Timely 2.8 rebuild forces use of 2.4cis in 914/6 :(

FransE36 · 05-12-2009, 05:43 PM

Kind of silly, but I threw a rod bearing in the 2.8l (nasty) motor in my 916/6 (real). I have a 2.4 cis motor, fresh and ready to go, however, the injection system (cis boot) would require trimming of the body (NO!

), so I am wondering if Carburetors would be able to be tuned for this cis engine? I have a set of 40s that were on the 2.8. Any help would be appreciated...

2.8l

2.4cis with big injection system

I really do not want to trim or "modify" ANYTHING on this car, or either engine..

kenikh · 05-13-2009, 07:18 AM

no issues with using carbs

kenikh · 05-13-2009, 08:22 AM

To be clear, the intakes shots are from the 2.8, not the 2.4.

A 2.8L with big ports will run fine on 40mm Webers as long as you don't want to rev it over 6500 RPM, but would benefit most from 46mm PMOs with big manifolds. It sounds like has the proper induction for the 2.8 for after the rebuild is complete.

On the 2.4, you can just bolt up the appropriate manifolds (actually, anything 32mm-36mm will work fine) to mate the 40mm Webers up. Then you are just a rejet away from the motor purring away.

E Sully · E Sully's Garage

I've read that the 2.4 CIS cam does not work well with carbs.

kenikh · 05-13-2009, 04:22 PM

Quote:

Originally Posted by E Sully

I've read that the 2.4 CIS cam does not work well with carbs.

Very counterintuitive. Mild, low overlap = no reversion, which typically wreaks havoc with carbs at low revs. Lots of folks running carbs on CIS cams on larger motors, not sure why the 2.4 would be problematic.

FransE36 · 06:29 PM

The top is the 2.8, that's why I have 2.8l above it and 2.4 above the 2.4.

I have come to realize that I will never be as happy with that car unless the 2.8l engine is back in it, or something better (nothing IMHO).
I am going to tear them both down and take the crank out of the 2.4 (70.4mm) and rebuild the 2.8 with that. I guess the 2.4 would have been cool for the street, but the 2.8 IS cool anywhere. Funny that you say the engine would not run well over 6500 rpm, because that engine made 280 at the wheels at 7200rpm..

I would be interested in getting bigger carbs for a dyno tune though. Thank you two gents for your insight/opinions. I will return here if I need further assistance.

kenikh · 05-14-2009, 06:21 AM

Quote:

Originally Posted by FransE36

Funny that you say the engine would not run well over 6500 rpm, because that engine made 280 at the wheels at 7200rpm..

I would be interested in getting bigger carbs for a dyno tune though. Thank you two gents for your insight/opinions. I will return here if I need further assistance.

Interesting. Every 2.8 I have seen on 40mm carbs just seem to choke up at that point.

FransE36 · 04:43 PM

The 2.8 really pulls hard in the top end, and has been around 8500 before.
I have a 7200 cutout rotor in it to prevent over-revving and it is easy to blip the limiter in this car with the top end power it produces. The 2.8 is all the way apart and we are going to get it back together soon, so I will post up when it is back up and running.

Retro · 05-14-2009, 10:21 AM

How can you get 330 hp, 280 rwp from a 2.8??

FransE36 · 04:43 PM

330hp? Where do you get this number? Are you assuming that the transaxle sucks 60hp?
I would guess that the HP at the flywheel is somewhere around the 300 HP ballpark. Maybe less.

Originally a 2.7, got a set of slipper skirt pistons that boost the displacement to 2.8, ESSSSSSSSSS cams, headwork, compression, headers, and presto! There is more that can be done too, but I think 280 is all I need.

kenikh · 05-14-2009, 10:44 AM

Quote:

Originally Posted by FransE36

330hp? Where do you get this number? Are you assuming that the transaxle sucks 60hp?
I would guess that the HP at the flywheel is somewhere around the 300 HP ballpark. Maybe less.

Originally a 2.7, got a set of slipper skirt pistons that boost the displacement to 2.8, sc cams, headwork, compression, headers, and presto! There is more that can be done too, but I think 280 is all I need.

I am not trying to be hostile in saying this, but the pieces don't add up.

The specs of those SC cams don't support 280 HP from a 2.8L. SC cams are not 100HP/L cams, although I can now see why it revs to 7000 RPM while making power. You'd need at least GE60s to get close, with GE80s or even 100s more likely candidates for those targets. SCs just don't lift and scavenge enough to make that kind of power. Add nitrous and you'll have something.

No doubt the motor is very fun and torquey as hell, but it would take a VERY optimistic dyno to get anywhere near those numbers.

Retro · 05-14-2009, 11:14 AM

I got the 330 HP, from your statement of 280 at the wheels. Everyone accepts that you loose 15% from fly wheel to whhels. So 330 minus 15% = 280 that you stated.

FransE36 · 05-15-2009, 11:16 AM

Retro: That is a great theory. If it is fact, that is really awesome.

Ken:
I called my dad, who built the motor in 1987, and he said the cams are S cams not SC, so my bad. I also asked him about the dyno runs in 1987 and he said the car put down runs between 260hp and 280hp, because of chassis dyno wheel hop, and the power was made @ 5500 rpm not 7200 rpm. My bad, I am still learning Porsche-ism from my former VW type 1 habit. The bugs are still in my blood. Haha.
I am going to be getting into taking high speed turns in a porsche, but I am coming from this:
http://vids.myspace.com/index.cfm?fuseaction=vids.individual&videoid=3785466

kenikh · 05-15-2009, 12:50 PM

You aren't unique. Try to find the thread on Porsche guys that cam from VW - you are a majoirty member it seems.

I still have my '71 Type 3 with full Berg motor and Berg 5 speed tranny as evidence.

FransE36 · 05-17-2009, 04:41 PM

OOOH, that trans is the beez kneez man. I ended up making my own 5 speed by mating up an old 914 trans with the 912 shifter on the end and it is pretty golden, but your berg sounds cool. I still got two bugs, one of which was posted in the above vid link, and the other is a litttle autocross/canyon killer. 140hp, 1500lb car with all drivetrain done, and the body left poo poo. The bug is white with black BBS style mesh black wheels and I am sure there are some angeles, mulholland, and GMR people on here who have seen me on their ass/or passing them in it. Hahha.
Update: I took apart the 2.8 and the #5 rod bearing is @#$%'d so I am just going to see if our crank guy can fix it , as I do not want to take apart a perfectly good 2.4 to rob it of the crank. Cam carriers and heads are all cleaned and the rest is being worked on, so I will keep this thread posted if it stays afloat. CHEERS ken!