Thread: Compression

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I have got 43 th head gaskets on my 489 if I drop them to 23 how much compression would I gain my car is 9.7.1 I'm looking for more power I got the big 335 afr heads with flat tops in her, I got it in a 68 chevelle. My buddy got a 69 camera with less power but he can out run me by 2 or 3 links mind dynoed at 649 Hp 591 tq. He said his camero is just as heavy idk

Hey Ken – way too many unknowns here.

Are your 335 heads the 121cc or 114 cc combustion chambers?

What is the deck height? Most big blocks are 9.800 – 9.820 stock and true zero is 9.78. Was your block decked before build?

What cam are you running?

Recommended gasket with these heads is .039. Thinner is not good – definitely not the way to increase compression especially with a true flat top piston where clearance may be tight already unless you want the valves to perform a custom fly-cut in those flat tops!

These heads perform best in the 3,000-7,000 rpm range. What is your RPM through the traps?

Did you build or buy this engine? To get those kind of numbers one needs to invest well north of $10K - and I mean well north.

Did you see the dyno run? Do you have the dyno printout? I’m not busting your chops, but something just doesn’t sound right to me.

Your buddy is right – weights of the two cars are close. In raw terms, assume 10 gallons of gas and 200 pound driver, the calculated ET for these two are as follows:

Chevelle weight: 3800
Flywheel Horsepower: 649
60 Foot Elapsed Time = 1.6
1/8 Mile Elapsed Time = 7.01
1/4 Mile Elapsed Time = 11.04
1/4 Mile Trap Speed = 136.52

For the Camaro to beat you by two or three car lengths in a quarter your buddy’s car would been to be pushing 700 horsepower.

Camaro weight: 3750
Flywheel Horsepower: 700
60 Foot Elapsed Time = 1.52
1/8 Mile Elapsed Time = 6.80
1/4 Mile Elapsed Time = 10.71
1/4 Mile Trap Speed = 140.62

Give us a bit more information.

Best,
Glenn

Or..... https://www.procharger.com/

Got 640 lift Howard's cam,121 runners,all callies,got 19000$ in build standard deck height, I got Dyno print out an I was there when dynoed

Was that engine or chassis dyno numbers and what kind of dyno????????

Switch cars with him for a run or get someone else to drive yours

I'd like to know where this fellow in the Camaro is skinnin' you, is it on the tree or at the 60 foot or 330 foot mark or the 660 or at the very top end......or is he just outpowering you everywhere? If he's skinnin' you on the bottom end, then you don't necessarily need more motor, you need more converter or more gear or a smaller diameter tire or all the above. What are you taching through the eyes?

A 489 BBC with a -21 cc pop-up piston, 121 cc combustion chamber, 0.020" piston deck height and a 0.043" gasket will produce a 9.73:1 static compression ratio. Same motor with a 0.023" gasket will produce a 10.1:1 SCR. You would want to closely check piston to valve clearance before making this change though, as mentioned by Glenn. I would want 0.100" clearance on the intake and 0.120" on the exhaust, as measured from 20 degrees before top dead center to 20 degrees after top dead center at overlap.

Do you know the piston deck height and the block deck height of your motor? Where does max torque occur? Where does max hp occur?

BOTTOM LINE: The aluminum heads will not like a steel shim head gasket, that's why AFR recommends a thicker composition gasket, to prevent fretting the aluminum material.
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Some good information going on here…

So, let’s drill down. Let me restate my questions and elaborate a bit:
1. Did you build the engine or have it built?
2. What pistons do you have
3. What is the deck height?
4. Why wasn’t the block decked?
5. Is your cam a stock Howards roller (like 120345-10) or a custom grind?

As to “where” you’re getting beat (Tech’s questions)
1. At the tree (hole shot)?
2. First 60 feet?
3. 330, 660 or top end?
4. What’s your RPM at the traps?

Couple other questions?
1. What is your 60 foot time?
2. What’s the 1/8 mile time
3. What’s the ¼ time and speed?
4. What transmission?
5. What converter (if automatic)?
6. Rear end type and ratio?
7. Tire size and type?

With the money you’ve spent I would certainly hope there is 650 (or more) horsepower at the flywheel and you should see mid to low 11’s all night long.

Keep the information coming and we can certainly help you dial this in.

Best,
Glenn

My cam was custom grind , and my block was decked ,and we ran out in country not on strip , I got 308 gears with low profile 17 inch nittos drag radials with no hop bars on rearend , he has same tires but he got a lot more side walls his is 15 tires and he got cow track bars I hop I'm saying that right he got 330 gears his is a 5 speed tremec transmission . Mind is a turbo 400 tranny , Lynn rays custom sped shop built my engine , I have Dyno sheet I will try to put it on here tonite. I have trouble hooking up. Also I got a Ambrose tq converter I might have spelled that wrong 3200 stall. He would out power me about the 1/8 mark an pull away. I got also a cfs carbuater I think 1060 cfm

Okay – your rear end is geared too high and you probably need a bit more converter to take advantage of the RPM range.

If you have 315/35R17 drag radial tire (diameter = 25.71) with your 3:08 rear end you’re at 3.36:1 equivalent as the Nittos are smaller in diameter than your stock tires. A stock TH400 1st gear is 2.48: 1 so your launch is at 8.33:1 (3.36*2.48). Your buddy’s actually hurting his launch with the 275/60R15 Nittos (larger than the stock 215/65R15 on the Camaro) and he has an effective rearend ratio is 3.07:1. However, the Tremec T-5 first gear is 2.87 so he’s launching at 8.81

When you hit second the TH400 is effectively 4.97:1 (1.48*3.36) but the Tremec had two more gears so his second is 5.80:1 (1.89*3.07).

In third, you’re at 3.36:1 – your buddy is at 3.93:1. If he hits 4th, he will be at 3.07 – but my thought is he’s smoking you in his second and third gears.

Going to 3:73 gears and 3400 stall will probably put a big smile on your face and the Camaro in the rear view mirror
Glenn

Yea 2 nd an 3 rd Is were he is getting me

Well - there you have it! Looks like new gears and maybe a new converter and you'll be ready give him a big surprise. Check to see if this is the converter you have - if so, try just the gears first.

GM TH-400 Stall Converter - 3200-3500 RPM Stall :: Assault Racing Products

Glenn

What about putting a 190 shot of nitrous to have for back up , my builder says won't hurt my engine if it is put on right , I got a lot of money in this car don't won't to hurt it .

Put 4:56 gears in it

Will I have to run 110 octane if I spray 190 shot on my engine or will be ok with 93 , going to back time dn to 30 degree

Originally Posted by glennsexton

Well - there you have it! Looks like new gears and maybe a new converter and you'll be ready give him a big surprise.

Originally Posted by Ken1960

.....I got a lot of money in this car don't won't to hurt it .

Ken, Glenn gave you the answer and it's the safest way to go unless you've got to keep the tall gears for highway MPG. To me, nitrous is rolling the dice every time you push the button. It's what the kids throw on for "easy HP", and even if you take all the steps for a "safe" system it's still loosely controlled. I'd say that your concern about not wanting to hurt your engine rules out nitrous, but others may not agree.

Back in Post #3 I linked the ProCharger site, and if you're not wanting to change your gears but wanting more HP & Torque it's a good way to go. You can control the boost by changing the drive pulley, and the pop-off valve is there to protect you, too. When you're cruising there's basically no change to your system. I think it would be worth your time to give the guys at ProCharger a call, and talk through what you've got with them.

My $0.02? Change your rear gears and I think you'll be smiling, just like Glenn told you or if you can stand the cruise RPM jump to 4.56's like Jerry says; but if you gotta have more power, consider a blower.