High Compression/ Boost on the street...

[Ben@SpeedTech]

Hey everyone-

I’m preparing to install the 406 SBC engine from my old drag car into my wagon. This motor is 12.5:1 compression but I still plan on street driving it near daily. The cam has a ton of overlap, it’s 260/262 dur at .050 and is ground 4 deg advanced on a 110 centerline. I used to drive this engine daily when it had flat tops and roughly 11:1. This engine has World Products iron heads on it. Guesstimated power is a little over flywheel 500 hp/ 500 ft lbs.

I don’t have much experience with driving a pump gas higher compression motor so I’m looking for suggestions to keep it from rattling apart with detonation. I am at 3000 ft altitude in Southern Utah so that helps a little, but I’ll be driving down to Vegas and So Cal for events.


I can run 91 octane for daily use and something better for track days.
I’ll plan on retarding the timing for street driving
I was thinking to set up a methanol injection system for those occasional “freeway entrance ramp full throttle pulls”


Anybody use the Crane or MSD timing retard dials for non boosted applications?
Here’s a link to the Crane version- http://www.summitracing.com/parts/crn-6000-6425

Those of you running the meth inj, is it something you run anytime you’re at full throttle or is it just occasionally to clean carbon build up out of the cylinders?

Any other suggestions?

Thanks!

[Neil B]

I just dropped a 13.6:1 compression 372ci small block in my Camaro. It has a 268/[email protected] solid roller. I wouldn't dream of trying to run it on pump gas. However, at 12.5:1 if your calculated DCR is in the 8.5:1 range it might work at low speeds/low throttle. I've never run meth on a N/A combo, but I ran it on my supercharged C5 Corvette. The meth system was boost referenced and had progressive activation based on boost level. It was 'always on'. That motor had 9.6:1 static compression and I was able to make over 800rwhp on 16psi boost using pump gas and 50/50 water/meth.

[Flash68]

Is E85 available in your area? That's what I am doing with my 13:1 engine. Under $3 a gallon round here.

[Ben@SpeedTech]

Thanks for the insight!

We're in a bit of a secluded area and I haven't seen any E 85 pumps locally. :/

I put maybe 100+/- street miles on this motor in the Nova when I rebuilt it. I did plenty of hard first and second gear pulls and one really hard full 1/4 mile pull on 91 octane at 16 deg initial timing, no pinging at all. That was at 4500 ft altitude, so I'm assuming the high altitude's thin air and clean pistons helped. I'm more worried about what happens when carbon starts to build up on the pistons that could contribute to detonation issues.

Although I will be driving it to work and back most every day, I will only be hard on it on occasion, and that will only maybe for first and second gear and then slow down. Whenever I race it I will use race gas, so it's not a huge concern, I'm just trying to play it safe. I'd hate to waste a brand new motor because of pinging.

[Twoblackmarks...]

Maybe check your cranking compression to get an idea where the low RPM pressure will be around?

As cold plugs as possible and a real lazy ignition curve. Try no hotter than 8s if NGKs, and ensure a real good spark.

And the air temperature the engine sucks in has a big impact on knock and performance anyway, try to get it from outside of the engine compartment and keep heat down under the hood.

I would guess the worst "knock" situation would probably be at low to mid RPM under a bit load. like under 3000RPM.

A SMALL amount of knock most engines can handle, but it is the pre ignition that kills. Maybe get an oxygen sensor to look at lean spots, to insure engine gets what it needs.