I've been comparing data from built up 400's with 2V and 4V heads, and although I'm only working with a few sets of data that I've been able to dig up on this site and others (would love anyone else's dynos), I've been very suprised so far with what I'm seeing.

Pretty standard 400 builds (CR 9.5-10, 4 barrel, straight up timing, free flowing exhaust, moderate cam and springs) with both 2V and 4V heads offer suprisingly similar power through most of the rpm range.

In the engines I've looked at, the 4V heads seem to offer about 20% more peak HP, and peak about 1500 RPMs higher than a 2V head. (Slightly less difference than I had expected)

What really suprised me though, is that the 2V heads peaked at only around 10% more TQ, and only about 500 RPMs earlier than the 4Vs! The 4V torque curve also shadowed just 50 ft/lb or so under the 2V one all the way down to 1500 rpm, where I ran out of data points.

Like I said, these are built examples of these engines, not stock, but since anyone who is considering the 4V option is likely going to be going through their whole engine anyway, I think it's a fair arguement that a 4V headed engine is a better option even in our heavy trucks for all but the most extreme applications.

Support? Arguments? More dynos?

AleX

 

Headers are a problem with the 4v heads. No one makes a big tube header that I know of. A while back I had a Hooker header stub kit for the 4v heads that I bought back in the 90's. I don't think Hooker makes them anymore though ? They sold quick on ebay a year or so ago for a lot more than I thought I'd get for them.

 

a 4V 400 should be able to clearly step away from a 2V if it's built to. back in the old pages rests the story of Shazam, claiming 799hp. i'll suggest that the 4V builds you're looking at are still in the 'one small step for man' rather than the 'one giant leap' catagory. the 351C's stomped the 7 liters in Nascar and every racing niche they ran in until they got factored out or outright banned, can you imagine what woulda happened if some good-ol boys built some 1971 400 4V's and went to Talladega?

i just ran across this again the other day, many points in the article make ya think, just plain common sense but the myths to the contrary seem to take precedence. like small valves are better for low end torque... No, small valves will just never make big end torque. big valves are still better for low end torque
Engine Masters Challenge - Popular Hot Rodding Magazine

many can't get past the 4V's are just TOO BIG idea. how many times back in the day was a poor performing combo thrown at 4V heads and it became the heads fault? overcam & ungergear a 2V and see what happpens

 

I agree..if you are starting from scratch...start with the best heads you can. The 4V is clearly the better choice. I don't agree that 4V's don't make good TQ. Lets look at this comparison of factory engines:

http://www.hotrod.com/techarticles/e...y_lt1_350.html

Specs At A Glance
'71 LT-1 '71 Boss 351
Displacement 350 ci 351 ci
Rated output, horsepower 330 hp at 5,600 330 hp at 5,400
Rated output, torque 360 lb-ft at 4,000 370 lb-ft at 4,000
Bore/stroke 4.0/3.48 4.0/3.50
Compression 9.0:1 11.0:1
2/4 bolt block 4 4
Crank (cast or forged) Forged Cast
Rod length 5.7 5.778
Forged rod Forged Forged
Rod ratio 1.637:1 1.651:1
Head casting No. 487 D1ZE-B
Chamber volume 74 to 76 cc 64 to 67 cc
Valve sizes 2.02/1.60 2.19/1.71
Peak flow rates (intake/exhaust) 217/151 274/176
Screw-in studs Yes Yes
Guideplates Yes Yes
Cam hydraulic/solid Solid Solid
Cam lift 0.459/0.485 0.514
Cam duration (0.050) 242/254 228
Cam lobe separation 116 114
Intake manifold Dual-plane Dual-plane
Aluminum/iron Aluminum Aluminum
Carb Holley 3310 4V Autolite 4300D
Carb rating 780 cfm 715 CFM
Tested output, horsepower 359 hp at 5,900 383 hp at 6,100
Tested output, torque 376 lb-ft at 4,100 391 lb-ft at 4,000

Remember this bone stock..no headers, mild cam, factory intake. The boss 351 is almost at 400hp/400tq - it wouldn't take much to get there. The boss is making 1.09 HP/CI and 1.11TQ/CI. A 400 built to the same specs could make 436hp/444tq.

TMeyer built a pretty nice 400 2V with aussie heads and after market goodies. for comparison - TMeyer, Inc. Precision Automotive Machining

However, I will concede that if you are looking for diesel like TQ at low engine speeds - the 2V's make it easily.

 

this is the way I build my 4wd motors. big valve small port within reason?? but on your specs you forgot one important factor. the type of fuel these motors are running. 85 octane or 91 octane?? this is a big factor in your hrspwr calculation. If I have a 500 hrspwr engine on 91 than drop to 85 lets see the difference in useable power. is the engine gonna detonate itself to death in the low rpms before it get to the 3500rpms or more rpm? the engine is a air pump! the more air your engine can pump through it efficiently the more power. But what kinda of power do you need drag strip or stump puller?? Its a never ending debate. but for your test the 2v heads are simple to make decent power. 4v heads require more money and parts availibility can be difficult sometime. Extra fabrication with the 4v heads and is it justified compared to the 2v heads. intake and exhaust work isn't just a bolt in application with the 4v heads. I'm building a 4v headed engine but I just happen to stumble into a deal and it will be worth it and I have some cool parts laying around also to back up my idea!! Catch you guys later!!

 

from a very smart person I know told me once. If you just drop a big valve into a head and don't work the bowl and turn down into the valve area your kinda wasting your money. also valve shrouding is another issues especially the non canted valve engines. So everything isn't as simple as it seems. The cam has a huge effect on how lazy the motor is or how crisp. type of cam and proper componets to back up your idea of a good motor.

 

Well I do wonder if the new Trickflow 335 heads are the way to go. They are suppose to be a cross between 2v and 4v heads, and they have upgraded exhaust ports, which are a definate hold back on the 2v heads, and they have small valves. Personally I think the valves are plenty big enough and You shouldn't need more than 2.10 in 1.65 exhaust. We need more builds and data though to make a proper decision. If I won the lottery I would build a short block and do all the heads on the dyno to see what the differance is. Honestly there is plenty of power to be made with stock 2v heads with some porting work done.

 

Mark A., that's the biggest problem I've run into. I'm talking with a guy about a 4V engine right now, and so I've been on the hunt, but ya, it might come down to aloooot of careful welding and alot of burnt out cutting wheels, if I even decide to try. I guess talking about this currently and practically that is a very good reason that 4V isn't the best all purpose way to go. I was talking much more in the theorhetical sense when I posted, comparing the power of the different setups more than their physical workability, but it's a good point.

Grclark, to you first point, yes, I am looking at what in my mind are moderately built engines (and I know, for someone with more experience, these might be pretty mild), but this is the price and usage range I (and a great many others here) am operating in, and so this is what I wanted to start a discussion on.

To your second and third points though, that's exactly what I'm saying, and am happy about. I started a long thread recently about the general differences between 2V and 4V, and alll I heard was that 2V systems are torque monsters, and pulling down trees and all that, and that your 4V engine drops below 3500RPM and your car essentially dies on the road and all the extreme views like that. I haven't found any stock engine dynos, but with comparably built ones, the difference is not really all that marked.

The question that I was trying to get answered in the 2V 4V thread was just what's being addressed here, is a 4V really just more powerful up top, or a better head all around, and how big is the difference?

A question that I have remaining though, I've heard one of the main problems with the large ported 4V's is that fuel doesn't atomize well enough at the lower engine speeds of a truck. What do you guys think about that?

AleX

 

I think that the fuel atomization is probubly very true. the air isn't being force through as much, and so it doesn't hit off the sides of the ports like it would with the smaller 2v ports and there for not as much atomization. Now I don't know if you have read the mustangs and fast fords build with the procomp heads, but they first upgraded to cleveland pistons for 9.5 to 1 compression, and they did a dyno run on a stock 400 with stock heads and cam and even two barrel intake, with a 500 cfm holley two barrel, and headers, and msd distributor and made 265hp and 419ftlbs tq. All at low rpm. So you can imagine what else would happen if you just put the dual plane edelbrock intake and a little bigger carb like a 600 or 625 road demon, and a RV cam. On my motor I used the elgin cam thats the same grind as edelbrock dyno tuned performer cam. Which is designed to be used with headers, intake and a 600cfm 4 barrel. I think it should be a 300+ hp and 450+ tq motor. Thing of it is the stock 2v aussie heads have the better combustion chamber, so they are probubly the best choice, or 2v aluminum heads. both can except big valves, so I think bigger valved 2v heads will do the best for a truck motor, exspecially if you plan on turning big tires, or towing. Both of which tq is more important than hp. Remember hp is only good for lite vehicles, and tq is what moves weight. Thats why a semi can only have 300hp but have 1300lbs of tq and move 80,000 pounds. An RX7 might make 400 hp with a turbo on it, but put a small trailer behind it, and it just won't move.

 

the link in job1bf's #4 post is probably as good as you're gonna get 40 years after the fact, for a magazine to show Ford win they must've gone a long way to make it fair. most comparo articles i've seen they give the chevy a good aftermarket intake, better cam & headers and call it stock

Big Detroit as a whole did a LOT of carb work to make things work right, they didn't just pick a PN from a catalog, make a few easy adjustments and go with the best setting. they'd try different internal metering calibrations that no 'end user' can play with until they found the results they were after, sometimes changing to an annular discharge carb and tuning the chit outta that.

low airspeed metering quality makes or breaks a finicky engine combo. 'at home' sometimes a few similar off the shelf carbs are tested but none really shine, so the motor... or the 4V heads take the blame

 

I understand the downfall of the 4V swap - parts. But it's not too bad - to me anyway. 4V headers for a 71 mustang 351C will fit my 77 2wd truck. No welding should need to be done. I had to purchase the intake spacers - while not cheap - exponentially increase my intake options - now i can run any intake i want. And all of the latest designs are for the C block (except for the CHI 400 of course).

 

Well I have a 4 wheel drive, so that's where I'm having alot of trouble, but I think it's very likely I'll be able to make some shorty's work, lengthening my exhaust will be alot easier than home building a set of headers. What brand header is that that you're running job1?

To Jfive, your engine sounds alot like what mine was before I blew it up. Stock pistons and 2V open heads, but medium cam, heavy springs, dual plane intake, Holley 600, headers, and a straight up timing set, and honestly, it was powerful. I loved it when I built it. It usta smoke the tires, and the torque at the like low low looooow RPM's was nuts, like high idle speed type thing, the brakes could barely hold it. It wasn't a friend of the highway though, and of course, it blew up.... But all of this is why I chose to stick with my 400 over the immensly popular 460 swaps and all that, with a little help, these engines haul.

Nother question though, for anybody, in the above specs for the 350 vs. 351, the only value that is drasticly different between the two is the compression ratio, 9-1 for the Chevy, and 11-1 for our guy, how do such otherwise similar engines with such different CR's generate such close power?

 

a) mag articles are notorious for being fulla crap. there's a Powerblock Cleveland build that if you do the math the numbers don't work

b) Ford exagerated the CR of the Boss351 by about a full point, maybe they just used published data & the chevy actually had more CR and was understated(see a)

what about using a car set for the flanges/some tube and a truck fenderwell exit to create a step tube set, that's what a couple guys did. Windsor or Cleveland fenderwells wouldn't matter, whatever's cheaper and available, 460 fenderwells would need spacing changes but give you bigger tubes

 

Well from the math on those combustion chambers it looks to be closer to 9.5 chevy, 10.5 ford, which is more reasonable, still a fair difference though... but I guess doing that math is sort of useless anyway until you know how far in the hole the pistons were, and how thick were the head gaskets.

And ya, that's one option, I don't want to spend the money on a new set, just to tear them up, but if I can find some used I'd definitly like them as a donor for the flanges and pipe starts. My exhaust is pretty well tailored to being between the frame rails, but I guess it wouldn't be so bad to change that, considering the other options are all also complicated. Honestly I would love to just take 2 flanges, and have 8 chrome pipes sticking straight up about 18" out of my hood, but that would get old fast as a daily driver, if I even got to drive it before the neighbors killed me.

 

vertical exit rocks! i wonder if mufflers on baffled collectors would quiet enough? legal?

YouTube - 351 Cleveland finished...

this guy pulls on asphalt with used racing tires, they only last 1 run

Ford 335 "Cleveland" Series Engine Forum: Rob's Garden Tractor weekend

open collectors on a Cub cadet

http://www.youtube.com/watch?v=wAjObHbOn9U