what do you guys suggest? i've been considering the new trickflows, any other #1 choices for heads on a blown engine. i have 6 lb paxton, every bolt on thats out there and all fuel upgrades, looking for most possible power, i'll also be doin a cam with the heads, and by the fall i;mm be doing a 383 with a vortech and would like to use these same heads...for now im on the stock shortblock, and though trickflow a good idea due to bigger combustion chambers reducing my compression ratio. thanks for yah help guys. its a 95 lt1 m6.

 

Not too many people are using the trick flows. AFR's are proven. You can get them up to 76cc combustion chambers.

 

AFR's. As TimbrSS suggested, the availability of large combustion chambers is important in order to achieve the desired low CR.

Rich Krause

 

oook sounds good guys, but what size AFR?? lt1 or lt4, i want to eventually be in the 10's while still being streetable, i kno its rought but im not a wimp i can handle it lol. how big of heads, what stage? and any good websites to buy off that you suggest?? also what size combustion chambers do you recomend, what will be safe for my stock short block, but still good for my next 383 or 396 that i build at the end of summer. thanks for your help guys

 

I would contact Phil at Advanced INduction. He seems to be extremely knowledgeable when it comes to heads.

 

Either the LT4 195's or the 210's should work well for your goals. You'll need around 64cc's to get you under 9:1 CR with off the shelf pistons for a 383. Obviously bigger cc's if you want to run lower CR. Like mentioned before, your best bet is to contact Phil at AI... He'll set you up good.

Use the search feature, do a ton of research... It shouldn't be too hard find what you need to put together a streatable 10 sec blower car.

 

Why large combustion chambers?

Wouldn't you be better off keeping the chambers small and using dished pistons to achieve the compression ration you want?

 

Depends what CR you want. But keep in mind that there is a limit on how large a dish is available. The JE pistons I use have an ~31cc dish, which is about as large as you can get. If you want to be in the ~8:1 range, you will need ~72cc chambers even with a dish this large on a 383.

Rich Krause

 

Cool thread and great timing! Especially since I'm totally confused about what to do with my motor. I am trying to pick a head, but am concerned about which combo to go with. For example- How would a 72cc combustion chamber affect the amount of swirl in the cylinder head- and how would a dished piston affect the swirl rate, if you added it to the 72cc chamber??

And seeing we're talking combustion chamber/piston combos- I was considering roughly 8:1 compression, but am a tad nervous about how it will drive around town. I want to use 15-18psi- so any higher on the compression might get dangerous.

Will this also affect how I pick a camshaft??

 

Steve: you can drive mine to see how 7.8:1 is around town. No problem smoking the tires at will.

Yes, you are right, cam choice and CR are intimately related. You want a dynamic CR in the low 6:1 range for running moderate boost on pump fuel. DCR is function of the bore, stroke, and size of the combustion space (which is to say the same things that determine static CR) along with the intake valve closing point. Compression doesn't begin until the intake valve closes. With a typical blower cam, a DCR in the low 6:1 range works well on pump gas. If you are using a very big (long duration) cam, you will need a higher static CR to achieve the desired DCR.

As far as effects on combustion efficiency, any modern head/piston combo has a "squish" area. Old dish pistons had the whole piston crown recessed and this did promote lazy combustion. But modern designs have a "D" shaped dish along with a flat area on the "outside" of the piston crown. This flat area and the adjacent flat area of the head deck provide the "quench" or "squish" needed to promote efficient combustion. This works especially well when the quench height is correct. The quench height is the distance between the head deck and the flat part of the piston crown. For a steel rod motor, most people aim for between 0.035-0.045". Aluminum rods need a little more height to avoid piston to head contact. So, there is no down side wrt combustion when using good pistons with a "D" shaped dish.

BTW: blower motors do not lose much power from lowering the CR. This has to do with a subtle interaction of positive pressure cylinder filling and the larger "combustion space" of a low CR combo. The "combustion space" refers to the total area above the piston crown at TDC. With positive pressure in the manifold throughout the period when the intake valve is open, a larger mass of fuel/air will fill this space compared to the siutation where the volume was less (a higher CR setup). This larger mass of fuel and air will partially compensate for the loss of hp due to the lower static CR. Another way to say this is that the low CR setup will have a higher "apparent VE".

Sorry if the above wasn't too clear. But just keep in mind that if you want to run pump gas and boost you want a low CR setup to avoid detonation.

Rich Krause

 

He Rich, please rephrase this. When i ran 600rwhp I did have around 8.3 DCR fpr 10psi boost.. that was with 9.07:1 CR and my cam.

I am using a cam with less overlap (wider lsa) and now im running 8.8:1 SCR (from 58cc chamb to 62cc). So I expect the DCR goes in the 7.8 or so. How is this bad for a pump gas 12psi boost engine and around 700rwhp? I have a chance then to go with a thicker gasket (stock or similar, was using felpro) which will enlarge the quench gap which is not a tremendous idea. Unless I go with a bigger bore gasket and not necessarily a thicker one.

let me know waht you think

Thanks

 

I'm waiting on AFR's 225 blower heads to hit the market.

 

I suspect an error in calculation. I don't see how your DCR could be as high as 7.8 if the static CR was 8.8. How did you calculate this?
Rich

 

http://www.rbracing-rsr.com/comprAdvHD.htm

Guess I need to use a different calculator...

Actually I used my engine analyzer pro program and it said DCR 6.83 so you are correct...

 

The compression on my car is 9.60:1. thats what i was told. I have ported heads but untouched combustion chambers.. Should I go from 58cc to a 62cc Combustion Chamber? Bigger? stay the same? Need help here.. Im running a Vortech T trim SC with a 2.50" blower pulley and untouched crank pulley.. Im also running this as my daily driver on pump gas.. The cam im running is the 224/236 114lsa, low lift version..

Thanks