350 to 403 swap observations and tips...

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Old March 29th, 2013 | 09:10 PM
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1970-W30's Avatar
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350 to 403 swap observations and tips...

I used #5 heads shaved .010 and had the bumps ground out of the exhaust ports and 2” intake valves installed. The heads needed the headbolt holes reamed out to 17/32” and since one of the two head locating pin holes on each head was to small, they needed drilling out to 5/16”. There were no extra “steam” holes in my block that need matching holes drilled in the heads, so the head swap was an easy job. My heads (#5s) ended up with 67cc. I also used ARP head bolts for extra insurance with the siamesed bores of this engine. This combo with Fel-Pro 403 head gaskets gave me a static 9.0 to 9.2 compression ratio with the stock style 19cc dished cast pistons. It runs fine with 89 octane with a initial timing of 13 to 14 degrees at 800 with advance hose plugged. Thermostat is 180 degree. I also installed a 281/296 duration with .448/.474 lift with 51 degrees overlap Elgin E976P cam. It still has a very decent idle and doesn’t run out of steam up to 5200 RPM, which is my self imposed redline for this engine, though it seems happy to rev a lot higher, I don’t trust the bottom end to set my RPM limit higher, but that might change as I get more comfortable with this engine. This is running a 3.42 differential. The Qjet was the original 350 carb #7040250. It had #71 primary jets which I changed out to #73s and I swapped the secondary rods from the original “AT” rods to “AX” rods. Float level is ¼ inch. These small carb changes made a huge power difference, no more off idle hesitation lot more midrange and top end power, and way better secondary response. Also found out that the Edelbrock manifold #3711 would not work with my cruise control because of the EGR pad, of course this was after Ihad bought and installed it. It’s now on Ebay………
I had to buy the 7111 Performer RPM to get the cruise control servo arm to clear. But with the RPM manifold the stock air induction will no longer clear, but a 70 Chebby cowl air induction plate ring is a perfect slip fit right on the air cleaner base, that and the BBO foam glued on it matches nicely on the bottom of the fiberglass hood.
It’s a great combo and I couldn’t be happier. Got about $2800 in to it give or take a bit.
I realize that just because this worked out great for me, it might not in somebody elses case, but it's still a good starting point If your considering this kind of swap.
Old March 30th, 2013 | 02:21 AM
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Seems like you got a fun ride, though I think that cam is a bit too small for your combo.
Old March 30th, 2013 | 03:13 AM
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sounds good! what do you have for cooling? Have you used it in the heat of summer yet?
Old March 30th, 2013 | 08:55 AM
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Get a 4 core rad or big aluminum replacement, 7 blade clutch fan/shroud or a good electric setup. A good 160 or 180 high flow thermostat won't hurt either.
Old March 30th, 2013 | 09:14 AM
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Aren't budget builds fun.
Old March 30th, 2013 | 09:35 AM
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Sounds fairly similar to my 403. It replaced the 307 in an '85 442. Ran it at the end of last summer, some hot days. Stock 85 442 307's radiator, fan, and WP/pulleys combo. Once the timing was set right, and the distributor set right, and the jetting happy... no issues with overheating at all. Rock steady temp at the thermostat opening mark.
Old March 30th, 2013 | 10:31 AM
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I did replace the old radiator with a new three core and have a seven blade fan with a new thermal clutch and shroud, yesterday did come close to 90 degrees in Phoenix. Running down the freeway at 3100 rpm, it runs at 200 degrees, a bit warmer thenI would like but still acceptable. A 200R4 transmission is the next big project, running at 3100 is not good for mileage or long term engine life and I planning to make many trips to Sedona this summer, need that overdrive gear........ I have about 300 miles on it now, ready to dump the Joe Gibbs breakin oil, what do you guys think about the Quaker State "Defy" oil, that comes with extra added zinc? It's a synthetic blend. oil.......
Old March 30th, 2013 | 10:40 AM
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double v I ran the comp 260h in a mild 9 to 1 budget build 350 and it ran high 13's all day. I am too a big fan of budget builds . I just installed my new 355 in and i do rotella 15w40 with lucas zddp additive. some guys dont like it but this combination had never failed me and it's cheaper than some of the zinc rich oils.
Old March 30th, 2013 | 12:35 PM
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I just took a few pictures to share and noticed that it has a 6 bladed fan, would it be cost effective and help cooling to swap to a 7 blade fan? Did not know that the AC cars could have 6 or 7 bladed fans...... have to check that out....
As far as the cam being a bit to mild, I would rather have that then being over-cammed. This is a daily driver that has to run smoothly around town and will be a freeway cruiser, hence the cruise control. Anyway here are a few pics of how the car and engine look now.
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Old March 30th, 2013 | 12:56 PM
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Very nice.
Old March 30th, 2013 | 05:34 PM
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Originally Posted by coppercutlass
double v I ran the comp 260h in a mild 9 to 1 budget build 350 and it ran high 13's all day.
I'm not saying his cam choice sucks or it won't work. It'll work perfectly fine. Just saying a bigger cam would wake it up even more. I think a 403 with a shade over 9:1 CR would enjoy something a little bigger than the 'generic' 204/214 cam ( which I think his cam is ). It should be a fun ride either way.
Old March 30th, 2013 | 05:39 PM
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It looks like he is running full till accessories., a/c, power steering, etc. a bigger cam sometimes does not work well with accessories.
Old March 30th, 2013 | 06:08 PM
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Interesting results, and you did not fall into the too much cam dilemma, I think you did just fine.
Old March 30th, 2013 | 06:19 PM
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200 degrees isn't bad at 3100 rpm! The 7 blade sure won't hurt and get that OD trans in.
Old March 30th, 2013 | 06:32 PM
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I contacted Bowtie Transmissions about the TV cable that would be proper for my Qjet, but it's been a week and haven't heard back from them. I'd rather not have to cobble up something, but their website pics for Qjet TV cable adapters/fittings don't show anything that is near my Qjet configuration. Anybody else have a 200R4 Tv cable hooked up to a Qjet arm like this one?
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Old March 30th, 2013 | 07:18 PM
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That is a tough one. Try a base plate off a 80's CCC carb with the 2004r factory. I am seriously looking at the just coming out 750 cfm Street Demon for my 403 based stroker. Based off the Thermoquad and AVS with better choke and many options including proper geometry for 2004r trans. I love the Qjet but have a feeling it will idle poorly without modification.
Old March 31st, 2013 | 12:03 AM
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Originally Posted by coppercutlass
It looks like he is running full till accessories., a/c, power steering, etc. a bigger cam sometimes does not work well with accessories.
Yes, big cams can have issues in street cars but he's no where near running into that problem.

1970-W30, it appears to me in the pic of your carb shows that it's an earlier style Qjet? If so, I'm not sure about interchangability, but on my carb ( later style Qjet ), I used the whole primary throttle shaft from a 307 carb which was set up for a TV cable hook-up. You can also buy a screw in 'nub' and install it on what you have.
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