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Thread: Factory TBI w/ flat top pistons?

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    Factory TBI w/ flat top pistons?

    Hey guys, I have a low mile 350 roller block out of an '87 3/4 ton. It has the factory dished pistons. I'd like to put flat tops to bump. compression up from 8.5:1. Bores appear to be ok and I think will get away with a hone. What years came with flat tops? any of the TBI stuff? I'd like to go used route to keep costs down.

    Thanks!

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    Here are some fairly inexpensive pistons from Summit which will work. https://www.summitracing.com/parts/s...make/chevrolet When buying pistons, be careful of the compression height. There are a lot of rebuilder pistons out there with a 1.540" compression height. You want to get 1.560 1-565" comprssion height unless you plan on decking your block .020-.025"

    Brian

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    Quote Originally Posted by tayto View Post
    Hey guys, I have a low mile 350 roller block out of an '87 3/4 ton. It has the factory dished pistons. I'd like to put flat tops to bump. compression up from 8.5:1. Bores appear to be ok and I think will get away with a hone. What years came with flat tops? any of the TBI stuff? I'd like to go used route to keep costs down.

    Thanks!
    1991 B-car like a Caprice or Cadillac L05 should be flat top.

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    LT1's should be flat top pistons also. 1992 - 1997 B and F cars. Have to make sure it is the 5.7 in the B cars. Some of them had the 4.3L "Baby LT1". I have built engines with used pistons but if I am that far into it, I now would rather go new, especially if I am having to install pistons on the rods with press fit wrist pins.

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    Quote Originally Posted by sturgillbd View Post
    LT1's should be flat top pistons also. 1992 - 1997 B and F cars. Have to make sure it is the 5.7 in the B cars. Some of them had the 4.3L "Baby LT1". I have built engines with used pistons but if I am that far into it, I now would rather go new, especially if I am having to install pistons on the rods with press fit wrist pins.
    My suggestion was more along the lines of selecting that application to get a rebuild kit with pistons included. LT1 pistons are fairly lightweight and the balance will be off pretty bad. A 305 crank actually has a better balance for LT1 pistons.

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    Thanks sturgillbd, I was looking at new pistons today. Found Sealed Power H345DCP, but I'm getting conflicting information on what the compression height is. Those summit ones look like the ones I'll have to go with. Want to keep quench around .040" without decking block.

    Fast, motor is going in my Caprice not trying to "over" do it like last time but can you recommend a cam? I have a B-body LT1 cam I was going to put in. stock 191 TBI heads with compcams 981-16 valve springs (got for cheap). compression will be close to 10:1 i would imagine if i get the quench to .040". have a 350 TBI intake manifold from a 3/4 ton, seem to remember you saying these flowed better? have a 454 tbi if it's needed if not have a freshly rebuilt SB TBI W/ cop. car injectors. going to try and get the LT1 exhaust manifolds to work. I. don't want to mess around with headers.
    Last edited by tayto; 1 Week Ago at 07:19 PM.

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    Quote Originally Posted by tayto View Post
    Thanks sturgillbd, I was looking at new pistons today. Found Sealed Power H345DCP, but I'm getting conflicting information on what the compression height is. Those summit ones look like the ones I'll have to go with. Want to keep quench around .040" without decking block.

    Fast, motor is going in my Caprice not trying to "over" do it like last time but can you recommend a cam? I have a B-body LT1 cam I was going to put in. stock 191 TBI heads with compcams 981-16 valve springs (got for cheap). compression will be close to 10:1 i would imagine if i get the quench to .040". have a 350 TBI intake manifold from a 3/4 ton, seem to remember you saying these flowed better? have a 454 tbi if it's needed if not have a freshly rebuilt SB TBI W/ cop. car injectors. going to try and get the LT1 exhaust manifolds to work. I. don't want to mess around with headers.
    The LT1 cam is plenty mild. I ran one on a stock tune for close to a year in my G20 van without issues. Ran well on the stock van ECM even better on a 1993 Cop Car ECM. If you have the clearance seal to retainer a set of 1.6:1 full roller rockers can be used. Just make sure to drill the pushrod holes to 1/2". LT1 manifolds are also easy to adapt. Just need to get an EGR block off plate and drill the manifold flange to match your older heads. I used a Vortec 350 exhaust manifold gasket as a guide to properly drill the holes needed in both manifolds. The LT1 exhaust should also bolt right on if you pickup the dual exhaust crossmember. You did not say what uear your Caprice us but using the truck intake manifold can present a problem when you fit the distributor if your car is a whale body. I would use a 1995 S10 4.3 CPI torque converter. Should give you a brake stall speed around 2,500 rpm. I would also get a Sonnax replacement governor for a 1990 L98 TPI Corvette. Will put your shifts in the 5,000-5,200 rpm range at WOT opposed to the 4,000 rpm shifts of the stock TBI governor. Your part throttle shifts will also be at a higher rpm to better match the cam and converter. A low rise single plane intake like an Edelbrock Torquer 2 would be a better intake than an OEM truck intake if you are able to eliminate the EGR with your smog testing. They also made a number of single plane smog intakes in the past that could be used if you can find one on Ebay or the like.

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    Quote Originally Posted by Fast355 View Post
    The LT1 cam is plenty mild. I ran one on a stock tune for close to a year in my G20 van without issues. Ran well on the stock van ECM even better on a 1993 Cop Car ECM. If you have the clearance seal to retainer a set of 1.6:1 full roller rockers can be used. Just make sure to drill the pushrod holes to 1/2". LT1 manifolds are also easy to adapt. Just need to get an EGR block off plate and drill the manifold flange to match your older heads. I used a Vortec 350 exhaust manifold gasket as a guide to properly drill the holes needed in both manifolds. The LT1 exhaust should also bolt right on if you pickup the dual exhaust crossmember. You did not say what uear your Caprice us but using the truck intake manifold can present a problem when you fit the distributor if your car is a whale body. I would use a 1995 S10 4.3 CPI torque converter. Should give you a brake stall speed around 2,500 rpm. I would also get a Sonnax replacement governor for a 1990 L98 TPI Corvette. Will put your shifts in the 5,000-5,200 rpm range at WOT opposed to the 4,000 rpm shifts of the stock TBI governor. Your part throttle shifts will also be at a higher rpm to better match the cam and converter. A low rise single plane intake like an Edelbrock Torquer 2 would be a better intake than an OEM truck intake if you are able to eliminate the EGR with your smog testing. They also made a number of single plane smog intakes in the past that could be used if you can find one on Ebay or the like.
    This design is a bit unorthodox but worked well and has EGR provisions. Would run great with a big block TBi on an adapter.

    https://m.ebay.com/itm/Holley-Street...wAAOSwdIFbFrPv

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    Quote Originally Posted by Fast355 View Post
    The LT1 cam is plenty mild. I ran one on a stock tune for close to a year in my G20 van without issues. Ran well on the stock van ECM even better on a 1993 Cop Car ECM. If you have the clearance seal to retainer a set of 1.6:1 full roller rockers can be used. Just make sure to drill the pushrod holes to 1/2". LT1 manifolds are also easy to adapt. Just need to get an EGR block off plate and drill the manifold flange to match your older heads. I used a Vortec 350 exhaust manifold gasket as a guide to properly drill the holes needed in both manifolds. The LT1 exhaust should also bolt right on if you pickup the dual exhaust crossmember. You did not say what uear your Caprice us but using the truck intake manifold can present a problem when you fit the distributor if your car is a whale body. I would use a 1995 S10 4.3 CPI torque converter. Should give you a brake stall speed around 2,500 rpm. I would also get a Sonnax replacement governor for a 1990 L98 TPI Corvette. Will put your shifts in the 5,000-5,200 rpm range at WOT opposed to the 4,000 rpm shifts of the stock TBI governor. Your part throttle shifts will also be at a higher rpm to better match the cam and converter. A low rise single plane intake like an Edelbrock Torquer 2 would be a better intake than an OEM truck intake if you are able to eliminate the EGR with your smog testing. They also made a number of single plane smog intakes in the past that could be used if you can find one on Ebay or the like.
    Car is a 1988 Caprice have lots of room for taller intakes vs the whale body style. Full roller rockers aren’t in the budget, but I do have a set of 1.6 stamped rocker arms that only have about 50 hours on them. I believe with the LT1 B-body cam the exhaust valve lift is right around .460”? Is this to much for the TBI heads? The machine shop that went over the heads installed the compcams 981-16 valve springs with V6 vortec retainers I believe.

    I have a 700R4 out of a 9C1 that hassimilar shift valves as the vette, If i keep the car I will rebuild it and throw it along with the S10 converter and correct governor.

    I am going to try and get that intake, with the heated plenium I dont think tuning a single plain will be a big deal?
    Last edited by tayto; 5 Days Ago at 08:09 AM.

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    Also, do you think the BB TBI will be necessary? I have a SB TBI that I have rebushed, done the “ultimate” mods to and refreshed with AC Delco rebuild kit. I have a set of standard 350 injectors as well as a set of cop car injectors that were flowed by Witchhunter some years ago. I was hoping to sell the BB TBI if I don’t need it to recover some costs.

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    I was able to get that intake Fast. Just gotta find a 454 TBI adapter now.

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