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#1
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Advice Needed on raising compression on SD455
I hope this has not been covered too many times in the past. I did couple searchs and found nothing. Looking for advice on options for raising the compression on a .030 bore SD455. Will be putting motor basically back to stock but I would like atleast 9.2 compression maybe as high as 9.5. probably run a Ram Air IV cam. 1973 Trans Am, Auto, 3.42 Gears.
Picture just becasue people like them. LOL
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Brad Pringle Wellston, Michigan 1973 SD 455 TA Auto 1974 SD455 TA 4 Spd |
#2
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I think with those heads you will need a piston with a small dome.Tom
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#3
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Hi Tom,
Thank you for the input. Do yo have any experiance with Piston Manufactures who will "make" them to spec order? I see Keith Black has a 10CC dome for the 400, but nothing similair for the 455. Thank You
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Brad Pringle Wellston, Michigan 1973 SD 455 TA Auto 1974 SD455 TA 4 Spd |
#4
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Racetec can make a custom piston for what ever CR you want.I think Autotec is their street piston version.I have them in 3 of my engines.Tom
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#5
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With a Ram Air IV camshaft you could move to a 10-10.5 compression in this engine and still run 93 94 Pump gas
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Rich Johns Owner/Operator of Pure Stock Auto Restorations Inc. www.purestockauto.com 1969 GTO Judge Ram Air IV M21 4 speed 3:90 1970 GTO Judge Ram Air III M21 4 speed 3:90 Oshawa Built 1970 GSX Stage 1 M21 4 Speed 3.64 # 67 of 678 Original Paint 1970 GSX Stage 1 Auto 3.64 # 603 of 678 12.44@109.73 mph 2011 Buick GS Nats Pure Stock, 12.71@110.64 mph PSMCDR 2011 1970 GS Stage 1 Convertible Auto 3:64 12.71@109.15 mph PSMCDR 2009 1970 GS 455 M21 4 Speed 3.42 1987 GN Astro Roof |
#6
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Comparable to what I run with HO heads, and I agree. No ethanol pump premium and it has never disliked it.
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72 Bird |
#7
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I used the SD 455 'pop up' pistons with the one knobby milled flat and the big knob, milled off the extra tall protrusion.
Probably lowered the CR to around 10 or little less with SD heads. That small increase in CR helped a bunch for HP.
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John Wallace - johnta1 Pontiac Power RULES !!! www.wallaceracing.com Winner of Top Class at Pontiac Nationals, 2004 Cordova Winner of Quick 16 At Ames 2004 Pontiac Tripower Nats KRE's MR-1 - 1st 5 second Pontiac block ever! "Every man has a right to his own opinion, but no man has a right to be wrong in his facts." "People demand freedom of speech to make up for the freedom of thought which they avoid." – Socrates |
#8
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Autotec & Diamond can both provide a small dome piston more suited as a street piston to up CR in 455HO & 455 SD engines. Autotec can mfg to accept metric ring packs. Ancient TRW dome forgings & Ross slight domes are something I've shyed away from.
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Buzzards gotta eat... same as worms. |
#9
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If the heads are stock CC the best deal is to use a piston with a dome. If the heads have already been milled you can use a piston without valve reliefs, zero deck the block and get the compression around 9.25.
If you want your TA to rip with the RAIV cam I'd get the compression ratio closer to 10:1. This is a build I did using some custom pistons without valve reliefs. https://forums.maxperformanceinc.com...errerid=134156 |
#10
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Brad, Dan used Diamond mini-dome .040 over pistons in the '73 SD455 engine he rebuilt back in 2015. It was already .030 over, so went to .040 with the new pistons. He was shooting for 9.8 but got 9.5 actual. Mini-domes save you from having to cut the block and heads too much.
Dennis |
#11
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Quote:
You'd loose about a quarter point of compression by removing both. Those were some tough military grade pistons that we still use occasionally when we come across some of the early forgings. |
#12
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True.
But this was also about 20 years ago. (about the only pistons available cheap)
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John Wallace - johnta1 Pontiac Power RULES !!! www.wallaceracing.com Winner of Top Class at Pontiac Nationals, 2004 Cordova Winner of Quick 16 At Ames 2004 Pontiac Tripower Nats KRE's MR-1 - 1st 5 second Pontiac block ever! "Every man has a right to his own opinion, but no man has a right to be wrong in his facts." "People demand freedom of speech to make up for the freedom of thought which they avoid." – Socrates |
#13
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I used the KB's with a mini-dome last year. Just enough to negate the valve relief, so "zero" dish/dome. No problems with them, seem to work great.
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'73 T/A (clone). Low budget stock headed 8.3:1 455, 222/242 116lsa .443/.435 cam. FAST Sportsman EFI, 315rwhp/385rwtq on 87 octane. 13.12 @103.2, 1.91 60'. '67 Firebird [sold], ; 11.27 @ 119.61, 7.167 @ 96.07, with UD 280/280 (108LSA/ 109 ICL)solid cam. [1.537, 7.233 @93.61, 11.46 @ 115.4 w/ old UD 288/296 108 hydraulic cam] Feb '05 HPP, home-ported "16" D-ports, dished pistons (pump gas only), 3.42 gears, 275/60 DR's, 750DP, T2, full exhaust My webpage http://lnlpd.com/home |
#14
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Thank you everyone for the input. For future reference this is a complete 73 XD SD455. I Will be running all correct parts Intake, Carb, exhaust maniflods etc.
Considering I do not want to hog a bunch off heads and they will more less be 110CC and 0 deck. Now what size dome are we talking? 10 to 15CC? Who's Compression Calculator do you recommend? Thank you agian for your input
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Brad Pringle Wellston, Michigan 1973 SD 455 TA Auto 1974 SD455 TA 4 Spd |
#15
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This is my SD with 'knobbys' (I think this name will stick) I plan to machine one off. Oddly, the guy I got this engine from still had a NOS set.
Brad I look forward to seeing what you come up with. Maybe it's time to go 'new school'.
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"Spend all your time and money on that Pontiac GTO pile" - The Go-Gos, 1981 |
#16
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Quote:
Machine the knobby off on the spark plug side but leave the one on the opposite side. It's hard to find those pistons with the knobbys intact. johnta1 gets credit for coining the phrase. |
#17
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You guys do realize that this is all "Static" compression ratios ? Once running, you get about 1 whole point less. This is why many can say they have a 10:1 engine with pump gas. In fact its around 9:1 when running ( Dynamic compression) .
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#18
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Prototype high compresion SD 455
Is there any factory research upon the original 1970 or 1971 high compression SD455?
Say the short block as created but with the ultra-rare #96 (I know, the same number as the 1968 Ram AIr II) high compression heads? Was such an engine tried in say that gold 1971 TA test car seen in various publications with the custom fuel entry? Quote:
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1970 Lucerne Blue Firebird Trans Am, deluxe blue interior. Original Ram Air III, M-21, 3.73. Being built as a 4" stroke "434" with SR 614 Ram Air IV heads 1972+ Lucerne Blue 4-door hardtop "what if" T-41 Le Mans Sport GT/Grand Am concepts. Equipped with future 3" journal "455 HO"/"what if" prototype "SD 455". What if GM had continued production of the 1970-72 GM A body somewhere in the southern hemisphere? |
#19
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I rebuilt my 455HO about 14 years ago. I did what you are proposing and raised the CR to 9.3 with pistons from Ross. They are very good to work with and will make exactly what you want. Tell them the bore size, the CR you want to run, valve sizes etc. Takes about 6 weeks so plan ahead. I am very happy with the result as the skirt to bore clearance is perfect and I have good ring seal. On the downside pop up domes do make the octane requirement go up so you’ll be running 92-93 octane to avoid knock.
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#20
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if you don't have to use the stock crank and rods, i would consider a stroker crank 4.35 / 4.5 stroke should get the job done.
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“We don’t build a ‘luxury’ car. We build a performance car then we make it luxurious.” |
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