EFI or 20/21 cams?

[911sc79]

Once exhaust has been replaced with SSI, what would be the next best improvement to a 79 SC? EFI or 20/21 cams?

[emcon5]

Displacement.

[dd74]

Originally posted by 911sc79
Once exhaust has been replaced with SSI, what would be the next best improvement to a 79 SC? EFI or 20/21 cams?

Anything more than SSIs (and a good dual-in-dual-out exhaust), may not be beneficial as far as cost goes. 20/21 is a nice upgrade, but very expensive as you might have to also do some valve and cylinder head work to comply with the higher lift of the 20/21s. Asking the same question as you, I've found that 20/21 cams, in most cases, is a poor upgrade unless you need to do other work on the engine - say, for example, a top-end job. There is some improvement with the upgrade, but for the money I've been quoted that this upgrade will cost, it's not worth it.

If by chance you need to split the case entirely, the consensus for more power suggests non-CIS pistons, more radical cams than 20/21s and a more direct injection system than CIS. This is where I would think about EFI.

Also, the displacement comment is a good one - a 3.2 short stroke with good cams and injection could easily see 250 hp. But by that point, unless you're emotionally attached to the 3.0, there's really no practical reason to not go up to a 3.6.

Meanwhile, more effective ways of modifying your motor is to not modify it and instead, modify what's around it. Put your car on a weight-training program, and think about slipping in a 7.31 ring and pinion in the transmission. As stands, with SSIs and exhaust, you probably have close to 200 hp. That 200 hp in a lightened SC with shorter gears will be quite rapid.

[rdane]

20/21 cams are good. Problem with all this stuff is you need to do a number of things to get just a little bit past what SSIs do.

Tom has it right, "displacement". 98mm P&Cs are the easiest and least expensive.

Or just buy my 7000 mile 3.4 with 98mm P&Cs with 20/21 cams that really rocks as is.

Or a 3.2 or a 3.6. Either can/might be more economical than rebuilding a 3.0 for more power but it really depends on how you do it.

[911sc79]

I am really surprised to read that 20/21 cams require valve and head work. I was sure that 20/21 were direct replacement for an SC. Thanks guys for straightening me out.

Do 964 cams require engine modifications as well?

From what I have read in the past 98mm P&Cs are very expensive and as my engine is in perfect shape, I would feel bad replacing my P&Cs. Just out of curiosity, how many HP chould I expect to gain with these 98 mm P&Cs. I guess I could gain approximately 7% (roughly 15 HP) form the larger displacement and an additional 10 HP going from my stock compression ratio of 8.5 to 9.5. So, is 20 - 25 HP realistic?

Going to a 7.31 ring and pinion could be an interesting option. I did a similar modification to a Corvette (forgive me I was young) some 20 years ago and was shocked by the improvement. This represent a 14 % increase in gearing. I guess a similar improvemnt could be gained by going to 14% higher ratios in 2nd through 5th gears. Am I right?

[rdane]

20/21 is a direct replacement as is the 964. Nothing else you have to do. You'll change the rev range and the torque curve. You won't add any HP.

To get the most out of either head and valve work will help. So will a light fly wheel. But you won't get much.

98s will get you a better torque curve and a bump in hp and torque. 210 should be about right at the wheels.

Lower gearing will always make the car quicker...and louder in the cabin.

[MichiganMat]

Aren't guys seeing a HP increase from CIS to EFI? I mean, theres a nice HP jump with carbs over CIS, I have to assume theres a similar increase with EFI. Am I wrong? I seem to remember an old thread on this...

The throttle response improvement of the EFI will feel like a +10HP over the CIS lag anyways!

[dd74]

Originally posted by MichiganMat
Aren't guys seeing a HP increase from CIS to EFI? I mean, theres a nice HP jump with carbs over CIS, I have to assume theres a similar increase with EFI. Am I wrong? I seem to remember an old thread on this...

The throttle response improvement of the EFI will feel like a +10HP over the CIS lag anyways!

10 hp for $3-5K, not including dyno time to tune the EFI...

Carbs would be a better cost investment, but still only 10 hp for a PMO setup that costs $3K, or old Webers for $1.1K

And, um, what "lag" are you referring to? Keep your CIS engine above 4,000, then trounce the accelerator. There's no lag...

[dd74]

Oh, and one more thing concerning the 20/21s: I've seen a dyno sheet somewhere on this forum comparing two SC motors that had identical exhaust manifolds and mufflers, but one had 20/21 cams. Know what the power difference was between the two? Five horses.

In short, there are more prudent ways of spending that kind of scratch on these cars...

[911nut]

Originally posted by dd74
10 hp for $3-5K, not including dyno time to tune the EFI...

dd, I assume that you are not referring to the Bitz Racing EFI which cost $1600 and can be tuned with a laptop?
People using this setup are claiming a 20 HP bump due to better breathing.

[rdane]

Originally posted by 911nut
People using this setup are claiming a 20 HP bump due to better breathing.

Nice claims but I doubt it. No one has done a direct dyno comparison and posted it either. Claims are impressive. Facts say different.

Like DD said 5hp. is more like it. Cams even less on a CIS car.

Lots of conjecture here. I actually did all of this and more to a 3.0 CIS engine so it isn't just speculation on my part. I also made direct dyno to dyno comparisons on the same day to 4 or 5 other SCs while I was at it.

[Craig 930 RS]

BTW, know what's funny?
No one has ever done a back-to-back dyno comparison of before SSIs to after ---

[rdane]

Originally posted by Craig911
BTW, know what's funny?
No one has ever done a back-to-back dyno comparison of before SSIs to after ---

Been done a few times Craig just never same day that I have seen. Mark Wilson did it same dyno while he was here just not same day.

[911sc79]

Even tough they took place on different days, what was the HP difference between the with and w/o SSI dyno runs?

[RSupdate]

well....just to jump into the mix here....

Rdane is pretty much of my same thinking here. I think 911sc79 ya really have to figure out your overall goal as what appears as a one shot deal. Any mods to a 911 engine really have to be approached in a "systems" type of thinking, as in changing one thing affects a couple other compenents load req'mts as well.

Problem is that you have so many choices.... Speaking as someone with a moderately modded 3.2L/915 and the $$$ it's cost me to get there, the most simple thing in retrospect is to just get a 964 3.6L ......before you put it in...put it a set of John D's "super cup" cams (you've already got the heads off so they're at the machinist getting freshened up..) and you'll be a lot closer to 300 reliable H.P. and never look back in regret.

I know, it's easy to spend other peoples money .....

good luck !!!

Originally posted by 911sc79
Even tough they took place on different days, what was the HP difference between the with and w/o SSI dyno runs?

10 HP addition with SSI's.

[Craig 930 RS]

I'd love to actually *see* the results from one of those tests...by anyone. Where are they?

I've never seen a concise, published report that substantiates the SSI legend.

I don't doubt it.......I just want to see a reliable result on paper -

[Craig 930 RS]

Posts came in at the same time - thanks, Mark.
What before & after muffler/do you still have the charts to show -

Before was a Flowmaster 1 in 2 out. After was 74 Carrera 2 in 1 out. I prolly have the sheets somewhere, but with big ass cast on my leg, I can't go seach right now.

Carb Connection has the data under my name if you want to run by and get he printouts.