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31
Wedge List / Re: Comp ratio and performance
« Last post by Robert Lang on November 05, 2019, 03:32:54 PM »
Hi - I totally disagree with the notion that you need a cam to get more HP

absent changes in compression ratio.



Compression ratio increases mean more BMEP, hence more power assuming no other

changes. By way of example (note that I'm a TR6 guy), going from around 8:1 to

12:1 results in about 40 HP. I get folks all the time that slap in a cam and

bump compression from 8:1 to 9:1, add a 290 degree cam and then get frustrated

that they dyno maybe a 10 or 15 HP gain at the wheels.



Cam changes move the power curve up or down. More seat to seat duration moves

the power band up in the RPM range. While you may see more power with a cam

with more seat to seat time, you will only see that power at higher revs.



Head changes like porting will help total flow through the system and if you

tune correctly will increase the volumetric efficiency.

To the original question, 10 or 15 HP increase assuming no other changes than

the 1.5-ish change in static compression. Assuming no porting or exhaust

changes, you may not see that gain if the system can't breathe at the

necessary RPMs.



Remember - it's a system... things need to work together to get the power.

Regards,Bob Lang
32
Wedge List / Timing? - Re: Comp ratio and performance
« Last post by Bill on November 05, 2019, 02:32:22 PM »
I put the car away for the winter and have some tuning to do in the
spring.B  Mild cam (Crower 231), ~9.7:1, mild port job etc. Running stock
carbs & airboxes with alternate needles so the motor feels constrained.B  
Running a lumenition with coil and timing at 4deg BTDC at engine
cranking speed, vacuum disconnected.B  Stock motor was running real well
with 8-10 deg BTDC.

Anyone done some dyno work and have advice on where to set the initial
timing on the new hotter spec motor??

Bill

On 11/4/2019 9:58 AM, William Parris wrote:
> You wonbt see much gains just from a bit more compression.   A better cam is
> really needed.   Head work also really helps with these engines.  Ibd
> recommend the wedge shop for a cam.  My favourite is the Erwin TQ20
>
> Will
>
>> On Nov 4, 2019, at 5:52 AM, Farrell Leslie
> wrote:
>> o;?Hi all
>> My TR8 is originally from Michigan and therefore has a CR of 8.13.  I am in
>> the process of upgrading the engine and have purchased a set of 9.75
> pistons
>> from Rimmer Bros.  These are oversize by .020b as standard size is nla and
> a
>> rebore is planned.  I expect to have to change my timing accordingly and
>> wondered if anyone who has made this upgrade could suggest what it should
> be
>> set at.  What could also be interesting is just what sort of performance
> gain
>> I could be looking to.
>> Any help appreciated as always.
>>
>> Leslie
>>
>> Sent from my iPad
>>
33
Wedge List / Re: Re: TR7/8 Digest V1 #9207
« Last post by Bill on November 05, 2019, 02:26:49 PM »
Have to agree with Ted on this one.B  FYI when I cc'd everything & did

the math my actual measured stock CR was 7.9:1.



You don't need a full on race style porting job.B  These heads are so

ancient in design that a knowledgeable head porter can give you quite a

bit with not much work and with no other changes.B  Headers are fine but

their help is minimal if the head is plugged up.



I also recommend taking about 11lbs out of the flywheel.B  That helps

acceleration and is easier on the drivetrain when you hit the next gear.



Not to mention you need a limited slip diff and some bigger tires to get

the power down.



Realistically if you want to get it into 5th gear for cruising with a

cam you need to drop the rear ratio to 3:45 unless you have fuel

injection which still meters fuel appropriately when the engine is way

out of its sweet spot.



It is a slippery slope, buy hey, winter is coming!
34
Wedge List / Re: Re: TR7/8 Digest V1 #9207
« Last post by Bill on November 05, 2019, 02:26:43 PM »
Have to agree with Ted on this one.B  FYI when I cc'd everything & did

the math my actual measured stock CR was 7.9:1.



You don't need a full on race style porting job.B  These heads are so

ancient in design that a knowledgeable head porter can give you quite a

bit with not much work and with no other changes.B  Headers are fine but

their help is minimal if the head is plugged up.



I also recommend taking about 11lbs out of the flywheel.B  That helps

acceleration and is easier on the drivetrain when you hit the next gear.



Not to mention you need a limited slip diff and some bigger tires to get

the power down.



Realistically if you want to get it into 5th gear for cruising with a

cam you need to drop the rear ratio to 3:45 unless you have fuel

injection which still meters fuel appropriately when the engine is way

out of its sweet spot.



It is a slippery slope, buy hey, winter is coming!
35
Wedge List / Re: Re: TR7/8 Digest V1 #9207
« Last post by Ted Schumacher on November 05, 2019, 02:12:07 PM »
John, you are correct.B  It seems that everybody, sorry Will , missed the

math on ratio increase. Going from 8.13 to 9.75 is not a minor

increase.B  On top of which an overbore is involved which increases

compression even more.B  Just do the math. Formula for CR is on our

website - http://www.tsimportedautomotive.com/factsfiguresformulas.html.

The gain for this CR increase will be in the order ofB  7 - 9 %. So, onB  

a stock 135 HP TR8 you will wind up at about 145 HP. Then everything

else can build from there.B  See below for formula. Ted



*How to determine compression ratio*



CR =



   



_V1 + V2_



   



V2



(V1 = volume of cylinder in engine block; V2 = volume of space above

piston at TDC b

V2 includes volume of the combustion chamber plus the volume of head gasket)
36
Wedge List / Re: Re: TR7/8 Digest V1 #9207
« Last post by Ted Schumacher on November 05, 2019, 02:11:59 PM »
John, you are correct.B  It seems that everybody, sorry Will , missed the

math on ratio increase. Going from 8.13 to 9.75 is not a minor

increase.B  On top of which an overbore is involved which increases

compression even more.B  Just do the math. Formula for CR is on our

website - http://www.tsimportedautomotive.com/factsfiguresformulas.html.

The gain for this CR increase will be in the order ofB  7 - 9 %. So, onB  

a stock 135 HP TR8 you will wind up at about 145 HP. Then everything

else can build from there.B  See below for formula. Ted



*How to determine compression ratio*



CR =



   



_V1 + V2_



   



V2



(V1 = volume of cylinder in engine block; V2 = volume of space above

piston at TDC b

V2 includes volume of the combustion chamber plus the volume of head gasket)
37
Wedge List / Re: Re: TR7/8 Digest V1 #9207
« Last post by William Parris on November 05, 2019, 09:43:28 AM »
Totally fine.  But thatbs not what webre saying.



Will



>
38
Wedge List / Re: Re: TR7/8 Digest V1 #9207
« Last post by William Parris on November 05, 2019, 09:43:24 AM »
Totally fine.  But thatbs not what webre saying.



Will



>
39
Wedge List / Re: Re: TR7/8 Digest V1 #9207
« Last post by "John M. Sanders" on November 05, 2019, 09:22:11 AM »
But if you have to re-bore the engine and buy new pistons, why not go for more

compression?

I did in both of mine with no issues.

Cheers

John



Sent from my iPhone



>
40
Wedge List / Re: Re: TR7/8 Digest V1 #9207
« Last post by "John M. Sanders" on November 05, 2019, 09:22:06 AM »
But if you have to re-bore the engine and buy new pistons, why not go for more

compression?

I did in both of mine with no issues.

Cheers

John



Sent from my iPhone



>
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