I preface with stating I have very good skill mechanically, Ive built and tuned plenty of motors over the years, but this one is just really not making sense. I purchased a 71 with a 454 and a 4-speed. It appears to have low gears, as I am doing 3000+ when going 65-70. The motor was rebuilt as a stroker motor topping out at 496CI. It does have a smallish cam (Comp 11-430-8, which is 224/224@.050" .566 lift), but it does have stock cast iron manifolds, 2 1/2 exhaust, and Magnaflow mufflers. It has Brodix heads, a Brodix intake, and an 850 Holley DP. Plugs look fine, and it has 200-210 compression, and the CR is 10.5:1. Ignition is stock distributor and coil and a Pertronix conversion kit. I've checked voltages to that and adj gap; it's fine.
In troubleshooting this, I took it out this morning after a while of not working on it. It's got some power, but going around a corner in first, I punched it, and it barely chirped the tires. I would expect it completely sideways until I left off - nope... Even with the small cam and small exhaust, I would expect this combo to be around 500HP and 550 torque, more than enough to nuke tires, which it can barely do. The only way to describe it is that it feels like it's in a 5000 lb Cadillac or I have the rear brakes on.

Some things Ive looked at and tried

• Bumped timing to 20 initial, 36 all in by 2800
• Verified throttle is opening all 4 barrels (I had to buy a new bracket and cable holder)
• Verified 12V at the pertronix, and re-shimmed the gap
• Re-adjust the valves to verify the roller rockers have the correct preload
• Measured compression (200-210)
• Floats look good on carbs
• Plugs look of maybe a tad rich. (I need to verify what jets and power Valve I assume whatever they came from Holley with new)

Just doesnt pull like other big blocks I had in Camaros, and they were only 396. A 496 feels like my stock 270 HP 350 in 71. Since I didn't build it, I cannot verify that the cam is installed correctly. A severely retarded cam could have these low-end torque symptoms, but the cranking compression wouldn't be 200+. The next thing I am looking into is getting a hotter coil and an MSD 6A, and getting that out of the way, as 200PSI is pretty high compression, and if ignition isn't up to it could cause issues.

 

What size runner heads ? Dual plane or single plane? What rpm does it stop pulling at?

Disconnect the secondarys and how does it feel ?

I would expect that thing to be wheezing by 5000rpm with such a small cam. Maybe it isn't a 496 ?

 

Gear Ratio.

Those rear gears sound like 3.36.
And my 72 BB came std with them as well as a 2.20 1st gear Muncie trans. That was std BB trans/diff gear combo for years.
It is only 7.4 gear reduction in 1st gear, and makes it feel like a dog.
1st gear revs to 50 mph in first right?
Compared to my LT-1 with 411s, this thing stock felt like it was starting out in 2nd gear. Yuk!
It would not stand a chance from a dead stop.

That cam is actually too big for that gear combo, the cam picks up well at 2000 rpm, and you are already moving almost 20 mph by then.
That gear set needs a stock cam that makes power from idle. Or a lot of clutch slipping. Or really just more gear.
Basically you do not enough enough rear gear for it feel like a BB.
It is so choked down by gearing it feels almost like a SB right?

That engine should be close to 550/550. So that is not the problem. Say 50 less with iron manifolds.

You need at least a Autogear wide ratio gear set with a 2.52 or so 1st gear., or a TKX with a 2.87 1st gear.
Don't change only the rear gears because that alone won't cut it. A 336 to 370 is only a 10% improvement. Ho-hum.
A 2.52 WR Muncie and 3.55s has the same 1st gear as a 2.2 CR Muncie and 411s. BTDT. Those combos ran terrific back in the day. The trans makes more difference, unless you change the rear a LOT.
A 252 WR trans is 15% more in first gear. That and the 355s or 370s would really wake it up with 21% or 27% more grunt than stock.
That will feel like an extra 150HP! And 150 more tire smoking TQ!
2.52 x 3.70 = 9.4 in first gear vs 7.4 now.

Plus you will need the autogear Italian gears strength to keep the trans together under the 496 TQ. A stock Muncie will not last.

Plan B is a 2.87 TKX 5 spd O.D. will give you 9.6 in first gear overall, with the 336s, and it will highway cruise at 2000 vs 3000 rpm, and handle the TQ.
That is my combo.

And more gear than that with the TKX will make it feel like a rocket, at least until the IRS starts breaking.
There is a reason all the BBs came stock with 2.20s and 3.36s, even L88s. Less IRS breakage under warranty. They did not put that much more TQ to the half-shafts with those gears.

I know at least 2 people with a TKX, warmed over BBC, and 411 diff gears, and both of them easily broke IRS parts.

Past 400 HP you have to be gentle with the IRS!

 

Leigh is spot on.
I’m running a 496 in my 73 with a TKO600 2.87 first gear and .82 fifth gear, and 3.08 rear gearing.
As Leigh pointed out, the first gear ratio in your transmission is also killing off the line performance and like he suggests swapping to a transmission with the better first gear ratio will work better than swapping to a taller rear gear.

Your cam is hurting your lower end torque and you would be much better with a camshaft that starts coming on at about 1500 and cuts off at around 5800 rpm.
When my engine builder dyno’d my engine he immediately suggested swapping to a smaller cam to bring the torque into the rpm range I wanted so we swapped cams and it made much better numbers on the dyno off idle and all through the rpm range.
I lost some torque and hp at the upper rpm range, over 6000rpm, but I would never run the engine at that rpm on the street so it didn’t matter.

Unless you have verified the engine is bored and stroked to 496 cu in I would do that before I would drop money into it elsewhere.
The oil pan could be a dead giveaway.
If it’s truly stroked to 496 cu in the stock type oil pan would never work.
One other thing I would question is the use of the original heads.
I’m sure they could work, but I would imagine anyone spending the money to build a 496 stroker big block would want better flowing aluminum heads to make everything work.
Do you know if the heads are oval or rectangle port heads?
Rectangle port heads were designed to increase flow in the upper rpm ranges and oval port heads will actually make better torque in the lower to mid rpm range which make the oval port heads a better choice for a street engine.

Let us know what you find.

 

He has all the parts reciepts and the machine shop work so I know its a stroked 496 using the Scat kit. It has Brodix BRO-2061018 which flow approx 325 @.550 lift. CR is 10.5:1 This combo should make 550/550 even with stock exhaust. They went with a small cam due to the stock exhaust. Honestly feels like my old 71 with the 350/270HP motor. I would think just a touch of gas and this thing should be skating around even with not that great of gears. My next step is a MSD ignition and coil as ChatGPT thinks with 210 PSI of cranking that I need better spark due to high compression. Its a stock coil with a pertronix. The MSD wont hurt...

 

Rectangular port Brodix heads with 315cc port volume.
Slow velocity down low = low rpm TQ suffers.
Another strike for TQ at 1500 rpm off the line.

Not an ideal combo. By the time the heads start flowing well (3500+) the cam soon runs out of steam. Those heads could pull to 7000, but the cam won't.

Now is the Brodix Intake a single plane or a dual plane?

 

Sorry I read cast iron manifolds and thought iron heads.
My bad.

 

You don't necessarily need a new ignition system. If it was a big problem, it would be banging and popping. My car made well over 800 HP with single points and a Bosch VW coil.

The cam is definitely small for a 496....but if anything it would help low end power and tire spoking ability. The heads are 315 cc...not an issue there eight. 210 cranking compression is pretty stout....if anything I'd be expecting some detonation possibly depending on temps and altitude. Your gearing sounds like maybe 3.36's? Maybe 3.55's?Not sure on your tire sizes or how much over 3K you're spinning at 70 mph. 3K with 3.36's and 26" tires is about 70. 3500 would be 3.70's with 3.55's inbetween.

If you have a close ratio 4 speed it could be a little week down low..but again...once it lit the tires up it would keep them burning forever. Throwing a deep 1st gear 5 speed in it would wake it up for sure...but it still sounds like something is way off.

Have you tried it with no air filter? Many drop base ones are too close to the inlet and choke the heck out of them? Especially the 3" ones everyone uses to get hood clearance.

JIM

 

THis was supposed to be posted last night, but I got screwed buy the related thread bullshit...
I would start with the easy stuff...lots of could be's

verify tdc and your timing mark. If you pull the timing cover to verify how the cam is installed you may as well just get bigger one so avoid that for now. Are you running vacuum advance? Is it on manifold vacuum? It will help at low rpm by increasing your timing and compensating for the lag of mechanical advance..

Consider headers but you are correct, you should be getting some torque out of that motor as is but it sounds pretty corked up. You could take your exhaust off and run an open down pipe or just a glass pack as a test.

I would look at your idle settings and jetting, you could be pig rich at idle and your dying in the transition...you said your plugs look good but is that a nice light tan or a heavy dark brown or black after a long 2000-2500 rpm cruise

What are your lifters...if they are stock 1.7, try a 1.8. It will effectively make your cam bigger. Old school chevy guys did that with ford lifters all the time...ford always ran bigger lifters from the factory.

Its difficult bench racing without knowing all the specs but your compression sounds perfect

Food for thought.....Your rpm for 70 at 3000 rpm says you are running a 3.55 rear gear which should be fine for a 496. If you were running a 327 that wouldnt be enough at low idle..Im running a 427 580hp but Im set up with a light weight balancer and flywheel for fast revs and mine spins the tires easily will rolling with the pedal to the floor... yours should be annihilating your tires even with a close ratio transmission. Do you know what transmission you have? Muncie? M20, m21,,,?...when my carbs were rich at idle through the transition it was a dog down low until the revs climbed and it could eat all that gas. If your jetting is fat but you are hiding it with your idle mixture screws you could be drowning the motor ...

 

Thw heads you are using - RR BB-2 PLUS no. 2061018 port volume 312cc chamber 119cc presumably is a rectangular port item?

I've been using - RR BB-O PKG no. 2061000 port volume with 270cc chamber 119cc. on my 489 for the last 10/12 years on my '68. I chose these heads specifically for the higher port velocity of an oval port head and a sensible rev limit of 6000 rpm. Cam is hyd flat tappet - 232/240 (I think) @ .050. With RPM dual plane and 950 cfm DP it is somewhat over-carb'ed. With the cars 3.08 rear and 2.20 1st gear M21 it really pulls fine from 1000/1100 rpm at rest and doesn't easily spin the tear tires too easily off the line. (But I am wary of mistreating the driveline) I see the 'tall' gear set as an advantage with 1st running up to approx. 70 mph.
Torque maxes at 606 ft/lbs at 3850 rpm. TBH I wish for a 5th gear or overdrive unit as the combo I'm sure would comfortably pull 1400/1500 cruise rpm at 70 mph (rather than the current 2550'ish rpm).

 

A stock 1970 L48 350 makes 320# TQ at 1200 rpm, right when you let the clutch out.
A stock 1970 LS5 454 makes 410# at the same rpm. (GM numbers)
Both of these mild cam engines make 83% of their max TQ, just off idle..
And the BBC makes 28% more TQ.. Should be a tire-smoker right?

But the story changes once you work in the gear ratios.
A stock L48 comes stock with a 2.48 W.R. Muncie and 3.36 gears.
An LS5 comes stock with a 2.20 C.R. trans and 3.36 gears.

The L48 puts 2670# TQ to the half-shafts.
The LS5 puts 3030#.
That is more, but only 13% more.

That is the reason it does not feel much stronger out of the stoplight. It's not, not by much.

Add in a large duration cam, and a single plane intake, that both kill low rpm TQ, and you could easily have less TQ at the half-shaft.
That is the reason cars with big cams, also need big gears.

I'll ask again, is your Brodix intake a dual plane, or a single plane?
That makes a huge difference at low rpm.

By buddies EFI / dual plane intake / ZZ427 / 2.87 TKX / 411s puts 4480# TQ at the same rpm, to the half shafts. ( That is 68% more.)
That is why the stock shafts twisted like a pretzel!

Gear reduction is KING!

 

Gear reduction plus powaaaaaahh!!
And running your tires really low for extra grip!!!

 

Big Power will always find the weakest link!

 

Just don’t give it any go pedal until you’re in third gear.
Then ease into it.

 

[QUOTE=

What are your lifters...if they are stock 1.7, try a 1.8. It will effectively make your cam bigger. Old school chevy guys did that with ford lifters all the time...ford always ran bigger lifters from the factory....[/QUOTE]

Do not do this with Ford rockers. I am an old school Chevy guy, and it is an effective way to jack up lift if you have the valve to piston and retainer to guide clearances, and spring height available. But Ford rockers are vastly different in several critical aspects. And please stop calling them lifters.

 

Again the engine is not the issue here. The combo all has to work together.. If things are mismatched performance will suffer and be underwhelming. There have been many cases of people buying these old cars and thinking the answer is just building the biggest hp combo they can and not realizing its a trade off, the more hp you get the more torque you typically give up in the street performance range down low. a lot of disappointed folks sold those cars afterwards.

This is the reason Car and driver preferred the peppier l48 for city driving performance over the l82 when these cars were new. I just installed a 3.55 rear end and an overdrive auto trans with a lower first gear for this reason myself even though I have an optimistic on paper 500hp /500lb torque 406

 

I realize your quoting some other missing comment but it should be mentioned a bigger cam will only give up more torque below 2000rpm and hurt off the line performance more.

 

im wondering if you have carb issues. how hard does the motor pull? just normal shifting thru the gears?

stabbing the gas like that is where proper accel pump and secondary tuning really comes into play. if those are off you could just be bogging the motor down.

 

Agreed - in the moment I couldn't see past the Ford rocker suggtion.

 

OKay...The ford rocker suggestion was an example of what was done in the 60s and 70s....No One is going to find an old set of ford rockers and put them in a new engine...have some common sense. If he has a newly built motor, then of course he would be smart enough to buy bigger rockers for his specific motor...God, some of you guys are as dense as Joey supporters...

His camshaft is a tiny cam for that motor that has a tiny powerband from 2000-5500. Upping the lift and duration with a 1.8 lifter would put the power band somewhere closer to 2500 to 7200. he wont be giving up precious power down low and would be gaining a lot above 5252. I bet it would increase the toque down low as well.

by all accounts that engine is being strangled. the 3.55 gearing should be low enough for that size motor provided he has a wide ration tranny