ITB size for 3.2ss?

[YTNUKLR]

She will like that GE40 3.2 long-stroke. Probably scare her nicely and then she won't want to drive it again

Or she will like it ...and there's not much hotter than a girl who drives a pumped up 911 like that!

The real question is, Does she like RSR cams?

[78SCRSMAN]

I have not purchased cyls or pistons yet. I've thought about a 3.0 but figured if I need to buy new cyls, why not go w/98mm?
I have a budget too so would all this be better suited for a 3.0?
Usable 95mm jugs will save some $ but not much.

I think the engine sounds a bit confused.



In general:

ITBs and a short stroke are better for high rpm to run race cams and have durability.



Yet, you plan to have a relatively low redline to use GE20 or 40 cams. Pretty mild.



If you are doing a 3.2 displacement, I like Aaron's recommendation of a 40mm port and 42/44mm throttle plates.



However, a street motor with a 6500 redline would be a better 3.2 as a long-stroke 3.2 in my opinion. Stroke, rod length-to-stroke ratio all indicate the long-stroke 3.2 is going to fill the cylinders better at lower r's, and that is what power is all about. If you already have the pistons and cylinders, you might play with the rods to get this to work, and yield a 3.4L. (98X74.4) But I think you will have more fun with your engine as a long-stroke than short. Dynamic compression ratio is a bit high with a GE20 cam , I'd go for the GE40 or drop the compression down a tad, 10.3:1 would probably be OK on pump gas. Other than that a nice GE40 long-stroke 3.2 @10.5:1 will make a fantastic street motor. 40mm ports and 42mm-44mm throttle plates



If you do indeed want to trade off some torque and build a 3.2SS, it is a nice motor for sure. But then you probably want to rev it, to 7000-7500 (or yes, even up to 8k), get a cam to suit, like a DC60 or more. This would be what I would do personally, because I like big cams and revs. A 40mm port is still probably adequate for this..maybe 41.



Best of luck.

Scott

[safe]

Originally Posted by 78SCRSMAN

I am planning to use motorcycle throttles as many here have done. I've just been looking at the gsxr600/750 sizes, 38/42 respectively. The ignition will be crank fired and controlled by the MS using EDIS. As for heads, I was planning on the later ones so the ports can be sized accordingly. So far it sounds like the 42mm TB's are a good bet.
They will be mounted atop some weber or equivalent manifolds.
As for the redline, I just threw that out there. I have no issues going higher. I might cap it off around 7200?

Simular to what I have done.
The best advice I can give you is to ditch the MS and get a proper EFI, most MS installation I have been in contact with/heard about has had lots of problems. Most tuners will not touch them. My other advice is to take the car to a tuner with a rolling road dyno and get it dialed in. I promise, it will be the best money you spend on this project.

[jpnovak]

I think MS is a proper EFI system. Most tuners do not understand the true capability of the system.

I am using 46mm ITBs on my 3.2SS. Personally they are too big. Great at high rpm but the low speed and off-idle transition is tricky to tune since the swept area is very large. If they made a 42 or 43mm ITB I would probably have them on my motor.

My car has a street rev limit of 7K. I have pushed this to 7300 at the track with no ill effects. Of course, the cams DC40 are pretty much done by this point.

[78SCRSMAN]

jpnovak, thanks for posting. I'm almost wondering if the 38mm throttles would be best. Perhaps I should look for some 40's for this street motor. I'm more interested in low end torque since that's where most of my driving will take place.

[brads911sc]

I have no issues with MS.. took me 2-3 hours to tune. no hesitation, no stumble. a rocket. not sure if you have ever worked with MS, but your argument shows how little you know about it.

Originally Posted by safe

Simular to what I have done.
The best advice I can give you is to ditch the MS and get a proper EFI, most MS installation I have been in contact with/heard about has had lots of problems. Most tuners will not touch them. My other advice is to take the car to a tuner with a rolling road dyno and get it dialed in. I promise, it will be the best money you spend on this project.

[brads911sc]

if you go large port 3.0 heads, the 38s are abit small. id go 40's. 42 max.

Originally Posted by 78SCRSMAN

jpnovak, thanks for posting. I'm almost wondering if the 38mm throttles would be best. Perhaps I should look for some 40's for this street motor. I'm more interested in low end torque since that's where most of my driving will take place.

[brads911sc]

GT2-108 or 40's are a great cam for a street car. 3.2SS will top out at 6500 RPM with this cam... so perfect mid range. 3000-6500 is the heart of the curve.

[quaz]

Megasquirt has added an improved ITB mapping mode to make blending tables quicker and easier to tune. Just make sure you get an MSII processor or an MSIII if you can swing it. You get the bigger tables and more tuning options. I would say MSI is fine for fuel only on a stock manifold, but if you want to do ignition and ITBs you will need MSII.

That being said properly sizing your ITBs will make all the difference in the world in throttle response. If the are too big you will have a B*^$H of a time tuning them with any EFI. I used the 38mm throttles on my 2.2 and figure that setup would be good up to 3.0L max. If I was going 3.2L start with I would use the 42mm which tapers down from a 48mm opening. Then port match your manifold to the 42mm throttle. You will have more than enough surface area, but won't be oversized to the point of impacting tunability.

Here are some options if you have not already looked at this site.
Sylva Mojo Build Diary

[YTNUKLR]

I think it's hard to say what you should build. It's a taste thing as much as anything. You have to figure out what you want.

A 3.0 or 3.2SS will be a bit revvier and have a bit less torque than a standard 3.2 and 3.4 etc. What's worth it to you on the hp/$ curve? A 3.0 is probably the best on the hp/$ curve but maybe you want more.

My personal taste is a hooligan ride as I stated. I do trade off some torque for that. Needs gears to really make it work. Probably over-cammed for some drivers. To me, a 3.4 on DC40 is a tractor motor and you can cam it up with RSR cams and it will still work OK around town, as long as you didn't go bigger than stock 3.2 ports.

Your preference might be torque, and you might be faster round town waiting for me to get up on cam. In that case a 3.2 standard stroke (95x74.4) motor with compression and some GE40s is hard to beat. It really is.

I do think a 46 TB is too big on a 3.2, unless it is cammed up. I think a 38 TB is much too small though for any of this.

Generally you want your TB to be 2-4mm bigger than your port. 3.2 stock 40mm ports will flow well all the way up to a DC60 3.4 engine.

A recommendation if I may, I'm guessing from your response what you're probably looking for:
3.2 Carrera core engine
-stock heads and ports
-GE40s
-42mm TBs
-Use your standard 3.2 Pistons/Cyls, machine valve reliefs for the GE40s. 9.3;1 CR. Maybe try to find some nice used Euro 3.2 P/C for a little more CR.

A similar slightly more expensive rec>
-Same thing, but...
-44mm TBs
-98mm pistons and cylinders with 9.3-9.5:1 or 10.5:1 on twin plugs
-MAYBE switch the cams up to DC60 if you're game

As I learn more and more, I realize power is mostly about air velocity. Big throttles can really slow down flow. Also, 1-2mm may seem like a small change, but realize that what you are changing is the cross-sectional area all the way down the throttle body. That can be a lot more volume if you make it only a little bigger. Remember the formula for area of a circle, pi*r^2, r is being squared , so a small change in the r has a big change on the area.

[78SCRSMAN]

I have a 3.0 short block. Still need heads, cams, jugs, pistons.
Car weighs (will weigh) 2300lbs.

[rsscotty]

You might consider CP pistons. Jeff Gamroth @ Rothsport can help you with this.

[safe]

You read a lot about Tb-size and everybody has an opinion. I found my 50mm very cheap so I tried them. I was scared dead when I read here that they would be waaaay too large.
In reality the engine pulls over 300 nm from 2000-6000 rpm with stock cams, that's more than a stock 3.6!!
The "problems" I have is that it is a little on/off on the throttle and under 2000 rpm its a little notchy and I have to run it real rich.

But if you want a silky smooth street engine, DIY ITB ant DIY EFI is not the best approach...

I would rather err on the large side.

I did a lot of research of different EFI systems when I did mine. I stand by my opinion that MS is a toy. There are good, inexpensive EFI systems out there. I decided on Emerald, its been around forever and its still developed and top notch. Ended up double the cost from a pre built MS.

[78SCRSMAN]

Thanks Magnus for your input here. I am a subscriber to your thread and have read the links there. It seems there really is no "chart" to go by. Lots of determining factors to look at. I think I'm going to settle on the 42mm plates for my project though. As for cams, I'm still in the part collection phase and am in no hurry... well if I had the $ I need now... Anyway, I'll wait and see what comes up cam-wise between now and then.
As for the DIY aspect, if you only knew me. I love to tinker on things and have the skills.

[lindy 911]

If you have the "skills" you're home free. Consider this:
3.0 Mahle cylinders (stock de-glazed)
10.5 : 1 JE pistons
Stock re-built '78 SC heads with race springs and retainers
GE60 cams
Aaron Burnham twin plug
46 Webers (easy to tune)

3 out of 3, drives away from a 2008 350Z from a roll on; no contest. Drives perfectly around town, you'd never know it had big cams. Let it run up to 4K and hang on.

Brad, maybe you and I can do a little heads up running now that your car is back on the road and report back here what we find.

[78SCRSMAN]

Lindy,
Love your motor too. I've read your thread many times over. The trouble with 3.0 cyls is when they can be found they just aren't reasonably priced compared to 98mm jugs.
What I've found is usable 95mm jugs tend to sell for about $600 and NEW 98mm jugs can be had for $1200. By new, I mean the Japanese ones OR 95mm cores that are punched out and re-plated. So we're talking a difference of $6-7 hundred. HP per $ ratio is to low to pass up given the pistons cost the same either way.

[GaryR]

Originally Posted by BURN-BROS

The stock redline for a 70.4 stroked S was 7300rpm with stock rods and bolts.

Throttle plate size should be a minimum of 2mm over the port size.

I like 40mm ports with 42/44 mm plates.

Sounds like I will be using 40mm ITBs on my 38mm ports, as Brads911SC is doing. 3.2SS, 10.5:1, SS cams, 90% street car..

[brads911sc]

Sorry Lindy, I missed this. Would be happy to test these out...

Good Choice Gary. You will be happy.