What's the bottleneck in my engine?

[blykins]

The more that I look at other people's profiles, the more I see smaller and same size engines making more horsepower. Mine made 484hp and 500 lb-ft. I wonder what my problem is?

Here's the guts:

1979 stock block, 4.060" bore, 4.100" stroke, 425ci.
Main cap girdle
10.5:1
Edelbrock Vic Jr. heads....2.05" I, 1.60" E
Comp Cams Hyd Roller Cam 230 duration, .544" lift...110 LS
Heads bought bare, assembled with springs, shims, etc to match cam.
Vic Jr. intake
Comp roller lifters, Magnum roller rockers
Demon Mighty Demon 750cfm carb
Eagle 4340 ESP crank
Eagle H-beam 6.200" rods
MSD Distributor, 6AL Ignition Box
Ford Racing 9mm plug wires
MSD Coil

Numerous dyno runs....changed timing, ended up with best results being at 12 degrees initial, 36 total. Changed distributor springs....Retuned carb.....ended up with 88's in the front and 98's in the back. Engine was making more horsepower (492) to start out with, but was too lean to be safe.

Peak hp was at 5400, peak torque at 4500.

I think I've mentioned all the essentials.....

One of the things that I think I've done wrong is mismatched the cam with the heads/intake combo. I think the top end is made more for higher rpm use....the cam really necks it down. But that's what Comp Cams recommended with my combo....

Any input is appreciated.....But I'd like to know where I really went wrong....not that 484 isn't enough for a Cobra....but if I stuck the wrong cam in it, I would like to know.

[PatBuckley]

What kind of mufflers are you running?

It could be that your dyno numbers are the only ones that bear any resemblance to the truth?

[MidOHasp]

I'm running a very similar motor, major differences being Dual Plane intake and AFR heads. From what I've heard, the heads may be a small bottleneck. I agree, the cam is better matched to an RPM intake rather than the Vic Jr. So if you kept the cam and put on the RPM manifold, you'd probably see an increase in torque, but not much more power.

Our power is about the same...within a few percent. Could have been the day it was dyno'd. Yes, there is a correction factor, but my dyno guy said it isn't that accurate. We dyno'd on a pretty hot day, and he said that if we were truly at sea level and 60 degrees, it would've been better than w/ the correction factor. But I don't live at sea level and it's not 60 too often when I'm out.

My torque is probably higher because I'm running 185cc AFRs on a 408. From a power perspective, that size motor (and yours, too) would need at least 205CC heads (and a bigger cam and a single plane intake). But running that narrow of induction (RPM intake) and heads, it's a torque monster.

I would say that a lot of numbers may not be terribly accurate. If you believe ALL that you read, the average 427W stroker from Keith Craft or Roush is making about 600-650HP and runs on pump gas, etc... I doubt it.

FYI my power peak is 5700, TQ peak is 4400, but TQ is between 540 and 544 from 4200 to 4800 RPM.

I'd have to agree w/ Pat. Your numbers (and mine) are more realistic. The 600+ smallblock numbers (naturally aspirated) are less realistic. Possible, but not without a very nasty cam, 11:1+ compression, huge intake runners, etc...

That's my opinion, at least...interested to hear others.

[blykins]

Hey Pat...if I get what you're saying....it was with the Cobra 1-3/4" 4 tube headers on an engine dyno....no muff's....

[Cracker]

I'd also agree with Pat regarding the #'s. Your cam (to me) looks fairly mild and with your peak hp @5,700 represents your go-fast parts are a waste - to an extent. That figure represents most stock redline figures in which case all the forged goodies are nullified. My similiar CI motor (427 BB) has similiar components and runs 11:1 with a .600 solid cam (edge of streetability) and makes peak HP at 6,300 but sings to 7,200 without complaining. It was built as to all out race motor standards without the compression (gas) and cam (streetable) but all other components allow it to explore the 7,000 rpm range safely. I would HOPE the benefit of a SB motor is to do the same as it appears your components would withstand the abuse. I'd say convert to solids (if possible) and take advantage of your intake/carb/internals, etc. and get it to REV. Based on where your engine is now now you should have just selected a low reving BB power plant. Best wishes!

[MidOHasp]

And also, speaking of realistic... I've read too many stories of people with 350-400 horsepower (and similar TQ) numbers being "sideways in 4th".... what kind of tires these guys running? What rear gear??!?! 225mm tires and 4.11's??

With 295 Goodyear Eagle GTII's, I can roll on in 2nd and keep it straight at full throttle. Granted, it's dancing a bit, but it's straight. In 3rd, traction is a non-issue unless I'm shifting like a moron.

I'm not calling anyone in particular out at all, not like I could even remember who's said what and when, but... just seems like sideways in 4th is not something that's happening with 295mm tires and 500+ horsepower.

[blykins]

If I remember correctly, aren't the Vic Jr's 210cc's? I'm pretty sure they are...

[MidOHasp]

That sounds right. My point was more along the lines of mine are theoretically "too small" but i wanted torque. If I did it all over again, as much as I LOVE my motor, the way it sounds, revs, etc... I'd do things a LOT different.

[blykins]

Are you running a dual plane intake? I'm thinking that would be the easiest step for me...get rid of that Vic Jr intake that is suited for 3500-7500 revs and get an intake that is suited for my rpm range.

Everytime I look at your 540 lb-ft torque number, that idea really starts dancing in my head. Shoot they're only $230....and it would give me another 1.5" under the hood...hehehe

[Gordon Levy]

Your cam is to small to make more power. With the air flow you are capable of, you can use a far more aggressive cam profile. Your jets are also to big. Go with less jet but more pump shot.
Next would be the air cleaner. Most I have found out there will cost a substantial amount of HP, especially the oval cobra air cleaner. Exhaust can also be holding you back. primary tube size and the types of mufflers used can really choke an engine if not properly matched to the air flow of the engine.
I build many engines that are simular to yours and regularly get 530-550hp out of them. The 408 really likes the heads and intake you have chosen because of the volumn of air that a 408 requires to build real hp. They are also a 6500 rpm engine, turning them any harder over a long period will end up hurting the bottom end. Because of the added cubes, the Vjr heads and intake will work better at lower revs than they will on a 351. You would need to turn a 531 7500 to make the same power and it will never produce the same torque.

[trularin]

Welcome to the world of race car developement. No two cars are the same. No two combinations of engine parts are the same ( they can get close ). No two drivetrains are the same.

You now own a rather large experiment with four tires. Get a good set of tools and a lot of time and you can try various things to see what works best in your car.

Or, you can live with what you have and worry about the price of gas.

Hey, it's just a thought.

[blykins]

I can live with it...sure....like I said before....484 hp and 500 lb-ft isn't anything to sneeze at....But I just hate knowing that the engine has a lot more potential.....if only I had chosen a better cam or a different intake.

At this point, changin the intake seems the better route....than pulling the water pump, timing chain, valve covers, rocker arms, lifters, pushrods, etc to change the cam.

I work at a Valvoline engine test lab....most of the engine builders here who change parts and routinely do dyno work urge me to just swap the intake and get the intake range down to where the cam can use it.

[Mike Simard]

Those jet sizes sound huge. Why did you settle on them? Did you test mixture while on the dyno?
Did you degree your cam? They usually make them advanced to benefit low rpm at the expense of high. You could possibly retard it 2-4 degrees to get more usable power 2-3 hundred rpm higher.
I don't think your numbers sound bad at all, in fact they're probably some of the most realistic to get thrown around. As far as bottlenecks go there's always those stock exhaust port bolt spacings which force the header flange to be too narrow.

[blykins]

Yes, I degreed the cam and followed what Comp Cams recommended on the cam timing.

The jets are rather large. It was running way lean with the stock jets in it. We kept bumping them up until the cylinder temps came down...in all actuality, it could have stood more. That Vic Jr intake didn't help much either....it was not uniform across all 8 cylinders....one side varied more than the other, etc.....

What size carbs are you guys running for this cubic inch size? Is a 750 too small?

[MidOHasp]

blykins...

honestly, if you went to the RPM intake, only do it to "match" everything together. The added torque is kind of wasted on a 2500 pound car. That's why I said I'd do it differently next time. The fact that I'm easily putting all I have to the ground in 3rd (and in 2nd without a lot of finesse, really) tells me I could live with 100 more HP.

If I ever decide to tear this motor apart for fun, I might try to go solid cam (bigger), and run the appropriate carb, intake, and heads. Go for 600+ HP.

But then again, I built a 408 for a reason. Not going to spin it up real high (6300-6500 RPM), wanted torque, got it.

Gordon...

How much HP loss have you heard of on the Cobra Oval Air Cleaner? I was thinking of getting a second air cleaner setup for driving and keeping my oval for the occasional show I go to.

[MidOHasp]

blykins... with my air-gap RPM, i also saw very uneven cyl temps...and they were all pretty warm, too.

i'm running a BG Speed Demon 750DP.

[Gordon Levy]

If you go to a RPM intake you will pick up some very low end torque, but you will kill the hp by as much as 50hp.

On the flow bench, we can only get about 400cfm out of the oval air cleaner with the 1" eliment that it comes with. If you have the hood clearance to use a 2" eliment, it will work much better.

[blykins]

Hey JP....what are your cam specs?

[Ford of France]

Blykins:

Gordon is right. Your cam is too small, given your other components.

[djseed]

Cam is a bit light for maximum HP and TQ numbers. I think this would make a great streetable engine. I bet it will pull from 1200 RPM. I have a very similar configuration on my BB. Light cam and an RPM manifold. It only makes 525 HP and 600 TQ, but it sure is a champ on the street. I spend most of my time cruising around 3000 RPM and it pulls from 1200 RPM. I rarely shift above 5500 RPM. Depending on what you want, I think it sounds like a great combination.