Hydratech Hydraboost RPM Drop?

[Rob68427]

Hello,
I have a 68 Chevelle, 402 worked out to a 409, about 550hp with vintage air front runner and detroit speed power steering pump.
With wilwood brakes 6 piston front and 4 piston rear. Hydratech with 1 1/8" wilwood master.
The brake setup works great and stops on a dime.
But, rpms drop at least 400 rpms when I apply the brakes.
I'm not sure if this is a common problem or because of the radical cam?

I am debating on going manual.

Any help would be great

Thanks
Rob


6225962260

[NiteOwlNY]

I'll be watching this, sorry I don't have an answer but I have pretty much the same setup and looking to go for a Hydroboost in my 68...

[73RSZ28]

Mine does not affect rpm.

[tflyboy77]

Mine does the same thing but I don't know why.

[73RSZ28]

What pump are you running? And what does your return line set up look like? I have a pump from a diesel truck that came with hydroboost and it has dedicated returns no Tee. I have heard of problems with Tee'd returns.

[Rob68427]

I emailed Hydratech, I'll post the response when I get one.

73RSZ28, what kind of moter and setup do you have?

tflyboy77, I know it puts a strain on the motor. Most people I talked to their's drop between 100 and 200 rpms. But they mostly have stock motor or LS motors. But, I have my idle in park set at about 1600 rpm. And when I press the brakes in Park it drops down 400 rpm and that pressing lightly. The harder I press the brakes the more the rpms drop. So I have been 2 footing it, when I'm driving.

Thanks
Rob

[Hydratech®]

The hydraulic brake assist systems function the same way that the steering does, in that cranking the steering wheel loads the pump the same as applying the brakes. No steering input or no brake input = no load on the PS pump. This means that you will find the RPM drop when steering the vehicle - the harder you steer, the more load is placed on the PS pump, and same goes for the braking. These late model mini pumps *should* provide a more efficient operation, meaning they should draw less power under load - about 2-4 horsepower under maximum pressure (such as when you have the steering wheel cranked either full right / left all the way against a steering stop) (I still prefer the classic fullsize Saginaw P series given a direct choice). Normal braking should only load the pump slightly, max braking (such as staging a car in the lights at a drag strip and placing full power onto the brakes to load the chassis against full engine power) will load the power steering pump the same as having the steering cranked fully against the steering stops).

If you cannot crank the steering to a full stop without the engine stalling or experiencing high RPM drop, then either the PS pump is drawing way too much power (due to high internal friction or sticking max pressure relief valve) OR the engine tune is so far off that it cannot handle 2-4 horsepower of additional engine load. By way of comparison, a high output alternator can pull up to 6-8 horsepower under maximum load. Some carburated heavily cammed tight LSA (lobe separation angle)(107-110 degree) engines have a hard time idling of course, where as the fuel injected ones have automated idle compensation that handles it seemlessly (also when tuned properly). One issue I have found common with overcammed carb scenarios is running a full time vacuum signal to the vacuum advance pot on the distributor. When under a load, the vacuum signal to the distributor drops off, which cuts back a few degrees of timing. If you are running a full time vacuum to the distributor, you may be loading the engine just enough when steering or braking to hit the point of dropping the vacuum advance out, retarding the timing to cause large RPM drop. The workaround here is to connect the vacuum advance line up to a 'ported' vacuum source on the carb (that does not provide vacuum at idle / only at an eighth or so of throttle or more). Retune the engine to run a stronger idle by adjusting the idle mixtures slightly - four corner idle circuits are vastly superior in idle / off idle tuning. Drilling 1/32" air bleed holes into the primary throttle butterflies helps also (by allowing you to back off the idle speed screw a tad to get the carb truly back onto the idle circuits instead of the transition slots)(highly advanced high performance carb tuning is also one of my direct specialties). An auto trans with a tight low stall torque converter can challenge a heavily cammed engine at idle - are your cars stick or auto?

A 100 RPM drop is normal for a medium apply of the brakes. Just rolling up to a stop light with minor pedal pressure (and then holding at a stop light) should only be about 50 RPM. A max power brake apply would be the equivalent of cranking the steering wheel all the way which should only result in a maximum of 150-200 RPM drop. Good cold, but worse when hot? Throw a small trans cooler into the PS system:

https://www.pro-touring.com/showthread.php?75341-hydro-boost-on-track&p=753759&highlight=#post753759

Here is a link that speaks of pumps and some diagnostics that may help you to better understand these systems:

http://www.lateral-g.net/forums/showthread.php4?t=36999

Adjusting the max pressure relif setting in the PS pump dictates how much pressure the PS pump can build, and therefore how much a pump can load. The higher the max pressure relief setting, the higher the load the PS pump can place on the engine. The lower the setting, the less load the pump can place on the engine (as it will go into bypass sooner). Here is a link for the kit available on Summit Racing:

http://www.summitracing.com/parts/BRG-899001/

62294

This additive has also helped to reduce friction in the power steering systems:

http://www.lubegard.com/~/C-198/LUBEGARD+Power+Steering+Fluid+Protectant

The Redline and Royal Purple synthetic PS fluids also help dramatically reduce friction in the power steering pumps too.

Feel free to call to discuss: http://www.hydratechbraking.com/contact.html

[Rob68427]

Thanks
73rsz28, I have detroit speed mini pump.

This is how my plumbing is setup.
Is this right?62933

[Hydratech®]

Your flow routing appears to be correct. From what I understand, you are experiencing proper overall basic functions, though experiencing a larger than normal RPM drop when applying the brakes. This means that you are functional overall, though have an issue of either too much pump horsepower draw (due to higher than normal internal PS pump friction under load) or an engine tuning issue (where the engine is having a very hard time idling sufficiently to handle a minor load as previously discussed).

What PS fluid are you running? We have found that the PS systems run much smoother on the Royal Purple or RedLine synthetic PS fluids, along with a dose of the LubeGard additive (cuts PS pump internal friction way down on certain installations). I don't know if this is a trend or not, though we have recently observed the GM late model mini pumps (with the built on plastic reservoirs) as being problematic over the last few months - maybe there is a rash of bum pumps running through the distribution channels lately?

https://www.pro-touring.com/showthread.php?91514-Need-some-Serious-Tech-Advice-regarding-a-Hydratech-System-and-Issues-I-am-having

A normal to medium brake apply shouldn't drop engine RPM more than 50 RPM on the average musclecar. Say you take the RPM to 1500-1800 RPM - does the RPM drop seem insignificant / negligible at that point?

[Rob68427]

Hydratech, thank you for the quick responses.

I'm using royal purple.
The setup I have is a little over 2 years. And it's a detroit speed mini pump. I have no trouble with steering or braking, just keeping the idle up.
I'm worry once I get the A/C charged and going it's going to be even worse.
Last summer was the first I had it out. And only took it out a couple of times and I had to use 2 feet all the time.
I'm not sure if I have a heavy foot. In park rpms are at 1500, and if apply the brakes about 300 to 400 rpm drop. So when it in gear it idles about 900 rpms with very light brake. But when driving I have to 2 foot it. And a couple of time I had to make a quick stop it just about shut off.

My motor isn't really setup for street. Not sure if this is the problem? I have a lot of work done to the heads. 11.5 compression.
Cam Duration: intake & exhaust 294, Valve lift both intake & exhaust 0.595 and lope lift is 0.356.
It has a very rough idle. Making about 550hp.
I feel like it's the cam? Opinions?

Thanks
Rob

[Hydratech®]

No doubt in my mind that it's the cam giving you troubles at idle / low RPM. With such a rowdy cam, a much looser torque converter (higher stall speed) would help ease up your idle issues. In your current state of tune, I don't know how in the world it's going to handle the load and extra heat when the A/C comes on - may have to install an idle kicker solenoid to keep it running to offset the load of the A/C. Have you done any carb and ignition tuning to help generally strengthen up the idle characteristics? There was a discussion on Chevelles.com about a similar topic that I ran across recently, though cannot seem to find it now. Take a look over there and see if the tuning gurus can give you some pointers. It sounds like the hydraulic brake assist system is working properly, though your state of tune is creating idle issues that are the bulk of this discussion.

[Hydratech®]

Found the thread I was thinking of (regarding too rowdy a cam with idle issues) - it wasn't in Chevelles.com, it was www.camaros.net :

http://www.camaros.net/forums/showthread.php?t=209446&highlight=hydratech

[Rob68427]

Thank You