DuPuis Family Cobra Build

I don't have any bore gauges, but I did spend some time with my calipers this evening. The pistons are right at 4.040", as you'd expect. The bores all measure (at the top) at 4.042-4.050". With that and the scoring in the one, I'm fairly skeptical that this block will be usable. But I can buy blocks for $100 or so so that's not really a big deal. Almost makes me wonder if it's even worth considering using this block or if I should just get one that has the original 4" bore and can do with it as I please.
 
Another thing is that I can't find any casting stamps on the crank. Makes me wonder if it's aftermarket.
 
Good Lord...as I mentioned above, I expected the oil pump pickup to be installed incorrectly, but it's definitely done more creatively than I could have imagined.

You should check the dipstick length. It probably wasn't even touching the oil.

If your connecting rods have square head bolts and a piston oiler they are 289 HiPo, oval bolt heads are 69-70 Boss 302. Your photo shows oval heads, so thereya go.

If there isn't a four figure prefix followed by 6303 dash single letter suffix on the crank it's not a Ford part.

I recommend that you use an Edelbrock cam and lifters, they will suggest a hydraulic roller grind that complements your Edelbrock heads and suits your performance goals. You might have to change the springs. I doubt any effort was made to match your existing springs to the installed cam, and they might not be compatible with a hydraulic roller.

When you get a good deck height measurement, you can determine piston pin location, and decide what the piston installed height will be...usually equal to deck height, then the head gasket selection will allow .038-.042 adjustment of piston to head clearance. You may first have to mill the deck height .004 to true it up before determining the other numbers.
 
Last edited:
3393RP said:
Good Lord...as I mentioned above, I expected the oil pump pickup to be installed incorrectly, but it's definitely done more creatively than I could have imagined.

You should check the dipstick length. It probably wasn't even touching the oil.

If your connecting rods have square head bolts and a piston oiler they are 289 HiPo, oval bolt heads are 69-70 Boss 302. Your photo shows oval heads, so thereya go.

If there isn't a four figure prefix followed by 6303 dash single letter suffix on the crank it's not a Ford part.

I recommend that you use an Edelbrock cam and lifters, they will suggest a hydraulic roller grind that complements your Edelbrock heads and suits your performance goals. You might have to change the springs. I doubt any effort was made to match your existing springs to the installed cam, and they might not be compatible with a hydraulic roller.

When you get a good deck height measurement, you can determine piston pin location, and decide what the piston installed height will be...usually equal to deck height, then the head gasket selection will allow .038-.042 adjustment of piston to head clearance. You may first have to mill the deck height .004 to true it up before determining the other numbers.
Click to expand...

I need to check the crank more for numbers. The real question is whether to try messing with the block or not. I’m conflicted there. It’s already way overbored at 4.050” and with that scoring in the one hole I doubt if 4.060” will clean it up, but it might.

302 blocks are cheap, sleeves less so. But this is one of the “better” blocks.

I’m leaning towards acquiring another block (short or bare) or maybe even just buying a short block already done, just spec the pistons and cam appropriately.

Something to think about while I wait on parts.
 
I’d recommend saving yourself the grief and getting a short block. That way your short block would be covered by at least the engine builder’s warranty. You just need to fit the oil pickup and pan, and the top end. Given how the rest of the engine looks, I’m not really trusting any kind of work done on that block. If they bored it .50 over and there’s no cross hatched pattern in the honing, I’m not sure if they used a torque plate or even honed the block properly.

Speaking of pans... check the one you took off. Given the light weight chassis, you’ll have plenty of accelerartive forces. A baffled oil pan would be ideal, and I’m not sure if the one that’s on your existing motor has one. It looks like a Canton pan (colored in gold, which is a good pan) but I can’t be sure.
 
@rtk11 At this point I'm starting to lean towards the short block that's built by a reputable builder. I'd customize the pistons to get what I want there, and if it's one that they put a cam in, obviously I'd spec that as well. But it seems like the price delta I can get with that vs. buying another engine and messing with it myself isn't worth the hassle.

One interesting thing is that ATK, who seems to be one of the preferred short block providers for these projects, has 351 short blocks cheaper than 302s. So while I've been pretty convinced on the 302 up until this point, that aspect is making me rethink a bit. I'm going to ask some opinions on the Factory Five forum.
 
Boss 429 clone, 529 CID. A little tight to fit under the hood, but easy to get to the spark plugs....

mdmp-1112-drivetrain-upgrade-muscle-builder-000.jpg


http://www.mustangandfords.com/how-to/engine/mdmp-1112-b2-motorsports-529ci-engine-build/
 
Last edited:
You might need a shoe horn to fit that in there.
I still have a 429 sitting at a friends machine shop. I abused the hell out of it for years:)
 
Last edited:
DaleB said:
School me a little. Why Windsor over Cleveland, other than the availability of aftermarket parts? I thought the 351C was a pretty good engine.
Click to expand...

Windsor engines have had a long history, so parts are plentiful and cheap. The heads have evolved over time, so you can get some Windsor heads that will outflow the Cleveland heads.

Cleveland motors are popular as you can get 2 bold and 4 bolt mains, but the ports (especially exhaust ports) are HUGE. It'll work great for high RPM operation, but have soggy low-end. Hence why someone invented exhaust torque plates that act as a gasket for the exhaust manifold, but have a tab that inserts into the exhaust port to reduce the size of the port to improve gas velocity. Parts are more expensive for the Clevelands given the limited years of use of that motor.

(FWIW, I had Grabber Blue 1970 Mach 1 with 351 Cleveland 4BBL... who stupidly sold it for next to nothing when the then (now ex) girlfriend said, "It goes or I go." I chose...poorly. :confused::()
 
Ted DuPuis said:
@rtk11 At this point I'm starting to lean towards the short block that's built by a reputable builder. I'd customize the pistons to get what I want there, and if it's one that they put a cam in, obviously I'd spec that as well. But it seems like the price delta I can get with that vs. buying another engine and messing with it myself isn't worth the hassle.

One interesting thing is that ATK, who seems to be one of the preferred short block providers for these projects, has 351 short blocks cheaper than 302s. So while I've been pretty convinced on the 302 up until this point, that aspect is making me rethink a bit. I'm going to ask some opinions on the Factory Five forum.
Click to expand...

There's a lot to be said for having a builder do the internals of the engine. Back when we did our own motors we mostly selected the pieces and handed them to the machine shop to put them all together. There was a lot of guesswork involved as to what would work with what, and we eventually found out that guys who did this sort of stuff frequently built the best engines. (Who knew, right?) When you do select a builder, he (or they) can probably help you with the 302 vs 351 question. Or you could just ask your wife, she seems to have a pretty good handle on this project.
 
  • Like
Reactions: Ted
I vote for an assembled short block.
 
DaleB said:
School me a little. Why Windsor over Cleveland, other than the availability of aftermarket parts? I thought the 351C was a pretty good engine.
Click to expand...

@rtk11 summarized it well. Plus the 351W is basically a 302 with 1" taller deck. So a lot of parts are common between them, and it's one of the "stock" engine options for the Factory Five Cobras.

Plus, the only reason that I was even considering that path was the fact that I can buy a fresh 351W short block for a cheap price.

FormerHangie said:
There's a lot to be said for having a builder do the internals of the engine. Back when we did our own motors we mostly selected the pieces and handed them to the machine shop to put them all together. There was a lot of guesswork involved as to what would work with what, and we eventually found out that guys who did this sort of stuff frequently built the best engines. (Who knew, right?) When you do select a builder, he (or they) can probably help you with the 302 vs 351 question. Or you could just ask your wife, she seems to have a pretty good handle on this project.
Click to expand...

My wife always has good thoughts. Of course, I'm the one who has to maintain the thing. :)

Her answer to "how much power?" was "all of it". So the 351 would be the answer there. Reading up on some threads people say that extra inch makes a noticeable difference in which intakes and air cleaner options are compatible, and does impact maintenance. Plus the extra 50-70 lbs (depending on which number you go with. Of course I'm also doing a lot to keep the front weight down already, and plenty of people go with big blocks or mod/Coyote engines which weigh even more (and are also "stock" options).

The one concern I have with a 302 is whether it will be torquey enough for my liking, as I am a torque person.

Something to consider...
 
PaulS said:
I would guess if you want a vote, you need to contribute to the process, motors ain't cheap.
Click to expand...

Gee, I'm stung by your abruptness. Why, I just might quit the internet and smash my phone to bits.
 
Last edited:
PaulS said:
I would guess if you want a vote, you need to contribute to the process, motors ain't cheap.
Click to expand...

Compared with the frankenmotor a quality short block is cheap.
 
Ted DuPuis said:
The one concern I have with a 302 is whether it will be torquey enough for my liking, as I am a torque person.
Click to expand...

The zen approach: The question is not whether the engine is torquey or not but rather whether the chassis is light enough. :)
 
  • Like
Reactions: Ted
Ted DuPuis said:
The one concern I have with a 302 is whether it will be torquey enough for my liking, as I am a torque person.
Click to expand...

Ted, just my thoughts: the 302 will make plenty of torque for a 2,400 pound chassis application... but if you're looking for a higher winding motor and a camshaft and intake to support higher RPM operation, that torque may not arrive until later in the RPM band. Alternatively, you could use an RV cam and build plenty of low-end torque, but the motor is going to run out of breath by 5,000 rpm.

If low end torque, but higher RPM capability is desired, you're going to want displacement. A 302 can be bored and stroked to 347 cubic inches (if the 1" taller deck height of a 351 will cause accessibility and hood clearance issues, especially if you intend to use a taller, single plane intake manifold). The 347 cubic inch bored/stroked combination is proven to turn to 8,000 RPM and make 546 hp and 435 lb-ft of torque. But this combination will also work to make more torque with a little lower horsepower if kept to a more streetable cam profile, dual plane intake, etc.


http://www.mustangandfords.com/how-...00-rpm-small-block-347ci-ford-build-and-test/

Screen Shot 2018-08-14 at 7.30.25 AM.png
 
Second the RV cam. Totally different concept motor, but I built a 300 six bored out to 302, threw in an RV cam and an Offy DP with a Holley 600 cfm and header, (alondg with a little bowl and port work), I could literally pull stumps with that thing's low end, yet it would wind to 6k rpm. Of course, anything over 3500 was noise, but still....it was a good noise.
 
If it's torque ye be looking fer........ 529 Boss.

(just keeping that option open...:lol::lol:)

I have seen A/C Cobra replicas with (horrors) Chevy, Chrysler and Pontiac engines. And one with a 331 Hemi. The Hemi was a show car and very rarely was driven.
 
FormerHangie said:
That sounds like the answer to your question.
Click to expand...

I'm starting to head that direction. But, I'm also used to bigger, heavier cars, and have never driven a Cobra.

asicer said:
The zen approach: The question is not whether the engine is torquey or not but rather whether the chassis is light enough. :)
Click to expand...

See above. :)

FormerHangie said:
Then he'd be building an 818.
Click to expand...

No. While a mid-engine vehicle is on my list, I'm building the Cobra for a few reasons:

1) Always loved the look (don't like the look of the 818 at all)
2) Want a roadster
3) Generally easy to build

rtk11 said:
Ted, just my thoughts: the 302 will make plenty of torque for a 2,400 pound chassis application... but if you're looking for a higher winding motor and a camshaft and intake to support higher RPM operation, that torque may not arrive until later in the RPM band. Alternatively, you could use an RV cam and build plenty of low-end torque, but the motor is going to run out of breath by 5,000 rpm.

If low end torque, but higher RPM capability is desired, you're going to want displacement. A 302 can be bored and stroked to 347 cubic inches (if the 1" taller deck height of a 351 will cause accessibility and hood clearance issues, especially if you intend to use a taller, single plane intake manifold). The 347 cubic inch bored/stroked combination is proven to turn to 8,000 RPM and make 546 hp and 435 lb-ft of torque. But this combination will also work to make more torque with a little lower horsepower if kept to a more streetable cam profile, dual plane intake, etc.
Click to expand...

And there's the whole rub, getting the power band figured out correctly. I am not particularly interested in a stroker at this point because of the increased cost aspect. I was going to go with a 302, and really my reason for now considering the 351 is the extra ~17% displacement for about a 15% cost reduction (from one reputable vendor).

The car is going to be driven primarily on the street with occasional track use. So this would tend to merit the 351 over the 302 as a preference.
 
I think the 331 cid based on a 302 block is the sweet spot for a cobra build. Rod angles and piston speeds are way better than the 347, you get a torque bump over a 302 and it’s still a nice compact package for under the hood mx.
 
Tarheelpilot said:
I think the 331 cid based on a 302 block is the sweet spot for a cobra build. Rod angles and piston speeds are way better than the 347, you get a torque bump over a 302 and it’s still a nice compact package for under the hood mx.
Click to expand...

I've heard others make the same point. 331 gives you the weight and size advantages of the 302 with most of the displacement of a 347/351. I could buy a rotating assembly for $1k, but then I still need a block and machining work, etc., which would push the price to well over the 351.
 
Ted DuPuis said:
I've heard others make the same point. 331 gives you the weight and size advantages of the 302 with most of the displacement of a 347/351. I could buy a rotating assembly for $1k, but then I still need a block and machining work, etc., which would push the price to well over the 351.
Click to expand...
Out of all the options the 347 is the only one I would avoid.

Otherwise it’s a tossup. There are sources to buy 331 short and long blocks.
 
Tarheelpilot said:
Out of all the options the 347 is the only one I would avoid.

Otherwise it’s a tossup. There are sources to buy 331 short and long blocks.
Click to expand...

I'd tend to agree. The geometry on the 347 seems sub-ideal.
 
I've gotten some feedback from the Cobra group, and it seems that nobody who has a 351 wishes they had a 302 or 302-based engine. One point I received was that the bigger crank and bearing surfaces of the 351 do make it respond slower, but of course the engine itself is overall stronger. I want something really responsive and revvy. On the other hand, I'm not looking at spending the money on a stroker, at least not at this point. So given that, I'm leaning towards a 351 now.

It seems like ATK is a commonly used company. Curious if anyone has suggestions. I'll just be looking for a build short block.
 
Ted DuPuis said:
I've gotten some feedback from the Cobra group, and it seems that nobody who has a 351 wishes they had a 302 or 302-based engine. One point I received was that the bigger crank and bearing surfaces of the 351 do make it respond slower, but of course the engine itself is overall stronger. I want something really responsive and revvy. On the other hand, I'm not looking at spending the money on a stroker, at least not at this point. So given that, I'm leaning towards a 351 now.

It seems like ATK is a commonly used company. Curious if anyone has suggestions. I'll just be looking for a build short block.
Click to expand...

The snappiness you're wanting will come from keeping the gas velocity up, so don't get too carried away with the carburetor, intake manifold, and headers. With all that motor in such a light car I can't see how it won't be responsive.

I was watching FantomWorks last night, and the crew put some insane big block in a 1953 Chevy pickup for some woman. If she stepped on in an any of the lower gears she got wheelspin.
 
FormerHangie said:
The snappiness you're wanting will come from keeping the gas velocity up, so don't get too carried away with the carburetor, intake manifold, and headers. With all that motor in such a light car I can't see how it won't be responsive.

I was watching FantomWorks last night, and the crew put some insane big block in a 1953 Chevy pickup for some woman. If she stepped on in an any of the lower gears she got wheelspin.
Click to expand...

The headers are pretty much already defined for the car, so that part's easy. Intake manifold I was generally thinking a dual plane streetable manifold of some sort. And carb, when I talked to the Edelbrock guys they were recommending a 650 cfm carb on a 302, and I think a 700 could be more feasible on a 351 while still maintaining good response. Vacuum secondaries, of course.

I'm also going to have very, very little engine drag. I've pretty much decided my only engine-driven accessory will be the alternator. Electric power steering, brakes will probably be vacuum (although I might investigate electric options on that), electric water pump. If I do AC (which I'm also leaning towards), go electric on that. For one it lets me experiment with some things I've wanted to experiment with already, and for two it keeps a really simple underhood layout and lets me reduce the drag on the engine.

As you said, it's going to be lightweight enough that it will be responsive. I'm thinking about my sportbike days and what I liked out of those, as I think this will in many ways be a blend of my sportbike and high performance car experience.
 
You must log in or register to reply here.
Back
Top