HELP Computer limits

[Vikingblu442]

Hay guys new here but have a question..
I have a 1985 delta 88 with a 307.
Wanting to know if my stock carb and computer will run this 403 motor?

#6 heads, 2.000" and 1.625" valves. Filled exhaust crossover and center divide
Milled, 67cc’s 9.5to1 compression ratio
Stock .030 over bottom end, but balanced
Howard’s roller cam, 219/229 @ .050”

 

[rfpowerdude]

It will run it, but the timing table in the firmware may not be ideal. Mostly, the computer affects ignition timing. Under closed loop steady state conditions, the fueling will be determined by O2 sensor feedback crosscounts and is not as much affected by engine size. With that said, you may need to use different primary rods to deliver enough fuel for a given duty cycle of the MCS (mixture control solenoid) in the carb. The timing table, however, is a fixed table that may be too little or too much under certain load/rpm conditions. Give it a try. That cam and compression may be just right for the timing already programmed in the ECM. You always have the option of getting a non-computer Q-Jet and standard HEI distributor if there are issues..

 

[Vikingblu442]

It will run it, but the timing table in the firmware may not be ideal. Mostly, the computer affects ignition timing. Under closed loop steady state conditions, the fueling will be determined by O2 sensor feedback crosscounts and is not as much affected by engine size. With that said, you may need to use different primary rods to deliver enough fuel for a given duty cycle of the MCS (mixture control solenoid) in the carb. The timing table, however, is a fixed table that may be too little or too much under certain load/rpm conditions. Give it a try. That cam and compression may be just right for the timing already programmed in the ECM. You always have the option of getting a non-computer Q-Jet and standard HEI distributor if there are issues..

This is what im installing..
My 403 build
.030” over bore with cast pistons
Crank was turned .010” rods and mains
Rods were resized and ARP rod bolts were installed
The crank and rotating assembly (crank, harmonic balancer & flywheel balanced together) were balanced
The block was line honed
Block was decked .20”
Melling oil pump, standard flow & pressure
Howard’s roller cam (you’ve seen the cam card)
Heads were fitted with the larger 2.00/1.6 valves and light bowl work
Heads had the exhaust cross overs filled as we’ve discussed, as well as the port dividers welded then resurfaced
Heads were milled (67cc chambers after it was all said and done)
Comp Cams valve springs, retainers and locks
Comp roller tip rockers and guide plates
Hardened pushrods (I think they’re Summit Racing)
Cloyes double roller timing set
Cam was degreed at 0° or straight up
Edelbrock RPM intake
Street Avenger 670 carb
New HEI distributor with brass gear (for the roller cam)
9.5 to 1 compression ratio

 

[Kennybill]

That's a nice build. I'd watch out for detention with cast pistons and keep the rpms under 55/5,600. What gears are you running?

 

[Olds 307 and 403]

That will have the very agressive swirl port timing curve, it may be too much for 9.5 to 1. Also that duration may be too much without a custom prom. What is the LSA on that cam? That should haul ass. You will need upgrades in the TH2004R trans and consider a 8.5" out of a Caprice with better gearing.

 

[Intragration]

It's my understanding that the reason for the computers on these cars, in conjunction with the mildly-built stock motors, was for economy and idle. It's kind of pointless to try to reuse the computer if you're going for performance, particularly with a non-stock motor of a larger displacement. You asked about the stock carb, but then mention that you're using a different carb and an HEI distributor. The computer won't even be doing anything in this scenario, except telling the check engine module to illuminate the check engine light. If you remove the computer harness coming from the passenger side of the firewall, it will clean up the engine compartment nicely.