408
fel-pro speed-pro unit
modified LT1 intake (ported close to an LT4)
trickflow G2 heads (ported)
bout a 510 lift roller cam with 112 degree lobe seperation
full exaust

what would you think anethes?
I'm not sure what cfm's it'd pull... maybe a 900-1000.

 

I would definatly reccomend a 58mm for 408ci engine.

 

or you could always go with a monoblade SWWWWWWEEEEEEEEEETTT

 

I would also recomend a 58mm tb as well.

 

58mm all the way!

 

Hi,

I think you're gonna need to flow about 720-740 CFM at a bare
minimum to keep that motor happy. This also depends heavilty on your cam specs tho. I'm assuming you wish to pull til about 6500RPM, and that your duration is something around 240 degrees.


Unfortunately i do not have a flowbench and can only rely on other peoples flow math, which my machinest seems to think is inacurate - however dry systems flow different than we systems obviously.

The 58MM suposedly flows 1000CFM, but then again so does a 52MM with an airfoil. Who knows for sure.


-- Joe

 

It's still a fairly mild street motor with a hydrollic roller.
I'm planning on only spinning it to about 5600 rpm.

Pretty neat hearing her suck the air in though. Breathing alot harder than the ole 305... when I had the long runner setup on it.

 

I'd Say 58mm too. On my engine it's not over kill, so on yours it should be good.

 

I'm running a 58mm with the big base and runners on a ZZ4. The only problems I had were with the infamous MAF code 33. With your combo I would expect airflow > 55gm/sec at under 2000 RPM at less than 25% throttle (GM code set). The right chip should take care of this, although I had to trick the TPS to get the code not to set.

All this assumes you're putting it in a TPI-like third gen car.
Good luck, sounds like a neat combo.

 

I run a 58mm on my 350 and like it, so on a 408 go for it.

JR4444 & 88IROC_CVTFAN

what times are you running?

 

I haven't carried it to the track yet...
I'll know once the efi races start back up.

 

I just got it running about a month ago and have not taken it to the track. I'm running 245-16R50 (stock tires) and traction is absent in first gear. I'm getting ready to do the suspension in the next month or so and hope things will improve.

 

Id say maybe a 52 or 58 MM for that engine.

Sounds like a good motor there.

For the guy with the ZZ4 engine the stock 48MM is as big as you want to go.
You get that code 33 because the ecm sees an unrealstic airflow into the engine.

As you found out, you need to adjust the min. air speed and set the TPS at the wrong settings to make it work.Theyre supposed to work at the stock .54 volts or so..if not they dont work with your combo.

Youre probably running slower then you would be..the ZZ4 with a TPI or SR is like a stock L98 with a bigger cam performance wise.I tried a 52 and 58 on my aluminum head L98 with a better cam and the stock 48MM had the best results.Best idle,best SOTP and etc.No codes and no prom work required.When I tested larger TB's I got the same code 33's and the slower driveability.Even when tricking the TPS and etc, it didnt have the take off or torque feel the stock TB had.

The stock TB doesnt exceed VE of the ZZ4 motor or L98 with a bigger cam..so a larger TB doesnt do anything.
When you exceed VE,thats when its time to step up to a larger TB.VE is volumetric efficiency for those that didnt know.

A guy on the Vette forum with an LT4 tried a 52MM on his engine and saw no gains.Thats an LT4 and they make alot of power stock.
Just wanted to pass this along.
While its true,you cant so much over TB the car like you can over carb a carbureted car,If you dont exceed VE,you dont make gains with larger ones.

Been there,spent that and learned my lesson.

 

I am running SD on my ZZ4 and no codes and no adjustments had to be made. A friend of mine has almost the same set up I do (different runners) and and saw 7rwhp and 3rwft/lbs. So it's working for me. With the intake I have I spin up to 5800rpm easy and 3800rpm and up I can feel the difference. As far as low end TQ goes I have not seen any loss in SOTP.

 

I've heard all the arguments and I'm sure that I haven't got the ideal setup - yet.

I can't really say if the larger throttle body helps or doesn't. For me it was a decision made partially on the basis of cosmetics (those big holes look good!) and partially on the knowledge that with an MAF system the restrictions provided by the MAF sensor, air filter arrangements, etc. would diminish the effect of the TB on the overall flow. I just wanted to get the ZZ4 the maximum amount of air that I could. The original 305 was weak with peak horsepower obtained at less than 5000 RPM. The ZZ4 gets it's peak at ~5400 - this whole TB, runners, manifold etc.. was my best first guess based on information obtained from friends and this forum.

I've made so many changes that the information regarding these differences is lost for now. The car runs great, has enough power to get me into serious trouble, and was a lot of fun for my first project.

Thanks for all the input - I'm learning a lot.

 

Ignoring the fact that SES 33 is a "High MAF Error", SD cars should not through ANY SES codes by installing a larger TB cars.

But MAF cars are different and may require some tweaking in the eprom related to the "test" conditions that trigger SES 33. There is a timer delay and %TPS setting. If you were to monitor and watch WHEN the SES 33 got trigger, you could compensate for it (provided your MAF is operating properly).

 

Hey guys,
Thanks for the updates..its a first for me to hear of any HP gains and if it worked for you,thats great.I went through the headaches of trying to use a larger TB with a MAF car and it just didnt justify the expense.

My car felt slower off line with them as well.Mid range felt somewhat stronger but no way to really know for sure.I think this may be more noticeable on automatic cars then say a standard.Tranny was shifting differently as well with my automatic.Had to play around with the TV settings and wasnt too happy with the results.

I was more or less trying to point out some problems so that others will not fall into the same trap.
I know the bragging rights and muscle looks these things can bring when you open the hood,nothing really wrong with that..people do it everyday and see that at the shows.
But glad to hear its worked for some,wasnt trying to put your mods down if it sounded that way to anyone.

 

To BillsVette:

This hobby has lots of room for opinions and experience. I didn't take any of your comments as a "put down" or anything even close to that. There is so much hype from manufacturers and distributors that eventually all of us get sucked in on occasion. The folks on this board represent the "real deal". Keep the information coming!

Thanks

 

Hi all,

I did not mean to come off as a jackass in my earlier post. I also did not mention that I had the benefit of a chip burned by someone that had a bunch of experience with a very similar setup to what I run, so for me it was plug and play.

Also though I am a firm believer that a bigger t-body can help a 350 I think it is one of the last mods you need to consider, more for fine-tuning than to make power.

 

I just rebuilt the motor, so I'll let you know in about 3000miles.

 

I usually break 'em in about 500miles, then head for the track.

This usually is a few runs up and down the high way, reving low, reving high, etc.

-- Joe

 

With how much I drive it won't take long to break it in, also with how Anxious I am to get it to the track, it should only be a week or two.