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compression ratio for the 2.8 v6 by LorenBateman
Started on: 11-01-2014 01:13 PM
Replies: 6 (529 views)
Last post by: TK on 11-08-2014 11:24 PM
LorenBateman
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Report this Post11-01-2014 01:13 PM Click Here to See the Profile for LorenBatemanClick Here to Email LorenBatemanSend a Private Message to LorenBatemanEdit/Delete MessageReply w/QuoteDirect Link to This Post
Hello boys!! Anybody know what the ratio is for these engines,,and what is the best fuel octane to use..88GT stock as a rock!!!!!!!
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dobey
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Report this Post11-01-2014 02:03 PM Click Here to See the Profile for dobeySend a Private Message to dobeyEdit/Delete MessageReply w/QuoteDirect Link to This Post
Around 9:1 stock, I think, probably slightly less after 25 years of wear. You should use at least 87 octane on a stock engine. Higher octanes won't hurt the engine, but won't help it either. So don't waste money on premium unless you're swapping in an engine which requires it, or modifying your engine in some way (such as extremely advanced timing) that would need it.
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RotrexFiero
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Report this Post11-01-2014 07:03 PM Click Here to See the Profile for RotrexFieroClick Here to visit RotrexFiero's HomePageSend a Private Message to RotrexFieroEdit/Delete MessageReply w/QuoteDirect Link to This Post
Yes, what he said.
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fierogt28
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Report this Post11-01-2014 11:25 PM Click Here to See the Profile for fierogt28Click Here to Email fierogt28Send a Private Message to fierogt28Edit/Delete MessageReply w/QuoteDirect Link to This Post
The spec is 8.5:1
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LorenBateman
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Report this Post11-02-2014 12:35 AM Click Here to See the Profile for LorenBatemanClick Here to Email LorenBatemanSend a Private Message to LorenBatemanEdit/Delete MessageReply w/QuoteDirect Link to This Post
Thank you gentleman
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BillS
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Report this Post11-08-2014 07:19 PM Click Here to See the Profile for BillSClick Here to Email BillSSend a Private Message to BillSEdit/Delete MessageReply w/QuoteDirect Link to This Post
Regular works fine.

I could get by with 91 octane on 12 psi of boost without knock.
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TK
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Report this Post11-08-2014 11:24 PM Click Here to See the Profile for TKSend a Private Message to TKEdit/Delete MessageReply w/QuoteDirect Link to This Post
It's 8.9 on the Fiero/Celebrity/Citation/U-Van iron head HO engines. The standard engines were 8.5.

The boost is a balance of pressure and spark advance. You can crank up the boost but you have to back off the timing. Rule of thumb is you have to trade 1 degree of advance for every 2 psi of boost. When you are starting with only 10-12 degrees of advance you don't have a lot of room. Intercooling will allow more boost and/or advance. You obviously get more power from boost. As the compression ratio goes up the boost/advance has practical limits. Unless you have a knock sensor you must be conservation with both. On the flip side if you lower the compression in an effort to increase the boost/advance you run the risk of the engine having little power when there is no boost (like before the turbo spools.) 8.5 is a nice balance for boost. 8.9 is starting to get up there on these engines if you want to run some serious boost. Only the laster aluminum head engines with intercooling and better pistons could start to run boost much over 15 psi and definitely with a knock sensor.

I am still amazing that my HHR SS runs 20-23 PSI of boost and gets 290HP out of 2L. Of course the advance is only about 11 degrees at WOT.

[This message has been edited by TK (edited 11-08-2014).]

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