Turbo 3.4DOHC cam timing

[pontiacjeff]

The latest tuning session on my 88turbo Grand Am (Daewoo 4-valve head swap) The Daewoo head is very similar to the 3.4DOHC head.

Here are the results. I think the same results will show for the TURBO 3.4DOHC when compared to stock cam settings. (We have seen similar results on originally n/a Honda/Acura engines, both V-tec and non-V-tec).

All runs in second gear, 7-8psi boost.

Stock (actually +4deg. int/exh due to thicker head gasket): Peaked 160whp at 5600. Very narrow powerband, 4500-6000.

Intake -11deg, Exhaust +4deg: Peaked 180whp at 5600. Gained 20whp from 4500-6500, 40whp at 7000, and 57whp at 7500. Boosted quicker, more complete filling of cylinders due to reduced overlap.

Intake -11deg, Exhaust -11deg: Peaked 190whp at 6000. Lost 20whp at 4500, gained 15hp at 7000-7500. Same power curve as stock, just 500rpm higher.

So we gained 75whp with just cam timing!!!!!!

I was limited by non-adjustable cam gears to one-full-tooth movement. One tooth is 7.5 cam/15 crank degrees. There are no such limits with the 3.4!

Summary: For a street-driven, boosted 3.4DOHC, I recommend +4deg. exhaust, -10deg. intake. For a auto trans/street/strip. For full race turbo where traction is an issue, I recommend -4deg. exhaust, -14 intake.

The reduction of 10 or more degrees in overlap is critical for good use of boost. My '96 is set up 0exh, -10int. For the sake of science, I will probably put it back stock before I put it in the car. Then I can make these changes on the dyno for proof. Still, I stick by my recommendations for all you guys running turbos. Again... free dyno time in Atlanta for anyone wanting to test anything on the 3.4DOHC.

BTW, the end result on the TGA: ran out of fuel with the stock injectors at 240whp at 17psi.

[Mechanic]

Geesh, 75hp out of a timing change like that is excellent! Good job!

[pontiacjeff]

I should clarify... we gained 30 peak whp, but at 7500rpm we gained 75whp. It went from 82whp to 147whp at 7500 with only cam timing changes!

Now on 17psi, the peak has moved to a flat 240whp from 6000-6500, but tapers off only slightly to 225 at 7000. The trans shifts at 7200-7300, so it's pulling hard right up to the shift.

The GMPCM is working like a charm! I emulated on the dyno, burned a chip, and am going racing tonight!

[pontiacjeff]

I ran the car tonight. Retarding the exh. -11deg really killed the car on the line. I can't get more than about 5# boost on the foot brake. I used to get full boost! (Granted, the old turbo was a little smaller.) And it doesn't hit 17psi for at least 100ft. The 60' times were the lowest they've ever been, hovering around 2.20's. Even going back to the old T-25 SOHC days, it would pull a 1.95-1.99. BUT, when it does boost up, the whole front of the car lifts about 1ft. and the car hunkers down and hauls a**! How's a best 8.72 @ 88mph?!?! (1/8th mile) The car weighs 3100# with me in it. It makes quite a bit less whp in 1st and 2nd gear due to load differences. I just hit 3rd at the end of the track. In the 1/4-mile it should really fly as boost levels out in high gear. I expect to see some mid-13's.

Back to cam timing... I think I'll run the exhaust back up the one tooth(+4deg adv from stock). It will boost quicker, make more average hp, might sacrifice a few hp up high rpm, but the car will drive much better. Lesson... keep the overlap TIGHT on a turbo!

Too bad for the 3100/3400 guys! Get a custom grind with wider l.c.

[slick94prix]

Good info. to know

[pontiacjeff]

My info is free, I guess I make up for it in parts sales!

[TurboGTU]

Now thats tunning! Try advancing the exhaust. Make it open a little early on the engine cyle... Keep the intake retarted..but start at 0 and work it out for both. Let us know what that does. Theoreticly..it should give you low end back and still have your cake!

What trans mods are you using?

[Froggx]

call me a n00b, but what engine is this?

[TurboGTU]

Grand am/sunbird 2.0l Turbo with Daewoo head swap. Not a v6 but its good to know what a 3.4 DOHC would do if you degree the cams on boost.

[Froggx]

ah, makes a bit more sense to me now, those are nice numbers for a little 2.0L turbo engine like that (at first I was kinda confused thinking it might be a 660 with daewoo head swap and I was like wtf but you live and learn right?)

[Kohburn]

I was kinda confused there at first with 240 whp after 17psi

but translate that 2.0 to a 3.4 and its 408 whp

[pontiacjeff]

And the 400+whp is the goal for my 3.4DOHC turbo I am working on now...

[fieromadman]

Jeff, does a bowl to drool in while i read this thread come free? That is awsome! Keep up the testing (god knows the 3.4 DOHC needs it too!)

[pontiacjeff]

That's the great thing about this engine! You can go from your 1.5/5 deg n/a timing to bolt on a turbo and completely change the characteristic of the engine. I was going to start the tuning at -10/0 and see what it does. then go -10/+5, -10/+10... then maybe retard the intake a little more. It is a AT with stock converter, so the power needs to come on at 3000rpm. I'd like it to peak at 6800 and shift at 7000. That's the beauty of this engine! You can play with cam timing until it does EXACTLY WHAT YOU WANT IT TO!!!!

[Kohburn]

well with a little luck I should have a christmas gift of photos of prototype adjustable cam cogs for ben to sell
so stay tuned on that.. I'll me making and testing them on my 3.4dohc turbo