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Small cam swap to early BC4
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By hogleg - Saturday, February 29, 2020 12:43 AM
I have a 78 Peterbilt 359 that has a small cam in it. We have been planning for a few years to swap to a Big Cam.

We recently bought a donor truck with a good running BC4 with low flow cooling. Driving it over, it ran solidly at 205 degrees. Since this was not under load, I don't know if this indicates future cooling issues. Overall it is a real good runner and we got it at a very good price.

It is an early BC4 model which I think makes donor parts from earlier BC's possible. Data plate info - build date 21 Aug 1985, CPL675, NTC-FOR 350, NH/NT855

If we decide to convert the cooling, will the small cam provide some of the needed parts?

Is it an easy job to bump it up to 400hp?

By Geoff Weeks - Saturday, February 29, 2020 8:21 AM
You could convert fairly easly to high flow cooling. But I have run both I have a 324 and 531 high flows and CPL676 and 840 low flow's. Low flow will give better fuel mileage by between .5 and 1 MPG. It does it by allowing the engine to run hotter while the intake air cooler.
I have two trucks, about the same spec's, one with a high flow 400 and the other low flow. The low flow consistently returns better fuel mileage. I can pull Parley's Canyon in the summer loaded to gross. The key is a good radiator, don't skimp and put the biggest that will fit. It also has to be a low flow core, with dimpled tubes.
The 675 has 14.5 cr and -.065 timing, the 676 (400hp) has 14.0 cr and -.070, different cam and injectors.
I'd leave it low flow, and put my money in a good radiator.
By Newto - Saturday, February 29, 2020 9:33 AM
Geoff is pretty much on the money again re leaving it as a low flow.

There's a lot of little things you need to do to convert from low flow to high flow.....we used to convert 444 road trains back to high flow because they couldn't handle the loads or heat in the Aussie outback.

You need to use the Small Cam thermostat housing & water rail so you get the outlet to the radiator up to the correct size & the Oil Cooler plumbing fit that you need to also use different Rocker Boxes because the STC boxes are slightly wider & foul on the water rail.

From memory tho that BC4 CPL has a different pushrod & rocker ratio so that could be a problem? (BIDSTBC)

Then to get water to the aftercooler.....(which has the inlet at the front instead of the SC/BC rear inlet) you need to drill out the plug in the back of the block on the oil cooler side (because usually its so tight it wont undo) and fit the BC aftercooler screw in plug & water adaptor. Then you need to get the water from there to the front of the aftercooler which we used to do by running a length of alloy 1" water pipe tucked up under the aftercooler base then up to the water inlet.

Custom pipes need to also be made to get the aftercooler outlet & air comp water line back into the thermostat housing loop.

BC4 thermostat housing gets flicked and the SC water pump inlet has to go on to get the correct size inlet into the water pump from the radiator bottom hose.

hope this helps.

By Geoff Weeks - Saturday, February 29, 2020 11:54 AM
He is working on an early Big Cam4, so no STC and it uses the Big Cam 3 rocker boxes, but still needs all else you noted. Not worth it in my book. Better to spend on the proper radiator for the low flow system.
I have the next CPL up (676) which is the last fixed timed 400hp Cummins made.
By Newto - Saturday, February 29, 2020 12:58 PM
Geoff.......My bad....I didn't pick up that it was a fixed time BC4......

We never had the 675/676 CPL's down here so I'll plead ignorant to those 2.........although I should have either realised it was only a 350 or consulted my CPL book before engaging my mouth!!

thanks for the correction.

By Geoff Weeks - Saturday, February 29, 2020 1:01 PM
They didn't stick around long, little over a year and they went with the STC 833 then the NT88's.
Good engine, but low compression.
I run an 1800 sq inch 4 core low flow radiator. With that, low flow works fine up here.
By Geoff Weeks - Saturday, February 29, 2020 1:11 PM
There was an industrial high flow thermostat housing that mated to the NT 88 water rail. The engine was 1/2 NT 88 and 1/2 big Cam3 . It used a big Cam 3 oil cooler, waterpump and lower water connection, NT88 rocker box upper waterrail (with the exception of the front section) and big cam 3 thermostat. It had STC injectors.
I used to have the part number for the special thermostat section, but the only place you could get one was from China.
By hogleg - Saturday, March 07, 2020 1:01 AM
I let the BC4 go down the road. We made a quick $2500 on it. Would prefer a BC2/3 400hp engine with hi-flow or perhaps a N14. Will keep watching.

Thanks for the advice.

By Geoff Weeks - Saturday, March 07, 2020 7:01 AM
N-14 would require an Air to air, can you fit one in the truck?
I don't know where you are, but don't pass up a Dieselrecon Magnum small cam 400.