2.8 Race Motor Questions/ Port size etc.

[jmz]

So, I've got an older 2.8 RSR type build that has been mothballed for years. ...part of a project I puchased years ago.

I've decided to have it torn down and reassembled as a back up race motor for my 914/6.

The motor shows to be approx 11.5:1 or more... It has 42mm intake ports and close to 39 or maybe 40mm D shaped exhaust ports.

I'm not sure about valve sizes yet.

So, should I simply reassemble the motor as is or are these ports too much for a 2.8?

I'm thinking a 2.8 with that CR and big ports like that is an engine that is on the edge...

Thoughts?

[prschmn]

At that comp ratio I sure hope it's twin plugged-piston crown shrouding is bound to be an issue
if not-detonation city. And yeah pretty damn big intake ports too. And maybe way oversized ehaust ports too.

[blue911rsr]

What's your bore and stroke I had a 2.8 with 92 bore and 70.4 stroke with stock valves and similar port size actually bigger intake then yours with ge 80 cams and twin plug made for very nice engine between 5 to 8 k rpms

[jmz]

Originally Posted by prschmn

At that comp ratio I sure hope it's twin plugged-piston crown shrouding is bound to be an issue
if not-detonation city. And yeah pretty damn big intake ports too. And maybe way oversized ehaust ports too.

...OK, yes twin plugged of course. In fact has uber rare Marelli RSR twin plug distributor. Someone did lots of work on ports with the D shaped exhaust ports.

[jmz]

Originally Posted by blue911rsr

What's your bore and stroke I had a 2.8 with 92 bore and 70.4 stroke with stock valves and similar port size actually bigger intake then yours with ge 80 cams and twin plug made for very nice engine between 5 to 8 k rpms

Thanks for that datapoint.


It is the same bore/stroke as yours. 92x70.4 bore and stroke... Built in a 7R mag case so I'm slightly concerned about the high RPM issues associated etc. It has 2.8 RSR pistons/cylinders and base gaskets to lower C.R. Otherwise it would be north of 12:1

I don't know what cams are in it yet.

I would like to do a simple tear down and reassmeble but also don't want to build a motor that is at risk of coming apart.

I wanted to do a simple tear down and reassemble to use as backup while the engine that is in now gets a tear down, inspection and reassemble.

[faapgar]

The D-shape exhaust ports work well.Ports are not too big.For another 20 ft.lbs.of torque from 4-5,000 rpm take down the center of the piston crown a few mm,s the width of the exhaust valve.You drop your C.R. a little but it will rev quicker to redline and increase mid range torque.The less the air climbs the mountain peak of the crown the quicker it flows through the exhaust valve.Fred

[jmz]

Originally Posted by faapgar

The D-shape exhaust ports work well.Ports are not too big.For another 20 ft.lbs.of torque from 4-5,000 rpm take down the center of the piston crown a few mm,s the width of the exhaust valve.You drop your C.R. a little but it will rev quicker to redline and increase mid range torque.The less the air climbs the mountain peak of the crown the quicker it flows through the exhaust valve.Fred

Somone also spent a lot of time making the pistons light... Not sure if there is enough meat to take down the crowns.

[Walt Fricke]

The real 2.8 RSR had 43/43 ports, and its peak HP was at 8,000 RPM, which means you'd rev it at least 500 RPM higher before shifting. But it had the 49/41.5 valves, which you can't do without the real RSR heads or some custom head.

I've got one of these non-RSR 2.8s. I've been wondering what I can do to get slightly larger valves, especially intake, in there. That has to be part of the magic in those factory engines (titanium rods can't hurt either), and part of the high max hp RPM.

The idea of a trade off of CR vs fuel/air flow is interesting. At 10.5 you can run pump gas, and that is all Porsche said the RSR had.

Is the header flange altered to match the D port shape?

If it has J&E pistons from back when I'd be concerned.

Porsche used the mag case on these, so my take there would be (assuming it is time certed) keep it, while maybe scoring a sand cast case as a back up against the day when the mag gives out. Doubtless you have seen the shop guys here saying that when you take one of these apart you most likely need to do the parting line shaving and line boring, plus spigot decking etc. Measuring would tell if that was needed.

[jmz]

Originally Posted by Walt Fricke

The real 2.8 RSR had 43/43 ports, and its peak HP was at 8,000 RPM, which means you'd rev it at least 500 RPM higher before shifting. But it had the 49/41.5 valves, which you can't do without the real RSR heads or some custom head.

I've got one of these non-RSR 2.8s. I've been wondering what I can do to get slightly larger valves, especially intake, in there. That has to be part of the magic in those factory engines (titanium rods can't hurt either), and part of the high max hp RPM.

The idea of a trade off of CR vs fuel/air flow is interesting. At 10.5 you can run pump gas, and that is all Porsche said the RSR had.

Is the header flange altered to match the D port shape?

If it has J&E pistons from back when I'd be concerned.

Porsche used the mag case on these, so my take there would be (assuming it is time certed) keep it, while maybe scoring a sand cast case as a back up against the day when the mag gives out. Doubtless you have seen the shop guys here saying that when you take one of these apart you most likely need to do the parting line shaving and line boring, plus spigot decking etc. Measuring would tell if that was needed.

Hi Walt,

This one has Mahle pistons and cylinders. The only issue found so far on this tear down is that one of the cylinders is a little out of round. ...trying to determine if we send them all in or just fix the one that is obviously a problem. I think the rest were in spec sizewise etc. but just in spec... That said I think that race motors were built loose anyway. Correct me if I'm wrong???

I don't have headers for it now when I got it the engine had a set of SSis bolted to it and they were not port matched...

I want to rebuild this one install it and pull out the sandcast case, short stroke, long rod Ferguson motor that we chatted about.

Jay

[Walt Fricke]

Ferguson motor - aha, that's why your name rang a bell. But that can't be a SS 2.8 - you can't fit the 95mm jugs into a sand cast case. You can into the early 3.0/Turbo which will take the 66mm crank. Short strokes weren't the hot ticket when the Ferguson motor was built in the '80s. But long rods were in the mix. Dave bought it in the early '90s, and I don't think he did anything special with it, as it was a good motor all along. I remember the timing because I bought his Grady Clay/Bob Benight 2.5 when he got the 2.8, and he had to modify some sheet metal to get the long rod motor to fit his 914. Of course, he may have done more later when he moved to California.

I'm not the guy to ask about what amount of ovality is OK for a race motor. Shops vary from one which was known to believe that somewhat out of spec parts were the thing to use, because cheaper and besides it is a race motor and will come apart soon, to others which are meticulous as all get out. Or Grady, who would use close piston/head/valve clearances because he would take his motors apart a lot just to see if a little wear was creeping up on this to catch interference before it happened.

[jmz]

OK, got it. I just assumed it was a short stroke 2.8 that was in the Ferguson car.

If you ever happen accross the case that came out of Ferguson's old 914 let me know. I know a guy that would like to have it.

Originally Posted by Walt Fricke

Ferguson motor - aha, that's why your name rang a bell. But that can't be a SS 2.8 - you can't fit the 95mm jugs into a sand cast case. You can into the early 3.0/Turbo which will take the 66mm crank. Short strokes weren't the hot ticket when the Ferguson motor was built in the '80s. But long rods were in the mix. Dave bought it in the early '90s, and I don't think he did anything special with it, as it was a good motor all along. I remember the timing because I bought his Grady Clay/Bob Benight 2.5 when he got the 2.8, and he had to modify some sheet metal to get the long rod motor to fit his 914. Of course, he may have done more later when he moved to California.

I'm not the guy to ask about what amount of ovality is OK for a race motor. Shops vary from one which was known to believe that somewhat out of spec parts were the thing to use, because cheaper and besides it is a race motor and will come apart soon, to others which are meticulous as all get out. Or Grady, who would use close piston/head/valve clearances because he would take his motors apart a lot just to see if a little wear was creeping up on this to catch interference before it happened.

[Walt Fricke]

You mean the Clay/Benight race motor case? Dave's green 914 was first made into a race car by Bob Benight, and Grady built the motor, which I ended up with. I have the ps and Cs (EMPI 88s), the twin plug heads, the 6 bolt cam carriers, the 6 bolt finned exhaust valve covers (bored for twin plug), the oil pump, and maybe some other bits. And the sand cast case, but it needs to go to a place like Ollies to have a major prosthetic repair to the slot extending up from one of the spigots to the case parting line or the sort.

But no 914-6 ever came with a sand cast case, did it? Back when, the T motors for 914-6s were not in any demand. And they were mag. But who knows, maybe it is still around if a guy knew the engine SN.

[jmz]

Originally Posted by Walt Fricke

You mean the Clay/Benight race motor case? Dave's green 914 was first made into a race car by Bob Benight, and Grady built the motor, which I ended up with. I have the ps and Cs (EMPI 88s), the twin plug heads, the 6 bolt cam carriers, the 6 bolt finned exhaust valve covers (bored for twin plug), the oil pump, and maybe some other bits. And the sand cast case, but it needs to go to a place like Ollies to have a major prosthetic repair to the slot extending up from one of the spigots to the case parting line or the sort.

But no 914-6 ever came with a sand cast case, did it? Back when, the T motors for 914-6s were not in any demand. And they were mag. But who knows, maybe it is still around if a guy knew the engine SN.

I have the serial number of the original 914/6 engine. That number is 6405179. That is really what I'm looking for... I wish I could pick up the phone and call Grady. He was always a great guy to chat with either phone or web boards and who knows... He may have either had the case or known the whereabouts.

If I ever get serious about vintage racing (doubtful) I will have to build up a spare 2.5 engine so some of your parts could possibly come in handy...

[jmz]

Originally Posted by faapgar

The D-shape exhaust ports work well.Ports are not too big.For another 20 ft.lbs.of torque from 4-5,000 rpm take down the center of the piston crown a few mm,s the width of the exhaust valve.You drop your C.R. a little but it will rev quicker to redline and increase mid range torque.The less the air climbs the mountain peak of the crown the quicker it flows through the exhaust valve.Fred

Relating to the D Ports; Walt brought up the quesion of port matching the headers with the D shape exhaust port. Is this a thing? Thanks!

[Mr9146]

Just rebuild it the way it was built before.

I think you'll be surprised at the results.

[jmz]

Originally Posted by Mr9146

Just rebuild it the way it was built before.

I think you'll be surprised at the results.

That's generally the plan I'm just going to make sure piston/cylinders are relatively within spec. I might send the pistons over to Poly Dyn and get them coated ...and of course I won't be using the SSis since it's going on my 914/6

It would be nice to be able to run on pump gas but I'm not going to sweat it and just run race fuel.

[jmz]

I'm bringing this one back to the top. I'm now thinking of possibly using this engine that we've been discussing in a street car of mine

If we swapped the crank to a 66mm crank and rods do you think the compression ratio would drop to something suitable for pump gas? I've read that C.R. drops 1 - 1.5 points by changing from the 70.4 to 66mm crank when doing these builds. Would the bad harmonics that I read about with the 2.8 Long Stroke engine go away?

[lvporschepilot]

Originally Posted by jmz

I'm bringing this one back to the top. I'm now thinking of possibly using this engine that we've been discussing in a street car of mine

If we swapped the crank to a 66mm crank and rods do you think the compression ratio would drop to something suitable for pump gas? I've read that C.R. drops 1 - 1.5 points by changing from the 70.4 to 66mm crank when doing these builds. Would the bad harmonics that I read about with the 2.8 Long Stroke engine go away?

Using the same pistons but shorter stroke crank will ruin not only severely lower static compression but also the squish factor which one typically wants, in these motors, to be around .040 just under the cylinder deck.

If you do use the 70.4mm crank, I can attest to these being outstanding motors. I just completed and am now running my second one of these after the first one turned out so nice. 39mm/38mm ports, Carrillo rods, twin plug (using COPs), 10.5:1 cpr, DC65 cam, upgraded valve train etc. The first one I did with MFI was great so I made one with full sequential EFI and ITB for myself. Just a fantastic flexible engine that revs like the dickens. With these cams I suspect somewhere around 270-280bhp (flywheel) is had with good drivable torque. Lighter the car the better obviously.

DC80/GE80 cams can even be used in these (MFI or EFI and twin plug with higher cpr only, no carbs! not enough vacuum) and one can still get away with it on the street and be ok, they're not like the old Ferrari P6 cam or even RSR cams which are literally an off/on switch. Still, I wouldn't recommend any bigger than Dc60-65 on the street as it's rare one is revving high enough to take advantage.

[targa72e]

pistons for 66mm and 70.4mm cranks have the pin in the same location. Rod length is different, squish doesn't change as piston is in same location. Lower compression is due to shorter stroke only. Usually swapped the other way to get higher compression ie 2.2S pistons in 2.4 engine. 66MM crank would not have harmonic issue and compression would be lower for pump gas.

john

[BURN-BROS]

I'm not a fan of the factory 2.8 pistons. They are very heavy. something like 650 grams with pin and rings...care to measure them and post?

I limit the 2.4/2.7 cranks @ 7000 rpm now and build around that redline. There are guys breaking cranks on smaller motors with redlines of 7500. So be mindful.

If you de-stroke, You will drop your compression .5 along with a little more deck may get you where you need to be. You will also be out of the harmonic issues as well.

Originally Posted by jmz

I'm bringing this one back to the top. I'm now thinking of possibly using this engine that we've been discussing in a street car of mine

If we swapped the crank to a 66mm crank and rods do you think the compression ratio would drop to something suitable for pump gas? I've read that C.R. drops 1 - 1.5 points by changing from the 70.4 to 66mm crank when doing these builds. Would the bad harmonics that I read about with the 2.8 Long Stroke engine go away?