Engine Build 3.2 -> 3.4 - What do you think?

[Steve W]

From what little I know, I think cam finish and accuracy is more important with regards to wear than anything else. Not naming any names, but some cams have too rough of a finish, aren't ground level so they may only make contact on half of the cam lobe, and/or are hardened too hard, causing all kinds of strange wear within 200 miles of installation. Oil with a good amount of zddp is important, and you should have the rockers refurbished and drcamshafts should be able to do that for you reasonably.

[tmaull]

No twin plug on this motor... running the Max Moritz pistons. Jon, what are you doing for valve springs? This is where I'm hung up right now.

[scarceller]

I've had a stock AFM flow benched and after about 13,000 g/min of flow we have a 10 inches of water column pressure difference and if you flow any more than this 13,000 g/min start to produce intake vacuum at WOT. A 3.4L ingests about that flow rate at sea level at 20C ambient. I have the actual flow data showing this. I think that a real hot 3.5L at 7200 RPMs could easily be at 15,000 g/min and at that level of flow the pressure drop becomes far more significant around 15 inches of water. 1 inch of water is about 0.032 psi so at 15" we have 0.5 PSI of vacuum. Doesn't sound like much but add a few more PSI for the Throttle body and the intake box and it starts to add up.

I agree that the AFM alone is not the source of a big restriction until you start approaching 15,000g/min. But you need to consider all the components and the biggest restriction in the 3.2L intake is the Throttle Body, spend some money opening it up as much as possible.

But don't disregard the other advantages of MAF, totally correct fueling across extreme altitude changes like sea level to 10,000' and throttle response but the system MUST process the MAF signal correctly. You can NOT make a MAF pretend to be a AFM that's a compromise. You need to re-write the code to process a MAF signal natively.

The reason I decided to do MAF is that many AFMs are 30 years old and out of spec or they have been messed with so they no longer accurately measure air flow. The MAFs I use are all calibrated to NIST standards and registered with NIST. They don't vary by more than 1% between MAFs. So I have a 99% correct air model, then I decided to do the same for the fuel model by going with brand new fuel injectors. If you just spent $20-30K on a engine build why would you not want to have a 99% accurate Air/Fuel model? Considering the costs of these motors why not take the time to properly address the fuel/air model?

I'm not saying you can't tune AFM, you certainly can and we have good resources for doing so on this board but it's hard to tune a AFM car across the entire operating conditions, not just WOT. But if you have the Air and Fuel properly measured and metered then the math simply works like magic. In my MAF I command a Lambda (AFR) value and that's what I see at the exhaust it's very easy to work in this mode quickly.

If you want to really understand this fascinating area I suggest you purchase both books written by Greg Banish they are a wealth of information into properly tuning engines. I'm not sure why so many tuners are so secretive? Once you learn how it's done and why you quickly realize that a lot of work goes into tuning and it's not really for the DYIer. How many megasquirt installs have you seen that actually work correctly? Just go to the track and watch folks tinkering with after market EFI because it's not working correctly.

[Steve W]

The motor above has just finished being reconfigured with a bit higher compression, and going twin plug. The pistons are also changed, as you need a different dome profile for a twin plug head, wedge dome is for single plug. You get a slight efficiency increase when increasing compression ratio (search otto cycle and analysis), and twin plugging allows you to run the reduced ignition timing necessary for the higher compression ratio when running 91 octane pump gas. The reduced ignition provides also a slight engine efficiency increase due to reduced work the engine needs to perform when pumping the piston up during the the onset of combustion after the initial spark. I don't expect much but every little adds up.

[Steve W]

Been there, done that. Just providing the final results vs theories.

Think about what Porsche did with the GT3 RSR when given an FIA restriction of two 28.6mm restictors to their intake. The engines still produce 500 hp because of the large long bell mouth velocity stacks leading to the restrictors.

[gliding_serpent]

His pistons are for single plug only.

[tmaull]

Yes, pistons are single plug only. I may go back and do the throttle body at some point, but not now. Also planning staying AFM. This is not a cost no object race motor, it's just a rebuild because I popped a head stud, and got a bit of "while I'm in there syndrome." But what I'm really trying to decide is whether I need to upgrade my valve springs. It is starting to seem like a bit overkill for a street motor. Thoughts? I've tried searching this topic, but not able to come up with much.

[Mehoff]

Originally Posted by tmaull

Yes, pistons are single plug only. I may go back and do the throttle body at some point, but not now. Also planning staying AFM. This is not a cost no object race motor, it's just a rebuild because I popped a head stud, and got a bit of "while I'm in there syndrome." But what I'm really trying to decide is whether I need to upgrade my valve springs. It is starting to seem like a bit overkill for a street motor. Thoughts? I've tried searching this topic, but not able to come up with much.

You zing that motor once you'll have wished you'd spent the extra $800 on ti valve springs and retainers. It's really, really, really cheap insurance.

[Jcslocum]

Originally Posted by tmaull

No twin plug on this motor... running the Max Moritz pistons. Jon, what are you doing for valve springs? This is where I'm hung up right now.

Sorry for making an error in my earlier post, She's using JE pistons for twin plugging, not the wedge design. The heads were done right for the cams, but I do not know what the springs are, Sorry for that. I "think" EBS did the heads, I know they did the cylinders and pistons. I can dig into the paperwork and see what she has.

Additional Info on Heads:

Carrera TWIN PLUG heads - heads done by Ollies, intake ports blended, exhausts polished.

No info on the springs.

[Josh D]

Originally Posted by tmaull

But what I'm really trying to decide is whether I need to upgrade my valve springs. It is starting to seem like a bit overkill for a street motor. Thoughts? I've tried searching this topic, but not able to come up with much.

John Dougherty recommends a valve spring upgrade with profiles that have higher valve lift than the 964 cam. His DC19 cam is the same profile as the Web 20/21 and he recommends "street performance valve springs" in the notes guide. I've read some of his posts on Pelican (he goes by camgrinder) and I recall he's reasoning as valvetrain stability. Sorry, but it's the only data point I have.

Dougherty Racing Cams

[scarceller]

I helped on the tune of this motor with DC 21 cams and twin plugs very snappy engine with tons of low end torque.
1985 3.4 build using MAF 279.56 HP, 237.63 RWHP
The overall torque in this twin plug was real strong. This motor will likely go to more aggressive DC cams this Winter. We are surprised how well the EFI system I did for this car can tolerate aggressive cams. Idles perfectly at 920RPMs.

[gtc]

Originally Posted by Mehoff

You zing that motor once you'll have wished you'd spent the extra $800 on ti valve springs and retainers. It's really, really, really cheap insurance.

And if he buys the $100 eibach springs posted earlier, and some Aasco retainers for $225, it's REALLY cheap insurance.

[tmaull]

OK, so I went with the Supertec springs and retainers from Henry.

That leaves me with:
Pistons: 98mm Mahle 9.8 compression, Max Moritz style
Cylinders: 95mm KS, to be sent out to EBS for bore out to 98mm
Cam: Web 20/21
Rod bolts: ARP M9
Crank: 930 Std/Std (When we opened it up, that's what was in there)
Case: 930 (When we opened it up, that's what was in there - identical to Carrera case though)
Head Studs: New steel
Heat Exchangers: Stock Carrera
Muffler: Stock Carrera
Intake: Stock Carrera
Valve springs and retainers: Supertec

Anything else I've missed that I should do while it's out and in pieces? I think I've got most of the low hanging fruit covered now.
-Tom

[scarceller]

If you can fit it in the budget, port and flow the heads. Not cheap but if done properly can have dramatic effects.

[panzerfaust]

Originally Posted by Steve W

The motor above has just finished being reconfigured with a bit higher compression, and going twin plug. The pistons are also changed, as you need a different dome profile for a twin plug head, wedge dome is for single plug. You get a slight efficiency increase when increasing compression ratio (search otto cycle and analysis), and twin plugging allows you to run the reduced ignition timing necessary for the higher compression ratio when running 91 octane pump gas. The reduced ignition provides also a slight engine efficiency increase due to reduced work the engine needs to perform when pumping the piston up during the the onset of combustion after the initial spark. I don't expect much but every little adds up.

im looking into re-boring my cylinders to accept 98mm pistons for a twin plug 3.2 "while you are in there". i thought about MM or JE (not capable expansion rate?)but what type of flat top pistons are available with street CR?

regards
pf

[CCM911]

I was just visiting with some PCA folks this past Saturday. They are building a 3.4 as well, and believe it or not, they are using Chevrolet pistons! How odd is that?

[fred cook]

About 2-3 years ago, I built a 3.3SS from a 3.0 SC engine for my 1980 SC coupe. The only thing that I did different (basically) is that I used 10.5:1 Mahle pistons and Electromotive XDi twin plug ignition. I kept the CIS intake but changed it to the early box with the large bore runners and used Carrera heads. I think that you will be pleased with the way your engine runs and pulls up to redline. You probably should have the Carrera rods rebuilt, balanced and shot peened to help minimize any stress riser points.

[tmaull]

Well I'm picking it up from Bruce on Thursday. Got a chance to drive it last week and I love it. Can't wait to put Sal's MAF system in it, and tune it.