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Ford 67-96 F-Series, 78-96 Bronco All discussions of 67-96 F-Series Trucks and 78-96 Broncos

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post #1 of (permalink) Old 04-10-2000, 03:32 PM
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Timing Set/Cam/Roller Rockers

90 5.0 liter EFI / Distributor has module on it. I'm in the middle of rebuilding motor. I've decided on the 1.7 Crane rocker rollers, and i'm looking at a 262/272 Sumit Cam, hypereutectic pistons (had to go .060), and also headers. The timing sets i've looked at talk about "true Zero" and "don't retard cam timing ...like factory timing sets do. The question: If i replace the cam should i use a "true zero" timing set, and what will this do to the timing, the EFI, and the stock ignition?
i'm trying to put the $ in the motor now, and add the easy stuff later ie. k&n filter, new ignition, computer chip,and fuel injectors.
I'd appreciate any advice i can get, or any reference books i can look at.

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post #2 of (permalink) Old 04-11-2000, 07:02 AM
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Re: Timing Set/Cam/Roller Rockers

This is just my opinion. You are building a 302 in a Bronco, so chances are you are not going to go out drag racing. The timing set you are looking at probably has three key slots: 4deg advance, 0 deg, and 4 deg. retard. This allows you to choose how you want to run your cam timing. For a basic, mild rebuild, just set the cam straight up to 0, and let the EEC take over. Have you bored the block yet? .060" is a bit extreme if it is not necessary. You are starting to run thin walls in the cylinder, which might not be the best for longevity. Another thing to consider on your rebuild: With a larger cam (you didn't specify lift), and a longer duration combined with the 1.7 rocker ratio you may want to check your valve to piston clearance. You will want at least .080" clearance. This should be no problem as long as you are running under .550" lift and low compression. This also leads to another question about valve springs. Make sure you are not crashing the spring with the higher lift/larger ratio rocker combo. Also, depending on the lobe separation angle, you may throw the manifold vacuum off enough to send the EEC into a fault loop. Plan on purchasing a mass air conversion kit.

post #3 of (permalink) Old 04-11-2000, 09:52 PM
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Re: Timing Set/Cam/Roller Rockers

You may want to rethink your cam. I have a friend that swapped in a setup like what you are talking about, and the truck had the stutters, wouldn't idle for anything, and ran like crap.

The problem was that the cam is too extreme for the EEC to work with. The only solution was for him to turn to Mass Air. Which he did not due to the extreme price. So, he swapped in a Mustang 5.0 stock cam (easily purchased from someone who swapped theirs out for something more extreme) with 1.6 rocker rollers. It made all the difference and runs great.

Since the F-150's and Bronco's are speed density, and Mustangs Mass Air, the Bronco will only except mild increases in cam lift before losing vacuum.

Hope this will help you make the right decision.

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post #4 of (permalink) Old 05-02-2000, 11:03 AM
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Re: Timing Set/Cam/Roller Rockers

Thanks for the help. I did stay with the stock cam. I got the engine, and she's running great.

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