How tall should a throttle body spacer be?

[Skunksmash]

I would like to put a throttle body spacer on my '87 1/2 ton 5.7 liter truck. This is known to increase power and fuel economy slightly. However, there are many different heights available for purchase. In other words, do i need a 1", or a 1.5"? Maybe a 1.8" or a 2" is best? Not sure of the exact measurements of them but you get the idea. I am afraid i do not know how to figure out which one is best for me. So i was hoping that the knowledgeable folk here could help me out. This will be only for the purpose of increasing fuel efficiency, not for racing or anything like that. Thanks -  Justin

[78 Chevyrado]

I had a 1 inch on my '87 and I did NOT have to extend the fuel lines.  If you go too high you'll need to extend the fuel lines to reach the tbi.

[Skunksmash]

Hmm, that's something i did not think about. But since you had an 87 as well i would like to ask you: Did you seen any sort of improvement after having installed the 1" spacer?

[78 Chevyrado]

It seemed a bit more responsive off-idle to about 2000rpm.  It was enough of a difference I'd do it again.

[Skunksmash]

All right thanks for the info. But anyone happen to have any info on my original question? I guess i could modify it now: How do i know what size spacer is best for me if lengthening the fuel line is no issue? Is it just - the taller, the better? Is the tallest one that i can fit in there going to yield the most gain?

[Captkaos]

like everything, there is an optimum height.  Most companies like CFM Tech have done testing on stock setups with different heights and most likely picked the best for a range of duties.  At some point though, going higher is not going to help.

[Skunksmash]

Thanks for the replies. I took a look at CFM, and their spacer does seem to be a little different from the rest. It has some kind of niche down between the two holes, whereas the other brands just have two holes with no little niche. Here is CFM's:

http://marine-performance-parts.com/cfmtechpowerplatefor435057gmtbiwsingleaircleanerstud.aspx

And here is one form another reputable company, Trick Flow

http://store.summitracing.com/partdetail.asp?autofilter=1&part=TFS-31520001&N=700+115&autoview=sku

Which one would you go with?

[Captkaos]

It supposed to help flow.  I can't recommend one, but I can tell you I have a TBI truck and if I purchase one, it will be CFM tech.

[eventhorizon66]

I agree with Capt, go with the CFM Tech unit.  The design seems like it would really help breathing.  Phenolic is a heat insulator.  Such spacers are designed to help deal with heat soak, which I would think isn't a concern for TBI.

Another thing to consider is a replacement for the restrictive air cleaner spacer.  They shroud the airflow around the injectors and really hurt flow into the throttle body.  Here's a link for a good alternative.

[Captkaos]

You know I was thinking about getting these and putting them on my 305 TBI truck before I remove the 6.0L.  I was talking to my brother the other night about taking it to the track and running it for a 1/4 or 1/8th mile baseline and dynoing it for a baseline and then do it again after the 6.0L swap.

[eventhorizon66]

LOL.  You really need to compare a 305 TBI to a LQ4 6.0L?

[Captkaos]

just wanted to have the numbers.  Figured I would do it again when the twins were added.

[eventhorizon66]

Let's see:

150 hp baseline with 5.0L

300 hp with LQ9; yep that's more.

700 hp with twin turbos; yep that's more again.

There, I saved you alot of time and money.

[Captkaos]

Well it won't cost me anything except for the twins.  Motor is already bought.
Hopefully it will be more like 800-900hp with the twins, unless you were talking about 7lbs of boost.

[eventhorizon66]

I meant money on dyno runs.

Wow, with 800+ hp it'll be a real beast.  I guess I'd be shooting for high numbers too, if I invested in twin turbos.