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Discussion Starter #1
Here's the set up so far.

AEM CAI (3")

GSR intake manifold ported out to a 68 mm TB opening. Runners also ported. Butterflies removed.

In two weeks JDM CTR pistons go in giving me roughly 12:1 compression. I'll probobly put a thicker spoon headgasket in, to lower it a bit, maybe 11.7:1.

Thinking about going with Rockt Motorsports M24A cams. Or Skunk2 Stage 2's.

Odvioudly the throttle body is going to be a 'choke' point. I need at least 68mm to have the same diameter as the TB port.

Suggestions?

Oh, the Comptech Race header and Hytech exhaust arrive this week too... Yea! (No I didn't forget about fuel, I'll be running 310's initially, maybe move up to DSM 450's if need be.)
 

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With a 11.7:1 or higher can you still run 93 octane pump gas? or will you need to use high octane race gas? I want to do this exact setup, except I have a Skunk2 IM, and different header and exhaust, but done want to lose ALL street drivablity. As for the TB, you should use a Tapered TB design, This creates air velocity which is need for N/A motors. Possiably a 68mm to 66mm Taper, I am not sure exactly how it goes, I too am still in the research phase of the motor. Try the search here.
Ryan
 

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I have used STR, BBK and Edelbrock TB on my GSR.
I felt more power with STR but I could not get the idle correct with the AC on.
Edelbrock worked the best for me. The TPS was not set right but once I got that set I had no problems with it.
If I did not need AC I would have kept the STR throttle body
 

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docputnam on Feb/10/04 said:
Odvioudly the throttle body is going to be a 'choke' point. I need at least 68mm to have the same diameter as the TB port.
obviously?

obviously you don't understand how a single plenum IM works and fills.

you choose the TB size based on the plenum volume not the IM port diameter.

if you go too big, then you kill the flow speed into the plenum (momentum, flow energy, pressure differential) and kill your accelerating capability in the high rpm powerband. a huge TB will give your butt dyno (low rpm) satisfaction but your et will suffer.

we covered this in multiple TB posts (enter throttle body into the search window and see what you get or do a throttle body topics search geared for just the performance forum or MD Tech forum using an advanced search to get rid of the FS or WTB posts) and on the last page of the IM article here.

it's not the choke point. The IM and head/valve angles/valves and cams are your choke points.

Consider that Chris Rado's old 800+ whp turbo GSR used a 62mm TB...the Kinsler IM he used had a huge plenum...that's why he went that size.

If you really believe that bigger is better, do what the guys at honda-tech used to recommend and learned to their chagrin: get an Infiniti Q45 TB 75mm bore and bore your IM to portmatch and tell us what happened to your et.

bigger is not always better. You have to understand how something works with other parts before you buy it. That's why we're here.
 

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Down-Nola on Feb/10/04 said:
With a 11.7:1 or higher can you still run 93 octane pump gas? or will you need to use high octane race gas?
if you know how to fuel tune on a dyno using a wideband O2 sensor for realtime AF ratios and can reprogram your ECU, you can use 91 octane in 12.5:1 CR motors. Having an accurate oil temp gauge or water temp gauge or readout also helps. You'll need to upgrade the fuel delivery (injectors and pump once you get up to 12:1). those stock 240 injectors won't do the job for you.

if you are running a stock ECU (I don't care if it's OBD1 or not..because it makes no difference anyway because the fuel tables and ignition tables are identical to the OBD2's despite the hype) and can't fuel tune then you can't run 12:1 with 91 octane and have a decent powered motor. It'll run like sh*t and detonate.
Most people who don't have access to fuel tuning don't push past 11.5:1 (the stock ECU can handle that with a VAFC and FPR).
 

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Think about it in terms of how the air enters the cylinders at different engine speeds. More air mass at lower rpm's means more torque whereas more air velocity at higher rpm's equates to more HP and lower ET's (theoretically).
 

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Discussion Starter #10
MichaelDelaney on Feb/10/04 said:
obviously you don't understand how a single plenum IM works and fills.
No, I don't. I'm a comlete noob an engine tuning. I'll go read those articles you suggested. Thanks.
 

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Discussion Starter #11
I read a couple of those articles, and learned something new. Thanks TI.net!

So, I'm sticking with the OE GSR TB for now, and looking for a good deal on a ITR TB. Will the ITR TB bolt right up to the GSR IM?

Also, learned my AEM CAI may not be the best choice for a big cam motor like I'm building. Is there a J's racing style intake for the GSR? I've only seen the two for the ITR....

Thanks again.

Oh, and these just arrived in the mail today!
 

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tegboy1342 on Feb/10/04 said:
Think about it in terms of how the air enters the cylinders at different engine speeds. More air mass at lower rpm's means more torque whereas more air velocity at higher rpm's equates to more HP and lower ET's (theoretically).
this isn't theoretical. this is what people have shown that works in our engines.

restrictor plate racing has also shown this to be true in Tegs as well.

the low rod ratio of our Tegs already causes the piston speeds to be optimized for cylinder filling during the intake stroke at low-mid rpms. So if you already are having enough suck at low rpms an oversized TB bore will just make that more apparent. But as rpms increase, the time spent in the intake stroke shortens. Our low rod ratio and the pistons speeds away from TDC don't help cylinder filling under these conditions. The low rod ratio engine needs help filling at high rpms from ram air and scavenging. You need good flow speeds out of the IM plenum and down to the head to create the ram air. If the TB is too big, the flow speed dies. Couple that with a shorter fill time and a big TB bore just kills filling at the top rpms where you need it the most for low ets.

This isn't theory. People have theorized it and then shown this theory to be true in real life.

You have to understand how the engine parts work together: rod ratio, cam spec, port size, IM plenum volume and runner dimensions, and TB bore. They are all connected. Each one determines the other's size. They inter-relate. They all center around where your powerband
should be placed along your rpm range.
 

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docputnam on Feb/10/04 said:
So, I'm sticking with the OE GSR TB for now, and looking for a good deal on a ITR TB. Will the ITR TB bolt right up to the GSR IM?
the channels are slightly different but it will bolt up fine.

You have to bore the 60 mm GSR IM port to match the ITR TB's 62mm bore on the plate side.

The throttle cable positions are a bit different and you may have to fiddle with that a bit to make it work but nothing insurmountable.
 

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Discussion Starter #14
MichaelDelaney on Feb/11/04 said:
You have to bore the 60 mm GSR IM port to match the ITR TB's 62mm bore on the plate side.
Well, the original reason I wanted a 68mm or bigger TB is that I bought a nicely ported and gutted GSR IM that has a 68 mm TB opening.

So I guess I'll have an 'anti-reversion' step there.

Here's the IM I purchased-

LINK!
 
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