How racy can I go with a 4R case?
 

I am seriously thinking of following the route Bill V suggested in the racing forum. My 2.5 has a 4R case. Can I use this case, assuming it is sound, for a 2.7 RS motor? Goal is to run my 73 as a Carrera lightweight (runs in D stock), hence the 2.7...

bump before it goes to the tech forum

Well I can at least say 190HP is ok with a 4R case since that was the amount a 2.4S made on a 4R case. More than that I don't know.

Thanks Tim
Perhaps I should be more specific. Thinking of a HC 2.7 or RS, around 210 HP. Anyone?

I know people have rebuilt 2.4S 4R/5R motors into 2.7RS motors with no problem. I don't see why you couldn't even go out to 2.9L. The important thing is to provide the proper cooling for the motor in the form of an external oil cooler. Casesavers as well as oil bypass mod should be done and Dilivar studs for a large displacement mag case might be a good choice. (I'm not looking to open that Pandoras box however!)

Hi Mike:

No worries, Sir. If you properly prepare that case for what you wish to do, you will not have an issue. Even the 7R cases do crack behind the # 3 cylinder from constant high RPM.

I would NOT use any cylinder larger than 92mm (2.8) since the cylinder walls are too thin and unstable for good ring sealing. You'll have good luck with a 2.7.

Have the case decked, line-honed, shuffle pinned, do the oil bypass mod, and use a Carrera oil pump at the very least (turbo or GT-3 is best). If you anticipate constant RPM's above 7300, I'd have the crank cross-drilled and the case modifed for that, accordingly.

Enjoy,

Hello, Steve.

This si great advice, steve.

please could yoy explain the details of cross-drilling and case prep accordingly please?

Kind regards
david

7R cases can be found so cheaply, that I would start with the strongest base yet. You can easily find the 2.7 7R cases on eBay for about $100 - I wouldn't mess with the 4R if you don't need to...

-Wayne

Hi Wayne:

The 4R is really OK for these applications. Later 7R cases are SOOO stressed from heat and wear they take a lot of expensive machine work to get all the problems fixed and in many cases (no pun intended), its much cheaper to prep the 4R and simply open the spigots to 97mm. The very best mag cases are the 2.4 7R ones.

I've seen just as many cracked 7R's as 4R's so I don't think its a big issue in an engine at the 200-230 HP power level.

Now, if one had an aluminum 7R, that would be different. :)

Similar to my Euro 3.0 case, huh?

Yes, I guess it's a toss up. Walt recommends doing the full-schebang to the 7R and 4R cases, so if you are going all the way, I would still recommend the 7R. If you are not going to fully prep the 4R case, then Steve makes a very good argument in that the cases probably didn't serve as difficult a life...

-Wayne

LOL,...Nope.

The aluminum 7R case uses the older stud spacing as the 2.0-2.7 cases,..its VERY rare.

The "case" to make about which one to use should be based on engine operating RPM range and usage.

Street and DE use up to 7200 RPM, you can use any case you want as long as its prepared and modified accordingly. If sustained RPM at or above 7300 RPM is anticipated, then I'd use a 7R or an SC case, appropriately modified. Some years ago, we made a 2.8 from an SC-based motor and it was a totally bulletproof 325 HP engine,....:)

OK, you've got my attention.

How do I get started down this path?

Shuie:

You'll need LOTS of money for this one. Its was done for a client that was notoriously hard on engines and he needed a competitive, yet bulletproof (as possible) race engine.

My bad, as this was based on a 3.0 Turbo case & crank, not SC.

We used a 3.0 Turbo case, with many many mods, 70.4 Turbo crank (again, many mods) and a GT-3RS oil pump. We made some custom 95mm Mahle cylinders with steel sleeves reduced to 91.5mm. JE pistons at 12:1 and some massaged 935 heads with very big titanium valves. Then, PMO 50mm carbs with tall manifolds, manifold spacers, RSR distributor w/MSD's, and some 1.75 headers with our own Flowmaster Series 80 muffler.

Cams were our own profile.

You must use 935 heads to fit the smaller stud spacing of the 3.0 Turbo case. Properly modifed, they flow VERY VERY well,....:)

This engine was over $ 30K but survived a 1 hour enduro without a fan belt when the owner missed a shift on the first lap and tossed the belt. He drove the whole race with oil cooling only and finished 2nd. Oil temps were over 310 deg F for the hour and after teardown only the rings were scuffed a tad.

IMHO, it was really worth the $$$$.

Hello again, Steve.

I'm very very interested in making my engine live at extended High RPM.. there is not much known here in UK on this topic.. would you feel able to share your expertise on crank and case prep please?

A simple analysis of the 911 motor suggests it has breathing capability for increasing power to well in excess of 10,000 rpm.. but other factors limit it...

Kind regards
David

Hi David:

IMHO, the 911 engine's valve train will not support RPM's in excess of 9000. Even using titanium valves does not mask the problems keeping the valves and rocker arms following the cams at that RPM range.

I"ve been after this since 1978. One would need double overhead cams directly actuating the valves to get close and even then, the big valves used in most 911 motors are the limiting factor at the top end.

At the bottom, crank and rod oiling are the big issues as the crank is lubricated from the ends and the center journals starve at high RPM.

LOL,..If you need your case & crank modified to live at 8000+ RPM, I'd be pleased to perform these services for you. Some hard-earned lessons are not public knowledge,....:)

Thanks, Steve.

I fully appreciate and respect your need to protect your livelihood!

In fact, I am sure that I am not alone in expressing my gratitude for the really excellent advice you do give here, for free...

PS If you are looking for a UK agency, please let me know!

Kind regards
David

Hi David:

LOL,..You are the top of my list,....:) :)

I do appreciate your kind words, Sir.

The learning curve is quite steep and very expensive over the past 27+ years with 911's and its taken literally thousands of dyno and flow bench hours learning what works and what is a disaster.

Take care,

Good Gawd!

That's a testament if I ever heard one...

(...but then you DID say he was hard on motors. :D )

"Good Gawd" is right,....:)

Needless to say, we were all stunned in the pits when he cruised in after the race and we happened to notice the alternator warning light on. Oil temp guage was pinned at the top and the belt was found in shards.

The motor looked amazing,...cams, rockers, bearings, pistons, crank,.......we simply replaced some things for insurance. given how tough this gentleman was on equipment.

A real testament to Mobil 1, IMHO.

Just to add one more data point on the 4R vs 7R discussion I'll tell you about my engine. 2.7 RS spec with MFI engine on a 4R case. This engine was fine as a street engine for 9 years and 60k miles. On it's second racing season the case cracked at the lower farthest aft headstud on the passenger side. The case cracked at about thread depth on a flat area where that stud bottom is. I'm now rebuilding with a 7R case. The 7R case is thicker there and hopefully won't crack. The studs are Dilavar and the case was shuffle pinned.

is it by the #4 or #6 cylinder?

Eagle Driver:

FWIW, 7R's do crack behind the #3 cylinder in the rear case wall after sustained 7500 RPM usage. How long its lasts depends on how much time is spent in those RPM ranges and how many races you do per year.

I would not hesitate to keep a good spare 7R case around.

Sorry about the late reply, I was out of town for a few days. The crack was on #4. There is only one head stud that doesn't have a case through bolt next to it. That's the one where the case cracked. Thanks for the advise Steve. I keep the revs to 7300 max and normally shift at 7k.

-Andy
72 RS replica E stock racer

I don't know about a 4R case, but when I compare my 7R case with a 3R case there are a lot of reinforcements done. It seems to me that more is better in this regard.

3R

http://forums.pelicanparts.com/uploa...1072488575.jpg


7R

http://forums.pelicanparts.com/uploa...1072488596.jpg