So it was back to the dyno last Tuesday for round 3 of the blower wars. This time I think we got a decent outcome and I am very happy with the results.
There were several differences and upgrades from the last effort, where we were plagued by high speed miss issues which I attributed to ignition problems coming from the dual sync distributor. This is both puzzling and disappointing, as I have a dual sync on my ’69 GTO and have not had issues with it, but here we are.
The fix was to switch to an external crank trigger, and just use the dual sync to fire the coils and provide the cam signal. This turned out to be the correct move as virtually all my issues went away, and it was apparent from the first few pulls that this was a very different engine.
Originally, I had 3D printed all the crank trigger mounting brackets and hardware using a high temp material, but I discovered that one of the 3D printed parts (throttle body spacer) had softened during the previous dyno run and had loosened to the point where a bolt actually fell out inches from the throttle body intake. So I took all the 3D printed parts out of the motor and remade everything out of billet aluminum.
The plan was to start with the smallest (boost -largest diameter) pulley and work my way incrementally into the higher boost numbers.
We did not quite make the 700 hp number I was looking for, but the torque was just ridiculous.
So here are the results:
- 5 psi (lowest boost pulley) made 546 HP 5300 rpm w/643 TRQ
- 8 psi boost, made 611 HP 5300 rpm w/685 TRQ
- 11 psi boost made 656 HP 5300 rom w/784 TRQ.
These were pump gas pulls, after the last torque number we put some better gas in, ~100 octane.
After that, the smaller pulleys started to show belt slip, so we did not get any full pulls on the higher octane, but we did see a 817 TRQ number before the belt started slipping.
Next steps are to get some Grip-Tek pulleys, I’m kind of kicking myself for not buying a few and bringing them just in case.
Keep in mind this is a stock 2 bolt main block with a factory cast crank, and perhaps the worst flowing cylinder heads (cast iron 4X, untouched) possible, so I feel this is a great result and clearly with regard to torque we are reaching the limits of the factory block.
A better head with say 300+ cfm flow will make a bunch more power at lower boost due to improvement in restriction as compared to the 4X heads.
But the goal of this project was to see what could be done for the guy with cast iron heads and a stock bottom end- making power with cylinder pressure and not RPM.
This time I set up a different (identical) blower with the fuel rails mounted externally, just to test this configuration. It worked well and there was no difference between this configuration and the previous config with the fuel rails and injectors mounted underneath in the valley. Note the stock valve covers LOL.
Some data:
Partial pull with belt slip. Take a look at that torque number before the belt slip kicked in:
