Is this possible??

[911 tweaks]

I was wondering...you know the "tweeks" thing in me... is it possible to have the best of both worlds??

Specifically, how can one spec an engine AND trans to achieve low end torque AND power?? i.e. suck you into the seat feeling when floored!

I have heard of using a 915 w/7:31 to help the low end OR to use a shorter stack of gears?? suggestions...ideas...(base your suggestions using a 915 trans or something to trade it for or...)

As far as the engine goes, (presume normally asperated and a 3L long block), as cool as it is to has a high reving 2.8 like Henry swears by as THE BEST ENGINE Porsche made, what about the expresion "there is no replacement for displacement"?? suggestions...ideas...(base your suggestions on using this long block, hopefully no machining, interchange parts of which may need to be slightly modified/cleaned up them selves but I am on a restricted budget and cant swing a 3.6 transplant or Bens' lo boost turbo...I don't think??

***To help define what I am fishing for, I am restoring a stk 81' 3L SC going into a 82' Targa and am trying to achieve a 0-110 MAX MPH screamer or "sleeper" as I call em'. I would like to achieve as close to 300 hp at the wheels, I know this will be tough, but would settle for this at the flywheel which would give me 275 at the wheels figuring 15% loss throuth the 915. If necessary, I am willing to have 2 915's set up for the different drive needs i.e. above is the daily driver and the other would be track/DE set up where sustained higher revs would be happening since on the track. Maybe I need 2 engines and 2 trans that would give me 4 options...please dont go there as $$ budget wont allow... wishful dreaming

I am open to any and all suggestions for engine(primarly) set up and trans ideas and maybe my goal would greatly shorten engine life - which I don't want! The best pump fuel around MA is 93. More abundantly 91 is almost everywhere. This is probably my limiting factor and I would rather not be required to mixing "up" octane to avoid pre-me detonation.

Maybe a 2.8 like what Henry loves and just run the snot out of it at 4-7k all the time?? How long would that engine last operating it like that??

Any ideas on major weight saving areas and keep some creature comforts??(lighter the car the better the engine can perform)

Thats where I am at now. Thanks for any and all of your ideas.
Bob

[MBEngineering]

HI if you are to use that BHP then you will need a 8:31 (or if you can find one a 8:35 =7:31), and a set of ratios:1st=11:35, 2nd=17:35, 3rd=19:30, 4th=23:29, 5th=25:27 MAX speed at 7000 rpm @126mph depending on tires, and a engine 3.0lt SC with PMO carbs, JE 10.5 pistons, DC60 cams, mod the cases, gas-flow the heads , twin plug , exhaust?? approx bhp 280 at the flywheel, with SSI heat exchangers and STD back-box. you lads can build this lot cheep as chips, as I have import duty and vat to pay.

regards mike

[911 tweaks]

Thanks for your response Mike! So this is do-able???

Please provide more details to confirm what you are saying -
1. IF I want 280hp @ flywheel I need to do the following:
use 8:31 r/p w/ gears as you state...where can these gears be had?? Are they porsche gears?? Special order Porsche or aftermarket?? If Porsche gears, what box can I get these out of?? Or, whom aftermarket get from?? Any idea on $$??

2. As for the engine, use the 3L SC longblock and change out the CIS pistons for the JE 10.5 pistons...use the stk 3L mahle cyls??

3. Which PMO carbs?? 40, 46,... any specs on the jetting...or will PMO know what to set them at??

4. DC60 cams as is?? Any special/unique tweeks to them??

5. What mods to the case?? pinning?? boattailing?? larger piston oil squirters?? knife the crank?? any of these and/or other??

6. Any mods to the crank?? use the stk 3L crank??

7. What flow rate for the heads?? What valve size?? What type of valves?? What type springs(double??), retainers?? what type rockers??

8. any particular dizzy?? burn-bros/supertech offering??

9. ssi heat exchangerheaders...what muffler...2 in w/1 or 2 out?? What brand??

10 any particular flywheel?? sach super clutch kit ok??

Did I miss anything Mike?? Do you have any est. for what this would cost??

Thanks again??
Bob

[afterburn 549]

Go A/A and a 4 speed.....

[911 tweaks]

Hello Mike... any answers to my above q's??

thanks afterburner...but I dont know what A/A means...I would guess since you suggest a 930 4 spd trans it is some type of turbo or blower set up. Please explain the engine set up and what model & yr trans.
Also, are you suggesting to part out what I have or save it for future pcs I may need??
Thanks!
Bob

[afterburn 549]

with tongue in cheek and hand in wallet...the turbo is the wave of the future. No its not for everyone...but for serious speed it might be your best option

[Walt Fricke]

Tweeks - just about anything you do will affect drivetrain life/reliability. Unless you seldom use much of the extra power, in which case it might have been more economical to rebuild a stock motor to stock specifications, and tranny too.

However, I suppose it just isn't possible (and certainly isn't wise) to flog things as hard on the street as on the track, where wide open throttle is the name of the game. The more tweeked a track motor (or dual purpose) is, the shorter the time between rebuilds of something (rod bearings especially). 40 hours is a figure you often hear for race motors, though a whole lot of us run ours at least triple that (perhaps not wisely).

If you want to run higher compression (as you will have to do to make the kinds of power you aspire to), be sure to twin plug the heads. But I don't think you can expect to get 100 FWHP limiting the revs to 7,000. You'll need to be able to spin up to 8,000 or close to it, especially if you keep to a CR you can make work with pump gas. That means a HP peak around 7,600. The factory 2.8s developed their peak HP at 8,000.

My favorite low buck 915 is a 7/31 with the gearset out of an 8/31. Just swap out 4th and 5th (the others are the same) in a 7/31 box and save yourself setting the differential up (me, I did it the other way because I had an 8/31 box). While you are in there be sure to install one of the one piece bearing carriers in place of the two separate ones Porsche used. A 2.4 or '74 mag case box saves weight, and those boxes have a steel insert cast into the area where those two big bearings go already, making the tranny sideplate perhaps the weak point of the mag case (which you can deal with by using a late 3.2 side plate or an aftermarket reinforced design). Mike is considering the fact that the 7/31 is a weaker gearset than the 8/31. But swapping in all the gears (you can move 3d to 4th - it makes a nice 4th, and changing 1st isn't really worth it, so I guess all really = three, but they will not be stock/less expensive gears) is going to raise the price. How much do you want to pay?

I once ran a short box and a long box on my track car, depending on the track. I got pretty good at swapping (maybe 2 hours out and back in by myself), but that gets old. I also had both a 2.3 and a 2.7 I swapped back and forth. That got old as well, though not as old as tranny swapping.

You ask about cost. Well, you won't achieve your goals starting with your 3.0 for less than the cost of a 3.6 transplant, I'll wager. Have you asked a machine shop what they want to twin plug heads? Not astronomical, but it is not $100. Or what special valves cost? Even brand new stock ones - look at what Pelican sells them for as a reference. Cheap as chips is relative, as you know speed costs money. I gather it just costs us a bit less than it costs Mike on the other side of the pond. Use the power of the internet to price out trick parts and head work costs - they are out there.

Since you say you can't afford the 3.6, here is a suggestion: the late Euro 3.0s were real screamers. In Porsche Club racing they are bumped up a class from the US spec 3.0s, and their competitors say they should be put up two classes. Find the heads and intake from a '78-79 US 3.0. (or swap your '81 for a '78/9) Buy new Euro/ROW 9.8/1 pistons (and probably cylinders, as chances are the old ones are worn or are Alusil). Maybe get a 964 or reground set of cams. Replace the stock rod bolts with Raceware or ARP. Put on SSIs (or find a stock '74 exhaust) and a muffling system of your choice. Build this engine (you will learn a great deal I suspect you do not yet know) and run it with whatever transmission you have. You'll have great fun. If you aren't an old track hand, you will not need more horsepower than stock to begin with anyway on the track - it will just cause your crashes to be more damaging if you try. And while the Targa has a whole lot going for it in the grin department, it is not the optimum base for a track car (unless you weld in a full cage, which greatly narrows the gap).

Not what you want to hear, but there is no getting around the costs involved even if, as I assume, you do all the engine assembly yourself.

Walt Fricke

[911 tweaks]

thanks Walt and well put! I like your summary and yes I am still a little wet behind the ears on this subject though well read and I spend several hrs/day on Pelican surfing and learning...can never stop learning about anything in life is my viewpoint!!

I believe your view and I agree that it is a great starting point. Learn to use (customer and me) what we have and go from there to be smart on the budget.

However, in the event the doner engine I have is a dud please explain further what you are offering on the engine and trans tweeks!! The engine you describe with Euro/ROW 9.8:1 pistons, use JE or Mahle? Is this going from 3.0 to 3.2? Should I go to 3.2 if this Euro is 3.0 since I am buying new anyway? Also, should I go short stroke and stop there... and if yes to the ss, did Porsche make this type of conn rods which I can then maybe can find used ones reasonably? I have a used 78-79 set of heads and intake system from a Katrina swimmer of late. After twin plug holes, what valve & spring type/brand/size do you recommend? I will be keeping the CIS so is 964 cam most aggressive with these Euro p/c?

And finally, trans wise...I have a 1982 915 with crunchy 1st gear so I was told. I also have a factory LSD with 50% lockup that was rebuilt. And I also have a complete (used) 1976 915 from a 912 car that has the 7:31 r/p that will allow the elect speedo to work. What should I do to make 1 or maybe 2 trans? If one trans made, I would like to do the aggressive street set up with the 110-120 max mph.

I am sure you will have q's so let me know what I can tell you to so you can best answer my q's.
Best!!
Bob

[Walt Fricke]

My somewhat conservative suggestion is to build what basically is a stock late Euro 3.0. This has nothing to do with a goal of being able to outrace anything at a stop light. As for the track, you need some seat time there before you can decide what car/motor/transmission combination you want. Different tracks benefit from different gearing, but that won't make as much sense (especially when deciding what marginal returns - bang for the buck - might be between gearing A vs B). More importantly, unless you already have a street/track car, isn't it more valuable to have a 911 you can actually drive around and also gain track time in while you engage in the normal scheming to go faster?

Back to a Euro 3.0 (based on what you have): The non-stock parts would be a slightly hotter cam (optional, and slightly because of the CIS's limitations), stronger rod bolts (though these are not strictly necessary on such a motor as they would be for one with the 3.2 crank in it), and a good exhaust (the only must have, and a stock '74 would do as well). Assuming you can't get "good" used Mahle 9.8s, I'd buy a new set with cylinders. That will eat up a good part of your budget in itself, but it is good stuff.

I think you do not want to run J&Es with CIS, because the CIS pistons have funny looking tops designed to help the CIS. J&Es pretty much just have a dome, with valve pockets cut in as needed, and some of the dome shaved to adjust CR. Good stuff and good value for speed equipment (I have a set), but not for CIS (which also limits the cam).

I think you would run into the same CIS piston dome problems trying to bump up to 3.2. These had EFI, so I don't think they needed help from the piston dome. And to get to 3.2 with stock parts you need the larger 3.2 crank, along with rods to match (these do require the stronger rod bolts), which will also fit the pistons for these engines. No, 3.0 rods won't work - check out Anderson's or Dempsey's books on rod specs.

You could use 98mm aftermarket Ps and Cs to boost the displacement. But the CIS dome issue remains, and you are into cost creep again. Maybe I overestimate this dome issue with the CIS and someone can comment. But for hot rodding most go to carbs (a set of 40s might come to you for $1,000) or EFI. MFI is really great, but expensive and tricky, especially if you need it modified. Home brew EFI is a real tinkerers delight - look up Megasquirt. Maybe you can keep within budget with something like that, use the CIS intake minus the fuel injection part, and run a hotter cam and whatever larger Ps and Cs you can afford. But it is not off the shelf stuff you can just bolt together (carefully) and fire up. All this delays getting the car on the road.

Gears - first off, I'd use that stock SC ear 915 you have. Decide for yourself if the crunchy 1st is a problem. You only need first to get going. Certainly not on the track. I have never speced out a drag race tranny (or, for that matter, an autox tranny). But on a track speed from 0 to 30 or 35 is irrelevant, as no corners are slower than that. Some tracks have no second gear corners (using the term loosely).

Then, while driving around with your nice, mostly stock, motor and a stock transmission, figure out what it would be like cruising down the interstate at 60-75 driving to Watkins Glen or Mid-Ohio from MA. See what RPM in 5th you would be running at those speeds, and shift into a lower gear to approximate it. Hell, drive over to Lime Rock that way. See what you think about an four or five hours driving at 5 or 6 grand. Ask your DE buddies what they think they hit for top speeds in their stock SCs at the Glen. I liked my relatively cheap 7/31 with shorter 4th and 5th. Noticeably more poop to the car - my wife asked if I had done something nice to the engine. But some say they get tired of it cruising the interstate on the way to a track. We all are different.

You want to match your tranny somewhat to your engine. When you have your engine in your car you can go to a chassis dyno and get your torque curve. You can use that to determine optimum shift points. And if you do it with a spread sheet, you can play with gear ratios.

Anderson explains that ideally you want to size gears for each track and its specific corners. But this is impractical unless you are a sponsored pro or running a Formula Ford or the like. So you pick a likely top speed (and for a dual purpose car, a street/track compromise), and then space your gears so you run an approximately equal increase in mph in each. My track tranny has, for my tires and shifting at 8,000, a 60 mph 1st gear, an 80 2d, 100 3d, 120 4th, and whatever 5th I might like (150 nowadays). Turns out I shift at 7,600, but the spacing is the same and I've not driven Daytona to challenge the top end.

What gears? Well, look up what is available from the guys who make and sell gears. With enough references you can figure out what stock is. Here is one place you can get stock gear ratios (it will tell you what is in the two trannies you have) http://www.rmrporscheclub.com/files/Chal_Series_Rulesbook_2006_final.pdf. Then you plug that into a spread sheet with rpms and speed for a given tire diameter and R&P (very few choices there) and see what you get.

And we haven't even gotten into the full roll cage you will want if you track a Targa a lot, nor what the suspension modifications will cost. The fact is you don't want to think in those terms because it all ends up costing too much for most of us. So you do it a bit at a time so you don't notice. And what if you decide DE isn't enough and you want to race? Well, you probably will have to take the mods out if you want to run in the stock classes. If you run with the modified cars, you'll get killed by guys who spared little if any expense.

Enough sermonizing on the virtues of patience and practicality. I have to get in my SC and drive 80 miles to talk to some guys about financing the building of a race track. Race seat is bolted in place and it has a full cage with low door bars, so I have to use the removeable steering wheel to get in and out. The shoulder belt doesn't work with this seat, so I use 4 of the 5 point harness. The suspension is pretty stiff. The 60 series tires are about the only thing that keeps the tooth fillings in place. Oh

Walt

[MBEngineering]

HI Bob the gear sets you can get from www.powerhausii.com and www.carquip.com or www.guardtransmission.com all have good gear sets, If you must use a 7:31 CWP then fit a gearbox oil pump and spray bar set to lube/cool the gears/CWP. The 81 engine should have nicasill cylinders, so a JE piston set, if the cylinders are OK that is , boat-tail the case, twin-plug the heads and flow the heads, std valves with the angels re cut to flow , DC60 cams from 'camgrinder' and springs to match, TI retainers if you like, std rockers re- faced and bushed, std rocker shafts, not re-furbed, dist from supertech with the advance to match the engine, carb's from PMO 46, manifold to match the heads, Richard at PMO will do a basic jet setup when you order the carbs, which is usually pretty close, exhaust is std back-box 2 in/1 out, std flywheel and clutch, unless the $$will go to something lighter, and then there is the gasket sets, nuts/bolts, bearings and bits you cannot see till the engine is in bits that require re-placing, as for the price, well, if you put the labor in then it is only the price of the parts/head/balancing jobs'which will save you $$ but not time , if you get the job into a tuners , well you will have to ask for a est' for the work, over hear it will be £10-12,000 ($19000)+ the engine, which you have, it will be a lot cheaper in the USA and a lot cheaper if you DIY.

regards mike