BBC gen 4 to 5 repower

Due to Cv19 I could not find a 454 gen iv so I bought a remanufactured gen5. I got conflicting info. from those who "know" about which parts can be moved to the Gen 5 from the Gen 4. If anyone has "real deal" feedback on these issues please let me know here or email me at AdamsRichardLee@Gmail.com
Gen IV is becoming harder and harder to find so this should help others too.

I know there's no option for mechanical fuel pump so I need to get electric one. Low pressure rated for 350hp or so. Probably 9-12 lbs. My valve covers have 7 bolts and appear to be a match.

Here's what I was told by the supplier:
The following gen iv parts will not transfer to gen V:

1. Harmonic Balancer - Mine fits and looks like same form, fit and function but I'm thinking they said that due to different balancing needs of the crank? I hate to waist $

2. Oil Pan - Parts research tells me the gen 5 has 20 bolts and my gen IV has 22. Seems they are most likely correct. Anyone confirm?

3. Timing cover- Gen IV will bolt right on (I tried it). Perhaps this must change to fit with oil pan change?

4. Flywheel - Would fit but I was told gen V has different balancing than IV. And V has 2 different balancing specs based on the crank used ( forged vs. Cast ) SO, I need to have it balanced for about $50 or buy a Gen V/VI flywheel? Any experts to confirm this?

5. Coupler - I was told no change. It should bolt right on.

Rikki said:

Due to Cv19 I could not find a 454 gen iv so I bought a remanufactured gen5. I got conflicting info. from those who "know" about which parts can be moved to the Gen 5 from the Gen 4. If anyone has "real deal" feedback on these issues please let me know here or email me at AdamsRichardLee@Gmail.com
Gen IV is becoming harder and harder to find so this should help others too.

I know there's no option for mechanical fuel pump so I need to get electric one. Low pressure rated for 350hp or so. Probably 9-12 lbs. My valve covers have 7 bolts and appear to be a match.

Here's what I was told by the supplier:
The following gen iv parts will not transfer to gen V:

1. Harmonic Balancer - Mine fits and looks like same form, fit and function but I'm thinking they said that due to different balancing needs of the crank? I hate to waist $

2. Oil Pan - Parts research tells me the gen 5 has 20 bolts and my gen IV has 22. Seems they are most likely correct. Anyone confirm?

3. Timing cover- Gen IV will bolt right on (I tried it). Perhaps this must change to fit with oil pan change?

4. Flywheel - Would fit but I was told gen V has different balancing than IV. And V has 2 different balancing specs based on the crank used ( forged vs. Cast ) SO, I need to have it balanced for about $50 or buy a Gen V/VI flywheel? Any experts to confirm this?

5. Coupler - I was told no change. It should bolt right on.

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Carbs don't like more than 6-7 lbs. Any more and they will flood. 4-5 psi would be better.

Is one motor internally balanced and the other externally balanced?That could be The flywheel and balancer differences.

Who gave you that list? I use these guys and they are exact what works on a IV and a V. perfprotech.com

9-12 is way too much for a carb......4-6 is the way to go. Holley Marine Red Pump.

hottoddie said:

Carbs don't like more than 6-7 lbs. Any more and they will flood. 4-5 psi would be better.

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Won't the float close off the input? Also, not sure if 4-5 psi will provide enough fuel for a 7.4Ltr 350HP motor at WOT??

Espos4 said:

Is one motor internally balanced and the other externally balanced?That could be The flywheel and balancer differences.

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Research shows all BBC 454 are externally balanced. So, gen 4 and 5 are externally balanced. I no expert, but I think due to the crank changes the balancing needs changed. Although my gen 4 fits and has 168 teeth and appears identical the balancing must have different needs. It's not worth pulling the motor to save the money so I ordered a gen 5 flywheel today for gen 5.
Jury still not out on the balancer. I found several sites saying the damper is same from 1970 to 95 (gen 1,2,3,4,and 5) and perhaps beyond. Part searches online for gen 4 and gen 5 have lead me to the same part numbers too! Also found that my Mercruiser balancer is 9" and the automotive harmonic balancers available stop at 8". Ugh?

Rikki said:

Won't the float close off the input? Also, not sure if 4-5 psi will provide enough fuel for a 7.4Ltr 350HP motor at WOT??

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Psi and volume while somewhat related are 2 totally different measurements so even at 4-5 psi more volume than could possibly be consumed can be supplied by a good pump.

Rikki said:

Won't the float close off the input? Also, not sure if 4-5 psi will provide enough fuel for a 7.4Ltr 350HP motor at WOT??

Click to expand...

Depending on the pressure it can easily overwhelm the needles and seats and cause a rich condition and flooding.
Four is low to me. 6 would be where I'd want it set. Any fuel pump that's worth a damn will be able to provide what you need. Just stay away from efi fuel pumps. You can use them and I actually do run one in my 69 Camaro for a few different reasons, but I have to run a return off my regulator so all the extra fuel will get bypassed and sent back to the tank. You can't just dead head it.

Rikki said:

Won't the float close off the input? Also, not sure if 4-5 psi will provide enough fuel for a 7.4Ltr 350HP motor at WOT??

Click to expand...

The float will keep the needle closed up to around 7psi. After that any more pressure will force the needle open and allow too much fuel into the bowl and cause a rich mixture or worse the engine to stall due to flooding. I've had it happen twice with brand new mechanical fuel pumps. Had to install fuel pressure regulators to reduce pressure to 5 psi.

My current 7.4s rub fine with 5 psi feeding quadrajets.

Wanderer 290 said:

Psi and volume while somewhat related are 2 totally different measurements so even at 4-5 psi more volume than could possibly be consumed can be supplied by a good pump.

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This ^^^^^^


A Holley Red Marine Fuel pump is rated to free flow 95 gallons per hour on 3/8" fittings and 71 gallons per hour at 4 psi. That is good for over 600 horsepower. What you don't want to do is go over 7 psi and start pushing fuel by the floats.....that is asking for an epic backfire.