I am new to the I6 arena, and need some info. I am rebuilding a 300 for my 79 F250. I have an Offy DP intake for it already. I have read that I must use headers with an aftermarket intake. Would factory Ford split exhaust manifolds fit, or do I have to use headers? Also, does anyone know the difference between 2 & 4wd headers for a 300? I can't think of anything that would be a fitment problem, but most say for 2wd trucks only. Last question: a 390 cfm carb is recommended. Is 500 or 600 cfm gonna be too much even with the easy breathing exhaust and slightly hairier cam?

Thanks in advance
Steve

 

I have a '79 F150 4x4 with a 300-6 that I am in the process of building up with an Offy intake, Comp cam 260H swap, and a Clifford header, if they will ever get it to me. All the work is done and I can't fire it up for lack of an exhaust system. I ordered it in the middle of May and today they promised to have it for me Aug. 7. It wouldn't be the first or second promise they hadn't kept to me if it doesn't show. As far as I could ascertain, Clifford is the only supplier of headers for the '79 4x4. The split manifold is supposed to work. I don't know from actual experience. I was unable to find one in my area, but you may do better. I am putting on an Autolite 600 cfm 4-bbl from a 460 that I am jetting way down. This advice comes from racer buddies who say it works well on the street. If you go with a similar setup, you will need a 3" stub stack on top of the carb if you have A/C and you will have to do some minor fabrication to relocate the throttle cable mount. Also, you'll need an 8" longer throttle cable. Good luck

 

First the offy intake you have is great. You can get a header from summit racing for the 4x4 maid by pacesetter. It has dual outlets for true duals. I think mine cost about $200. I use that intake this header and a comp cams 270 with an edelbrock 600 and it runs great. I also had a holley 600 on it that worked good aswell. This is in a 79 150 4x4. But I beleive the header would work in the 250 also.

 

thanks for the info, but I'm wondering what the difference would be with a 2wd header. every time i call clifford i get some answering machine that says its full, and then it hangs up on me. If the newer factory split manifolds will work with the offy intake, i'll probably just get some off of ebay or see what they cost new from ford. actually, some of the other techs probably have some laying around. I just started at this dealership and some of those packrats have everything. Any other cam and carb advice will be considered also.

Steve

 

[updated:LAST EDITED ON 28-Jul-02 AT 10:43 PM (EST)]Hey there, just finished my 300 I6 rebuild and everything is as well as I had imagined. Put a Holley 390 on an Offy DP intake, put a Crane 260 cam and the high lift springs, and found that the later model exhaust manifolds bolt right in with a little grinding.

My muffler shop buddy welded a nice collector/y-pipe, 2" stainless, and went to 2.25" back from there. Used an OEM equivalent muffler and exited at the stock location. I did have some minor concerns but everything is working very well except the Holley is being the regular pain to get dialed in properly.

The exhaust note is unusual, it just sounds like a bigger truck until I put my foot in it, then we get the famous "angry bee" sound. The original engine was pretty beat so I don't have alot to compare it to, the rebuild is so strong an engine, I'm pleasantly surprised.

Remember that others who have done this say these engines need back pressure to work to optimum, my muffler guy did one that ran like crap with 3" trick exhaust.

My truck is a 79 F-100 and the starter location gave the muffler guy a little worry, but he snaked the pipe right past the starter, I may have to put a shield on it but I don't think so. My recommendation? The manifolds cost 9.95 each + GST at Pick-Your-Part in Calgary. Sure beats 199.95 + shipping + exchange + broker fees, and on and on. And these sealed the first time with the steel intake/exhaust gasket from the rebuild kit. Do it, it's easy.

Good luck!

 

Have any of you guys had problems with the headers sealing? I got the Clifford setup and can't get any of the back three to seal. Need some suggestions.

 

I had problems with the Cliffy headers and intake sealing on my '68 240 turns out it was the Fel-pro one piece gasket. Are you using that one or the one Clifford supplied. I know the Fel-pro one piece does not line up on the three different heads I have on the #6 exhaust port. Also, I found that the intake runner on #5 and 4 are kind of thick on the bottom and you have to grind the clamp washer down in order to have clearence or they will hit the bottom of the runners and prevent them from raising up enough to cover the ports. Hope that helps.