How much overbore safely?
Thread Starter
|
More Turbo
Joined: Jul 2005
Posts: 579
Likes: 7
From: Auburn, CA
I've gone over what you said and I'm not convinced of what you are saying (no disrespect intended).
I can't imagine any modern designed for EFI cylinder head not flowing enough for 2500 RPMs. I'm not saying SMALL gains can't be made at that target RPM by what you have done and suggested. What you have done has helped a little bit but it is no silver bullet.
To get more power at 2500 RPMs the requirements (as long as no huge basic design problem exist) is displacement, compression, valve timing and fuel.
I've built a Chevy 250 back in 1982 with a forged crank, custom 10.1 forged pistons, custom designed cam by Chet Herbert, 327 Chevy valves, ported head, split six headers, Carter 400CFM 4BBl, the last Crane electronic distributor and MSD ignition box. The engine was in a 1966 short bed and it could pull a 6500 trailer up a very steep grade in top gear (4 speed) at 75 MPH with ease at half throttle.
I don't have the time or money to that again.
I'm thinking that changing the cam alone could help quite a bit and the next step would be milling the head .030.
I'll keep the group informed and I might do some before and after dyno work just to quantify (whatever I might do!).
Silver Streak: Can you send me your dyno raw data? Dynojet?
Thanks again!!
Vince
I can't imagine any modern designed for EFI cylinder head not flowing enough for 2500 RPMs. I'm not saying SMALL gains can't be made at that target RPM by what you have done and suggested. What you have done has helped a little bit but it is no silver bullet.
To get more power at 2500 RPMs the requirements (as long as no huge basic design problem exist) is displacement, compression, valve timing and fuel.
I've built a Chevy 250 back in 1982 with a forged crank, custom 10.1 forged pistons, custom designed cam by Chet Herbert, 327 Chevy valves, ported head, split six headers, Carter 400CFM 4BBl, the last Crane electronic distributor and MSD ignition box. The engine was in a 1966 short bed and it could pull a 6500 trailer up a very steep grade in top gear (4 speed) at 75 MPH with ease at half throttle.
I don't have the time or money to that again.
I'm thinking that changing the cam alone could help quite a bit and the next step would be milling the head .030.
I'll keep the group informed and I might do some before and after dyno work just to quantify (whatever I might do!).
Silver Streak: Can you send me your dyno raw data? Dynojet?
Thanks again!!
Vince
Postmaster
Joined: May 2002
Posts: 3,241
Likes: 3
From: Broken Arrow, OK
I think you misinterpreted my statement. The head flows plenty of air in stock trim at 2500 rpm and it is a significant restriction by 3500 rpm. Any item you add to the engine to increase its airflow capacity will reduce the rpm at which the head becomes a restriction. For example, when I added headers and exhaust my engine went from pulling to about 3600 rpm to pulling to only 3100 rpm because that was all the air the head could flow. You can actually watch it on the air/fuel ratio display when it runs out of air and starts getting rich. If you add lots of displacement the rpm potential drops even further. The point is that the head is the key component in the engine. Without working it over you will not get your money's worth out of anything else.
What types of raw data do you want? There are several of my dyno charts floating around. One is in the thread titled "EFI 300 vs EFI 302" or something like that. There are also a few in my gallery.
What types of raw data do you want? There are several of my dyno charts floating around. One is in the thread titled "EFI 300 vs EFI 302" or something like that. There are also a few in my gallery.
Thread Starter
|
More Turbo
Joined: Jul 2005
Posts: 579
Likes: 7
From: Auburn, CA
For my needs I don't have much interest above 2700 RPM. I just need a little bit more torque between 2000-2500 to make towing a little less demanding.
If you used a Dynojet you might have downloaded the data file that resulted from your runs. I would like too see the differences in your curves using the Dynojet software.
TIA,
Vince
If you used a Dynojet you might have downloaded the data file that resulted from your runs. I would like too see the differences in your curves using the Dynojet software.
TIA,
Vince
Postmaster
Joined: May 2002
Posts: 3,241
Likes: 3
From: Broken Arrow, OK
You might try installing a timing gear set that installs the cam straight up instead of retarding it. That should help on the bottom end.
All my pulls have been on a Dynojet, but I just have the charts. My first chart is in my gallery, the other one is in the thread I mentioned previously.
All my pulls have been on a Dynojet, but I just have the charts. My first chart is in my gallery, the other one is in the thread I mentioned previously.
Thread
Thread Starter
Forum
Replies
Last Post
IDI guy
Pre-Power Stroke Diesel (7.3L IDI & 6.9L)
22
Mar 3, 2013 11:25 PM
Aaron-71
Small Block V8 (221, 260, 289, 5.0/302, 5.8/351W)
13
May 13, 2011 12:12 PM
trinogt
Big Block V8 - 385 Series (6.1/370, 7.0/429, 7.5/460)
14
Feb 19, 2003 09:57 AM
