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Update on the Carbed 3100 by trotterlg
Started on: 09-29-2013 12:22 AM
Replies: 7 (244 views)
Last post by: trotterlg on 09-29-2013 06:31 PM
trotterlg
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Report this Post09-29-2013 12:22 AM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
It is in the car and running well now. About 150 miles on it plus the run time on the cradle. Muncy with the 4.10 ratio, the car is still pulling strong at 80 in third turning about 6,000, so I think it will proably limit out at about 90 before you havfe to go to 4th, will wait until it has a few more miles on it to spin it that high. The engine starts running well about 3,000 to 3,500, you can drive it in town at 2,500, but not much lower. It has a really odd performance band, holding the throttle in one place (down a lot) from about 3,000, it increases power as the RPM builds, so that you need to let off throttle to keep the same acceleration as the cam comes on, kind of the opposite of what a stock Fiero will do. Not bad, but if it is wet out you need to take care as it builds quickly and can bite you. The weather is bad here, so it it hard to get to a place you can really do stuff, but it sure looks like life is good. It is not a brute force V8 for sure, but it sure seems to suit this nice little car, bet it will be hot one at the Auto Cross. Larry
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Arns85GT
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Report this Post09-29-2013 01:19 PM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
This sounds like the carb is too big. On your 3100 you need something below 500 cfm I recoll the 390 cfm 4 barrel would work because the primary venturi are on the small side, making your lower rpm band more efficient. Or is it an aggressive, lumpy cam?

To make a comparison, my 4.9 works pretty much perfectly with a 500 cfm, and my 2.8 ran a bit rich with the 390 cfm

Any idea why your under 3000 is weaker?

Arn

[This message has been edited by Arns85GT (edited 09-29-2013).]

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trotterlg
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Report this Post09-29-2013 02:49 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
It has a agressive cam, very small LSA angle (99 degrees) and lots of overlap. It runs exactly like it should with that cam. Idle is lumpy at 1,200. Larry
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Arns85GT
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Report this Post09-29-2013 04:47 PM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
So it's set up as a screamer? Sounds like fun. What is your top rpm before it runs out of steam?

Arn
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trotterlg
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Report this Post09-29-2013 05:45 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
Had it to 7,000 in second and it was still pulling nice, it only has 200 miles on it now, so I am afraid to turn it high very much, I really don't know how high it will spin, has LS6 springs and there was no sign of valve float, but it does have hydraulic lifters, so I don't think it will do much more than that before they pump up. Just from the short time it has been running I think a high spinning engine is the way to go, it is just pure fun to drive, it starts really running good about the place that the stock 2.8 starts to fall on it's face, so it is hard to get used to, totally changes the character of the car for sure. Larry
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Report this Post09-29-2013 06:02 PM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
With the 4 speed I agree. My carb'd 4.9 spins up to 6000 no problem, but I have aluminum valve trees and before I really let it out I need to swap them for Allante steel ones.

The engine gets pretty buzzy at anything over 60 mph, and 5th gear looks awfully good at that speed. However, my tranny is the 3.65 and for the amount of highway I do, I am just as happy with the power to 6000. Once I get the new clutch in, I'll dyno it. My suspicion is it is turning out about 220 hp and 310 torque at 3,000 rpm. based on the clutch breaking loose there and the seat of the pants test.

I'll bet the 3100 has a rising power curve through the rpms and that equals muchos fun

Arn
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Report this Post09-29-2013 06:03 PM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post

Arns85GT

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Member since Jul 2003
With the 4 speed I agree. My carb'd 4.9 spins up to 6000 no problem, but I have aluminum valve trees and before I really let it out I need to swap them for Allante steel ones.

The engine gets pretty buzzy at anything over 60 mph, and 5th gear looks awfully good at that speed. However, my tranny is the 3.65 and for the amount of highway I do, I am just as happy with the power to 6000. Once I get the new clutch in, I'll dyno it. My suspicion is it is turning out about 220 hp and 310 torque at 3,000 rpm. based on the clutch breaking loose there and the seat of the pants test.

I'll bet the 3100 has a rising power curve through the rpms and that equals muchos fun

Arn
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trotterlg
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Report this Post09-29-2013 06:31 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
Rising power curve is a good explination, holding the throttle at a given opening has the result that the acceleration increases as the rpm increases without putting in more throttle, very strange to drive if you have not experienced it before, but I can say it is fun for sure. Checked the mileage it gets, freeway with some on and off ramps is about 17. Larry

[This message has been edited by trotterlg (edited 09-29-2013).]

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