A couple SL-C questions from a new guy

Hey everyone. I will start off by introducing myself. I am currently a graduating senior at Cornell University, and will be finishing up here in the next couple months. Upon graduation, I will be moving back to boston to pursue an entrepreneurial venture that I have been working on for the past few years. Hopefully, in the next year, I will have saved enough money to pull the trigger on an SL-C (already about 2/3 of the way there).

So, the questions:

1) Do you guys think its worth it to go with the brembo brakes? It's a pricey add on, increasing the price of the roller by well over 10 percent. I just don't know too too much about Wilwoods, other than that I see them on a lot of tuner cars.

2) I have noticed in some of the pictures that the welds on the chassis (which are absolutely beautiful welds) are not continuous in some areas. In other words, the bead goes for about 6 inches, then there is a small gap, then the weld begins again, then a gap, etc. What is the reason for this? To save weight? To prevent warping? Can anyone explain? I've never seen it before.

3) I see ALL sorts of transmissions being talked about. People are saying that for high HP applications (500+), the ricardo should be used, but I was always under the impression that G50's can handle up to 600 easily. This is coming from years of research on the factory five gtm (which I was originally going to build until I saw the light). Can anyone shed some light on this?

4) I am planning on going with an ls3 crate engine. Seems like the best bang for the buck, as they can be found for about 5k brand new, and make 450 hp with some very simple mods. So, with around 450 hp, will I need a limited slip diff?

Thats it for now. I'm sure I'll think of some other questions. Thanks so much for everyones help! I look forward to many years of fun with this car.
 

Craig Gillingham

Banned because I can't follow the forum rules.
i can take 4)
depends on what your looking to do with the car?
As a street car for me I went with the LS376/480 which is 20horses short of a LS7 at maybe half price. Obviously not dry sumped but its a street car. If any driver can really tell this 5% shortfall on the street in a 1000kg car then please get his autograph.
LSD is not absolutely nessesary for the street (snake it baby-more to go wrong?) but it certainly will help to sell the car as the more buzz words the better in this area ;-) I went for it with G50/03
If you make a couple of these neglegible real word changes your well on the way to having the cash for a Nemesis - 2 for the price of one so to speak. Keep that minimal track spec for weight and with slicks / chassis set up....jobs a good un.

So your first decision street or track?

so which leads me to also taking 1)

The wilwood 6pots (were also on my radical but only 4 pot) are great brakes specd from the off by fran as the ample standard brake.
Its nice for people with an option to upgrade if the want...bit like LS3 to LS7
 
Ted,

Craig's insights are a good practical approach to arriving at your own specifications for the SL-C. Driving style and use of the car are the most important determinants. You don't need LSD for touring but you might want it for the track going into corners, etc. The same for those Brembos and the roll-cage offering. Craig at CarQuip can answer G50 questions better than anyone. But there are differences in G50s and he can provide good counselling. Do you need a Ricardo? Not necessarily, as some G50s can handle high HP/Torque IF set up correctly. Do you need LS-7 power? Again, not if you tour or even for occassional track. DP prototyles are limited to 500HP, 5-spd gearboxes and they don't use the LS-7 (too large of a displacement) and those cars "rock"! BTW, glad to see that you "saw the light" :drunk:
 
A continuous weld is often not necessary. If you think of a bolted or riveted part, the connection occurs at spaced intervals. The welding on the SL-C is done by experienced pro's using the latest machinery (one of the advantages of being in Detroit) and I suspect they would have cried foul if they thought the welds were insufficient.
 
Ted,
Any LSx is well suited to the SL-C, as is any SBC. I choose a modded LS1/930 LSD combination for mine. It will be a well done street car. I will be adding a few things such as gearbox oil cooler/engine oil coolet, etc. just because it's neat. Not really necessary, just as the Brembo brakes are not necessary. The 6 piston Wilwood's are
PLENTY!
 
Ted
The Porsche 930 is from a late (1987) Porsche 930 turbo. It was available with LSD.
There is an earlier version which has a bit shorter bell housing. They are 4 speed and the gear ratios are well suited to our big V-8's. You can still find them for under 5K.
Try CarQuip or California Motorsports (CMS). Very strong and will handle 500-700hp when easily prepared.
 
So why would someone go with the 930 over a g50? It seems the g50 is nearly as strong (capable of 600hp), and offers 5 or 6 speeds.

The 930 box has the output shafts even with the input. The G50 doesn't. So when you flip a G50 you end up having to sit the engine and tranny up a little higher, IIRC. I'm using a 930 box in my 917K project for this reason, plus the fact that the original gearbox in that car was a four speed. Oh, the 930 gearbox is even beefier as it can handle something like 750HP with very little modification.

Pretty sure everything you need is already available to get the gear ratios exactly like you want them in a 930 box, too.


--Donnie
 
I'm just concerned about the lack of overdrive in 4th. This will certainly not be my daily driver, but I do intend to drive it a lot. I will be driving it - not towing it - to car shows, and that can mean 3+ hour highway trips.

Can anyone comment on the 'feel' of the 930 vs the g50. I know that the linkages had more slop in older porsches than newer models. Does this haveanything to do with the actual gearbox? Or just the linkage. I like em tight.
 
I'm just concerned about the lack of overdrive in 4th. This will certainly not be my daily driver, but I do intend to drive it a lot. I will be driving it - not towing it - to car shows, and that can mean 3+ hour highway trips.

I'm sure you could make fourth and overdrive if you wanted. But that's less optimal, sure. Everything is a compromise, just depends on where you want it.

Can anyone comment on the 'feel' of the 930 vs the g50. I know that the linkages had more slop in older porsches than newer models. Does this haveanything to do with the actual gearbox? Or just the linkage.

I can't say for sure, but I'm guessing it's fine.

I like em tight.

Don't we all! *cough*


--Donnie
 
Hi,

Give Eric at CarQuip a call and he can discuss the nuances of Porsche transaxles with you. There is a myriad of choices. Rennsport has a nice overview of Porsche transaxles as well, including the various LSDs over the years.
 
Hi Donnie,

I think you are not fully correct with your statements on the 930 vs G50

check this picture. The left 3 boxes are 930´s the right one is a G50

930sw950.jpg


it is clearly to see that the output on the 930 are also offset to the input shaft ( which runs center in the bellhousing). I have not measured it but i assume that actually the offset should be quite the same on both gearboxes ( just because of the fact that the 911 turbo has not another engine position heightwise, although due to the lenght of the bellhousing it is moved 1" further to the rear).

Another fact is if you turn this boxes upside down the engine sits lower at the same outputshaft height. because than the output shafts are higher then the input shaft.

It is a different story for the 917, because here you are running a flat six which cannnot be positioned even lower. The advantage of the 930 here is the fact, that you can flip the ring gear to reverse rotation and therefore enabling you to put in the gearbox right side up, thus having also the correct engine positioning.

For a SLC the G50 would be my clear reco. Depending on the power a G50/50 if you shooting for more than 500 HP, or a standard ( may be strenghtened) G50 / 01 / 02 / 03 /04/ 05) will be sufficient.

Ted i have added a excel file with the ratios of most of the G50´s. CHeck for yourself. I´m using a modified one with a longer 1st and 2nd gear, giving much nicer RPM Drops for the track purpose, on a street application and a engine like a LS 7 there is no need for modifying the ratios.
If you like a overdrive ratio the G50/50 ( or the more available G50/52) would be the choice

Thanks
TOM
 

Attachments

  • GearSpeedCalculatorG50030405.xls
    93.5 KB · Views: 276
Ted, peruse this info..
Final Gear Ratio : 4.22
Tire Size : 335-30-18
Max Power RPM : 430
Limit RPM : 6000
*******************************
*********************
Gear Ratio Compound
*********************
1 2.250 9.495
2 1.300 5.486
3 0.890 3.756
4 0.630 2.659
***************************************
Gear MPH/1000 MPH @430 MPH @6000
***************************************
1 8.12 3 49
2 14.06 6 84
3 20.53 9 123
4 29.01 12 174
********************************************
MPH RPM (in Gears)
********************************************
1 2 3 4
********************************************
5 616 356 244 172
10 1231 711 487 345
15 1847 1067 731 517
20 2463 1423 974 690
25 3078 1779 1218 862
30 3694 2134 1461 1034
35 4310 2490 1705 1207
40 4925 2846 1948 1379
45 5541 3201 2192 1551
50 3557 2435 1724
55 3913 2679 1896
60 4269 2922 2069
65 4624 3166 2241
70 4980 3409 2413
75 5336 3653 2586
80 5691 3896 2758
85 6047 4140 2931
90 4383 3103
95 4627 3275
100 4871 3448
105 5114 3620
110 5358 3792
115 5601 3965
120 5845 4137
125 6088 4310
130 4482
135 4654
140 4827
145 4999
150 5171
155 5344
160 5516
165 5689
170 5861
175 6033
********************************************
Gear Change RPM drop (change @430) RPM drop (change @6000)
*************************************************************
1->2 -182 (To 248) -2533 (To 3467)
2->3 -136 (To 294) -1892 (To 4108)
3->4 -126 (To 304) -1753 (To 4247)
*************************************************************
 
Wow, thanks for all the help guys. I really appreciate it!

Well I think I'm going to be hung up on gearbox choice for a while. But not a problem; I have a while.
 
it is clearly to see that the output on the 930 are also offset to the input shaft ( which runs center in the bellhousing). I have not measured it but i assume that actually the offset should be quite the same on both gearboxes ( just because of the fact that the 911 turbo has not another engine position heightwise, although due to the lenght of the bellhousing it is moved 1" further to the rear).

Another fact is if you turn this boxes upside down the engine sits lower at the same outputshaft height. because than the output shafts are higher then the input shaft.

It is a different story for the 917, because here you are running a flat six which cannnot be positioned even lower. The advantage of the 930 here is the fact, that you can flip the ring gear to reverse rotation and therefore enabling you to put in the gearbox right side up, thus having also the correct engine positioning.

Ah yes, you are correct, sir. I was misremembering. It's Fran's fault...if he hadn't taken so long to get my 917 done I would have seen all this again. ;)

I knew it was something to do with the up/down positioning, but clearly forgot the line of thinking there. Makes sense, now. Yeah, from what you've said I'd go with a G50, too. And if I needed it to be a street car, I'd have to do the six speed.


--Donnie
 
Ted, if it matters I am building on a very fixed budget and therefore have to accomplish all of any extra fabrication myself. The SL-C deluxe package has almost everything you need to complete the build less some fasteners and a few odds and ends. With some mechanical understanding it will practically build itself.

I choose the 930 because I like it, didn't have 10K laying around for a gearbox and I got a really good buy on my freshly rebuilt 930LSD unit. I did the mods to run it inverted and decided to add an oil cooler & pump. Not necessary at all, I just wanted to do it. I found a low mileage LS1 from a 'Vette and rebuilt it with new oil pump timing chain, cam/pushrods/valve springs/ mild head porting. Dynoed at 430HP @ 6000RPM. I'll wind up with a really good performing combination of engine/gearbox for less than the cost of a freshened G50. Fit my budget very well.
I'm putting a lot of hours into many, many personal details. It makes a difference.
 
Thanks for the info Tom. And the calculator. Better than the one I use. My first choice was a G50/52, then I found a fresh 930 for very little $$$. That's all to my story. For the SL-C any LS3/G50 or LS7 with the Ricardo is the best choice IMO.
 
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