My 1985 Spec RX7 (12a) is down some major HP. Any ideas? Here is the background.

Spec RX7s should get about 105HP at the wheels if everything is healthy. We don't run emissions equipment and a few other minor mods etc.

My car was running 85 HP but now is up to 92.5HP so still down a lot.

Things that have been done:
Compression test was fine.

Full tune up including cap, wires, plugs etc.

Carb rebuilt including rat's nest removal.

Was running stock muffler but now basically have close to a straight pipe.

Car dyno tuned with Oxygen sensor.

Fuel pressure gauge and regulator added. This is where things get a bit strange. Fuel gauge would never go higher than 2.0 PSI. And there is some rust in the fuel filter even though I changed it recently. The fuel pump is stock, but also brand new.

So current guesses are:

fuel pump, tank or lines causing fuel starvation.

power lost in either transmission or rear diff (just because don't know where else the power could be lost).

Any opinions? I really want to find this 12.5 HP!!! I just don't know of these things or other things what would cause such a large percentage loss. Just throwing it out there before I spend more money. Thanks.

 

They had 105 hp at the crank. Your 12.5 hp loss is the drivetrain loss. You
need a better carb or sterling nikki carb and probably a better exhaust setup.

With my mods I make 134 whp (to the wheels) on a stock port 12a. See my sig.

 

He can't add a Sterling for Spec7. The 105 rwhp he mentioned is after some minor modifications that are allowed under the rules of Spec7.

I would suggest changing your filter, or upgrading it. They are garbage and clog easily but cheap enough to replace often. The stock fuel pump is known to be weak for the stock engine, nevermind one that has been uncorked and tuned for performance. I would suggest replacing the stocker with a Carter/Holley/Mallory/whatever. Also check your fuel tanks check and cut valve. It seems that if the tank can not vent properly then the fuel pressure will not stay consistent. I've been having this issue for a while. I would adjust my fuel pressure and the next time I looked under the hood it would be at 5PSI or 0.5PSI. No real consistency to it going out of adjustment.

 

Ah if thats the case then this thread should be in the racing section as he might get more/better answers there.

 

Start with fuel. Replace filter. Test pressure and volume. You may have a partial blockage somewhere in the hardlines or at the pickup in the tank.

What's the timing set at?

You say compression is "fine", but what does that mean in terms of numbers? The power loss could certainly be from the difference of an engine with great compression and one where the compression is just "OK" (just enough for the engine to start and run on its own).

 

I think the numbers were like 120 or 130 if that seems to make sense. This was using the digital rotary compression gauge that is out there.