Internal Surge Tank (IST)
 

I haven't seen any posts on this forum about IST's, but I have seen some on fuel starvation, and or fuel pump aeration. I'm not sure about other models, but on my 3rd gen, there is a plastic tray that the fuel pump sock sits in. The fuel can make it in, but not out, the problem is if you get low on fuel, and you are turning left for any decent length of time, you can run that pan dry. I was at a track event, and met a guy who has a 1st gen with a turbo, and we got to talking, and I found out that he designed a surge tank that actually goes inside the fuel tank, perfect bolt in install, and it utilizes two Bosch 044 pumps, one to keep the 1.7 liter surge tank full, and an external pump to run it up to the injectors. He told me that he had fuel starvation issues in the past, so being an engineer, he decided to design and patent one, he has been running it for 5-years at track events with no problems. You could put just a gallon in your tank and not have any problems, because it contains a surge tank level indicator, and a trigger wire. If the fuel level in the surge tank gets too low, you can use the wire to kill boost, or ignition, pretty much anything that will tell you to stop. Check out his site, he has them for first and third gens, and if he doesn't have one for your application, he can make one, he's very accommodating. His site is Home Page.

thanks for sharing, this is a great item.

Currently working on something similar with a few 1 inch one way valves and the stock pump setup.

something along these lines , but attached to the stock unit

https://static.summitracing.com/glob...0-HP_EM_ml.jpg

the option you posted would be much more reliable as the fuel pick up box is fed by another pump

I've seen these (the one's OP is referring to) in person--they are a great design.

There was a user on the forum name Hyperion that made an item to help address this issue, don't think it's available anymore unless used. Just wanted to share - https://www.rx7club.com/group-buy-ce...-cover-647708/

The IST is different from anything else I've seen because it has a pump that actively scavenges fuel from the tank to keep the reservoir full. The inventor told me that the passive systems have limitations because they rely on the right combination of fuel slosh to fill the sump. With this setup, it will work under virtually all driving conditions.

Another benefit is the fuel level switch. Even though the IST works very well, it is still possible to run it out of fuel -- for example if you run the car until the fuel tank is totally empty. In that case, the switch warns that the reservoir in the IST is almost empty so lean damage can be avoided. We set mine up to disable my electronic boost controller if the switch is triggered.

What's the price on these?

I'd like to thank msb393 for being the first to install the IST for an FD in his car. As he mentioned, I've been running one of these in my FB for 5 years. It has worked flawlessly and achieved every objective I had in mind. I made a few last year for FBs --> https://www.rx7club.com/build-thread...a-fbs-1035921/

If you go to my website How to Order and click on the application "Mazda RX-7, 93-95", it will open up with the manual. In it, you'll find specs, instructions, pictures, whatever you want to know.

The price is $675. $100 of that is for a new OEM fuel level sender that I modify to fit the IST. I think a new sender is the best way to go. If you're still using the original sender, it's about 20 years old. These things fail with age, and it's better to spend the money now while you're in the tank anyway.

If you're interested, PM or e-mail me. I'm always looking to solve a problem, and I think I succeeded with this one.

Geeze, where's the royalties! :lol: Execution looks far better than the one I had on here years ago...and never finished I must say....although I did have concerns about the longevity of the lift pump under low fuel.

Eventually went this way for a little while, a tank cut in two, carbon lined and compartmentalized with lots of one way valves then bonded back together - only two ever made in the early 90s for the 12hr race.

Yes, it's true that pumps don't like to be run dry, but the length of time the pump will run dry is minimal -- unless the fuel tank is completely empty. If the OEM fuel tank is completely empty, you have bigger problems, like potentially detonating and damaging the engine. This setup includes a low level switch that will detect imminent fuel starvation -- whether due to absence of fuel in the OEM tank for the lift pump to scavenge or due to lift pump failure. If you ignore the OEM low fuel light and allow the tank to run completely dry, it comes down to the question of which you would prefer -- a failed lift pump or a failed engine?

Also, I intentionally ran my system dry to test the operation. When the lift pump started sucking air, it made an audible protest. The lack of liquid allowed it to spin faster which raised the tone, it got much louder, and it surged. After this went on for a while and the reservoir in the IST emptied, the level switch triggered, putting the system in "Safe Mode" = no elevated boost in my case. Finally, almost a minute after the lift pump first began to complain, the pressure pump also began protesting. At that point, I decided it was time to fill up the tank :). After filling the tank, both pumps reverted to their normal, happy sound. I ran that test about two years ago, and those same two pumps are still in service with no issues.

I realize a data set of one isn't much of a data set, but the point is that running the lift pump dry for a prolonged period (nearly a minute) doesn't necessarily cause immediate death.

Yes, like the sound of that safe mode refinement there, excellent!!

bump, wanted to see more feedback on this. redo-ing my fuel setup and was looking for a neat in tank package. Bueller?

the tnt group buy hasn't moved for a while
alternative was a radium or 034 motorsport style one behind the diff

False, Jim ran another small group buy for TNT kits in july/aug. I just finished putting mine together yesterday. I'll have to take pics when i get off. it looks great!!!

You should contact him as he might have made an extra.

Hmmm, the group buy thread's last update was july 29th. I'll talk to Jim directly. Thanks for the FYI.

FYI, this is my honest experience and I am not related to Hyperion or getting paid in any way.

I track my RX7 and it suffered fuel starvation at the track on left hand turns, if I had less than 1/2 a tank.
Once I installed the Hyperion cover, issue was gone.
I never had an issue with fuel starvation on the street.
So, any part to prevent this, if you don't track your car, is just bragging rights.

Contacted Jim, he does not have any extra in stock, he said he is planning to run/make more in winter, FYI to the lurkers.

I do track my car, and I normally keep it full to avoid any symptoms of this.
Friend who is faster then I, gets fuel starvation at 3/4 tank.
So since I am making fuel changes underneath/back there, I was looking into fixing this as well.