Pennock's Fiero Forum
  Technical Discussion & Questions
  3.4 pr with 2.8 crank. Lower compression and turbo?

Post New Topic  Post A Reply
Email This Page to Someone! | Printable Version


next newest topic | next oldest topic
3.4 pr with 2.8 crank. Lower compression and turbo? by Sideway-swede
Started on: 02-23-2015 03:12 PM
Replies: 7 (236 views)
Last post by: 2.5 on 02-25-2015 01:58 PM
Sideway-swede
Member
Posts: 19
From: Uppsala, Sweden
Registered: Jan 2015


Feedback score: N/A
Leave feedback

Rate this member

Report this Post02-23-2015 03:12 PM Click Here to See the Profile for Sideway-swedeSend a Private Message to Sideway-swedeEdit/Delete MessageReply w/QuoteDirect Link to This Post
Hi Guys!

Have you ever seen anyone use the crank from the 2.8 with the 3.4 block, pistons and connecting rods? I don't know the length of the conrods, is there a difference between the ones in the 2.8 and the ones in the 3.4? The point of these modifications would be to lower the compression and thus make it more turbo-friendly.

------------------
/Morgan

1988 Fiero GT 5-speed

IP: Logged
PFF
System Bot
Sigler85GT
Member
Posts: 209
From: Elkhart, IN
Registered: Aug 2010


Feedback score: N/A
Leave feedback

Rate this member

Report this Post02-23-2015 05:13 PM Click Here to See the Profile for Sigler85GTClick Here to Email Sigler85GTSend a Private Message to Sigler85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
You'd need a custom piston as the wrist pin location causes an issue. Someone else can chin in with more detail. Or google a 3000 hybrid.
IP: Logged
Joseph Upson
Member
Posts: 4908
From:
Registered: Jan 2002


Feedback score: (2)
Leave feedback





Total ratings: 88
Rate this member

Report this Post02-23-2015 06:26 PM Click Here to See the Profile for Joseph UpsonClick Here to Email Joseph UpsonSend a Private Message to Joseph UpsonEdit/Delete MessageReply w/QuoteDirect Link to This Post
Do not lower compression if it's only 9:1 compression and you intend to run no more than 15 psi, it would be counter productive. Remember these motors are designed to run 87 octane so premium fuel and programming should be sufficient to accommodate a good level of boost. As for using the 3" stroke 2.8L crank in place of the 3.31" stroke 3.4L crank, don't do it, unless you're planning on custom pistons, otherwise you'll ruin the quinch area (distance between the outer top perimeter of the piston and the cylinder head) which can cause spark knock. The piston should be no more than about .040" from the cylinder head especially on the old iron heads which are not as efficient as the aluminum heads. The rods are the same between the engines at 5.7" as well as the journal diameter.

[This message has been edited by Joseph Upson (edited 02-23-2015).]

IP: Logged
Sideway-swede
Member
Posts: 19
From: Uppsala, Sweden
Registered: Jan 2015


Feedback score: N/A
Leave feedback

Rate this member

Report this Post02-24-2015 04:22 AM Click Here to See the Profile for Sideway-swedeSend a Private Message to Sideway-swedeEdit/Delete MessageReply w/QuoteDirect Link to This Post
Ok, thanks for the info...

------------------
/Morgan

1988 Fiero GT 5-speed

IP: Logged
E.Furgal
Member
Posts: 11708
From: LAND OF CONFUSION
Registered: Mar 2012


Feedback score:    (23)
Leave feedback





Total ratings: 278
User Banned

Report this Post02-24-2015 11:23 AM Click Here to See the Profile for E.FurgalSend a Private Message to E.FurgalEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Joseph Upson:

Do not lower compression if it's only 9:1 compression and you intend to run no more than 15 psi, it would be counter productive. Remember these motors are designed to run 87 octane so premium fuel and programming should be sufficient to accommodate a good level of boost. As for using the 3" stroke 2.8L crank in place of the 3.31" stroke 3.4L crank, don't do it, unless you're planning on custom pistons, otherwise you'll ruin the quinch area (distance between the outer top perimeter of the piston and the cylinder head) which can cause spark knock. The piston should be no more than about .040" from the cylinder head especially on the old iron heads which are not as efficient as the aluminum heads. The rods are the same between the engines at 5.7" as well as the journal diameter.



I'd not be so quick to say don't do it,, yes the way the o/p asked, would not be a good idea...
but a 3" stroke with a longer rod in a 3.4 might be just the ticket.. finding a rod to work tho, hard isn't as hard as it used to be...
all of them use 5.7" rods (2.8/3.1/3.4) same length as the chevy v8 , the v6 •Rod journals are 1.998 to 1.999" The v8 are 2.00" small journal or the 2.1" for much of everything after '67 ish
The 3.4 bore is 3.62" the 262v8 was 3.671 and the 265 was 3.75
making the 262v8 piston an opinion maybe. 3.4 60 over is 3.68 30 over is 3.65 40 over is 3.66" and 50 over hits the magic 3.67" almost the same size as the 262v8 of 3.671 so a 3.4 50 over and a hone to get it from 3.67 to 3.671 .. now nascar chevy v8 rods use a rod journal size of 1.89" and the 60*v6 it's 1.998/1.999" offset grind the v6 crank to get the 1.89 make up the stroke difference of the 2.8 crank of 2.99" to the 3.4's 3.31( a .32" difference) and you are mighty close, as the v6 deck height is 8.819" and the v8 9.02 for a difference of .201" straight grinding the crank rod journals gives you .109 add that with the deck height differences and you get .31 out of a needed .32" offset grind the crank a tiny tiny amount, and BOOM.. you are there..
a short stroke, 50 over 3.4ltr using cheap parts, as used nascar rods are cheap and will be overkill in this.. If a 3.4 block will go to 3.75" it opens huge piston options, as far as cheap.. 262 pistons are cheap also, but forged ones might be a one off..
oh you could have tons of fun building oddball stuff.. offset grind the v6 crank, nascar 6.25 rods, and pistons with the correct pin height.. the 3.4 piston height is 4mm less than the 2.8

[This message has been edited by E.Furgal (edited 02-24-2015).]

IP: Logged
Joseph Upson
Member
Posts: 4908
From:
Registered: Jan 2002


Feedback score: (2)
Leave feedback





Total ratings: 88
Rate this member

Report this Post02-25-2015 11:46 AM Click Here to See the Profile for Joseph UpsonClick Here to Email Joseph UpsonSend a Private Message to Joseph UpsonEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by E.Furgal:


I'd not be so quick to say don't do it,, yes the way the o/p asked, would not be a good idea...
but a 3" stroke with a longer rod in a 3.4 might be just the ticket.. finding a rod to work tho, hard isn't as hard as it used to be...
all of them use 5.7" rods (2.8/3.1/3.4) same length as the chevy v8 , the v6 •Rod journals are 1.998 to 1.999" The v8 are 2.00" small journal or the 2.1" for much of everything after '67 ish
The 3.4 bore is 3.62" the 262v8 was 3.671 and the 265 was 3.75
making the 262v8 piston an opinion maybe. 3.4 60 over is 3.68 30 over is 3.65 40 over is 3.66" and 50 over hits the magic 3.67" almost the same size as the 262v8 of 3.671 so a 3.4 50 over and a hone to get it from 3.67 to 3.671 .. now nascar chevy v8 rods use a rod journal size of 1.89" and the 60*v6 it's 1.998/1.999" offset grind the v6 crank to get the 1.89 make up the stroke difference of the 2.8 crank of 2.99" to the 3.4's 3.31( a .32" difference) and you are mighty close, as the v6 deck height is 8.819" and the v8 9.02 for a difference of .201" straight grinding the crank rod journals gives you .109 add that with the deck height differences and you get .31 out of a needed .32" offset grind the crank a tiny tiny amount, and BOOM.. you are there..
a short stroke, 50 over 3.4ltr using cheap parts, as used nascar rods are cheap and will be overkill in this.. If a 3.4 block will go to 3.75" it opens huge piston options, as far as cheap.. 262 pistons are cheap also, but forged ones might be a one off..
oh you could have tons of fun building oddball stuff.. offset grind the v6 crank, nascar 6.25 rods, and pistons with the correct pin height.. the 3.4 piston height is 4mm less than the 2.8



I admire the enthusiasm but the total expense involved in what you suggest above far exceeds in parts, modification and labor expense for what will be a disproportionately low return in performance for the investment compared to the other options available. Thicker Cometic head gaskets would save a lot of time and money, as well as putting iron heads on an aluminum head short block of the desired displacement (which I have done before and received excellent performance and fuel economy despite what many have said would result), or just use the rotating assembly. The combination of de-stroking and sending the compression ratio into the basement will pretty much be a lateral move in the end in terms of power output.
IP: Logged
Lou6t4gto
Member
Posts: 8419
From: Ocala, FL USA
Registered: May 2008


Feedback score:    (7)
Leave feedback

Rate this member

Report this Post02-25-2015 01:07 PM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
All this work and expense just to end up with a 2,8 ?? even with all the "improvements", it's still a 2.8
IP: Logged
2.5
Member
Posts: 40898
From: Southern MN
Registered: May 2007


Feedback score: (1)
Leave feedback





Total ratings: 178
Rate this member

Report this Post02-25-2015 01:58 PM Click Here to See the Profile for 2.5Send a Private Message to 2.5Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Lou6t4gto:

even with all the "improvements", it's still a 2.8


That may be why its cool.
IP: Logged

next newest topic | next oldest topic

All times are ET (US)

Post New Topic  Post A Reply
Hop to:

Contact Us | Back To Main Page

Advertizing on PFF | Fiero Parts Vendors
PFF Merchandise | Fiero Gallery | Ogre's Cave
Real-Time Chat | Fiero Related Auctions on eBay



Copyright (c) 1999, C. Pennock