Originally posted by mattwa: I highly doubt removing the restriction on the TB neck of the stock upper 2.8 intake will effect low RPM operation, yet it will very much improve CFM where this cam wants to go.
The CompCams 260H is designed for mid-range torque (in the 2000-4000 RPM range). The stock Fiero intake should flow up to 4000 RPM without much parasitic power loss. Granted, porting the manifolds and heads would extend the torque band a bit. But the cam isn't really going to waste.
I was actually reading the thread thinking to myself "why did he put such a mild camshaft in it?" But with the stock heads and manifolds, it makes sense.
Nothing yet. I've been busy with my ChumpCar race car, work, school, etc. I've been thinking it's about time to get it on the dyno. Perhaps Soon. I'd like to know before summer.
meant to compliment you on your write up with photos. very nicely done and is proving helpful to me for my 3.4 swap. I don't expect to have mine running until April or May.
ManMade.... If you had left the original 3.4pr pistons in and upgraded the rockers to 1.6 could you have raised the compression ratio above the stock 8.9:1 and also allowing for #17 injectors.....or is this a direct function of internal top end space ?
If one leaves the original 3.4L pistons, you are going to have the stock compression ratio of 9.5:1. Installing ratio rockers won't change the compression any, it will simply open the valve more. With lower compression, the motor will make less power, and you could run the stock 17lb/hr injectors from the 3.4L. I had only the 15lb/hr 2.8 injectors from my Fiero, as the 3.4 I started with was a longblock, without any accessories and such. I believe you could still run the 1.6 rockers with the DOHC pistons, I just didn't know for sure, and didn't want to experiment.
Upgrading the pistons in the 3.4 is about the easiest way to get more compression. The .040" 3.4L headgasket for the iron heads is the thinnest stock one available, so you can't go thinner there too easily or inexpensively. Cutting the heads changes the geometry of things too, which is a pain. Custom pistons are going to be many hundreds of dollars, so I figured the DOHC pistons are the cheapest means of upping the compression.
Update - this engine now has 17,000 miles on it. Running great, just as strong as when I broke it in. Very pleased with the results. Ironically, it must be more efficient too. I have been getting between 1 and 2 MPG better than I did with the 2.8, in the same driving style. Open it up a lot, and you have the potential to get worse mileage for sure, but if you behave this has been an improvement. Still no money or time to get it dynoed, but I hope to soon- my college just got a new auto shop facility, and is setting up the dyno there.
Another couple points to make: in my later builds for my racecar, I have found better parts in a couple different spots. I now prefer the Fel-Pro PermaTorque Severe Duty head gaskets, as these have a nice built-up ridge around all the openings. I have not had HG problems with this engine, but I like knowing I have the better parts on there.
In addition, I highly recommend upgrading to the Volkswagen aircooled exhaust gaskets. These are much more robust than the stock one-piece gasket. If your manifold bolts loosen even a little, the stock style gasket blows out very quickly, leaving your Fiero sounding like a single cylinder go-kart or a lawn mower. Not nice. Buy six to do a whole engine. Costs about the same as a Fel-Pro exhaust manifold gasket set, but these last forever rather than having to be replaced all the time.
Drive one Fiero to rebuild another... This is my Dad's 1985 SE V6 that he's had since new. At about 170,000 miles he replaced his 2.8 with a 3.1. Now 110,000 miles on that motor and going strong. It should hit 300,00 miles next year.
what wheels are those? they look good.
------------------ 1st class A**hole.
we're in desperate need of a little more religion to nurse your god-like point of view...
I think this is going to be the swap I end up doing mainly because of the cost. What was your total cost for this whole project including an engine rebuild? On a different note did you ever get this beast dyno'd? I would love to know what the HP and Torque is with your mod's.
I spent about $1500. You could do it for less, and you could easily do it for more. Take whatever you expect to spend on a project like this and double it. You'll forget about every last little thing you're gonna need. I just went through a stock 2.8 build with a friend, and you can't believe how many little things nickle and dime you along the way.
Still no dyno info. I'm a broke college student with a racing habit. I don't have the time or the cash to get it done yet. Soon, I hope! Y'all will know as soon as I do.
A dyno is $60 for 3 runs and a good investment just to make sure you're not gonna blow anything up because of leaning out. With normal 3.4 pistons, your compression ration is 8.9 but with the TDC pistons it's 9.8 with the 3400 gasket and 9.965 with the 3.4 gasket. I forget if you shaved the heads on your build...
I used a GM performance cam on a 3.4 with 100k and got 149.8 rwhp out of it with lightly ported heads and intake and 1.52 roller-tip rockers. With your 10:1 compression ratio, you should exceed that a little. I think with the 15# injectors you are making closer to 160rwhp but running lean at WOT.
Back then I didn't use PIP so the images are lost... Wow reading thru that old thread, I didn't remember the shark vane was removed in the port job. Don't ever do this - my 3400 bottom end with stock 3400 cam made 187/249 leaving it in, but I was using a proper exhaust as well so you see the Fiero exhaust is a huge restriction...
[This message has been edited by lou_dias (edited 04-03-2014).]
I know it's not leaning out. I have 19 lb/hr injectors. Even with the 9.95:1 compression, it runs just a bit fat all the way up. I did not shave the heads. I have a CompCams 260H cam and 1.52 roller tip Magnum rockers. I'd be pleased with 150 at the wheels. We'll see.
I know it's not leaning out. I have 19 lb/hr injectors. Even with the 9.95:1 compression, it runs just a bit fat all the way up. I did not shave the heads. I have a CompCams 260H cam and 1.52 roller tip Magnum rockers. I'd be pleased with 150 at the wheels. We'll see.
Sorry, I thought you mentioned re-using the 2.8 injectors... I was using 16# Tomco injectors with higher fuel pressure...worked great for me back then...
"Flat Top" 3.4 DOHC pistons attached to the 3.4 Pushrod connecting rods. Should be right about 10:1 compression. This was one of the upgrades I talked about earlier. These pistons share all the important dimensions with the 3.4PR pistons, but don't have the dish, so it raises the compression. These cost about 1/4 as much as a custom set of truely flat topped 3.4L bore pistons.
I know this is a super old thread, well... 12 years old.
Can anyone tell me where I can get these pistons? 10:1 compression sounds pretty awesome.
How would this work in an otherwise stock 3.4 V6/60 with ported heads, and a port-matched Fiero 2.8 V6 intake system with a bored throttle body and a DAWG mod?
I also have the H272 cam w/ 1.52:1 roller rockers... am I good with compression?
Finally... what kind of power / performance difference would you guys assume someone might get by swapping out the stock 3.4 pushrod pistons to the DOHC 3.4 pistons? Thanks!!!
UGH... holy **** I'm impulsive. I just bought a set of .020 overbore SEALED POWER H684CP (H684CP20) DOHC pistons for a 1995 Monte Carlo (3.4 DOHC). Would you guys mind answering the other questions? Thank you!
[This message has been edited by 82-T/A [At Work] (edited 07-31-2024).]
UGH... holy **** I'm impulsive. I just bought a set of .020 overbore SEALED POWER H684CP (H684CP20) DOHC pistons for a 1995 Monte Carlo (3.4 DOHC). Would you guys mind answering the other questions? Thank you!
Fantastic... thank you. Standard I think was 9.0, and my H272 Cam requires AT LEAST 9:1, so I was concerned... but even if I'm only getting 9.3:1, that's still better, and slightly more power. I appreciate the link!
does your car have A/C? if not I have an option to boost that engine if you are interested. requires a custom bracket to hold a vortech SC where the ac compressor would go. Fierosound has a similar set up.
does your car have A/C? if not I have an option to boost that engine if you are interested. requires a custom bracket to hold a vortech SC where the ac compressor would go. Fierosound has a similar set up.
Man, I would love something like that... but I live in Florida... and sometimes South Florida... so I desperately need A/C.
But that sounds awesome...
I'm OK though, I do appreciate it. I want the car to look as stock as I can possibly make it. I'm even rethinking how I can do the DAWG mod so I can make it less obvious.
I've kind of quasi ruined it though because I went with WCF stainless shorty headers and Y-Pipe. They are close to looking stock... if I manage to convince myself that's true.
