3.8 MFI slide valve build

[Turbo_pro]

It seems like Hastech Engineering was trying their best to imitate the early Porsche forged rockers and yet ended considerably heavier.
They look very nice and are readily available. When Henry runs out of his early rockers I'll think about using the Hastech rockers. I only have two engines turning those RPMs so I don't anticipate a need anytime soon.

[winders]

Early adjustable forged rockers with elephants feet installed weigh in at around 122 grams. That is with a smaller pad than the Hastech rockers at 125 grams. I fail to understand where the "considerably heavier" idea comes from....

[Turbo_pro]

You are correct, I didn't include the adjuster so the Porsche rockers are just slightly lighter.

[Neil Harvey]

Just to add a little info for those that may not.

You cannot successful regrind the pads on these rocker arms on a valve grinder attachment. There will be those that say they do and can but the geometry of the pad is not something that can be replicated on a Valve grinding attachment.

Common fault by doing it that way is, the adjuster swivel foot will stop lifting the valve and then slide across the Valve tip.

For those don't care, that way is good enough I guess, but for those that want it correct, ask who you have do this; do they have the geometry and does their tooling follow this geometry. Just because the pad looks good doesn't mean it will work correctly.

Add in poor cam profiles many copies of copies, then the wrong rocker geometry, you increase the hertz stresses and up goes the wear and down goes the possible performance.

Its all the little things that add up to more Torque.

[winders]

Originally Posted by David 23

I'm curious about the choice of Slide valve intake. Can you talk about the reasons and expectations for non-race application? Did Supertech do any work on the unit, Mittlemotor pieces seem to have had a lot of quality issues.

Most people that do slides these days do it to be period correct.

Slides are not what people pick today for racing unless rules require it. Slides just don't work as well as butterfly setups...partial throttle is not very good and they tend to stick after a while. Butterfly setups are much better except at maximum flow rate wide open. That's where slides have a big advantage. But, you can get roller barrel ITBs which don't have the same issues slides have. Or, you can get AT Power shaftless butterfly ITBs which have all the advantages of a butterfly setup with 98% of the flow characteristics at wide open of the slides and roller barrels.

F1 went away from slides and ended up with roller barrels or butterflies...depending on the team.

[MST0118]

Did Supertech do any work on the unit, Mittlemotor pieces seem to have had a lot of quality issues.

I had Supertec inspect the slides because the older version of Mittlemotor slides did have issues. However, the current version of slides incorporated the issues that Henry identified in a previous thread, so not much had to be done with mine.

Having said that, Mike found some minor issues when fitting them on the engine. For instance, the cross shaft was too narrow between the bearings so Mike pulled out the snap ring out 4.5mm to make it fit. He then machined a circlip groove to keep the cross shaft from moving.

Also, some of the ball sockets were tight to make it a stiff effort to move the slides, so he added grease which fixed that. That's just a maintenance item. So, just a few things like that. Now the slides work good and move easily.

Most people that do slides these days do it to be period correct.

Slides are not what people pick today for racing unless rules require it. Slides just don't work as well as butterfly setups...partial throttle is not very good and they tend to stick after a while. Butterfly setups are much better except at maximum flow rate wide open.

I think the sticking issue can be fixed with maintenance, but I agree with your observation of the superiority of TBs and barrels as compared to slides, especially as you point out F1 abandoned that technology.

But when looking at the older technology in the mid 70s, it seems there was a split of opinion as to whether the slides or HB set worked better. I have never driven a 73, 74, or 75 RSR so I don't have personal experience, but there must have been reasons why Porsche changed to slide valve from high butterfly for its RSRs during 1974 which continued through 75. The slides bumped HP at WOT from 315 to 330, but I'm not sure if this change impacted how the RSRs performed in the races overall comparatively during this time period. I did see some slide valve RSRs win races in Europe, but don't have enough data to see the impact of the change.

The late Steve Weiner thought the slides worked better than the old HB set up due to the lack of throttle linearity in the geometry of the HB. Here's what he said about it on a 911s registry post, which I thought was interesting because he thought slides were better on the street as compared to HB. Steve is probably in the minority. Of course, the new butterfly and barrel set ups are not comparable to the old technology.

[winders]

Originally Posted by MST0118

I think the sticking issue can be fixed with maintenance, but I agree with your observation of the superiority of TBs and barrels as compared to slides, especially as you point out F1 abandoned that technology.

But when looking at the older technology in the mid 70s, it seems there was a split of opinion as to whether the slides or HB set worked better. I have never driven a 73, 74, or 75 RSR so I don't have personal experience, but there must have been reasons why Porsche changed to slide valve from high butterfly for its RSRs during 1974 which continued through 75. The slides bumped HP at WOT from 315 to 330, but I'm not sure if this change impacted how the RSRs performed in the races overall comparatively during this time period. I did see some slide valve RSRs win races in Europe, but don't have enough data to see the impact of the change.

The late Steve Weiner thought the slides worked better than the old HB set up due to the lack of throttle linearity in the geometry of the HB. Here's what he said about it on a 911s registry post, which I thought was interesting because he thought slides were better on the street as compared to HB. Steve is probably in the minority. Of course, the new butterfly and barrel set ups are not comparable to the old technology.

Slides are sticky at partial throttle because the vacuum sucks on the slides at a 90 degree angle and that greatly increases the force required to move them. Factor in dirt and it gets worse. At partial throttle, the way the air flows around the slide as it opens is not exactly smooth nor is the shape ideal. Think about how the air comes in and then hits the slide surface straight on and then has find its way to the opening.

I have not done the research but I bet the reason the Factory went with slides is that the rules had a max intake diameter. Slides will always flow more air wide open than butterflies at a given diameter intake. They didn't have shaftless butterflies back then so the flow difference would be quite large at around 11%. That's a big difference!

I think the problem with the high butterfly setup is that the butterflies are just too far from the heads. It seems the best way to go these days is to get the injectors and butterflies as close to intake valves as possible.

[MST0118]

Well, engine on the way to dyno today. Mike put 50 PMOs from a 3.8 racing motor on first so we can get a baseline for something to shoot for. Then he’ll put on the MFI stuff and see what it does. I’m traveling next few days but will share results next week some time.

[David 23]

Originally Posted by winders

Most people that do slides these days do it to be period correct.

Slides are not what people pick today for racing unless rules require it. Slides just don't work as well as butterfly setups...partial throttle is not very good and they tend to stick after a while. Butterfly setups are much better except at maximum flow rate wide open. That's where slides have a big advantage. But, you can get roller barrel ITBs which don't have the same issues slides have. Or, you can get AT Power shaftless butterfly ITBs which have all the advantages of a butterfly setup with 98% of the flow characteristics at wide open of the slides and roller barrels.

F1 went away from slides and ended up with roller barrels or butterflies...depending on the team.

Thanks Scott, that is pretty much what I thought.

[MBruns]

[MST0118]

Thanks for uploading dyno sheet. I was very pleased with results. Mike did a great job building and tuning motor. The first pull with 50 PMO carbs yielded 395 hp at 7100 rpm but the motor gained 15 with MFI/slides and runs great. Thank you Mike Bruns for building this great motor!

Mark Jung also did a great job with injection pump. It’s perfect. I’m trying to upload the dyno video but need to make file smaller.

[jj911c2]

Congrats - those are great results - going to be a fun drive!


Sent from my iPad using Tapatalk

[stownsen914]

Wow, great result

[Tonger]

Wow - what a fantastic build! If the OP is willing to share, I’d like to hear and see more about the car this is going into - transaxle, suspension, etc. Was it hard to dial in the MFI on the dyno?

My engine builder is about to start putting together a similar large displacement 3.65L engine with high butterfly MFI built around a 4.0L RS crank and a 3.0L case - so I’ve been following your build with great interest.

[MST0118]

I have a 73 RS lightweight replica built on a 72 chassis (about 2,000 lbs).

For trans, I’ll be putting in a 77 mag 915 that was rebuilt by CMS that will hopefully handle the torque of the 3.8. Some of the upgrades include NPR mainshaft with taller first and then close ratio gears thereafter. 915 has NPR LSD, CMS retainer and billet side plate and wevo gate shift. 930 flanges/axles.

Maybe Mike can chime in on tuning since he did all the work. The pump worked out great and I know he tried various settings to come up with the right combo. As it turned out he richened up the pump a bit from the posted dyno sheet shown to lower the AFR to about 12.9 at peak power. I think he spent a good part of a day to get it dialed in, including running it on carbs first to get the baseline.

Also for suspension, I am using torsion bars - 33 rear / 23 front, bilstein front and back, tarrett sways bars. Will be using 930 brakes. Unfortunate with RS flares, I’m limited with width for rear tire options but will still be fun.

[winders]

Originally Posted by MST0118

For trans, I’ll be putting in a 77 mag 915 that was rebuilt by CMS that will hopefully handle the torque of the 3.8. Some of the upgrades include NPR mainshaft with taller first and then close ratio gears thereafter. 915 has NPR LSD, CMS retainer and billet side plate and wevo gate shift. 930 flanges/axles.

The magnesium 915 should work great assuming you don't do hard launches from a standstill. I used a magnesium 915 with Bill Rader bearing retaining plate and side cover. It had a Guard mainshaft with a useable 1st gear for racing. It also had a Guard 930 LSD and Guard and NPR gears. It would have had all NPR parts by now if I would have kept it. Anyway, my 3.6L race engine had ~430 HP and ~340 ft-lbs torque and my only issues were annual replacement of some synchros as racing caused me to sometimes shift quite a bit faster than is ideal with a 915. Using Swepco 210 I never had any R&P issues and gears lasted a long time.

I used 930 flanges and custom gun drilled 300M axles from Kartek. I suspect the Sway-A-Way aircraft alloy steel axles would work just fine but I didn't want to take any chances. I did not use the thicker 930 CV joints. I used the later 930 CV joints that 32mm thick outside race. With the more powerful engine, I discovered that the Redline CV2 grease wasn't really cutting it. I switched to Neo HPCC#1 grease and that seems to have increased the longevity back to what I was used to.

I used a Rennshift shifter (I still have it if you are interested). I actually bought a Wevo Gateshift kit for the 915 but my research caused me to sell it. Instead, I stiffened the centering springs on the Rennshift. Once I did that, I never again had any issues with shifting into the wrong gear by accident.

[JoeMag]

What was peak HP after you got the high RPM AFR in the 12.9 range?

[JoeMag]

I see data better in graphs so plotted this thing... Impressive! Even more so with CR being only 11-1 and this is engine dyno so none of the over-exaggerated engine to wheel losses.

[MBruns]

With the AFR at 12.9 it went to 407 and repeated that, 93 pump gas, 98 degree day and lot’s of humidity, it ran really well, I have got to hand it to Mark Jung at MFI Werks he has been amazing with his pump work , This has been a fun project
Mike Bruns

[MoreGAS]

Hi Mike
We typically find power falls of significantly at 14:1 and higher and can actually miss at about 14.5 and higher on NA high compression engines. Did you have a lambda sensor on both banks and what did you use for exhaust?
When you were able to adjust to(with what a main rack adjustment?) a richer 12.9 where was that at RPM wise , and what about the rest of the curve given that this is a Hotrod streeter and it was already very rich around 5K to 5400(we didn't see below) ? 13.79-14 at Peak Tqe (where cylinder pressure is the highest) is really lean and very likely to get in to knock . Can you post that "12.9" run as it should have picked up more Tqe and hP than the sheet shows under the same conditions. Perhaps that was a different day?
What brand of dyno?
Good work

Kevin
GAS Motorsport