My first V8. Iron or alloy Block?

Ok, its probably a no brainer but just wondered what you guys thought. I'm "building" (read sending off shell to have someone do most of it...) a euro touring car inspired Mk3 Cortina, for fast road and track use. If I was building a drag car (which I'm not) I'd go for iron block, as for equal money I could get much more power than with an alloy block.
As the car is going to be built with handling in mind, I'm contemplating taking a hit on the power and going for an alloy block.

Power will be at the lower end of things ~350 - 400 HP I guess, compared to getting towards 500 if I went for iron block. It seems to me that saving 100lbs/50kgs at the front end (about 5% of weight of car) is worth more than the power, even if the block is set back as far as possible.

Oh just realised I should have said I'm going for a 302 based engine.

Does anyone else make blocks apart from World / Dart and if so how do they compare? I'll be importing engine to UK, so I'm assuming its more cost effective to import a complete engine rather than the block and get it built over here?

Any advice appreciated. Cheers, Jono.

Randy V

Lifetime Supporter
Plan on adding $4,000 US to your block budget for alloy - Then add more for the required studs and alloy heads, etc..

Other than saving weight (for competition use) and having the alloy look along with bragging rights, there's not much advantage to an alloy block in my opinion..

Lynn Larsen

Lynn Larsen
The following comparison of iron vs. aluminum properties with respect to heat are considered important by some as well:

Thermal Conductivity:

Iron (300 K) 80.4 W/m·K
Aluminum (300 K) 237 W/m·K

Heat capacity (dt/dE):

Iron (25 °C) 24.200 J/mol·K
Aluminum (25 °C) 25.10 J/mol·K
Since your car is front engine/rear drive and designated to race on a track go with the all alloy. The weight reduction will pay off every time you-- accelerate/deccelerate/corner-- and since you are going to be doing one if not two of those at any given time when racing its a win/win situation. Even if the class you race in is weight limited, just add ballast down low to make the weight limit. Dont stop at the alloy block, go with the alloy trans and diff as well. If your using a '9" Strange', watch out for the Lady who takes your phone call @ the desk, she reckons all us Kiwi's, English, & Aussies are mad using Alloy Diff components and will do her best to talk you into a Nodular unit!!

Jac Mac
Have you considered a Rover V8. Plenty around in the UK, fairly cheap and an ally block, can be made to give up to 400 bhp fairly easily (even more but then the costs start to spiral). This would give you power and low weight at a reasonable cost. The engine was based on a GM (Buick) design but became redundant when it was felt that thin wall iron block casting could do a similar(ish!) job for less $. So the design was bought by Rover and ultimately used in a variety of BL cars from MG to Range Rover .... If memory seves me correctly.....

Best of luck in your build

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Thanks for advice guys. I was kind of aware of the thermal conduction differences, but was fairly satisfied it wouldn't be a problem from reading another thread on here which goes a bit more in depth.
That was one reason I was asking about other block manufacturers and if they were any good compared to World/Dart as a well designed good quality bock would appear to limit any problems.

Jac Mac can I ask what alloy gearbox you had in mind? I was thinking of a Tremec TKO. (sorry, I know this is the engines forum :wrongforum: ) As for Diffs I've looked at the strange website but it seems a couple of years out of date?

Yes, I had considered RV8 a while ago, but kind of set on Ford power now....
Jerico- Plain - Simple- bulletproof-Just about idiotproof- !! Want more info PM me to avoid thread drift- I've done everything your contemplating 25 years & more ago.

Jac Mac
Jono, also worth noting that the lighter the car, the bigger the impact the weight delta between iron and alum is going to have upon accel/decel/cornering. Your MkIII is something like 2100lbs with the four banger so maybe 2350 with a SBF? 100lbs in a light car like that is going to be felt generally, particularly with regard to fore/aft weight bias. As you say, 400hp is plenty for your car so alum probably makes good sense, certainly from a handling perspective. Unfortunately, I don't know of another mfg of alum blocks so I can't be helpful with a referral for comparison.

The last time I looked at the pricing delta is seemed to me it was more like $3,000 to spec alum instead of iron. That's $30/lb. The best steak you can buy (in the US at least) isn't more than that if bought in the grocery store. Net, somewhat pricey but probably worth it if you're really serious about winning.


Gulf GT40
Lifetime Supporter

The cost for most bare Aluminum blocks are now edging towards 4k+usd. I have a pair Dart's (4.125 bore) and a pair of Ford SVO blocks (4.0 bore) all 8.2 deck blocks. The SVO blocks were at one time purchased for (I think) about $3300usd but are much more now. Don't forget a ton of extra machining for the aluminum blocks and some extra needed parts like studs, potential for expensive head gaskets, etc. I would look to Dart or possibly World whey they are ready and IMO skip the SVO (RDI is the only source). Look around on the site I think I posted various weights of some of the iron and alloy blocks at one time. Recall it was 80 lbs for iron to alum. For iron block one that looks good and inexpensive (relative to the alloy) is the new for Boss 302 block.

I can't comment on the power loss of the Alloy vs. Iron, but I'll bet it is not very much. Mr. Mac might have some hard numbers but I would toss that out as a concern.

I run the Strange Aluminum center section in my ford 9" and it works well and saves a bunch of weight. Running about 560 hp in the Mustang it is in. Yes they are strange at Strange unless you get the right guy on the phone, if you do ever get them to pick up :)

Skip the TKO unless it is at least the current model. I have an older TKO in the same car an it is not a happy camper to shift fast much past 7000 rpm and is very notchy to shift (I run the motor about 7300-7500). I think the newer ones address some of that problem and are may be stronger by can't say for sure. And unless you need the 5th, skip the exercise and go with a T10'ish trans. I have a Tex Trans T101A but have yet to remove the motor and trans to do the swap out of the TKO and put it to rest. The T101A and I think some of the Jerico's can be picked up rebuilt and geared to your choice by looking around some of the Nascar shops that do the boxes. I got a full rebuilt one direct from Tex Trans with shifter and gear choices for about the same cost as the TKO and I can pretty much be sure when I pull the gear shift (notice I didn't say knob) it is going to go into gear. The TKO is also a bit larger in the trans tunnel area It seems, but not for sure. One other thing about the TKO is that it may have limited bell housings, not sure what your looking for. What I did was get the T101A in Chevy style as most all teams seem to run that configuration, then add the Tilton Bell housing that mates the Chevy box to a Ford. Work in progress, but looks like it will all work just fine.

Bottom line if you can afford to pay for price get the aluminum block get it, if not plenty of good alternatives from world, dart, ford.

I have to get off the coffee again :)

That's very helpful, got a bit more research to do on gearboxes now!

Back to engines,
I'd prefer to get a complete (more or less turnkey) engine package as it would seem cheaper and less hassle than me obtaining everything separately and getting parts shipped here there and everywhere. from that point of view World seem more attractive than buying a block from Dart and then finding someone to build my engine. Is there much to choose between Dart and World? I suppose given the World ally blocks are pretty new theres no been much time yet for people to compare the two? IIRC Dart are slightly more expensive but that doesn't necessarily mean better does it?

. "I would look to Dart or possibly World whey they are ready ..."

Timing is everything.
Yesterday I photoed our very first Man O'War all aluminum fresh off the dyno. This is a 427, built to our "Hardcore" spec with our brand-new 18 deg heads. Normally these are rated 525HP. This one made 575 at 6400RPM so we're slightly:pepper: about it.
You can buy this one as you see it for $13,495-the alloy block adds $2500 to any complete we build.
To answer Sandy's quote, we'll have these blocks and crates available in three weeks.
Weighs 399lbs with 7 qts oil in it.
Here it is:

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Dave Wood

Lifetime Supporter
I might weigh the standard engine/trans for a weight comparison. I recall putting a 289 in an old Volvo P1800 in the early 70s and when we weighed the both engine/trans assemblies, we found less than about 50-75 lbs difference, and that was with an old cast iron FMX trans. If it was done today with a modern 5 or 6 speed and alloy heads it would probaly be equal or possibly lighter than the standard Volvo powertrain was. With the exception of the all aluminum Rover (B-O-P) engine, the smallblock Ford was the lightest production V-8 made.
Eleven months of tooling development and Jono asked this question at the perfect time. :)
I'd rather be lucky...
Chas, that is a sweet looking engine Made sweeter by that power figure no doubt. Think I'm pretty much set on an alloy block...
I was planning on a smaller 302 based engine though, due to engine bay constraints etc. Do you have a rough engine weight for comparison? If not much different then might be worth doing some chopping around to fit something bigger. Advice I've read so far suggests I need to stick to 8.2" deck height so headers can still fit between the chassis rails, so probably anything up to 347 stroker.

Now I'm on the subject, it seems to be more common to increase engine capacity on a 302 / 5.0 by stroking rather than boring. Is this due to thin castings to keep the block compact? I'm sure there'll be a thread on here somewhere comparing the virtues of each method but just wondered why. Is one method better for torque and the other for peak power? I'm sure I read somewhere that something like a 331 could be better for driveability than a 347 which is more at the top end of capacity for a 302 block? (feel free to correct me here, I'm still learning!):confused:
I recall back in the 80's one of my petrolhead mates put a 351 Windsor in a Mk3 Cortina exactly as you are planning. He used a C4 auto and 9" diff.
Id say go with the alloy block as it was a total pig in the handling department. I remember one day following behind him on my bike at about 110 mph, but was very reluctant to pass as he was actually fighting to keep the thing straight. Great for stoplight burnouts but a waste of space for anything else. Like anything though it can be made better, the more money you throw at it, the better it will be.
I managed to fit the Boss 302 & Headers in the Std chassis rails so you wont have any major issues with Windsor configuration even on the 9.5" block.
Having said that the 3.25" stroke with 8.2/ 4.125+" bore alloy block is a 'Happy' combo weight/size/power for your application( until someone else comes along with a bigger / better setup.).

Jac Mac