before i go changing pistons
 

just curious, my shortblock still isnt assembled but the parts were for a n/a build originally. but now i have the dyers 871 i wanna use so.


with my 310 72 cceheads and ross flat tops my 455 is 11.6ish cr which is less than ideal but i wonder, with pulleys to make 6 psi could i get away with it.

with e85 and a bug catcher converted to fast xfi and a good blower cam" solid roller" could it be done or should i figure on ordering a set of dish pistons to get back around the 9.1 mark?

That is a bit much for boost, were the rings file fit? Were they filed for boost? Boost pistons have the ring lands set down a bit too. I used regular forged pistons in a turbo build and lifted 2 ring lands. That was at 9 to 1 on 12 psi (pump gas)

Talked to a couple boost guys,quench not that important,put a thick gasket and run it.Tom

file fit is the plan for the rings and the ring lands are set down i was gonna use with nitrous, everythings still in boxes. i seen butler sells cometic gaskets in different thickness but wasnt sure.



i wonder what the effective cr of ur 9.1 cr was vs what mine would be with 6 psi and 11.5/6

Stan Weiss would be the one to ask on here.

i hope he chimes in here......i cant get the search function to work on the phone version

I’d go with a thick head gasket also! Also keep timing down.


GTO George

This info came from Tom V. and he doesn't like the .090-.120 clearance. He said it tends to cause detonation. I ran .145 down the hole plus 35cc dish with Marty's sealing ring with a 61cc heads to get 8.8 to 1 compression.

Assuming the below engine parameters: Wallace Racing Calculator.

Engine Bore = 4.181"
Engine Stroke = 4.210
Deck Height = .004
CCs in the head = 72
Valve Reliefs = 6.6
Head Gasket Thickness .041"
Head Gasket Bore Diameter = 4.250"

Wallace Racing says you would be at 11.64 Compression Ratio.

So to get to 9 to 1 compression ratio you would need a (Wallace says 8.96)
you would need a Head Gasket that was .170" thick.
FOUR TIMES AS THICK AS THE .041" THICK GASKET THAT HE HAS RIGHT NOW.

RIGHT, BET THAT SUCKER WOULD REALLY SEAL UNDER BOOST. NOT.

Personally I would stay closer to 8.5 or 8.75 to 1 compression ratio and be able to add boost at a later date by using the PROPER parts vs a bandaid super thick head gasket.

Tom V.

All you would need is to get the compression in the 10’s with e-85 and you’ll be fine!


GTO George

I have to agree with Tom on this,just too thick for this application,maybe a 100 gasket but not this much.Tom

i can change pistons if i need to since its not together yet....i already gotta take the crank in to be cut for a 2nd keyway. not sure if that will change the balance or not but if it dont then i was just trynna keep from buying new pistons and having to rebalance if i could make it work. ive read on yb of alot of guys running 6 psi with e85 and higher compression but just not sure if that goes for pontiacs too.

You put the correct pistons into the engine (while it is apart right now) you have a lot of room for growth with the boost system vs a bandaid with a high failure potential just to get to 9 to 1 compression ratio.

Send a PM to Charlie66 as he has been running e-85 with boost for years, He has run as high as 39 psi, He makes 750+ HP out of a 1/2 of a 400 engine (4 cylinder pontiac engine) with 4 more cylinders he would make 1500 hp out of a 400 cid engine on e-85.

HE can give you some very good advice on running a E-85 engine with boost on the street.

Tom V.

With e-85 you can run higher compression with no problems.

GTO George

You know what’s nice about running a little more compression is that you can still make HP while running less boost and spinning the blower less which is easier on the crankshaft! Just a thought!! ;)


GYO George

What he say's
I'm running an 8-71 with 7:98:1 on pump gas with 10 LBS of boost.
I pop a couple head gaskets but now I have a timing boost controller
that will make the difference and I plan on spraying mine too.
If you want some of my info call me 269-832-8122 and I'll help as much
as I can. Charlee 66 has good info too.He give me some good information.

GT.

With 9 to 1 compression and 6 lbs of boost your compression would be around 12 to 1 with 11.5 compression your looking at about 15 to 1.
Roots blowers are not turbos asking the wrong/right questions will get you the wrong answers!

GTO George

Work with Blueghoast and Charlie66 (once you get the right pistons in the engine) and you will be fine with e-85 fuel and whatever boost you decide to run.

And as was posted, a timing controller helps keep the new head gaskets in the engine performing properly. Be very careful with the timing though. Talk to Charlie66 about the reasons for that deal.

Tom V.

1,500 HP at 39 lbs of boost.....why so much boost? Im making around 1,400 at 11 lbs of boost!


GTO George

Since the Butlers and Travis Q (as well as Marty Palbylin, in 1996) run high boost (that is 45 to 75 on a typical engine
and the Tractor Pull boys with the diesels are over 100 psi of boost with their stuff, it is not worth my time to explain the difference between a 88 or 91 mm Turbocharger and a 8-71 roots blowers capabilities.

You have a large engine, you have a poor efficiency supercharger (50-55% typically) and you don't spin the thing very high rpm so you make 11 psi of boost pressure and run low 8s. Your supercharger will live for years racing at those boost levels. (unless you do something stupid).

Charlie66 could run 38 psi of boost pressure on a 400 cid engine and make 300 more hp with his small engine vs your 525 cid engine. Which is 125 cubic inches bigger just by adding more boost pressure vs what you run).

Marty could run 6.96 with old school diesel turbos in 1996. It is now 23 years later and you are happy running low 8s and making a lot of passes with your combination. Marty was in the mid 40s on Boost Pressure if I remember correctly.

Mahovitz with a 281 CID engine and high boost 75 psi range runs in the 5s with a door car in the quarter mile. Your Roots system on his 281 cid engine would be a POS.

So read some books on Turbochargers George and then post up and I will try to answer more of your questions on the difference between the two boosting devices. If I explained a Turbo Map to you, then you would understand that a turbocharger (TO BE HIGHLY EFFICIENT AT MOVING THE AIR - must to be over 70% efficient) and the impeller has to spin 75,000+ rpm vs your Roots deal spinning 7500 supercharger rpm.

Tom V.