DOhC turbo VS 3800SC

slow'n'steady · Post by **slow'n'steady** » Sun Mar 05, 2006 11:34 pm

i thought id seen a post about it before, but i couldnt find it so...

just curious as to how a turbo/intercooled DOHC would stack up against a 3800SC

say a 3800SC II with ported exhaust, 42#/255lph fuel, cam, intercooled

VS (same basic mods)

94-95 3.4 DOHC turbo, intercooled, 42#/255lph fuel, 13* timing mod, gasket matched heads and lower intake, custom intake (like the one pictured under "engine conversion" on the WCF site) running at like 10psi or so.

just curious as to how the turbo DOHC stacks up against other engines. (no im not having second thoughts, still a DOHC turbo!!) if my damn neon would sell i could finish buying my damn parts and get drivin!!!

Shaun41178(2) · Post by **Shaun41178(2)** » Sun Mar 05, 2006 11:53 pm

Too many factors to take into acct, but that wcf intake doesnt' do anything for power. Its being run through a 52 mm tb. 57 if you have DM port it out. Sorry, but that sucks for making power.

In fact I have heard a story of WCF's turbo dohc going down to a s/c 3800 while at wheatstock on the street. The 3800 wasn't in a Fiero if that makes any sense to you

Sinister Fiero · Post by **Sinister Fiero** » Mon Mar 06, 2006 12:00 am

Not quite on topic of what you are asking, but:

Assuming the 3.4 DOHC engine could be built to handle the same amount of boost you can put on a 3800; the DOHC heads should give you an advantage here. However, you can't build a 3.4 DOHC engine to hold up to the same amount of boost you can put on a 3800 Series II engine. Why? The 3800 engine has a deep-skirt design block. That means the strength of the lower block is MANY TIMES that of a 3.4 DOHC block; which doesn't have a deep skirt. (Deep skirt = the casting extends below the crankshaft centerline) The 3800 S2 blocks also have cross-bolted main caps.

I am sure you could spend a ton of money in having a special girdle or splayed main caps made for the 3.4 DOHC block; but eventually you are going to have to face the fact that the 3.4 DOHC block was not cast stout enough for boost duty. The money you would spend strengthening the DOHC block up to the stock specs of a 3800 S2 would negate the HP advantages of having the DOHC heads. The 3800 S2 stock block has been proven to withstand 700+ hp under boost. Same goes for the stock crank and connecting rods. However, the stock pistons are the weak link in the 3800 SC engine.

Now, to answer your question: I don't even think you could safely push 10lbs of boost on bone stock 3.4 DOHC pistons. You may be able to a couple of times, but any hint of detonation would send them to the oil pan. I am not saying someone couldn't or hasn't done it; all I am saying is durability is going to be a big factor on stock 3.4 DOHC pistons at any boost level over 6psi, in my opinion. If you could push the same boost amount on a 3.4 DOHC engine; assuming every other factor is the same between the two engines; the 3.4 DOHC engine should beat the 3800SC engine in HP; but maybe not in TQ; depending on the turbo you use.

Look at my setup for example. I am only running 10-13psi of boost on a stock 3800 with just ported heads; but I have a turbo and an intercooler; which is MUCH more effecient than any supercharger. My car runs 12.26 sec in the 1/4 mile on a STOCK CAM using STOCK ROCKERS. I don't think I have ever seen a 3800SC run that number on stock cam/valvetrain.

Aaron · Post by **Aaron** » Mon Mar 06, 2006 12:01 am

Well the 94-95 DOHC will be at about 350whp with the aforementioned mods.

So whatever it takes a 3800SC to make 350whp.

Seriously, stop talking about what a DOHC will do with this and what a L67 will do with that, buy a DOHC, and do the swap already. Worry about modding the 3.4 after its swapped. I'm beginning to think it won't ever happen.

slow'n'steady · Post by **slow'n'steady** » Mon Mar 06, 2006 12:03 am

yeah... i understand. i am just wondering if i should do something about the stock DOHC intake or if it will be OK.

and sense im at it.

WHEELS!! i found 17" rims i want, but dont want to run them at the track. would my stock rims be ok/better? do they make 14" slicks? any suggestions??

Aaron · Post by **Aaron** » Mon Mar 06, 2006 12:05 am

slow'n'steady wrote:yeah... i understand. i am just wondering if i should do something about the stock DOHC intake or if it will be OK.

and sense im at it.

WHEELS!! i found 17" rims i want, but dont want to run them at the track. would my stock rims be ok/better? do they make 14" slicks? any suggestions??

The stock DOHC intake is fine, just not if you're looking for high RPM, N/A horsepower, and a lot of it. Tim is pushing 400hp with 10psi through the stock intake. Yes, it is restrictive, but that won't hurt as much when you're boosted. And worry about th eintake after its swapped, swapping a stock DOHC is enough of a task for a beginner.

You won't fit 14" slicks. But even if you could, it would just break your tranny anyways.

slow'n'steady · Post by **slow'n'steady** » Mon Mar 06, 2006 12:10 am

i have the engine and a few of the parts, jus some bad luck and bad purchasing on my part.

the turbo i 1st had wasnt sized properly (my bad) so i got a different one.

the DOHC harness i bought has a bunch of cut wires, so im gonna buy a different one sense i dont know what the ones that are missing do i dont wanna ship an incomplete harness and waste even more money when i find out it wont work!

had to find some 94-95 cam coggs to go with my 94-95 harness and ECM

meanwhile my DD broke down so i had to fix it, and i now have a baby on the way, so i cant just blow all my money like i used to. otherwise itd be much further along!

cant fit 14" slicks? 14" diameter rim, not 14" wide.

stimpy · Post by **stimpy** » Mon Mar 06, 2006 1:38 am

Yes, BF Goodrich makes g-force T/A Drag Radials in 14 inch.

Only aaron would think 14 inch wide slicks on a Fiero. What a ricer!

The Dark Side of Will · Mon Mar 06, 2006 9:21 am

Sinister Fiero wrote:I am sure you could spend a ton of money in having a special girdle or splayed main caps made for the 3.4 DOHC block;

GM makes 4 bolt center caps for the V6/60. The part numbers are in the thread titled "DOHC stuff" in this section.

The aluminum V6/60 bow-tie block has been pushed to over 700 HP... Just because it hasn't been done, don't assume it can't be done. Did anyone 10 years ago think that the 3800 block would handle 700 ponies?

The Dark Side of Will · Mon Mar 06, 2006 9:22 am

Aaron wrote:Seriously, stop talking about what a DOHC will do with this and what a L67 will do with that, buy a DOHC, and do the swap already. Worry about modding the 3.4 after its swapped. I'm beginning to think it won't ever happen.

Hello kettle? This is pot...

Sinister Fiero · Post by **Sinister Fiero** » Mon Mar 06, 2006 10:38 am

The Dark Side of Will wrote: GM makes 4 bolt center caps for the V6/60. The part numbers are in the thread titled "DOHC stuff" in this section.

The aluminum V6/60 bow-tie block has been pushed to over 700 HP... Just because it hasn't been done, don't assume it can't be done.

I didn't say it couldn't be done. I merely stated that it might not be practical. I have no doubt a bow-tie block could handle 700hp. However, the OEM DOHC block is NOT a bow-tie block and the casting is "less than perfect". While you could throw 4 bolt caps in there, the question still remains: is their enough material in the lower block / main webbing area to support boost / high-HP numbers?

Just so we are clear; I think a factory 3.4 DOHC bottom end could handle about 10psi of boost; so long as you used the best fasteners available. I don't think the factory pistons could SAFELY handle 10psi of boost tho. I'm not saying it couldn't be done, I'm just saying I wouldn't feel comfortable with the stock slugs in there.

Aaron · Post by **Aaron** » Mon Mar 06, 2006 10:40 am

TimG is pushing 400hp out of a STOCK, 160,000 mile 3.4. No fancy bottom end, no rebuild, just a turbo at 10 psi. And it has been boosted now for quite some time.

slow'n'steady · Post by **slow'n'steady** » Mon Mar 06, 2006 10:48 am

The Dark Side of Will: im liking you more and more!! :notworthy:

The Dark Side of Will · Mon Mar 06, 2006 10:52 am

Your sig is freakin' hilarious

Pyrthian · Post by **Pyrthian** » Mon Mar 06, 2006 12:01 pm

slow'n'steady wrote:i thought id seen a post about it before, but i couldnt find it so...

just curious as to how a turbo/intercooled DOHC would stack up against a 3800SC

say a 3800SC II with ported exhaust, 42#/255lph fuel, cam, intercooled

VS (same basic mods)

94-95 3.4 DOHC turbo, intercooled, 42#/255lph fuel, 13* timing mod, gasket matched heads and lower intake, custom intake (like the one pictured under "engine conversion" on the WCF site) running at like 10psi or so.

just curious as to how the turbo DOHC stacks up against other engines. (no im not having second thoughts, still a DOHC turbo!!) if my damn neon would sell i could finish buying my damn parts and get drivin!!!

bah - stick with the 3800, ditch the SC and turbo that with some crazy boost.

Kohburn · Post by **Kohburn** » Mon Mar 06, 2006 12:42 pm

Pyrthian wrote: bah - stick with the 3800, ditch the SC and turbo that with some crazy boost.

agreed - if i had gone that route i'd probably been driving my car a year ago

crzyone · Post by **crzyone** » Mon Mar 06, 2006 2:23 pm

Pound for pound of boost the 3.4dohc should make more power. Figure out how much power you want before you decide on the engine. I would think the 3.4dohc could support 350 at the crank, but don't know how long.

Whichever engine you choose, don't go cheap on the turbo. Make sure its properly sized and efficient.

I personally would do a 3.4 for the cool dohc factor. If I was building a drag car and wanted reliable hig power, I would do the 3800 turbo.

TurboGT · Post by **TurboGT** » Mon Mar 06, 2006 4:30 pm

What about the trans. Would a turbo 3800 be good behing a manual?

Everyone says that the SC 3800 and auto is the only way to go, and the DOHC and a manual is the only way to go.

I understand why they are this way and I know turbos and auto go together better (dont loose boost during shifts, you can boost launch and preload your drivetrain), I had a Typhoon and could never see having that thing be a manual (you would have a hard time shifting that fast).

With a properly sized turbo on a 3800 would it have advanages/disadvanages being manual vs. auto?

Series8217 · Post by **Series8217** » Mon Mar 06, 2006 5:39 pm

I actually don't know of anyone with a turbo 3.4 DOHC that doesn't have stock pistons. Matt Hawkins? Stock pistons, 12 psi.
Chris West? Stock pistons, 10 psi, no intercooler! If anyone would have destroyed pistons it would be him since the motor was in a terrible state of tune for so long, and the intercooler doesn't help matters.
Tim? Stock pistons, 10 psi.
They seem to hold up fine.

Fastback86 · Post by **Fastback86** » Mon Mar 06, 2006 7:46 pm

Yeah, esp if you've seen the way Chris West drives that car, and the way other people drove it when he handed them the keys. If any turbo motor should've blown up by now, thats it. But, it takes a lickin and keeps on kickin ass.

Real Fiero Tech

DOhC turbo VS 3800SC

DOhC turbo VS 3800SC

Re: DOhC turbo VS 3800SC

Re: DOhC turbo VS 3800SC