Good day all!

want to talk about valves and look forward to any and all input before my head goes in the shop for that.

'86 4.9 with a stock bottom end, went with EFI exhaust and walker Y pipe and 2.5 " out the back with a flow master 40... offy DP and a holly 390 for intake and a DUI dizzy.

had the head P&P as well so now seems stock valves will be the biggest restriction?? if so is it worth it to go with over size and how much of an gain for the buck doing so? got a couple hundred left yet for the head budget.

thought I would ask here before I hit the shop for the no BS run around


thanks

 

You can go the valve route, but you could also go a camshaft route, or a 1.7:1 rocker ratio route. Depends on how much money you want to spend and how much you want to pull out of it.

The valves is probably most expensive.
The cam second.
The Big block chevy 1.7 rocker arm conversion the cheapest, but well owrth it money invested.

 

The larger valves would be an up-grade with or w/o a cam, but used with a performance cam would make the most power. Either way, have a 3 angle valve job done, with a 30 degree back cut. Also, you might want to think about boosting your compression by shaving the head, and/or block a bit, and add a bit of power that way as well.

Price out the machine work for the larger valves. You will need new seats, hardened exhaust seats, and bronze guides. SI valves sells the 1.94"/1.60" valves for $150 plus postage. These are not the sbc valves, but made for your engine. BUY Only THEM.

If you go with a performance cam, get the kit, and have your rocker studs changed to the screw in type--3/8 or 7/16". The latter will allow you to use bbc roller rockers, 1.7, which you can buy on ebay for about $100.

Use the Mr. gasket intake exhaust gasket, and Only the Felpro head gasket...the $60 one.

 

How do oversized valves affect gas mileage? Is it an automatic reduction? Or is it one of those that may mean easier power is less work when not under load (ie. better fuel mileage.)

 

Thanks guys for the input... not much luck in my research so far on what has been mentioned any links to the chebby conversion? and could alum rockers be used in the conversion?


any guess to gains from what has been mentioned so far? not after a high doller upgrade for just a few more pony's like....

I can get the 7/16 screw in type for free( Mr Gasket 1074 Competition Screw In Rocker Arm Studs SBC) will those work?
and no problem on the 100 for rockers... heard chebby 396 will work as well?

what cam would be best for off road use in a f250? and still pull the pass's at 65 with 32" tires


thanks for the input all

 

Good question AB and I have NO clue lol when my truck was new and on stock 15" tires I got 21 mpg on the highway empty but with 32" tires that went to 15 at best.... and a camper on and a boat in tow it's 8 lol

I have read alot on MPG on this forum on the 300 and it's just not there IMO. I have seen boost of 30+ but they are the 1% lol

I think when I'm done with mine I will have it breath'n about the best a 300 can do and will see what my MPG is on a highway drive.... one would think that the engine is indeed work'n easier no?


AB just food for thought.... wouldn't a bigger intake valve draw in more gas?

 

Bigger valves will affect the low end power, and raise the overall powerband. Fuel economy is relative to the position of your foot.

 

That's good! Every horse needs to eat. Every engine/vehicle combination has to find that mystical peak in hp where the engine is working least to move the vehicle, without crossing over into unneeded hp. Will adding the larger size valves use more gas? most likely. As will a larger than oe carb, hp intake, cam, sbc rockers, porting & polishing the head, EFI exhaust, etc. Every time you raise the hp from oem, you run the risk of lowering your mph. What you are trying to do is find the balance, the peak hp for your vehicle, that will move you with the least strain on the engine. Every formula is different, depending on needs, expectations, towing/hauling, gears, trans, tire size, and many more combinations. You are looking for the right combo for your vehicle.

If you are not willing to drop a few mpg for greater power, then stay exactly where you are with your engine.

 

Thats my thought as well, and myself for what I use my truck for, MPG has never been an issue and I could care less on what it is as long as the truck gets me back home


Think I will just have the valves reground for now and see how the engine does.... kinda want to get this back on the road since it's been close to 3 months since the moter was pulled and hunting season is close

maybe a winter project? which will give me time to research the options that have been mentioned so far and gather parts.


thanks for all the input so far guys

 

That's what I was after. Some things help with that quite a bit, such as a free flowing exhaust. They may allow you to put more gas through the engine, but when you don't need the extra power, a freer flowing exhaust isn't going to consume gas. From what I hear, a P&P is the same way. It makes your engine have to work less to do the same thing, which consumes less fuel until you want it to. I was curious how oversized valves fit into that category.

I'm all for mods that give the driver the option of using more fuel for power only when I need it, but then sip when not using the extra power (ie. cruising). Some engines (and mods) will just dump gas through no matter what you're doing.

It's good to have a grasp on which ones are which.

 

This is a great forum, a good source of info. But I would also ck Fordsix performance.com. Look in the FAQ sections.

 

guy,s i am asking here, looking for op,s even disagreement is fine with me if you would kindly tell why. here is whats up. i rarely talk about it , maybe briefly mentioned one or twice when a fellow member would bring it up. in my harley davidson world there has been over lets say an easy decade or more, a fastburn if you will of custom hd shops with full fledged, very hard core, very expensive, dyno,s and flow benches, quality stuff with very smart folks who know what to do with it. there is a trend emerging that is showing in many case,s , taking into account the whole build as a system, that in fact, larger intake valves can be good, but the exhaust is best left the stock size. in some case,s some of the most highly respected porters that exist in the trade have actually reduced the od of the exhaust only in some particular apps and are showing some very good numbers. the rules are not changing so to speak, but with the advent of these very sophisticated flow benches, new patterns are emerging. very serious straight up stuff... in a very basic way, the mighty 300 and a stock hd motor are reasonably comparable in the area of long stroke, low rpm, torque monsters, stump pullers that spend there real life in the lower rpm ranges where the heads run out of air quick, and huge exhaust valves that are put in to maybe gain in the top end , can actually be a detriment. the wrong way to go. it,s just like f-250 always teaches, its about the whole system. it has been known for years and years that there is a ratio between the two valve sizes that reaches a good comprise. but again, new study,s are showing that that ratio is a little more broad. lot,s of room in there and some engines are responding very well. i am asking, are you guys seeing or hearing any of this with our 300 and our porters. second, the man asking about oversize valves is a good example of what i am asking. we all know our head flows very poor. we know you can only go so far before we hit water. PROPER port work on our heads, can do a lot for them and is worth the $$$ if you are really trying to squeeze the old gal. but, is it possible he could make more power with oversize intakes only. and save money to boot because his oversize exhaust will not be required. before i go, i want to just say that a precision valve and seat work, guides and new springs set correctly is a given and is just assumed will be performed and has nothing to do with this question. the only real issue is the exhaust valve size only. are you guys seeing this, any talk on back channel pm,s. anybody ever actually try it. these are the things i am asking. i know from years as a member there are some real sharp folks here. i hope you respond. toss it around, even if your going to call bs on it. it is not a silly setup trick ? OR ANYTHING OF THE SORT. that,s not style. i do not know as much as i want to. i do know the trends showing in some case,s are legit so here i am, asking some of the best friends i have on the net, anybody, tx for the ear, its always good around here. paul md.

 

talk to me will ya, you gotta have some thoughts. i,ll tell you again. this is not a trick bs calling anybody out thing at all. i DO NOT know, and i am asking myself. it sorta makes sense in some ways for long stroke low rpm stuff. some of the points just made above about valves to big killing your low end power is exactly the point some of these porters are beginning to raise. the only diff is, the head seems to like the big intake, but not the big exhaust. wish i had the ducketts for a bench. we could figure it out right here on THIS forum. we got the brains, just lacking the tool. can any of these very nice, very expensive programs some of you men own do any runs with this kind of setup. .

 

father/son,

Reading your post reminded me that previously, I have read posts about using the Chevy rockers to increase lift from the stock cam. One person said that using the high lift rockers on the intake valves only was the way to go. This kind of goes along with what you are sharing.

 

I believe that is the logic behind the Crane cams for the 240/300, with higher lift on the intakes.