Going from 3.2 to 3.4, some questions. - Page 2

911st · 11-15-2009, 06:56 PM

Stole the following well tuned 3.2 stock block dyno chart from 911Chips.com for referance of what can be done:

"The following is from a custom built '84 3.2 by TRE Motorsports on a Dynojet 248c. The combination of the engine build, TRE's race exhaust system, along our chip programmed for the engine package produces 234.7 rwhp at 6500 rpm. Factoring a 15% drivetrain loss, crank hp is 276 hp, a 69 hp improvement over the stock 207 hp motor. Not bad considering the entire intake and fuel injection system remains completely stock and unmodified due to POC class restrictions. Examining the torque curve, not only does it build smoothly to 5000 rpm, but doesn't stop rising until it it peaks out at 6200 rpm! Area under the curve from 4800-7400 rpm is what allows this car to fly. This car outruns track prepped Vipers and E46 M3s at the track as if they were driving Miss Daisy. (Motec? We don't need no stinkin' Motec!"

Enjoy.

Jeff Alton · 11-15-2009, 08:18 PM

As many have stated, buying a 3.6 is a crap shoot of sorts.... likely it needs the same sort of work your current 3.2 needs......

Cheers

88-diamondblue · 11-15-2009, 09:28 PM

Jeff's 3.4 build is another amazing one. Starts here 3.4 has begun! (part 1) and continues 3.4 build part 2!
Ends up with 337 at the engine 997s territory

and those 997 are no where near 2200lbs

Sorry Jeff couldn't help posting the links

Geronimo '74 · 12:27 AM

Wow,
Guys, thanks for the many answers!!
You got me thinking again (pffff....

)

What I am aiming for is a streetable engine since I will not be doing a lot of trackwork. (only on occasion)
Since I am doing the rebuild anyway, I want to squeeze some extra ponies out of it, who wouldn't.... I am hoping to find 50 HP over stock (280 instead of stock 231), but I won't be disappointed with 40hp over stock.
Modifications that require twinplugging will make it a bit expensive I guess, because of the added cost of twinplugging...
A 3.6 transplant is out of the question. 3.6's donor engines are rare here, so good ones will be even harder to find.

I thought I was pretty sure that I wanted to go to 3.4, but then I shouldn't have asked here, I suppose. (I do appreciate all your opinions though, so thanks already)

911st, if it is feasible to gain 40-50 hp without going the 3.4 route then I would certainly consider this as well. (That 270 with stock intake sounds very interesting!)

We don't have smog regulations here like in Cali, they are not nearly as strict, so I'm not worried about that.
Engine has 120000 miles on it. Tranny is going away to, so different gear ratios might be an option as wel!

Thanks guys, appreciate it!
More info is still welcome of course!

Geronimo '74 · 11-15-2009, 09:37 PM

Quote:

Originally Posted by 88-diamondblue

Jeff's 3.4 build is another amazing one. Starts here 3.4 has begun! (part 1) and continues 3.4 build part 2!
Ends up with 337 at the engine 997s territory

and those 997 are no where near 2200lbs

Sorry Jeff couldn't help posting the links

Wow, that is one awesome build!! (a bit out of my league, but very cool!)

Geronimo '74 · 11-17-2009, 07:48 AM

Little bump to get some more info...

(sorry)

JeremyD · JeremyD's Garage

my engine specs:

3.4 mahle 9.8 to one jugs
~ 1MM taken out of pistons for valve pockets
Single plug
Magnecor Wires
Extrude hone intake
993ss cams (Dougherty Racing Cams)
arp rod bolts
Supertech Head Studs
Enlarged throttle body
competition springs and retainers (EBS)
993 Flipped Flange Heat Exchangers
MK 993 Bischof flange muffler
Steve Wong custom chip to pull it all together

sp_cs · 11-17-2009, 08:25 AM

My build thread here for ref: 3.2 > 3.4 top end rebuild

Dyno'd again recently (after 5k miles) on a different dyno at 272/243 bhp/ftlbs - so 270 ish give or take

Geronimo '74 · 08:40 AM

Thanks Jeremy.

I assume you bought a set of cylinders and pistons, did you need to take 1mm out of the pistons, or did you do it just to be sure to have decent valve clearance?
How come you have a CR of 9.8 to 1? Did you change the crank as well?
I am looking at this set from FVD (mahle p/c kit 3,2 -> 3,4 (pin 23mm), FVD Online Shop )
This set seems to keep the same CR as stock (10.3 to 1), how will that be different compared to a lower CR of 9.8 to 1??
Will I need to twin plug???
Why did you opt for the 993ss cams?

Thanks!

Shirish, thanks a lot for the link to your thread!!
Some very interesting stuff there!!

JeremyD · JeremyD's Garage

Quote:

Originally Posted by Geronimo '74

Thanks Jeremy.

I assume you bought a set of cylinders and pistons, did you need to take 1mm out of the pistons, or did you do it just to be sure to have decent valve clearance?
How come you have a CR of 9.8 to 1? Did you change the crank as well?
I am looking at this set from FVD (mahle p/c kit 3,2 -> 3,4 (pin 23mm), FVD Online Shop )
This set seems to keep the same CR as stock (10.3 to 1), how will that be different compared to a lower CR of 9.8 to 1??
Will I need to twin plug???
Why did you opt for the 993ss cams?

Thanks!

I'll try and answer in order

With the 993 SS cams - I had to take less than a mm out of the top of the pistons for valve overlap clearance. Crank is original 3.2 crank

With the 3.4's (98mm) one of the Mahle options was 9.8 to one.

Twin Plug? I'm not sure on the quality of Gas in Belgium - here in the US we have 93 octane. I have not had an issue with detotantion - even at Sebring running hard with 115 degree on track temps.

I opted for the 993 SS cams because of their relatively flat torque curve - and because at the time they were considered to be about the maximum cam you could have and still keep motronic and still be able to keep an idle. This was about four years ago. I'm not aware if there are any better choices out there now - I'd contact Dogherty Racing Cams.

I was telling Ed in a previous email that my car is about on the edge of idle with the 993 SS cams and motronic. It's a lopey idle - every once in awhile it will actually stall if I have the AC on {i know, I know, the travesty} Actually it's much better now with a new AC compressor - the old one I had really sucked some HP from the engine when it was turned on.

Really though, I have a great motor. I have a few local Pelicans that I have given rides or let drive that covet my engine - I won't leave them alone with my car and a garage full of tools, that's for sure

Geronimo '74 · 11-17-2009, 09:54 AM

After taking of 1mm of the pistons, how much valve clearance do you have?
Did you take of 1mm locally or over the entire surface of the piston????

JeremyD · JeremyD's Garage

Locally - just a 1/2 moon. Sorry I don't have a picture.

and my memory is not as good as it was - and this was four years ago (almost 5)

But I believe we needed 2mm valve to piston clearance. We were at about 1/2 that or 1mm. We relieved a valve pocket - localized half moon - ~ .8mm. That gave us 1.8 or so clearance.

Geronimo '74 · 11-17-2009, 11:10 AM

Thanks so far, I am like a sponge absorbing all this info. It's great!
Is there a reason that you chose the 9.8 to 1 CR??
We have 98oct gas here readily available (I believe it is the same as your 93).
I'm not sure what the difference in engine characteristics will be between 9.8 and 10.3 but I think I would like to go with a CR of 10.3 to 1 since that is the same CR as stock. ( as long as I can avoid twinplugging, too costly)
Unless someone can explain/conince me why the lower CR would be better.

Thanks thanks thanks again!

JeremyD · JeremyD's Garage

It was recommended by my wrench who builds plenty of 3.4 engines for HSR. With the bigger combustion chambers (98mm vs 96mm) you start running into the limit of flame propagation.

He recommended that I keep it under 10 to one with regular gas (vs 100 octane race gas) and I'd have a safety margin in place. Over 10 - 1 and all it takes is excessive heat and/or a bad tank of gas and you could have some major heart ache.

Geronimo '74 · 11-17-2009, 12:01 PM

Knowing that the stock CR of a ROW 3.2 engine is 10.3 to 1, does the problem of flame propagation become more prominent when the displacement increases? (3.2 to 3.4)

If it is, then twin plugging would be the right thing to do, I reckon....

JeremyD · JeremyD's Garage

yes, as the size of the combustion chamber increases - the effective safe limits for single plug decrease

Geronimo '74 · 11-17-2009, 12:36 PM

Is there a difference in power, engine characteristics between the 10.3/1 and 9.8/1 CR????

JeremyD · JeremyD's Garage

Engine Horsepower (peak) is 287
# Old Compression Ratio is 9.8
# New Compression Ratio is 10.5
Computation Results:
# Computed New Engine HP is 292, a 2 percent change

In reality - building an engine is like baking a cake. Not only do you need the right ingredients, you need them in the right proportions. The net of a compression ratio - all things being the same may be only 2%.

But - if you twin plug, go to 11.5 to one, extrude hone, bigger cams, throttle body or ITB's you can have an even bigger impact on the net change.

If you read Wayne's engine book - you will see a few engines that he recommends - because they are good combinations.

Geronimo '74 · 11-17-2009, 12:59 PM

I have his book on my lap right now!
He recommends S-cams and 46mm Webers.
I'm not sure if I'll be using S-cams, I want a streetable, powerful but torqy engine, not a high revving race engine with only power on top.
Carbs are out of the question, motronic stays, with custom chip

Jeremy, thanks for your time and info!! I'm turning in, early day tomorrow!
We'll talk later, thanks!

Jeff Alton · 11-17-2009, 02:32 PM

Be careful with the 10.3 CR spec. Most original motors actually measure out at a much lower CR value. Plenty of wisdom in staying at a TRUE 9.5CR or less on a single plug 3.4.

Jeremy's and Michael's motors would be good and strong and likely have more bottom end grunt (maybe a by a fair bit?) than my higher strung motor does. That makes them excellent dual use motors, great on the street and great on the track.

Cheers