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is a mexican block 302 worth a rebuild?

benkokes

Full Member
Joined
Aug 17, 2005
Messages
227
Hey all,

My 302 is starting to give up the ghost and it seems that it will need attention soon.
The Question: Is it better to use the block and build it into a roller engine? OOORRR should I wait around for an Explorer engine and fix THAT up?

I WOULD like to get about 300-ish HP out of it, is this unreasonable?

I was thinking it would be a good time to research 'ported' heads. Is there any consolidated thread on non-obnoxiously-expensive heads of this nature?

Thanks,
-Ben
 

G's Baja Bronco

Bronco Guru
Joined
Aug 7, 2010
Messages
1,362
Loc.
Sunny SO CAL
:cool: I am restoring my 73 with a HO 1991 5.0l with explorer heads (gt40p) I was lucky to find a rebuilt set with dual springs and matching GT40P headers. I am expecting 300 hp, am keeping the HO cam, for the most torque. new bearings, rings, gaskets, timing set, brass freeze plugs and oil pump. no smog, 2-1/2 w flow masters feed by a 750 demon, msd6. I am expecting 300HP, about twice the power of the existing 302 2 barrel.

i hear that the explorer engines have a smaller cam and a belt timing set, I have seen several at the wrecking yard in SD for 500 with 30 day warranty and about 120k miles.
 

NYLES

Bronco Guru
Joined
Aug 13, 2004
Messages
9,846
:cool: I am restoring my 73 with a HO 1991 5.0l with explorer heads (gt40p) I was lucky to find a rebuilt set with dual springs and matching GT40P headers. I am expecting 300 hp, am keeping the HO cam, for the most torque. new bearings, rings, gaskets, timing set, brass freeze plugs and oil pump. no smog, 2-1/2 w flow masters feed by a 750 demon, msd6. I am expecting 300HP, about twice the power of the existing 302 2 barrel.

i hear that the explorer engines have a smaller cam and a belt timing set, I have seen several at the wrecking yard in SD for 500 with 30 day warranty and about 120k miles.

750s too big! I know Ive had your motor. Try speed demon 575
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,355
Can't say whether it's better to rebuild or buy a roller, in your case benkokes, but generally speaking, I've heard more good things about the Mexican blocks than bad. Can't remember hearing anything bad about them in fact.
Seem to remember hearing they have a harder iron composition and good casting consistency. That last could mean better overbore capabilities down the road.

Otherwise, nothing wrong with hoping for a full roller motor all ready to go!

Have fun either way.

Paul
 

bmc69

Contributor
Bronco Guru
Joined
Jun 11, 2004
Messages
11,852
I swear by the Mexican blocks. Some of the differences are obvious..others are alleged or unproven..but the proof to me is in the results; they make bullet-proof short block assemblies. I have one engine that dynoed at 486 hP (@ 7300 RPM), spent 7 years being horribly abused in my 4x4 MX race truck..outlasted the truck..got stuffed in my 16' Donzi about 6 years ago..and is still in that and running strong.

Changed the oil and adjusted the valves (solid lifters of course) and that is all that has ever been done to it since it was built in the late 90s.

The number of times that the engine has seen 10K RPM while in the MX racer I could not count...its life in the Donzi is like retirement to an old folks home by comparions.

I've yet to see a non-Mexican block hold up like that..excepting the various SVO aftermarket ones, 'R' and the like.
 

broncosam

Contributor
Bronco Guru
Joined
Feb 8, 2005
Messages
1,178
One of the books I have here on Ford engines refers to the Mexican blocks as having a higher nickel content making for a stronger casting.
 

Viperwolf1

Contributor
electron whisperer
Joined
Aug 23, 2007
Messages
24,316
One of the books I have here on Ford engines refers to the Mexican blocks as having a higher nickel content making for a stronger casting.

Wouldn't it be more correcter to say it has a higher peso content?;)
 

65 mustang

Sr. Member
Joined
Mar 30, 2007
Messages
430
If you have a mex block by all means use it. To go and find one to build 300 hp. Factory roller 5.0 mustangs and exploders go 120k miles with no problems.
Also i don't believe there was a factory 320/351 with a belt timing set. Scott
 

pierr

Sr. Member
Joined
Jul 11, 2009
Messages
434
Loc.
Gordon,GA
ANY of the factory 302 blocks are fine for 300-400hp and should live a long,happy life. The differences(in durability) start to show up when you push them above 450 or so flywheel h.p.,or above 6,500 rpm on a regular basis. My opinion is based on experience w/ street & drag cars + the experience of my trusted engine builder(who's been a FORD man exclusively since the 60's;)). Also, stay below 600cfm w/ the carb...you'll thank us later! Pierr.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,835
There are retrofit roller conversions, just a little more money and work then a factory setup. But from everything I have heard about the Mexican blocks, they are the second best production 302 block (Boss 302 being better, extreamly expensive these days, and nearly impossible to find)

The rumor story I remember from back in the day...
When Ford wanted to start maing 302s in Mexico they took some molds and got a couple of castings back. They were horrible. Researched what was wrong, molds were good, metal supply sucked. Project was now behind so fix it whatever it takes. Took the tooling in the back room and threw metal at it. It the cast iron wasn't as good, put more in to compensate. While at it, use the 289 HiPo main caps as well. All the yelling also made it back to the cast iron suppier (who was worried about losing a HUGE contract) started sending some quality iron to the foundery. So when production hit they had a beefed up casting and a good supply of iron, thus the better then most mexican 302 block.
How true that is, I have no idea. Just an old story from years ago.

Now for heads. Lots of quality aftermarket out there. Expensive? Not so much. If you consider a set of stock castings, rebuild with new parts, machine work, bigger valves, then find someone who can actually do a good port job and repeat the port job the same over 8 ports, you now have a set of stock heads pushed to the limit that come in about where a set of off the shelf aftermarket heads come in. And you are still dealing with cast iron. Aftermarket aluminium heads are the way to go, especially if you are after 300 HP.

Speaking of the 300 HP target, what is your target torque? Broncos are heavy, they love torque way more then HP. Torque is what makes them fun to drive. Torque is what moves you, HP is what gets you there. Moving is more fun then flying down the road at some speed faster then the chassis can handle. But I don't know your intended purpose of this rig either. If it is sand drags, you want HP. Fun to drive around, fun to play on trails, you want torque.

May I suggest a 351W???
 

broncnaz

Bronco Guru
Joined
May 22, 2003
Messages
24,341
:cool: I am restoring my 73 with a HO 1991 5.0l with explorer heads (gt40p) I was lucky to find a rebuilt set with dual springs and matching GT40P headers. I am expecting 300 hp, am keeping the HO cam, for the most torque. new bearings, rings, gaskets, timing set, brass freeze plugs and oil pump. no smog, 2-1/2 w flow masters feed by a 750 demon, msd6. I am expecting 300HP, about twice the power of the existing 302 2 barrel.

i hear that the explorer engines have a smaller cam and a belt timing set, I have seen several at the wrecking yard in SD for 500 with 30 day warranty and about 120k miles.

I'd only expect about 220 hp your building a relatively stock engine with already proven numbers a HO cam wont get you 300 hp


Really nothing all that great about a mexican block if you have it and want to rebuild it then go for it. Although it is sought after by people who race so that may be a good engine to sell and fund other parts. Broncos are rarely high RPM machines so the block isnt really needed.
A low mileage explorer motor probably wont need a rebuild. Also since it allready has a roller cam you wont need to spend extra money on conversion parts. Cam and heads will get you to the 300 hp mark. While stock heads can get to 300 hp it takes a very healthy cam to get that number and really wont be a good bronco engine. Any aftermarket heads with at least 1.90/1.60 valves will be better than any stock ported heads and will probably be cheaper as well. A few years back I was going to get my stock heads redone to what I wanted larger valves and screw in studs when I looked at the pricing it was only going to be a little more $$ for aftermarket heads that would be better all around. So I went with aftermarket heads. I think you could get near the 300 HP mark with a HO cam and good aftermarket heads but thats about it.

I agreee with Broncobowsher you may want to consider a 351W for your 300hp build it will be easier and have much more lowend torque.
 
Last edited:

djhudson05

Sr. Member
Joined
Nov 29, 2008
Messages
542
Mexican blocks are stronger than a regular block. They have more nickel content in them and they use the heavier main caps like the Hipo 289's used.
 

Steve

Bronco Guru
Joined
May 5, 2003
Messages
2,986
Loc.
Grand Junction, CO
Speaking of the 300 HP target, what is your target torque? Broncos are heavy, they love torque way more then HP. Torque is what makes them fun to drive. Torque is what moves you, HP is what gets you there. Moving is more fun then flying down the road at some speed faster then the chassis can handle. But I don't know your intended purpose of this rig either. If it is sand drags, you want HP. Fun to drive around, fun to play on trails, you want torque.

This. For most applications you want to build for torque, not HP.
 

bax

Contributor
Old Member
Joined
Aug 22, 2005
Messages
14,491
yes they are good but keep in mind after lunch it may not start for about an hour.
 

G's Baja Bronco

Bronco Guru
Joined
Aug 7, 2010
Messages
1,362
Loc.
Sunny SO CAL
I understood that adding GT40P heads to a HO 5.0L added 60 horses, seen several write ups on this in the net. it is due to more flow, better spark location and lower chamber CC's. I have a hard time believing 220HP only, but i will take the 220 over the stock 2 barrel 302.

I agree on the below 600 cfm carb, and as far as 120K miles out of mustang and explorer rollers, I have owned 5 5.0 mustang and drove them to 250K miles with out any issues, I have seen several 250K explorer engined disassembled wit little or almost no cylinder bore lip.
 

Pedestrian

Bronco Missionary
Joined
Sep 10, 2008
Messages
2,299
IIRC the Explorer was rated at 250 horses with P heads. Getting to 300 will probably require a different cam and good headers.
 

Viperwolf1

Contributor
electron whisperer
Joined
Aug 23, 2007
Messages
24,316
IIRC the Explorer was rated at 250 horses with P heads. Getting to 300 will probably require a different cam and good headers.

Explorer 5.0 was rated at 210 hp. They had a slightly smaller cam compared to the car HO motors.
 
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