Case prep cost consideration, early AL vs 7R

Shuie · 08-18-2005, 01:09 PM

Engine would be a 2.5 or a 2.6.

Does it cost more to do 'all the mods' to an early aluminum case or a 7R case? I know the list is different for each; line & shuffle pin for the 7R vs oil by pass, piston squirters, spigots for the AL case.

Also, how much more does an AL case weigh than a 7R?

TIA

kenikh · 08-18-2005, 01:55 PM

I believe the weight difference is 22 lbs.

Eagledriver · 08-18-2005, 03:20 PM

You could price this out by talking to a machine shop such as German Precision (Ted Robinson). The advantage in my mind would go to the Aluminum case. The Mag case will crack, it's only a matter of time. For a street engine keeping the revs below 7000 RPM and not putting on alot of miles the Mag case would be ok, but the Al case will last longer in any application.

-Andy

rswannabe · 08-18-2005, 03:47 PM

I've been thinking about these same issues for my own 2.6 buildup. Here is where I am at so far.

Granted the Al case will definitely be stronger, BUT I think a mag case would be sufficient for a street engine. Look at all the high milage 2.7 and 2.8 RS MFI motors running around. Randy Wells has over 30,000 miles on his if I recall and its built on a 4R/5R case, not even a 7R. He drives it hard too. The 66mm crank of the short stroke motor also imposes less stress on the case. Of course if you are looking to rev it to 8,000 rpm, than you want to go with the Al.

blue72s · 08-18-2005, 05:07 PM

Quote:

The Mag case will crack, it's only a matter of time.

Crack? What crack? I think the main problem of mag is stud pulling, but if you use Dilavar, you should be ok. Just my .02

Shuie · 08-18-2005, 06:53 PM

Thanks for the help everyone. Ive seen the debates on the strength issue. That doesnt concern me. How about the cost of the prepwork?

Steve@Rennsport · 08-19-2005, 08:37 AM

Quote:

Originally posted by blue72s
Crack? What crack? I think the main problem of mag is stud pulling, but if you use Dilavar, you should be ok. Just my .02

LOL,..Oh, they crack alright,.....right behind the #3 cylinder at the back of the case. Its an RPM issue and sometimes imperfect balance.

This is precisely why the factory went to Aluminum for the race engines in 1974.

blue72s · 08-19-2005, 09:18 AM

Quote:

they crack alright,.....right behind the #3 cylinder at the back of the case. Its an RPM issue

Even by short stroke crankshaft?
If so, what's the safe RPM limit?

Steve@Rennsport · 08-19-2005, 09:59 AM

I've not seen the same degree of cracking issues with the 66mm cranks but there are far more factors at work here.

Bore size, compression ratio, and RPM all play roles in how much stress these mag cases undergo.

I would try to keep maximum RPM below 7400 to ensure longevity and I would NOT boattail a mag case. Removing metal in these things is the very LAST thing one wants to do,......

kenikh · 08-19-2005, 10:21 AM

Quote:

Originally posted by Steve@Rennsport
I've not seen the same degree of cracking issues with the 66mm cranks but there are far more factors at work here.

Bore size, compression ratio, and RPM all play roles in how much stress these mag cases undergo.

I would try to keep maximum RPM below 7400 to ensure longevity and I would NOT boattail a mag case. Removing metal in these things is the very LAST thing one wants to do,......

Are you saying that a stock bore 2.0L mag cased car shouldn't worry too much about stress cracks, even if you whip it around in the 7500 - 8000RPM range?

blue72s · 08-19-2005, 11:52 AM

Quote:

Removing metal in these things is the very LAST thing one wants to do,......

When you say bore size, do you mean spigot size?
Is a 97mm (spigot) case more prone to cracking than a 92mm one?

jpnovak · 08-19-2005, 01:18 PM

Has anyone ever welded stiffening ribs to a Mg case?

Steve@Rennsport · 08-19-2005, 03:07 PM

Quote:

Originally posted by kenikh
Are you saying that a stock bore 2.0L mag cased car shouldn't worry too much about stress cracks, even if you whip it around in the 7500 - 8000RPM range?

I am saying that a mag-cased 2.0 would have other issues to worry about (oiling) at 8000 RPM besides case cracking.

I would not lose sleep about a possibility of case cracking with such an engine and the same would apply to a 2.2.

Steve@Rennsport · 08-19-2005, 03:08 PM

Quote:

Originally posted by blue72s
When you say bore size, do you mean spigot size?
Is a 97mm (spigot) case more prone to cracking than a 92mm one?

My referral to bore size was basically a referral to spigot size, yes.

Steve@Rennsport · 08-19-2005, 03:14 PM

Quote:

Originally posted by jpnovak
Has anyone ever welded stiffening ribs to a Mg case?

Jamie:

Welding magnesium is NOT for the faint of heart,....

I've made small welds to mag cases in certain areas but I've not attempted to attach stiffening ribs.

Many years ago, I heard of someone who tried that with no long-term success. Due to the different alloys used in the mag case and the available materials, the case cracked all around the attached ribs.

Thats why the Factory (who patented magnesium pressure-casting in 1968) gave up and went back to aluminum.

Mag cases are fine if they have been properly prepared, but they simply have their limitations.

Shuie · 08-19-2005, 06:44 PM

Thanks again, guys.

Any thoughts on the relative cost of the prepwork of an early AL vs 7R case? 1.5x? 2x as much?

kenikh · 08-19-2005, 07:36 PM

Poor Shuie, he wants to know what it costs to buy a house not how to build it.

Steve@Rennsport · 08-19-2005, 07:43 PM

Quote:

Originally posted by Shuie
Thanks again, guys.

Any thoughts on the relative cost of the prepwork of an early AL vs 7R case? 1.5x? 2x as much?

Its about the same given all the things one needs to do.

Shuie · 08-19-2005, 07:50 PM

Thank you!

blue72s · 08-20-2005, 08:06 AM

Quote:

I would try to keep maximum RPM below 7400 to ensure longevity

The red line (I assume it means safe RPM limit) of a 1973 Carrera 2.7RS, which is long stroke, is 7300, so why the safe RPM limit for a short stroke 2.5/2.6 10.3:1 is only 100 RPM more?