safe static compression ratio 10-71 blown 422 sbc

putting together 422 CI - 4.165 bore/3.875 stroke 10-71 blown sbc alcohol dragster. Boost = +/- 25 lbs. What would be a relatively safe static CR. I'm thinking about 11:1? Thoughts? Thanks ITA

 

I’m thinking you’d be happier 12.1:1 . Send the fuel system off to a good company and you’d have no problems. It’s when you try and wing it when you start to tear stuff up.

 

Good to know. I'm using a 15gpm pump with loop, so fuel supply isn't an issue, but the system should be flowed I agree

 

With higher compression don't be afraid to run a bunch of fuel through it. Don't walk around the pits asking everyone else how much fuel they run because more than likely you'll have more compression than they do. I think jay70cuda is spot on.

 

I agree with him as well...I'm changing from a 357 to a 422, so I'm going to start off stupid fat...then nudge it leaner a bit at a time. No point on going on "kill"....It's just fast bracket racing. When we start touching the cad we stop...should be plenty quick like that

 

Opinions and belly buttons. Everyone has one. Mine is to stay between 10.0:1 and 11:1 . Reasons, less sensitive on the tuneup , easier on parts( it is a small block with small parts) . If your heads flow really well and the cam is not a parts killer , that big blower will make the power and not kill your wallet. Good friend of mine runs blown small block out here on Left coast. He was told alky likes lots of compression and boost. He had a bunch of both. 12.75:1 and 32 lbs. in the manifold. Kept crushing wrist pins and cracking cranks. His heads flow like a wind tunnel. I told him to lower compression down to less than 11:1 and give it a bit more blower. He runs faster now, doesn't kill parts, and has found the tune up to be less of a razors edge. It is your money and decision.

 

you cant cure too much compression with more fuel-once you achieve the octane rating of the alky it will still detonate

 

Hi Mike:

We started bumping compression years ago and added a bunch of fuel. There is a theory that says closing quench area reduces the chance for detonation as well so we tested it. Our tuning window didn't change at all as long as I added fuel...a lot of fuel. Also, I never just took the pistons out of the J&E box. We did a lot of profiling.

A handful of years ago I had a "C" screw blower on a well known pro mod car at 120% overdrive running more compression than the so called "experts" said you could run. I also ran a larger fuel pump than those same so called experts said you should run. And I ran a 16 nozzle system on it. It literally never hurt a part, and with soft timing he ran a world record door car run (any door car anywhere) without even getting after it. He would run all weekend without pulling the pan. It was an older heavy Jerry Haas car. I told him it would have been fine to get after it, and I expected it to run 5.50's to 5.40's in the quarter mile but he ran it with his daughter and girlfriend and didn't want to work that hard on it over the weekends. I showed him runs I made with my junk getting after it and he said he's already the fastest car so why bother.

Back then I told one of the so called hero's of pro mod how much fuel I was running through it and he said his car would fall on it's face because it wouldn't burn it. I told him that his 10.5 to 1 with a "C" screw at the same 120% overdrive we were running he's probably right. Since he had such a strong opinion I let it go. We were gallons per minute more than he ran, not tenths of a gallon.

Gordon's post above describing the damage tells you all you need to know. It was so lean it was killing itself. They reduced the compression and matched the motor to their lean fuel system.

RG

 

Great post randy^^^. I agree. Remember one size fits all parts aren’t for everyone. Call and talk to the manufacture , tell them your concerns. Breaking pistons is a weak wrist pin issue. Cracking cranks is lean issue. If a wrist pin flex’s it will crack pistons. I have one of the best small block engine builders around in my back yard. Competes with the top builders in the country for sprint cars. Message me if your interested.

 

yes what i am saying is with the same timing that is the normal you cant do it - any time you knock the timing back the octane rating changes - you cannot put out the fire[detionation by throwing more fuel on it it will cool it till it ignites again] - cant stop a problem once it starts

 

Well....You would be surprised how much timing I ran early with my stuff with a lot of compression and a ton of fuel. The standing rule for BAE stuff back then was 27 degrees max. While everyone else was running 2 and 3 generations newer BAE heads than I had our stuff ran right with them or better. And mine was a 511 CID while everyone else had a 526.

 

Another thing I did, too, was to run the larger diameter shorter A/Fuel pins, not the "pencils" they were selling the TA/FC guys. I weighed the two and they were nearly identical. The difference to me wasn't so much about the strength of the pin, which was important BTW, it was the significant increase in surface area inside the pin boss of the rod and piston. Pounds per square inch. The larger surface area made it a lot more difficult to trash a piston or small end of the rod with a larger pin with more surface area on the bores where power or detonation is trying to shove the pin through them. It was all about economics for me. A lot of people eventually followed suite. Whenever anyone came over to borrow a piston they were surprised to hear I wasn't running the off the shelf traditional wisdom pin diameter, or piston diameter for that matter.

The first race I started throwing a bunch of timing at it we won. It was the 2009 Las Vegas Fall National event. We struggled in qualifying but the last session I got in the box and hit it and it ran pretty good after that. Two weeks later we made it to the finals at Pomona running against Sean O'Bannon in a great 5.53 to our 5.54 loss. Again, we had 3 generations older heads than he did with high compression, a bunch of fuel and moving the timing around a bunch. We parked the car in mid 2010 after qualifying number 1 at the Spring Las Vegas National Event and losing because Daniel red lit in the semi finals. I brought it back out for one last race, the 2012 Winternationals at Pomona, and won it running fuel and timing you wouldn't believe. Again, we had an old set of BAE heads on it 3 generations behind everyone else we beat that weekend. During qualifying it was sticking the tires and shaking it's brains out so Daniel was peddling it every run, running 5.70's. Against Lombardo second round (first run Sunday) I got in the box and hit it hard out of the gate with timing. It picked up two tenths because it got up on the tire and made it through low gear without massive tire shake, running a 5.52 to Lombardo's 5.57. Against Bartone third round Daniel wacked the throttle so hard staging the car he hit the full throttle switch under the gas pedal and set off all the timers and they timed out before the tree came down, meaning he was main jet and no timing to the finish line, so it fell off to a 5.62. Bartone smoked the tires. We changed nothing for the finals and beat Jay, 5.53, to a 5.54. So moving fuel and timing around was a tenth of a second in my car based on back to back runs where the timers were set off early compared to runs where they weren't.

You guys got me all stirred up now. I was enjoying my retirement. I think I'll head over to the classifieds and see what's for sale now. LOL

 

Get unstired When you say old heads you mean big chamber? If so they do take quite a bit more timing-Example Bob newberry Veney setup -We ran 40degrees with blown big block every engine has a max that runs best and going and giving it more timing and fuel together once passed a certain point does not work hand and hand-old large chamber heads allways take more compression you answered why it worked for you

 

No they were the small cc BAE 6 heads. 96 cc's if my memory isn't gone completely. They are the same combustion chamber CC's as the 8's, 8X's, 10's, and most of the copycats out there. Last of the BAE blown alcohol big combustion chamber heads were BAE 3's. Veney heads and MBR are a totally different animal.

 

By the way, Mike, getting "unstirred" is good advice. I bet you still have some moments after quitting though.

 

Don't feel bad, I have been out over 35 years but still enjoy following many of these conversations.

 

i ran blown SBC's for years weak link will be head gaskets on a cast head deal.Also the siiamesed ext ports are a pain .if its a water head run water !!!! BBC crank snout is a must get the thickest .990 dia wrist pins. We ran 45 psi on cast heads and did not hurt much 32 timing was the max but that was with a super mag 5 had 10 hat nozzles and 8 port with a 110 pump gorr did the fuel system this was a 387 ci ran 11 to 1 CR this ran in a door car with a 4 speed and a clutch was a lot of fun lol