truck, ditch the booster.

 

Relying on standard calculations is meaningless here, because various pad compounds can make a HUGE difference. My 510 might be lighter, but it has to reliably brake from high speeds, over and over again. It has a shortened Wllwood MC with a Big Brake kit and PolyMatrix pads. Even under punishment, the brake response is consistent, predictable, and linear. Not heavy or stiff at all. Theres more than enough power, and if you're not careful, it can lock up sticky 205 track tires at any speed. For street driving, the race couch is a PITA, the brake are not.

 

Your first sentence tells it all. 

 

Take a quick look at the equations for momentum. Without hauling a load, but having a greater velocity than a stock truck would otherwise have, the momentum becomes equal. Heavy load, or engine swap, the braking need is the same. 

 

The calculations we were discussing previously had nothing to do with braking performance. Assuming all else was equal, we were simply developing a means to compare cylinder bore diameters, booster forces, and equate those to line pressure. The math provides a solid foundation for comparison without having to trial and error eveything, which in todays society is more costly than ever. I think they might call this process Engineering or something like that. 

 

No matter what path is taken, get as much braking as you can get, without wheel lockup. Proportion the front and the rears.