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  #1 (permalink)  
Old 11-24-2016, 12:30 PM
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Default Thoughts on Building a High Torque (flat curve) Street 428?

As the title says, I want to build a reliable, pump-gas-slurping daily-driver-worthy 428 to put into a street Cobra. I'm looking for suggestions for how to proceed--cam, input, compression ratio, carb. The car will have headers with 2" under car exhaust.

Here are my initial thoughts:
Holley vacuum secondary 750 with electric choke
Blue Thunder Dual Plane 428CJ 4V H/R Manifold
Blue Thunder med riser OE cylinder heads
Cam??
Double roller timing chain
Stock crank
Pistons, rings, and rods?
Aviad or Canton oil pan and sump
Pentronix ignition
MSD
aluminum water pump

Thanks in advance,
AC
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  #2 (permalink)  
Old 11-24-2016, 03:06 PM
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The cam will be the biggest proponent for a flat torque curve. You want a tight lobe separation, as much as you can get away with without sacrificing the amount of vacuum that you need. Duration will need to be around mid 220's.

Otherwise your parts selection is ok. If you don't have the Blue Thunder parts, you may want to look another brand....BBM, Survival Motorsports, etc.

I use Racetec forged pistons in most my builds with Mahle 1.5/1.5/3mm rings. On a factory 428 crank, I use Scat rods.

I'd concentrate on a compression ratio of 9.5-10:1.
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Old 11-24-2016, 03:54 PM
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Sounds like a solid plan.

If you already have BT heads, you may need custom headers as I believe their exhaust ports are raised a little. Now depending on your kit of choice, if there is nothing off-the-shelf and you are already in need of custom headers, then carry on.

If it were me, I'd certainly consider Edelbrock heads for a build like you describe. They are common, "plentiful" and for a long time the only "performance" heads readily available to builders. Or if I was after something a little more advanced, as Brent recommended also, I'd look at Survival Motorsports Head for a street build. It has a heart shaped chamber/bowl area which according to reports helps.

Good luck with it and keep us posted.
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Old 11-24-2016, 03:58 PM
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I rarely even consider an edelbrock head anymore. Money for money, the two I mentioned are cheaper and flow about 20-30 cfm more. The FE parts world has exploded in the last few years and the choices are so plentiful now.

Good point on the BT header patterns....
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Old 11-24-2016, 04:39 PM
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I rarely even consider an edelbrock head anymore. Money for money, the two I mentioned are cheaper and flow about 20-30 cfm more. The FE parts world has exploded in the last few years and the choices are so plentiful now.

Good point on the BT header patterns....
Re: the Header pattern - You taught me well.

Also I was thinking the 2nd hand market. If our man is shopping 428 blocks, the Edels may cross his path.
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Old 11-24-2016, 06:47 PM
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Remember pump gas is 91 octane and sucks in the Bay Area unless you can find a gas station that sells Sunoco gas. There's a nearby station on the Peninsula that sell Sunoco 100 octane unleaded from the pump and 110 octane leaded in 5 gallon containers from inside the garage. 10:1 may be too much here.
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Old 11-24-2016, 09:21 PM
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Remember pump gas is 91 octane and sucks in the Bay Area unless you can find a gas station that sells Sunoco gas. There's a nearby station on the Peninsula that sell Sunoco 100 octane unleaded from the pump and 110 octane leaded in 5 gallon containers from inside the garage. 10:1 may be too much here.
I can get Sunoco gas at the Andrade gas station, but that's not what I want. I want a motor that is happy slurping 91 octane from Chevron, Shell, etc. Perhaps I need to consider 9:1 compression ratio?
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Old 11-24-2016, 10:00 PM
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Quote:
Originally Posted by ACHiPo View Post
I can get Sunoco gas at the Andrade gas station, but that's not what I want. I want a motor that is happy slurping 91 octane from Chevron, Shell, etc. Perhaps I need to consider 9:1 compression ratio?
That's for you and your engine builder to figure out. Lots of variables, including timing and spark plug heat range. If you're not worried about max HP and just a DD, and want to use straight 91 gas, then definitely go lower than higher. I mix to be safe, but I think around 10:1 +/-. Not sure, I'd have to recheck my paperwork.
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Old 11-25-2016, 12:03 AM
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The cam will be the biggest proponent for a flat torque curve. You want a tight lobe separation, as much as you can get away with without sacrificing the amount of vacuum that you need. Duration will need to be around mid 220's.

Otherwise your parts selection is ok. If you don't have the Blue Thunder parts, you may want to look another brand....BBM, Survival Motorsports, etc.

I use Racetec forged pistons in most my builds with Mahle 1.5/1.5/3mm rings. On a factory 428 crank, I use Scat rods.

I'd concentrate on a compression ratio of 9.5-10:1.
Brent,
Thanks. I don't have an intake or heads, so will check out BBM and Survival.

Can I run >9:1 compression ratio with 91 octane without detonation?

AC
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Old 11-25-2016, 04:37 AM
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Yes, with the right camshaft and detail to the build, you could probably run 10.5-10.75 on 91. However, the horsepower difference between 9.5 and 10.5 is going to be negligible. IMO, it's best to stay on the conservative side and not have to have any worries in the back of your mind.

Not sure if Barry has any heads in stock, but BBM should have some. A BBM head coupled with a Performer RPM intake will make a very happy amount of horsepower.
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Old 11-25-2016, 05:02 AM
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Quote:
Originally Posted by ACHiPo View Post
As the title says, I want to build a reliable, pump-gas-slurping daily-driver-worthy 428 to put into a street Cobra. I'm looking for suggestions for how to proceed--cam, input, compression ratio, carb. The car will have headers with 2" under car exhaust.

Here are my initial thoughts:
Holley vacuum secondary 750 with electric choke
Blue Thunder Dual Plane 428CJ 4V H/R Manifold
Blue Thunder med riser OE cylinder heads
Cam??
Double roller timing chain
Stock crank
Pistons, rings, and rods?
Aviad or Canton oil pan and sump
Pentronix ignition
MSD
aluminum water pump

Thanks in advance,
AC
AC - if you are using ERA's headers/collectors, I would try to see if you can run a 2-1/2 or at least 2-1/4 collector pipe back to the muffler. The collector size on mine were 2-1/2 so they matched up with a 2-1/2 inch muffler inlet. Then for clearance and simplicity go with ERA's standard 2 inch tail pipes. I know finding a 2-1/4 inlet - 2 inch outlet muffler is not a problem. I would have to see if a 2-1/2 inlet - 2 inch outlet muffler is available.

And it will be important for ERA to know what head and exhaust port you have on the heads you are running so they can get the header exhaust flanges right. FE exhaust outlet patterns get confusing real fast.

If you now or later decide you want to make up some custom tailpipes that look a bit more original - run level to slightly sloped up at the tip - it's really easy to make a mock up out of PVC pipe to take to a muffler shop and have tailpipes bent. With an outside offset muffler outlet - the alignment into the wheel well and out the back is all in one vertical plane - all the way out. So the pattern just has to copy the bends up and down and final angle of the tail pipes.
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Old 11-25-2016, 09:27 AM
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You didn't say what power level you were looking for. That nice flat torque curve that I to love, come at a cost. You give up peak Hp.

If you are starting with no parts other than a block, and we are only scribbling on paper, right now. You should consider that you can drop any stroker combination you want for the same money, unless you already have a good part of your rotating assembly. There is no replacement for displacement (well other than a blower). Granted you will burn more fuel if that matters to you, but you could toss in a 4.25 stroke an get about 457 cid. That should buy you about 40 more ft-lb of torque, if it matters to you.
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Old 11-25-2016, 10:06 AM
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I would definitely talk with Tom Lucas of FE Specialities in Sacramento, who built my engine and also built rodneym's twin Paxton engine build. He's based in CA and knows the gas here. As you probably know, CA gets a "special" formation of gas from the rest of the US. I would not build an engine with a CR in the high 10's. You're probably going to spend a minimum of $15,000 on your engine and I wouldn't be rolling the dice with detonation with a $15,000+ investment.

I've had engines built in a bunch of cars over the years, Corvette, Tiger, Cobra, Mustangs, etc. and I've had problems with 10:1 CR engines. If you want to mix higher octane gas, then that's a different scenario.
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Old 11-25-2016, 11:32 AM
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I believe AC is planning to use one of the engine builders close in to ERA back east to install the drivetrain and deliver a turn key car. The comments about the stroker crank parallel what I ran into with Keith Craft. He convinced me that for the cost of finding a nice crank and rods and reconditioning them, he could put a SCAT crank and new Chev rods in for virtually no difference in cost. My engine wound up at 459 cu in and with a fairly mild 230/235 cam made about 535 lb ft of torque. Craft didn't like to start his dyno pulls until about 4000 rpm which was past my torque peak and it was already coming down around 532 lb ft at that speed.

Of course your builder in finding a block may just come up with a nice crank and rods with it by chance.
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Old 11-25-2016, 02:39 PM
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Originally Posted by ACHiPo View Post
Brent,
Thanks. I don't have an intake or heads, so will check out BBM and Survival.

Can I run >9:1 compression ratio with 91 octane without detonation?

AC
I use BBM heads.
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Old 11-25-2016, 02:58 PM
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Thanks for all the input!

I'd like to see something like 400 engine peak HP and 450 ft-lbs torque as flat as possible. In reality I'd probably be fine with 350 HP or less, but I'd like to have "braggin' rights" to have a 400 HP motor dyno slip. Redline of 6000 is more than enough--I'll never race this car--it's just a sports car.

I'd be ok with a stroker as long as I get the reliabilty, but not sure that I need it. I'd like mileage to be north of 10 mpg with reasonable driving. It seems like a bone stock 428 CJ would come close to my desired performance--maybe a bit lower than I'd like the HP to be? Need to look up the stock 428 CJ compression ratio--I'd think around 9:1, but maybe higher with the leaded gas available back then.

If I decide to have ERA do the complete build (which is how I'm leaning--still need to make sure I can swing it) I like the idea of the engine builder being close so any initial issues can be sorted, as well as reducing the chance of delays because of flywheel/clutch/tranny interfaces.

IF I end up doing some or all of the build myself, I'll look up Tom Lucas. I sure hope I won't be into this motor for $15k--estimates I've gotten both locally and back east are ~$11k for the motor I'm looking to build.

Last edited by ACHiPo; 11-25-2016 at 03:00 PM..
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Old 11-25-2016, 03:02 PM
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I got 425 hp and 460 lb-ft from an all-factory 428CJ (non-ported heads, non-ported intake, etc.) with a hydraulic roller....

Your goals are pretty easy to achieve.
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Old 11-25-2016, 04:06 PM
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I got 425 hp and 460 lb-ft from an all-factory 428CJ (non-ported heads, non-ported intake, etc.) with a hydraulic roller....

Your goals are pretty easy to achieve.
Cool! Things in life are hard enough--nice to know that the motor is doable!
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