getting ready for pistons for my stroker motor and wonder how much compression the big motor guys are running on pump gas premium? I have stock 89 L-98 computer which currently runs car on regular. realize a new chip is mostly likely in my future. Seems like it is real easy to exceed 11-1 with the 4.125 bore and flat top piston Thanks for help Ike

 

ttt

 

A lot of it is dependent on the valve timing (cam) events and combustion chamber of your head. Need more info.

 

I have GMPP Fast Burn heads haven't cc yet but figure 62-64 cc's Also have some of stuff for SR intake so figure LPE 219 is best cam choice. It always seems to put out good numbers while still being very streetable. Hope this helps some. GM 383 crank with 3.8 stroke on paper means 1.425 compression height piston should be close to 0 deck, maybe? Thanks Ike

 

Coating the pistons, intake runner, exhaust runner , combustion chambers and both valves is getting some press in the hot rod mags lately to control detonation. Also the quench area should be around .050, not much more to get good turbulance in the combustion chamber. This seems to be a big deal in avoiding detonation. Coating keeps the heat in the combustion chamber rather than heating up all the metal that the mixture touches and then the hot exhaust is fired out the exhust rather than super heating the valves and incoming mixure. You might want to consider that if you are borderline.

A big overlap cam will actually lose compession at low rpms because the compression stroke is coming up while the intake valve is still open so when the valve closes there is less mixture compressed. That is what causes the rough idle. Of couse that all changes up the rpm curve

 

I've also read several articles on coatings. It is sure a factor in the upper levels of racing. Not sure of cost to benefit level on street, but is something I'm consirdering for pistons when ordering. I'm asking questions know to try to avoid being borderline on compresion. Lingenfelter always seemed ready to run 11-1 or slightly more on his motors with the 219 cam.

 

hey my motor is 11.5 on pump gas , i add some 100 race gas when i go to the track just to be safe but i ran 94 all the time on the street

 

well thats at least one running 11+ compression on pump gas. I had also figured a little race fuel or additive for any track activities. Also wondered how many guys running forged vs hypereutectic on mostly street stroker motors. I know this is always hotly debated topic and would definately go forged if MR motor with high rpms but figure motor will be all in slightly over 6000 rpms. Just curious!! thanks for feedback Ike

 

i live in michigan too, what size motor are you biulding . i can get you a good deal on forged pistons ,crank ,rods

 

Red L98: Already have the GM 4340 steel 3.8 stroke 383 crankshaft and a set of the GM powdered metal 5.7 383 rods. The GM Bowtie Sportsman block comes bored to 4.117 so I figured would use std 4.125 bore piston with 1.425 cmopression height? That way could later overbore block if needed. With Fastburn heads probably want flattop pistons to be most effective as that is what heads were designed for. Thats why I was trying to get some idea on compression ratios on street. Hope this is enough motor that don't feel need for power adders in future.
Thanks for help! Ike

 

Stroker motor? Basically that's a long (?) rod 400 with a .050" stroke. That's another way of making a 406. I hope your "big bore" block came with the 350 sized mains. If the block is at the 9.025" spec deck height, you'll wind up with a zero deck with those pistons. Find out the CC options on the heads you're interested in. Have the block decked if necessary for a zero deck, use a .039" to .041" head gasket, and shoot for something under 11.00:1 compression. A point of compression is only worth about 4% in power, so it doesn't pay to take a chance at going too high. 10.00:1 to 10.50:1 would be fine, too. It DOES depend on the cam.

RACE ON!!!

 

Don't do 11.55 like on my 383 ... it took about 96-97 to have no detonation with good timing.

 

CFI-EFI: Yes I guess technically you are right, it's a long rod 400 except I didn't start with anything from a 400sbc. The block is a 350 main size block with one piece rear crank seal. want this route because of flywheel needed for ZF-6, otherwise would have went to one of the bigger aftermarket small blocks I don't know how close these cnc Bowtie blocks run to 9.025 deck height?? Fastburn heads should help with denotation and some say shorter rods are better for this than longer rods?? It seems that most Fastburn heads check out about 62+cc's. Glock LT4: it sounds like you setup is on the edge for pump gas. This is what I'm hoping to avoid. Thanks for input.

 

Camshaft specs/ comp ratio both together play a big role in being able to run pump gas or not. Cranking cylinder pressure usually will tell you what to expect. 180psi-200psi(max) is about right for a pump gas freindly engine. Anything below 180psi should easily be able to run on pump gas but won't be a snappy fun to drive engine! Don't get me wrong I've driven a car with an engine that has 140psi of cylinder pressure and it feels awesome (12.0's @115mph) but imagine if someone would have matched the cam to Cr properly to around 180-190psi! This psi # mostly refers to old style chambers and cylinder head designs like pre 96 small blocks, because a very efficient chamber/head like maybe a Honda, Toyota, LS1, and most 4 valve spark plug in the center style head would be able to run more cylinder pressure due to less advance requirement because of cylinder head design and material! You can get away with upto about 200psi, but you have to be a sharp tuner to get it to run on pump gas! It is possible to have 9.0:1 comp and have 180psi cylinder pressure, just like it's possible to have 11.0:1 and have 180psi of cylinder pressure! See what I'm getting at! So like anything else it's not just the CR that matters, head and block material, camshaft, displacement, application and tuning are some of the few factors. Good Luck in your quest for power! Hopefully I've been of some help!
BTW: Best way to achieve pump gas freindly compression is with a flat top piston with a small chamber (for flame travel) and a tight quench!

 

yeah it's kinda funny. my bike is 11.5:1 and runs better on 87 then higher octane grades.. It's a v4 Magna v65 - all aluminum block, heads, 4 valves/2 cams/cyl and it revs to 11,000.. Wonder what would happen if you butted 2 of them together, and enlarged everyhting 3 times so instead of 2.2L it'll be 6.6..

 

I do the same

 

the feedback looks like L-98 cars tolerate a little more compression than LT1/LT4 cars, or is that just a computer tolerance issue?? Looks like I will have to watch specs [cc's,deck height,etc] closely to stay close to 11-1. Surprised didn't see more opinions on hyper vs forged pistons???

Thanks for help