408 6pack setup

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RGL408

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Hi all, my names josh. From Aus amd have a 408 smallblock (stroked 360) in my valiant. Running a 6pack setup on top. Approx engine specs 11.1 comp, alloy heads, solid cam 244/252@50, 520/540lift, 5spd manual.
Just recently had on dyno to tune carbies, had 66 jets in center carb and approx .89 in end carbs. On the dyno pulls (chassis dyno) only made 340rwhp. Still stout but made pwr only to 4600rpm then nothing really after. Obviously heads need some port work and port matching the intake but curious as to what rpm and pwr the 6pack intake is good for? Wanted to bump up my cam to another solid flat tappet, lunati 582 lift, 255/255@50 108deg lobe. Would this be too big or ideal for 408ci with 6pack. Thanks josh
 
In 1970 I had AAR cuda that 6 pk saw 8000 all the time, I was 18 yrs old. Now my understanding of the stroker motor is they make there hp at a lot less rpm. I would have though 5000 would be it on your motor. Just my 2 cents.
 
when Mike build my 408 he set the rev limiter at 5600 RPM (allowing it to go as high as 5800)

the limiting factor on my build was the valve train though
 
To keep the plugs looking good I staggered the jetting on my six pack. This was a big block setup with mechanical carbs so the sizes won't be on for your setup but the right rear was 4 steps larger than the left rear and on the front the low side of the manifold was about 2 steps smaller. It wanted to rev to 7000 but 5800 was really where it needed to stay.
 
Sb 6 pack on my 360 pulls fine to 6,500. We need a bit more details.. Your using the stock holleys? Or aftermarket mechanicals, the ford carbs??? When you say .89 jets rear is that actual jet or drill size eqivelent? Fuel system and psi? Timing? Etc..etc...
 
The intake is rated @ 2500 - 6500 rpm. Exceeding 6500 is possible with port work.
The valve train must be up to snuff and stable for what ever rpm you plan on turning. More cam equals more spring.

The extra stroke lowers peak power and add's torque. So a what ever cam you use will have to be reduced in its operating rpm range by a few hundred rpm's.

That cam you list above is not so much as to big for the engine but is it to big for the rest of the car? The (if so equipped) converter stall speed and gear ratio/tire size of the car combined with its weight must be part of the over all combination to work well.

Some of the missing information is compression ratio and what heads and state of condition there in, as well as what they flow. At your level and what I understand is the direction of your build, a set of Hughes engines (.com) big mouth CNC ported heads is about as an excellent match with (IMO) a competition ported 6 pack intake on top of it all.

(FWIW, I just sent my small block 6 pack intake out 2 days ago for there fully comp porting work. The cam to be used along with it is also a Lunati. Solid roller, (40200733) 60433, 249/255 - .585/.600 - 110/106 - .016 lash, 1.6 rockers. 3000 - 7000 rpm range, which dips slightly on a 4" arm.

The rest is; '73 Cuda, 4spd, 4.10, Hooker Super Comps. Fiberglass AAR hood.
 
tekslk said:
In 1970 I had AAR cuda that 6 pk saw 8000 all the time, I was 18 yrs old. Now my understanding of the stroker motor is they make there hp at a lot less rpm. I would have though 5000 would be it on your motor. Just my 2 cents.
Click to expand...

You must have had the tach hooked up wrong...lol
 
I just looked up your cam. The 404A3, in the stroker should peak just under 7K and not the listed 7200 on the factory stroke. IMO of course. If you have the suggested 4.10 or greater gears and a decent weight car, I think you'll be fine with a really really nice street machine.

I think it would take my Cuda.
 
Ive always assumed dynos were done in a 1:1 ratio on the trans.

is it possible the dyno was done in 5th?

if it were dynoed in 5th wouldnt the actual hp had been 485@6600 assuming a .7:1 transmission ratio
 
Take note that a RWHP also takes a beating due to power lose through the converter (how efficient?) trans (727 uses more power over a 904. No idea on the manual trans onsumption power) driveshaft length (shorter the better), differential (how effec. It is, not size!), axle length (shorter is better) wheel size, and of course how the day is, state of tune and quality of fuel.
 
If peak power was only at 4600, there is something wrong. I would think that cam should make power to at least 6000, even in a 408.
 
that intake is restrictive, but it's not a limiter. It's just lower than some others. What heads are on it? It sounds more like a valvetrain issue if it can't rev. The cam should. The heads should. Something's not right.
 
Hi all, thanks for the input. I have mopar alloy heads similar to edelbrocks straight from box no port work as of yet. 3.45 gear ratio in diff. 5spd manual gearbox. Dyno was done in 4th 1:1. Carbies are genuine 2300 holleys. 3/8 fuel line pressure bout 5/6psi. 11.1 comp.hughes 1.6 rockers. Solid cam stated as above. Something is obviously wrong with it only making per to 4600. cam dialled in wrong maybe or heads/intake bit restrictive. Total timing was 31deg which it was fine with. We did vary it from 28 to bout 33 to find where it sat best. Was bit lean at times but think its getting enough fuel atm, just unsure of why only making per to 4600
I
 
Have you verified that your end carbs are opening? And if so, are the end carb throttle plates open all the way when center carb reaches 100% open as well?

Are you running the MOPAR reproduction 6-Pak carbs with vacuum secondaries currently available? If so, were they spec'd (and jetted) for the 340 engine or for the 440 engine?

Are you running the MOPAR over the counter high perf. replacement carbs with mechanical secondaries that were sold by MOPAR dealer in the 1970s to replace and upgrade the OEM 6-Pak vacuum secondary carbs?

Or the Holley Ford type mechanical secondary replacement carbs currently available?

Any of these carbs if functioning correctly should take a 408 cu. in. engine to 5,500 - 6,000 RPMs or more. Even the smaller Ford carbs.

What are the dimensions of your air cleaner filter element(s)?

Exhaust system and size? Type and size of mufflers?

(I'm looking for restrictions to flow.)

Best regards,

Harry
 
tekslk said:
In 1970 I had AAR cuda that 6 pk saw 8000 all the time, I was 18 yrs old. Now my understanding of the stroker motor is they make there hp at a lot less rpm. I would have though 5000 would be it on your motor. Just my 2 cents.
Click to expand...

My stroked 340 pulls to 7k, limiter at 7200.
But as mentioned previously the Valvetrain and cam are the deciding factors, not the crank and stroke(although a tad).

I wouldn't sixpack anything that I wanted peak performance from. Bottom line is buy a good 4 barrel intake matched to heads with a quality 750DP and tuning will be a breeze. I find sixpacks to be a factory gimmick. Power was so low back then they could have a shitty tune but no one cared be cause they had a "SIX PACK". I don't know of a single car owner looking for max performance running a sixpack setup. My $.02
 
There is something wrong,check to see how freely the outboards move w/the
rods off the vac. pot and throttle links.A new carb or the replacement throttle plate can
warp easily if over tightened and bind the throttle shaft,easily.....we're not talking bulging
vein in the forehead tight,just a bit too much FYI.If there is no exh heat to the intake the
jetting sounds lean,You said the dyno time was to tune,....what A/F numbers??
I've mentioned this in other posts,but 1st hand w/an AAR 9.7:1 340 292/.508 Purple
shaft,TA heads I ported..NOT all out,stock TA rockers netting only .476" lift. Turned best of
12.35@109,full street ride on pump gas and 9.5" converter only thing not as driven were the
slicks.Highest he ever shifted was 7200rpm, but split shifts of 6900/6700 seemed best.
Mopars power formula puts that almost the same RWHP as yours,so you've got some
hiccup in the works,keep us updated...:coffee2:
 
moper said:
that intake is restrictive, but it's not a limiter. It's just lower than some others. What heads are on it? It sounds more like a valvetrain issue if it can't rev. The cam should. The heads should. Something's not right.
Click to expand...
As above and
Stupid question , but; Are you looking at the torque curve perhaps?

I really like the idea of a 6-pack stroker, but I bet you will be busy with a 5speed!
 
Do you know what the heads flow. Just as an example my edelbrock alloys only flowed around 238cfm stock at around 500 lift and stalled above that. Your cam only has 520 lift on the inlet and once you take away the lash it's only just over 500 thou.

If yours flow around this figure and are stock with no porting they won't have a very large area and could well be a cork in your combo. I use the rough formula of 2hp per cfm maximum so it might only make 480hp with a huge cam,comp and ideal induction. Your cam isn't the biggest around especially in a stroker so 440hp flywheel may be what it's making or even less.

I have learnt my lesson with big cube motors and heads that don't flow enough / don't have enough port volume, anything I build from now on will have well ported heads on it over anything else. My heads are going to come off my 408 soon for a full port job and go back on for a back to back comparison to show what extra it can make with same cam and compression.
 
"I have mopar alloy heads similar to edelbrocks straight from box no port work as of yet."

Which heads exactly?
 
Do you have a printout of the dyno run we can see? there might be some information on there that jumps out as a potential indicator of something not right.
 
I wouldn't expect more cam than this (244/252@50, 520/540lift) would hurt the 408 much.

But 4600rpm is way off.
 
FredS said:
I wouldn't expect more cam than this (244/252@50, 520/540lift) would hurt the 408 much.

But 4600rpm is way off.
Click to expand...

I run that cam in my 360 mechanical 6 pack, it's a aggressive cam in a stock stroke, it pulls hard all the way up to 6,800 rpm in my car, I've run 12.20 first and only time out with it. Didn't notice any drop off in performance going from a holley strip dom with 750dp to the machanical 6 pack. I would make sure the outboards are opening and that fuel is coming out of the boosters when they are open. Also check the float levels. 6 packs are not easy to setup especially the vacuum ones. They may not make as much Hp as a single 4 bbl but the cool factor is way higher!!
 
Also wondering if anyone has some original carby parts for sale. willing to post to australia. would like spare metering plates for the outside secondary carbies and metering block for the primary. also any other carby parts that willing to sell. is there metering blocks that will fit the secondary carbies on the factory setup or wont it fit between the primary and back secondary. obviously front secondary os no issue just the back carby would be.cheers all
 
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