Big cam small head vs small cam big head

[JDR Performance]

I would usually tend to make it as fast as I could myself, but it's a 90" wheelbase with no roof or cage. It's not a drag car. All of them I've been around have manual transmissions. How will the car actually be driven? My point was just that if it's going to be driven in traffic, cruised through town, or taken through curves on rural roads an engine that is smooth and responsive would probably be a lot more fun than something that runs like it's got an on-off switch and tries to come around on you when it's on.

[plovett]

A converter makes up for a lot when it's not locked up...

Y'all need to hop on over to club cobra sometime and read the threads about guys wanting a milder engine.

I'll be honest, I like the peakier engines too, but they don't belong in cars with 3.08 and 3.31 gears that spend 99% of their time at 2000 rpm. It's just not a good match, especially for guys who are not familiar with high horsepower carb engines.

The converter does help. However if I had a 4 speed toploader I wouldn't shift into 4th at 25 mph and hit the gas. My wife knows that much, so a Cobra driver ought to be able to handle it. I do believe ya about the cobra owners wanting milder engines. I don't want to read about it though. It'd be too painful.

As for the original posters combo. Given the information we have, I still think a solid cam with around 246-248 degrees @0.050 with well ported big valve Edelbrocks, and 10.5:1 compression is conservative enough and would be very streetable in a 2500 lb car with 427 cubes, a 4 speed, and 3.54 rear gears. He mentioned wanting peak power around 6000 and shifting around 6500. The above combo would do that. Depending on how good the heads are, you might even take out a few degrees of cam duration and maybe drop the compression to 10.0-10.25:1, and still get there.

JMO,

paulie

[blykins]

I've done that combo for a Cobra.....a 428 with unported Edelbrocks (just a nice valve job, 2.09/1.65 valves) and a 248° @ .050" solid roller cam. Peak hp was 533 at 6500 on the pump and peak torque was 472 at a lofty 5400. With a 3.70 gear and a TKO 500, it was still a little fussy, especially with an aluminum flywheel.

Most of the customers I get from the Cobra crowd tell me that they would like the peak at around 5500-6000 with emphasis on cruising and street driving. The ones that "splurge" usually come back and say that they have to spend a little more time getting the carb right, and it's just not practical for what they do. Oh well.

[plovett]

I've done that combo for a Cobra.....a 428 with unported Edelbrocks (just a nice valve job, 2.09/1.65 valves) and a 248° @ .050" solid roller cam. Peak hp was 533 at 6500 on the pump and peak torque was 472 at a lofty 5400. With a 3.70 gear and a TKO 500, it was still a little fussy, especially with an aluminum flywheel.

Most of the customers I get from the Cobra crowd tell me that they would like the peak at around 5500-6000 with emphasis on cruising and street driving. The ones that "splurge" usually come back and say that they have to spend a little more time getting the carb right, and it's just not practical for what they do. Oh well.

I wouldn't have expected your 428 to peak that high with unported Edelbrocks. People freak out when I tell 'em I had a 428 that peaked at 6200 with a 240/246 solid cam. They think it should peak lower. It was a flat tappet though. I imagine a solid roller might have more area under the curve even with these fairly small cams, and keep the induction "inducting" a little longer than a comparable solid flat tappet? 533 hp out of unported Eboks is a lot. My wife would have no problem driving your cobra though. Maybe she's not the typical cobra driver.

Seriously, that 428 sounds like a really good, well thought out, cost effective combo. What do you shift it at?

paulie

[blykins]

I sold it several years ago. The current owner road races it at Mid Ohio if I remember correctly. It's shifted at around 7000.

It's also an 11:1 SCR, but runs happily (and dyno'd) on 93 octane.

[plovett]

I sold it several years ago. The current owner road races it at Mid Ohio if I remember correctly. It's shifted at around 7000.

It's also an 11:1 SCR, but runs happily (and dyno'd) on 93 octane.

Nice! I bet it was fun.

paulie

[289nate]

How many 360 cfm 427 FEs have you built?
What rear end gears do you run? Low end power is easily fixed with low gears in a street car and can mask plenty of problems..

I had 4.30's and went to a 4.56 because the rpm through the traps in the 1/4 mile showed I could ideally use some more gear. I have overdrive which makes the 4.56 act like a 2.90'ish rear gear if I had 1:1 final gear like a top loader four speed. So the 4.56 hasn't hurt it's abitlity to cruise down the highways. Here is a video of it on the highway on the way to the track. I could drive it like that all day and night.

http://www.youtube.com/watch?v=hbAmrVzQ ... r_embedded

You are 100% correct that low gears make a big difference by multiplying torque. However, look at the end of the video I posted where I open up the primaries in first and then second gear at about 2,800-3,000 rpm. Breaks the tires loose badly in either gear.

The dyno showed 274 lbs/ft of torque at 2,800 rpm out of my 297 cubic inch 10:1 motor. Would anyone complain about street manners and not enough low end if you had a 427 that made almost 400 lbs/ft of torque by 2,800? I don't think so. That is what I'm getting at. A larger, efficient, high flowing cylinder head can allow for a broad power band IF the combo is right. Screw up and you'll end up with now power, throttle response, or manners off idle.

I have come away from a stop or slow roll many times on the street in second gear. This makes it the equivalent of a 3.00:1 rear gear in first. So I know exactly how it feels if it had a 3.00 gear and four speed. The video shows it still has too much power to take WOT on the street with street tires.

[blykins]

Well, the issue is, a 427/428 FE will not have that much torque at that low of rpm. The last 427 that I saw dyno results for had 425 lb-ft @ 4000. My 428 that I've referenced only had 472 lb-ft @ 5400. That's the result of a high-strung camshaft. Pair that with a high rearend gear and the results are not beneficial for a street car that likes to be lugged around at 1800-2000 rpm.

[289nate]

Every time I buy a part for my car, I later wish I had bought a "bigger one" whether it be cam, gears, stall converter, heads, you name it.

Been there and done that. I tried to buy stuff that would also work for a future 347 build and have a cam designed to make it work well. I'm just surprised how well it has done on the little motor on the street. Especially considering I'm very confident I will get it to go a 10.9x at 123+ in the not too distant future. My perspective on what works has changed since I first pondered what it would take to get a pump gas .060 over 289 to run into the 11's on motor in my car.

At what port volume do you end up with 360cfm on an FE head? A 205cc head that flows 360cfm is going to be a lot more fun than a 260cc head that flows 360cfm. You take a cylinder head with big flow, low velocity, a long duration camshaft, a dual carb intake with some fussy carburetors, and a 3.31-3.54 gear, and you'll have a guy who will hate the car in not much time... I understand that that the OP doesn't have a dual carb intake, but I'm just trying to make the point that anyone who is buying an engine needs to be made aware of the total combination and what the results will be.

The ports on those FE engines will be very short. Talking cc will confuse most non-FE people like myself who are used to a longer port. But I do get what you're saying and agree.

I just have a hard time believing the 360 cfm head with a moderate cam and LONG runner dual plane intake will be a 7000+ rpm engine with low end power and manners issues. Certainly could be if it were a short runner single plane, big cam, big heads, and 3.0x gears.

Well, the issue is, a 427/428 FE will not have that much torque at that low of rpm. The last 427 that I saw dyno results for had 425 lb-ft @ 4000. My 428 that I've referenced only had 472 lb-ft @ 5400. That's the result of a high-strung camshaft. Pair that with a high rearend gear and the results are not beneficial for a street car that likes to be lugged around at 1800-2000 rpm.

Well the 428 has a lot more stroke than a 427 at the cost of smaller bore. I think it would be much easier to make good low end torque with a 428.

[blykins]

A 428 has more torque potential, but when you cam them for 6500-7000 rpm peaks, they are still lacking down low, unless you make up for it with a low gear.

Generally speaking, most FE heads have pretty good velocity....factory heads, Edelbrocks, etc. We can get about 325cfm out of them @ .650" on the intake side. That's enough to support over 600hp with a 482-496FE.

The Blue Thunder heads are a different animal, and will flow the 350-360 cfm range (ported), but they have a completely different combustion chamber design, require special rocker arm setups, etc. That flow range is also at .700-.750" lift with 2.250" valves....again, not really conducive to a "street vehicle."

I don't have as much issue with the head volume/flow as I do the camshaft. Any cam that's designed for a 6500-7000 peak is not going to be a good match for a car designed to cruise at 2000 rpm with a 3-3.5:1 gear.

[plovett]

Well there's no doubt a Blue Thunder FE head can make low end torque on a 427 cube motor. Look at the EMC entry from 2008. Ported BT heads, 10.5:1 compression, 429 cubes, 252/252 @ 0.050" cam. 445 ft/lbs at 2500 rpm. 564 ft/.lbs at 5000 rpm

Even so, it's almost unimagineable to have a cobra with a 4 or 5 speed and decent gearing to not have enough low end torque with a 7 liter engine. Anybody here ever drive an 86 hp 5 speed long bed 1985 Ford ranger with a heavy load in the back? I have. Now imagine a much lighter cobra with a TKO, 3.70 gears (overall 12.1: 1st gear ratio) with a 7 liter engine. You could drive thecobra with the ranger engine installed

JMO,

paulie

[blykins]

There hasn't been an apple to apple comparison in here yet. So far a Cobra with a 3.54 gear has been compared to a Mustang with a 4.56 gear and a Cougar with a torque converter and a 4.11 gear...

Comparing an EMC engine to an engine that's designed to be installed in a street car isn't exactly logical either. EMC street engines are designed to make the most average horsepower from 2500-6500 and there are quite a few tricks used to do that. If you look up some dyno results of the average Edelbrock or factory headed 427 with a stock stroke, the torque figures are nowhere near the results of Barry's EMC engine.

Getting away from the 3.0X gear to the 3.70 is a step in the right direction for making a combo like this a little easier to swallow on the street. Even so, it's still not for everyone and a lot of guys don't understand the implications.

[plovett]

I was talking about your cobra. I'm having trouble wrapping my mind around that much gearing with that little weight with ANY engine. Holy carp!

The original poster has a 4 speed with 3.54 rear gears. Still plenty of gearing in a very light light car with a comparatively big engine.

JMO,

paulie

[blykins]

Oh, my bad....sorry.

I suppose no one has asked the OP what his intentions were....

[plovett]

yeah, where is the original poster?

I do remember my old 428, the one with the 240/246 solid flat tappet had a torque peak of 522 lb/ft at 4200 rpm. It's the one that peaked at 6200 rpm. It certainly wasn't a "fussy" engine. I used it with 3.25 rear gears in the "heavy weight" Cougar. With a mild 2800 rpm converter, never once a stumble or buck in any condition. The fact that it has a converter is intentionally missing the point. It weighs almost 1000 pounds more. I'd wager you COULD put that engine in a cobra, shift into 4th at 25 mph and hit the gas. You can make a 7 liter motor with a 6000 rpm power peak and have enough low end to easily drive the original poster's cobra.

JMO,

paulie