I have a 86 Full sized Bronco with I-6 in it that I have been modifying over the years. Currently the motor is bored .030 over, a 260 Comp Cam, a Clifford RamFlow intake manifold, a 650cfm mechanically operated Holley double pumper, and a single outlet header. Not sure what the specs on it currently, but I guess its around 300hp and 400 torque.

My question is what should the next step I should take to get some more power. I've read a lot of forums about putting a 240 head on it to raise the compression ratio? Also I was wondering about putting bigger Valves in it as well. I've read off one Forum that putting bigger valves wouldn't raise power but lower it. Has anybody done this or know anything about it?

Also I'm wondering about what kind of gears I should put in it to get the most out of the motor. It currently has the stock 3.50 gears pushing 36''X12.5" Super Swamper TSL. I was thinking about 4.88? Would that be too much or not enough?

Any Feedback would be appreciated,

Ryan Whipple

 

A 240 head will make about a .5 increase in compression. 1.90/1.60 valves are a common upgrade. Before and after dyno runs will tell you what increases if any in HP/TQ. JMO, your guess on current HP/TQ is very......optimistic. Run it on a chassis dyno and post the slip.

 

What do you want to do with it? thatll determine gearing bigtime. You also didnt say what tranny you have.

The 300s head isnt too good for power, so if you want more, youll likely have to force air in. That will keep it more streetable and proper for a truck than building NA power (high rpm).

 

+1 on getting it dyno'd. im so tired of people guessing or doing desktop dynos. The DD of my mustang is WAY off the actual dyno runs i did, especially on the low end.

 

JFG, what is the EFI head worth for compression?--I assume the OP was carb to begin with.

 

IIRC, the EFI head and the 240 head are fairly close for CR when used on a carbed 300. I do recall that the EFI head does not lend itself well to larger valves due to shrouding issues that can't be easily "ported" away like on the carb heads.

 

a slight bump in CR alone isnt going to give the OP what he's looking for.

Boost it, go custom, or get a different engine. The OP has alread done pretty much everything to a 300 that can be done.

 

Flashy's build hits the 300/400 marks NA...and we know what it's made of. Unless Ryan has a build nearly identical to that, the dyno slip is not going to compare. Boosted may be the easiest way to get it there at this point.

 

AFAIK, flashman hasnt dyno'd his 300

 

As for the gears, 3.5s are probably a bit tall. 4.88s would really make you crawl though. I'd go right in the middle for some 4.11s.

Boosting the 300 is going to really get you power quickly. Fortunately, there's quite a dedicated forum here, and on fordsix.com that is all about boosting the 300. At the point your at, you're going to be doing the nitty gritty details to get more power out. It's definitely doable, I was reading up on a guy who dyno'd his 300 and it was at around 350hp/500tq NA, but he had a bottomless wallet and had put about $5000 - $10000 into it. It sounded.....amazing....

 

If you cannot get it dynoed, goto a track and get me the trap speed.

at speeds <100mph hp is well approximated by weight times the cube of the trap speed in mph divided by weight (hp = w* (trap/235)^3)

(me and another guy at IBM proved this out in 1990 over a few thousand test results and nailed it within a few hp)

 

oops, not divided by weight, divided by 235, but the edit button aint working...hangs the browser?

 

Very awesome formula. What is the "trap speed" exactly? Is that something like a 1/4 mile?

 

Thanks for all the feedback, and I apologize for guessing how much power my motor has. Unlike that one fella with the bottom less wallet I have a very limited budget so getting an actual dyno test done to it is probably out of the question, but I'll have to try that formula out for sure and get back with you guys about more details. Would you want to run stock tires to get a more accurate test or could I keep my bigger tires on it and get the same result?

To talk a little more about head work, I remember back when I totally rebuilt the motor back in 04 that the valve stem width of a chevy 350 valve is the same width as the 300 valves, but the diameter of the intake and exhaust valves were quite a bit larger. Has anyone heard of using chevy vals in a 300/250 head?

Also I only realy use my bronco for mudding/2tracking so I'm not concerned about it being legal. The transmission in it is a Bog Warner 4-speed granny tranny. My brother and I was thinking about putting a automatic in it, because of the long throw between gears. I know you can buy a short throw shifter kit but I'm not sure which settup would be better. Does anyone have any advice for this situation?

Again the bronco has 36.5"X12.5 Tires on it with 3.50 gears, with a 4-speed granny tranny. I'm looking for a power range no more than 5500rpm and use it mostly mudding/2tracking. What kind of set ups are you guys using?

Ryan Whipple

 

Dyno time isn't cheap but it is definitive. If you get to that point I suggest using the tires you drive on as that will give you the actual rwhp it's putting on the ground which is what moves your wagon anyway.

Your machinist can determine the valves for you...they will be after market items anyway and IIRC it is usually a Che**y valve...190 intake and 160 exhaust.