If my current lead on a 400 comes together I may be doing my first big block build. What are the limitations of the big block valvetrain in a high end street/strip build? If I do this trick flow heads will definitely be used. The flow numbers seem fairly close to stock LS (square port) heads, and I intend to keep it stock stroke (so c.i. will be similar). I know that 1.5hp per c.i. is no problem on the LS platform in the low to mid 6,000rpm range(and done with a reasonably friendly cam). I have never seen any dynos of Chrysler big blocks performing like this. How heavy is the BBM valvetrain...is it a volume/velocity issue...other? Is 1.5hp/ci even possible at reasonable rpms without a Himalayan cam?
Realistic valvetrain expectations.
- Thread starter Pascamp
- Start date
-
I'm glad you chimed in Andy. I've always liked liked your posts, and admired your work with these engines. I was hoping to keep it at 400 to keep stresses on the block low(side loading, piston stability, piston speed, bob weight, ect), and use either Pro-gram or BCR products to tighten up the bottom. Info from you and a few other guys has me confident with the oiling mods required.
My knowledge stops at the BBM valvetrain. Obviously cam profile and valvetrain weight contribute to the required valve spring pressures. I'm also very aware of the compounding effects of geometry and friction (the viscous cycle). The more things are offset...the more side loading...the more spring pressure required to fight the friction...the more friction created.
Is it just an architectural issue (port, intake, valvetrain, ect) that I don't see "in between engines"? Plenty of mild and wild builds, but not much in that 1.5hp/ci that I'm looking for. Thanks
Last edited:
Some further info. My expectations are 600hp gross(give or take) at 6500 or less, don't care about torque (car is 2700ish). Good machining and tolerances will be used, along with modern cylinder finishes, coil on plug, tbi, and overdrive.
I basically want to be able to live an LS lifestyle with a BBM. Turn the key and drive to New England, drive it to the office, take it to test and tune 3 times a summer, and only pop the valve covers every 10k for a valve spring check. Is this a pipe dream?
I basically want to be able to live an LS lifestyle with a BBM. Turn the key and drive to New England, drive it to the office, take it to test and tune 3 times a summer, and only pop the valve covers every 10k for a valve spring check. Is this a pipe dream?
moper
Well-Known Member
No offense but if you're expecting 1.5hp/in from these dinosaurs comparing to the LS platform - it's considered to be a very strong build and it's not something anybody can do. It can be reached, but a lot of the reason the LS are so good, is they share next to nothing with the comparable 454's of the same era. Basically apples to pears comparison. You should probably decide whether you want 600hp, or 600tq, and build for that in whatever means possible. I.e stroke it. Otherwise you will be really spending on block prep, camshaft, and valvetrain to keep it alive at very high rpms to get those hp figures. Like 7K plus.
Just copy the low deck that I built for my Duster. It makes 600 hp and 600 ft-lbs of torque on pump gas. EFI, coil per plug, hyd roller engine. You'll need $20K and an experienced engine builder.
I'm well aware of the expenses involved. I was figuring @13k in parts alone. What is it exactly that is making these goals so lofty? The bottom end strength, oiling, ect can all be improved. What is it that makes these new engines so damn potent and do it so reliably? A square port LS is putting out about 500hp @ the crank with 250k reliability, and 600 is a cam swap away. Where is the magic in these newer engines that we can't mimic?
Last edited:
Jesus Chrysler
Forgiving Sins Against Mopar Since 1983
Now, I don’t know much about anything, but I’m gonna guess it’s the 40+ years of development in cylinder heads, fuel injection & tuning. It’s also noteworthy that the 600hp LS motors are often 427 inches, so they still have a displacement advantage over a 400” BBM.
moper
Well-Known Member
Aside from having three rings per piston, and four strokes, there's not much of the same. If you're thinking it's that simple, ask yourself why at best the engines of the day, supertuned but using stock parts aside from maybe a cam, could barely muster 1hp/inch. Or why every oldschool V8 isn't reaching that potential even using modern parts.
As yourself what difference thing rings, short, lightweight pistons, much more solid foundation (block), a crank driven oiling system, valvetrain parts based on spintron development over years...
Seriously - not everyone can do it. I'll bet the vast majority can't, and that includes many professional builders. Toss yours together, get it down the strip, and tell us what it makes (dynos don't count).
Andy - what is the displacement of that low deck you pictured?
As yourself what difference thing rings, short, lightweight pistons, much more solid foundation (block), a crank driven oiling system, valvetrain parts based on spintron development over years...
Seriously - not everyone can do it. I'll bet the vast majority can't, and that includes many professional builders. Toss yours together, get it down the strip, and tell us what it makes (dynos don't count).
Andy - what is the displacement of that low deck you pictured?
We can throw injection and good flowing aftermarket heads on older engines. I just don't see where the difference is.
No need for big inches on LS engines to hit 600hp. A junkyard 6.2/378ci (ls3, l92, l9h, ect) with a cam swap will put out 570-585 at the crank no problem @ 6500rpm.
mygasser
Well-Known Member
you mentioned using tbi yet the good hp ls engines are all sequential injection with the injectors in each port of the inlet. that allows much more precise tuning for the power/drivability they make. i'm unsure why you're against increasing stroke at all. as andy says you can do it at 400 ci but you won't like it on the street. it won't be ls driveable for sure. also why do you need to rev to 6500 if you don't need to to achieve the required power goals? the ls has a much stronger block architecture (that 40+ years development thing again) with crossbolted mains etc than the mopar so revs are safer/more reliable. it's not an ls despite any suggested similarities, so just treat it as what it is and carry out any tuning accordingly. you can and will achieve the power you want but in a big block mopar way not an ls way. 
neil.
neil.
jbc426
Well-Known Member
Its almost foolish not to put a stroker set-up in that stout 400 block, especially for an injected street car. Hook that thing up to a 200R4 with a lock-up converter and you'll have a daily driver that can cruise on the freeway at speed.
The heads are much more advanced in the LS motors, 1st of all they are symmetrical as opposed to our old BBM, the assembly is lighter, rods,crank,pistons, the intake and injection system that GM perfected is way ahead of any FI that the aftermarket has, heck get a very tuned carb and it will outperform the modern FI from aftermarket. Don't get me wrong for what they are the 400 BBM is a good motor, I put together a 451 that has street manners easy to drive and made 610hp & 625tq, amzing thing that the LS can't do as well is the torque @ lower RPM how about 543lbs @ 2800 and stayed until 5800 getting 540lbs over 600@3700up until 4700. The modern engines are a completely different animal, Your goal can be accomplished and I would say AndyF has proven it with very respectable builds over the years but at the price of driveability. Stroke it to either 451 or 470 and you will be more than happy when that 2700lb car moves like a little rocket
moper
Well-Known Member
It's not up to me to debate or prove it's hard. It's really more up to you to prove it's easy. Go for it. I've done it.
famous bob
mopar misfit
Not an expert, but does the 400 engines have solid pushrods like the early 440`s had / A big amount of why they would float the valves so soon most of the time !
1.5 hp/ci isn't practical for a street driven BB Mopar. You can easily make 600 hp with a 400 inch BB Mopar, but it won't be daily driver friendly. If you want an LS then buy an LS engine. If you want a 400 inch BB Mopar then accept the limitations. There is no magic button that you can push that turns a BB Mopar engine into a LS engine. If you want a low deck engine that is reliable but powerful then I'd recommend building a 470 with Trick Flow 240 heads, a hyd roller cam, 10:1 compression, small headers (1 3/4 inch TTI most likely) and a Holley Sniper setup complete with Hyperspark ignition. That is a fairly simple combo that most engine shops can screw together and it will make gobs of torque and power. If you pick the cam wisely the engine will be smooth at idle but will put out enough power to put a 2700 lb car into the 10's.
PRH
Well-Known Member
IMO...... yes.
But, don’t restrict yourself to what a few old-ish farts like myself think.
Lead the way and show us how it’s done!!
Thanks for the honest response. I knew it wasn't possible for any engine years ago. I just didn't know if aftermarket parts and good machining would make it realistic today. My only reason for wanting to keep it at 400 was for block stress, but it's going to tax the valvetrain that much harder. The parts list you suggested was pretty much exactly where I was headed. Thanks again.
I really don't think I'm going to rewrite the book on my first BBM build. I'm pretty sure I'd be wise to listen to Andy's years of experience. Modern adaptations can only do so much for older designs I guess.
Here's where my thinking was going. Dead nuts machining on the block and use BCR or Pro-gram parts to tighten up the bottom end. Of course also use torque plates and modern cylinder machining to get good, long lasting ring seal. I was on the fence about which direction I wanted to go on bearing clearances. I was leaning towards tightening the engine up and running more modern oil weights.
The benifits of fuel injection to me are low speed manners, longevity, and day to day reliability. I don't think anyone can really argue that engine life dramatically increased as soon as fuel injection hit the scene. I really don't look at fuel injection as a performance increaser per say. It's been proven time and time again that a well tuned carb can hang with injection any day.
Ignition wise, again I see the advancements mostly in reliability. While more accurate timing can gain you some power, it's not an earth shattering difference.
I was hoping that some of the newer aftermarket port designs and cam profiles would make the difference, but I guess you can only go so far in the box you're given.
All you need to do with the block is put a set of ARP main studs in it and have the main line honed. You don't need a girdle or special main caps. Save your money and put it somewhere that will make a difference. Best place to spend money would be on a ported intake. I'd start off with a port matched Trick Flow intake from Hughes and then if the budget allows have Wilson Manifolds do a full competition port job. Put a 4 to 1 merge spacer between the Sniper and the intake manifold and you'll be good to go.
The critical item is the camshaft. It has to be big enough to carry the power upstairs but not too big or else the street manners really suffer. I've been going smaller and smaller with my street cams lately. The 496 that I just finished has a 239/245 cam in it with 0.600 lift. That engine made 630 ft-lbs of torque and 610 hp and it has a very smooth idle. That was with TF 240 heads, a ported Trick Flow intake and a Sniper. The cam was designed by Dwayne at Porter Racing Heads.
I used stainless rocker arms, conical valve springs and Gaterman lifters. These parts are more expensive and require additional TLC over more conventional parts but I think you have to use good stuff in the right spots to get the the results.
The critical item is the camshaft. It has to be big enough to carry the power upstairs but not too big or else the street manners really suffer. I've been going smaller and smaller with my street cams lately. The 496 that I just finished has a 239/245 cam in it with 0.600 lift. That engine made 630 ft-lbs of torque and 610 hp and it has a very smooth idle. That was with TF 240 heads, a ported Trick Flow intake and a Sniper. The cam was designed by Dwayne at Porter Racing Heads.
I used stainless rocker arms, conical valve springs and Gaterman lifters. These parts are more expensive and require additional TLC over more conventional parts but I think you have to use good stuff in the right spots to get the the results.
The 440 in my 70 Charger made 500 hp with stock pistons , .550 solid roller. home ported 906s, 6 pack and headers.
Ran 12.30s (3900#s) and idled/drove like a pussy cat.
Stroke it and get some modern heads professionally ported.
A custom roller cam , Good headers and a port matched sungle plane with a lot of carb.
VOILA !
Ran 12.30s (3900#s) and idled/drove like a pussy cat.
Stroke it and get some modern heads professionally ported.
A custom roller cam , Good headers and a port matched sungle plane with a lot of carb.
VOILA !
famous bob
mopar misfit
Wildest set of rocker arms I ever saw !!
Those are RAS rocker arms. RAS went out of business a few years back but there is a new company who has the same rocker arms for sale. I think these are the best rocker arms you can buy for street use but there are other good rocker arms on the market.
About Rocker Arms Unlimited
EchoSixMike
Well-Known Member
A good carb can hang with EFI on a dyno, for a given build. That's it. Where EFI leaves it in the dust all day, everyday, is living with the thing and designing the build. Dry ports are huge difference. Spot on mixture, all the time, huge difference.
Modern engines have tiny ring packages=low friction. I'me already sorta building the engine you're planning (6.800 rods, 3.380 stroke), and I can turn the engine over to set lash with my bare hands on the crank pulley, without blowing a gut.
Dry intakes mean huge ports and massive airflow without worry about vacuum signal and mixture fallout. I would spend a little more and get a Victor or TF single plane plumbed for direct port EFI and use the 270 TF's. Dry intake. More stroke would make sense too, but your build. 12.5:1 on E85 would be nice too. S/F....Ken M
Modern engines have tiny ring packages=low friction. I'me already sorta building the engine you're planning (6.800 rods, 3.380 stroke), and I can turn the engine over to set lash with my bare hands on the crank pulley, without blowing a gut.
Dry intakes mean huge ports and massive airflow without worry about vacuum signal and mixture fallout. I would spend a little more and get a Victor or TF single plane plumbed for direct port EFI and use the 270 TF's. Dry intake. More stroke would make sense too, but your build. 12.5:1 on E85 would be nice too. S/F....Ken M
-
