As the title says, What would be the adverse effects of using a 52mm fastman TB on a 318 motor that is stock? We know you use a 50mm fastman on 360's if towing is a concern. I purchased a used "50mm fastman" but the measurements seem to be comming up funky. I have a micrometer next to me as we speak I plan on using to check for sure, when I get home next weekend. But say it is 52mm, what is that going to do for me on a stock motor. Will there be enough of a bottleneck in the stock engine to make up for the extra 2mm / side,over what is recomended?

Thanks in advance,
pcfixerpro

 

Bigger than a stock 318 can make efficient use of. 50 would be best.

 

whats a bigger then stock 318?




It will run like hell if at all you need to give it to someone with a 360

 

Haha, funny. But in all seriousness, does anyone know?

 

You got a bottleneck alright , its called heads , valves ..

 

Sounds good to me. As long as ill get the 50mm performance out of a 52mm TB, with room for expansion, sounds like it was an error in my favor kinda.



- - - Edit

I'll call dan next week and see whats up. I need the bolts sent to me unless I can re-use my old ones, and to get the new s-bolt. Shoot, if I have too, I'll make a draw up a restricter plate in autocadand put it underneath the TB with holes at 50mm, so I don't lose that low end. I really dont need the upper end because I'm usually never over 2 grand. Thanks for the info PA. I'm putting it on reguardless.

 

If I understand the dynamics correctly, with a stock 5.2 and a 52mm TB, you will lose low end power until your mods catch up with the larger TB. Once the engine can actually use the increased air flow, it'll help, but until then its too much.

Someone correct me if I'm mistaken.

There's a reason why Dan does not recommend a 53mm or 55mm TB, which he does make, unless you have a seriously modded 5.9L engine or 408 stroker, respectively.

 

Thats what I was honestly afraid of.... I am going to measure it for sure when I get home, but if it is indeed 52, ... looks like I'll fab up a progressive restrictor plate maybe 1/16" thick or so. to the 50mm size holes. May not even take it that far... May just do a 1/32" thick piece and make the two holes @ 50mm and call it quits. (of course the other 4 holes as well) You know what??? How big are the stock gasket openings? Shoot, I may not need to do anything. Haha, guess ill just take a look at what I got before I start planning stuff out.

Thanks guys btw. I appreciate it

 

Well if anybody cares, I did some math today. (I took a trig quiz... jk but seriously) I ran some numbers through my head this evening and this is what I have come up with. I remember when I cleaned my throttle body last time, When mounting there is quite a bit of play with the gasket and TB position etc. I do remember that at one point, I could see the gasket by looking down the holes and stuck my finger down to move the gasket back. What that tells me is there is room to play in the gasket obviously. Lets look at some bore numbers

Fastman's 50mm TB ( 50.29mm )
F&B 50 Throttle Body( 50.80mm ) (a number I ran across while searching)
Fastman's 52mm TB ( 51.75mm )

So one of the things I ran across was how F&B this and that about how it outflows Fastman etc. Bla Bla Bla... To some the billet material made it flow 10x betteretc. Obviously not. But the reason the F&B does flow better is because it's a different bore. To convert my 52mm to a 50mm variety, I am going to use my gasket to slightly restrict the airflow back down to the size that was recomended.

Lets take a look at the differences. Fastman 52 vs. Fastman 50 = ( 1.46mm bore difference ) Fastman 52 vs. F&B 50= ( .95mm bore difference ) All of these numbers are for one side only, or flap. Since the gasket will be the same on both sides, by shifting the gasket forward, it will react to both holes the same. Basically, what happens to one side will automatically = the same change on the other side. Again, lets focus on one of the flaps. Since I need to move the gasket the least to convert to a F&B, lets play this out. This is where im probably gonna lose some. If I slide the gasket forward, this means that half of the opening will now see gasket appearing. The other half of the open space down the throttle body was now pushed forward as well. So... that means that the gasket affects half of one hole. Since I can only affect half, I need to multiply .95mm by two (to make up for the other half of the circle) I know have to make the gasket stick out 1.9mm on the semi-circle in order to make the bore now reduced to 50.8mm. The 1.9mm (or .07") is how much the gasket must be shifted forward in order to successfully reduce the size down to the F&B TB size. To go to the fastman 50mm, I would need to take the 1.46mm bore difference multiplyed by two (again for the semi circle), which gives 2.92mm of forward shift (.115")

The main reason I want to do this is to retain my low end. Having thought I bought a 50mm, but really is a 52mm aparently... is not quite what I expected. Even after doing all of this math, it will basically have to come down to the hole thicknesses on the gasket. Since I don't have a fastman TB gasket, I will have to see what size I get when pickup one at the parts store. Whether it is 48-50mm like stock, which will save me the hassel of everything and bolt on. or whether I will have to shimmy with it etc. We'll see what happens, but I can't wait to get home and put this thing on. Yes, I happen to be very bored at the moment if anybodywas wondering. lol.


- - Edit

Added a picture. The Black ring represents the hole of the bored out throttle body (definately not to scale). As you can see the gasket will cover a portion of the bore, thus... bring it down to the desired bore. Think it will work?

 

Maybe you could work out a deal with somebody for their TB spacer that they bought, wouldn't that restrict it back a bit? (depending on how open the spacer is of course.)