520R SV build has commenced

[JohnCh]

The dyno shop sent me two maps with different fuel enrichment strategies, and asked me to try both, then send logs for the one I prefer.  He would then refine the chosen map based on that data.  I had time at lunch to give them both a try and was really surprised; both felt great and addressed the issue.  Honestly, I could keep either one with no further changes and be satisfied.  Curious to see if I can sense any improvement from the next iteration he sends. 

[JohnCh]

I learned something interesting this week about my earlier fuel starvation issues.  During troubleshooting a couple of months ago, multiple conversations with both Holley and the pump manufacturer resulted in a consensus that the pump to Hydramat plumbing was too restrictive.  Those restrictions were subsequently removed but the issue persisted, which then pointed a finger to the tank design and the fact that when fuel is low, and when turning left, that side of the tank can quickly go dry.  Fine. The Caterham stock system can't reach all the fuel in the tank anyway, so simply treating it like a smaller tank was really no different than stock from an effective capacity perspective.

 

However, a follow-up conversation with the pump manufacturer this week contained a nugget that revealed the real reason behind the earlier issue: the turbine impellers used in most dedicated in-tank pumps, must be below the fuel line to operate effectively.  The impeller occupies the bottom 1/4" of the pump body.  Add in space beneath for the Hydramat plus a little buffer, this means at least 3/4" - 1" of fuel should be present in the tank for seamless operation.  Now throw in the fact the Caterham tank is wide and places the fuel pump at one end, and anything less than a 1/4 tank could easily put the impeller over the fuel line on a long left turn, thus creating starvation despite the Hydramat's ability to supply fuel as long as it can touch it.

 

The fix is a positive displacement in-tank pump that will fit the application.  These can create suction and don't need to be submerged to work (or so I'm told).  So far, I've only found one.  The Walbro GSS341/2.  It uses a gerotor rather than a turbine impeller, is rated as the same flow as my current pump and has the same 11mm inlet that works with my existing in-tank plumbing.  I'll give this one a try.  I suspect the lift is also sufficient that the earlier plumbing design with two elbows won't be an issue.  Reverting to that version will allow the use of the longer, more centrally located Hydramat that affixes to the tank bottom, solving another issue.  Unfortunately, the direct mount Hydramat currently in use can float up, contacting the bottom of the fuel sensor tube and cause wildly inaccurate readings.  My plans to reorient the sensor to gain a constant 1/2" clearance may no longer be required.

 

-John
 

[MV8]

Older oem intank single pump systems for high pressure efi are gerotor. You can always rework the tank for a sump in either corner or centered by cut and shut of the lower corner displacing unusable fuel. The return dumps into the sump. The capacity of the sump need only be enough for the length of the corner at high rpm/lowest return flow.

 

 

[JohnCh]

Thanks, but if the low suction issue is simply down to the pump design, and a direct fit replacement is available, that seems like a lot of unnecessary work.  The fact that the extra in-tank plumbing didn't create a restriction for low suction turbine impeller when it was below the fuel level, gives me hope that a gerotor pump won't have any issues and the Hydramat can do its thing.

[MV8]

If it does not work long term (a few miles on the special pump), consider correcting the tank to use a standard pump and strainer.

 

I went back to page 12 to look at your sump pump system. In my experience, strainers typically have a large, female opening that fits over the pump fitting. The hydramat appears to neck down in this area. Compare to a 1990 mustang strainer.

 

FWIW, the pump needing to be submerged doesn't make sense. All fuel should be going through the strainer and not leaking in through the seams as a design feature.

 

How is my fuel system conversion doing you ask? Great, though completely apples to oranges. Carbs have bowls/accumulators so line pressure needs to be no more than the needle and seat can handle. I used an aeromotive 13301 bypass regulator with the low pressure spring installed and with the adjustment completely backed off. The oem 89-97 ranger efi pump (in-tank/no lift pump) still provided 3.5psi to the carb. I used steel brake lines around the headers then transitioned to the oem nylon back to the tank with the oem efi filter. Very pleased with that.

 

The aeromotive regulators are typically about $200 but they sell the defective ones on ebay for about $33 and don't list them as Aeromotive. The body is machined slightly too deep before anodizing, so it just needs a de burr and another wrap of teflon tape.

[JohnCh]

30 minutes ago, MV8 said:

I went back to page 12 to look at your sump pump system. In my experience, strainers typically have a large, female opening that fits over the pump fitting. The hydramat appears to neck down in this area. Compare to a 1990 mustang strainer.

 

I believe you are referring to the Hydramat to pump interface.  If so, the pump is using an 11mm inlet which is quite common.  There are other pumps and Hydramats that use a 19mm opening.

 

32 minutes ago, MV8 said:

FWIW, the pump needing to be submerged doesn't make sense. All fuel should be going through the strainer and not leaking in through the seams as a design feature.

 

It's not that the pump needs to be submerged to prevent fuel leaking out of the body or air from sucking in.  It's that the impeller must be below the surface of the fuel (i.e. submerged) so it is not lifting it, but rather is displacing it forward. The gerotor is a positive displacement style and can create a vacuum beneath it, thus generating lift.

 

 

[JohnCh]

Last night I finally got around to updating my website with the Caterham story.  While uploading photos to the modifications page, I realized I didn't have one that showed the 3D printed battery hold down, fuse box lid, and coolant junction cover together.  Given they share the same ribbed design with the hope of making them look more cohesive and intentional rather than haphazard choices, that was a miss and was addressed this morning.  Adding that photo here as well to show the end result.

 

 

-John

[kayentaskier]

So professional in appearance. Well done

[UglyFast]

On 8/19/2023 at 4:10 PM, JohnCh said:

The crate engine, air box, ECU, dash, gauges, switches, dampers, factory fuel system, etc.  Anyone want to build a car from my leftovers?   

 

I did a little fettling today then took the car out.  Temps were still cool and the notorious oil over-cooling on these cars was present.  As a result, I never took it over about 4500rpm but the engine felt good.  I also seemed to really begin pulling strongly at part throttle at 4000rpm.  To temporarily address the cold oil temps, I fabricated a simple block off plate out of thin aluminum.  The clamping force is strong enough that it doesn't move once in place, and it is inset a bit, which results in the end caps preventing lateral movement.  A couple of zip ties should ensure it doesn't vibrate off.  I consider this V1, and suspect I'll make it to V3 or V4 before I'm satisfied.   

 

 

 

 -John

New crate Duratec that needs a good home did you say?  LoL I might know a guy. 

[JohnCh]

Scheduled to arrive at its new home on Tuesday  

[UglyFast]

9 hours ago, JohnCh said:

Scheduled to arrive at its new home on Tuesday  

I'm excited to see what we can do with your NOS leftovers. Insert happy Kermit gif here LoL 

[JohnCh]

Life got in the way, leaving the car untouched since October.  I finally got around to replacing the fuel pump with the positive displacement type, which seems to work better; It didn't start cutting out when cornering with about the same fuel level as the old pump.  However, more testing with less fuel is required before I declare it resolved. 

 

On the test drive, the oil pressure reading issue I mentioned earlier went into overdrive.  Rather than reading normally with instantaneous flashes to wildly incorrect readings ranging from 0 to over 100 psi, it suddenly went to 0 psi, with a few flashes to the 70-80 psi range.  Not confidence inspiring.  Although the issue could be with the wiring into the AiM, given all the other dash functions are reading correctly and that sensor has a reputation for premature failure, my money was on the sensor.  The new one went in this weekend, and so far, things are working correctly.  Hopefully they stay that way. 

 

I didn't have time for a long test drive but did manage to get a picture when reaching the turnaround point.  It was a cool, but very sunny day in the Seattle area.

 

 

Next up is going through various fasteners to make sure everything is still tight, then driving it hard for a while before tackling a few open items, including nonfunctioning heated seats, installing the short-cut button for the AiM's trip odometer, and recalibrating the fuel level sensor.

 

[CBuff]

Looks great!!!

[Croc]

On 3/31/2024 at 7:23 PM, JohnCh said:

Life got in the way, leaving the car untouched since October.

 

Ok...show us photos of the fur ball!

[JohnCh]

3 hours ago, Croc said:

Ok...show us photos of the fur ball!

 

The only photo I have of him with the car was taken when he was just 9 weeks old.  That was nearly 4-1/2 months and over 70 lbs. ago, so just a bit out of date.  If I get a recent shot of him with the car, I'll slip it in here.