3.4 DHOC vs 3800 II upgrade? (Page 1/2)
svocal SEP 17, 03:21 AM
Hi guys
I recently acquired a Lamborghini Diablo Coupe replica built on a 87 2.8L 5-speed. I am looking to upgrade the motor.
I am not a speeder nor do I have a lead foot. A little bit power would be nice. I am looking for the most easiest, hassle free, reliable, cost efficient engine upgrade.
Having a "Parts needed for upgrade list" would also be helpful. Since there are no Fiero guru mechanics here in San Diego Ca, my only option is to take the car to the local mechanic shop who can hopefully follow instructions and perform the install. I know you guys are well experienced in this topic so your advice is most welcomed. Which engine would you guys recommend?
cam-a-lot SEP 17, 06:57 AM
There is a lot involved... and I think you will lose your shirt trying to get a mechanic to do it who has never done one before and will likely charge you by the hour while going thrugh trial and error and head scratching....

It is (in my opinion) much more logical to ship the car to someone who has experience doing what you are looking for and getting it done properly. 3400 DOHC revs more nicely and feels more like a sports car engine.... The 3800 has more low end torque and pulls well, but doesn't sound as nice or continue to rev as nicely as the 3400 DOHC.

If you just want some more power without a lot of complication, look into the 3.4 pushrod engine upgrade- you can get an additional 40-50 HP at a very reasonable price, and much easier for your local mechanic to handle if you insist in leaving the car there.
svocal SEP 17, 08:56 AM
Thank you cam-a-lot for your input. I like the hi-rev sound of the DOHC so I am inclined to go that route.
Now the hurdle is to find someone or a shop that will do this. I'm in Southern Ca and haven't found anyone nearby.
fierosound SEP 17, 10:34 AM

quote
Originally posted by svocal:

I like the hi-rev sound of the DOHC so I am inclined to go that route.
Now the hurdle is to find someone or a shop that will do this. I'm in Southern Ca and haven't found anyone nearby.



One of our members opted to go that route too.
He took his car from Calgary to Couer d'Alene Idaho to have Fieroking (Joe) do the swap.
http://www.fiero.nl/forum/Forum3/HTML/000127.html

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My World of Wheels Winners (Click on links below)

3.4L Supercharged 87 GT and Super Duty 4 Indy #163

[This message has been edited by fierosound (edited 09-17-2019).]

darbysan SEP 17, 11:22 AM
Living in CA, are you going to be able to get past the SMOG police with an engine swap? You might be able to upgrade to a 3.4, using the stock Fiero intake,etc, and get away with it. Other than that, you may be in for some serious hassle...

You might want to talk to West Coast Fiero, if they are still operating, simply because they are close to you. https://westcoastfiero.com/

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'87 GT , '00 3800 Series II SC, 4t65e, Vue Power Steering. (SOLD)

cvxjet SEP 17, 11:45 AM
I did the 3.4 Long block swap......It uses the intake/headers/ICM of the 2.8 so it looks stock (not important for your setup)......you "only" gain 20 hp but 30 lb/ft of torque- and the power comes on at a lower RPM- Like if you went to a better rear-end gear ratio. My car is now in the 6.5 second 0-60 range and approx' 14.8 second quarter. The only down side is that the engine has zero power above 5000. I also get slightly better MPG on the highway.

GM actually sells only a 3.4 block for replacement of all the 2.8/3.1/3.4 engines- it is legal in CA- I did this swap in 1999 and have passed the smog test 10 times- I didn't even have to have it certified...It just passes.

If you want more power you can get the 3900 version of the 2.8 family- the last iteration; It has 240 hp and 240 Lb/ft of torque- with 90% of the torque from 1500-5500. The only problems are the front engine mount bracket and the computer- which is tied into all the other computers/sensors on the newer cars so it takes some serious reprogramming...
pmbrunelle SEP 17, 07:21 PM

quote
Originally posted by cvxjet:
GM actually sells only a 3.4 block for replacement of all the 2.8/3.1/3.4 engines- it is legal in CA- I did this swap in 1999 and have passed the smog test 10 times- I didn't even have to have it certified...It just passes.



Is the 3.4 actually legal in California, or does it just fly under the radar while masquerading as a 2.8?
cvxjet SEP 18, 11:57 AM
Originally, I thought it was just "Under the radar" but then somewhere I read that it was the only engine GM offered for replacement and so it was CA Legal...But I am not sure where I read it or how to prove it.....
ChuckR SEP 18, 12:26 PM
I have been researching the 3900 swap for myself, I dont have to worry about smog where I am so I can not speak to that. Depending on what you want to do for transmission, it is about as straight forward of a swap as you can get except for the 3.1/3.4 pushrods. If you have a manual it will bolt right up to it, not saying a stock 4 speed will not die to the extra torque from the 3900... The motor mounts requite some custom work but it doesnt look like a lot, and an alternator bracket will need to be fabbed to keep your hinge boxes and move the alternator down low like a stock 2.8. AC may be an issue if you want to keep it. If you do it might require notching the cradle there. I plan to use an auto trans personally and that is well detailed since it is the same trans as the 3800SC. West Coast Fiero sells the trans mounts, and Sinister has detailed instructions for axles Here. I also plan to keep all of the current ECU TCU and BCM and I plan for Sinister to do the tuning on that one.

A tuned 3900 stock motor has been dynoed at 213 WHP by another member on PFF.

That said I am just researching so I have not completed anything so a detailed instruction is not available nor am I saying everything above is 100% accurate.

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"HICCUPP" 1988 2.8 GT Ocelot SS exhaust

Dennis LaGrua SEP 18, 01:33 PM
The 3.4TDC engine has been swapped into Fieros many times. It gives decent high end power but the engine has a reputation as being somewhat problematic. It is also the heaviest V6 engine that GM ever made at about 465lbs. The mounting points on it are the same as on the 2.8L so with a new flywheel it is a bolt in swap. The tuning on this engine was very mild by design so the ECM/PCM has been reprogrammed for more than the 215 HP rating.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
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87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
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[This message has been edited by Dennis LaGrua (edited 09-18-2019).]